“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
CHAPTER -...
2
aims fundamentally at the details of the process in which a system converts
from one state to another and the time requi...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
absorptio...
4
The laser technology, Flash photolysis, rate of growth of malignancy in
cancer, rate of blood circulation in body, and r...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Selenium ...
6
Oxidation kinetics with Ketones
Riley[13] introduced selenium dioxide as an oxidant to oxidize some
ketone. They obtaine...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
carboxyli...
8
intermediate 3, which decomposes as shown to the rearranged carboxylic acid
4.
White has followed up the work of Sonoda ...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Schaefer[...
10
intermediate. The principal objection to the mechanism was the selenium
(II)keto esteris hydrolysed very rapidly to alc...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
rate of o...
12
perchloric acid. The reactions exhibited first-order dependency in [substrate],
[SeO2] and [H+]. The reaction was fully...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Sewanne[2...
14
The alkyl acid selenites can be obtained as crystalline solids from methanol[25-
26] or ethanol[27,28] solutions of sel...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
selenium ...
16
The stoichimetry studies revealed that 1:1 mole ratio of substrate and oxidant.
The oxidation product was glyoxals repo...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
reaction ...
18
reactions, while the effect in the benzyl groups to decrease the rate. According
to them, this fact is expected for an ...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
mechanism...
20
Oxidation ofolefins
Guillemonat[44] made the first serious attempt to explain the mechanism
of olefin oxidation by sele...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
(b) React...
22
yield of 11 was increased six fold, but without acetic acid present, there was no
reaction. When sodium acetate was add...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Heterocyc...
24
and varied solution conditions. The Mn(III)-GA reaction stoichiometry of 4:1
was determined and the products were chara...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Activatio...
26
CHAPTER - II
MATERIALS AND METHODS
In the kinetic investigation of glycolic acid by selenium dioxide acetic
acid-water ...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Standard ...
28
sodium thiosulphate solution along with 5ml. of 4N HCl. About 2ml of starch
solution was added to it and then un-reacte...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
𝑇𝑒𝑚𝑝. 𝑐𝑜𝑒...
30
4. Free energy of activation (G#)
The free energy of activation (G#) is obtained using equation-
–  𝐺#
= 2.303 𝑅𝑇 𝑙𝑜...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
CHAPTER -...
32
Fig.IIIA-1
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Table: II...
34
Fig.IIIA-2
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Table: II...
36
Fig.IIIA-3
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Table: II...
38
Fig.IIIA-5
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Table: II...
40
Fig.IIIA-6
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Table: II...
42
obeys first order kinetics concluded, that each system, under study obeys first-
order kinetics.
SECTION: III B
The exp...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
44
SECTION: III B -1
Dependence of rate of oxidation reaction on the initial
concentration of oxidant (SeO2)
The dependenc...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Fig.IIIB-2
46
Fig.IIIB-2(a)
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
SECTION: ...
48
passing through origin, hence, the reaction follows first-order behavior with respect
to the concentrations substrate. ...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
SECTION: ...
50
Fig. III B-4
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
SECTION: ...
52
Fig.IIIB-5
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Fig.IIIB-6
54
SECTION: III B-5
Dependence of rate on variation of temperature
The dependence of rate on temperature was studied at fo...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
SECTION: ...
56
Table: III B-7
THERMODYNAMIC PARAMETERS
[SeO2] 103 (mol.dm-3) = 2.50(1-3);
[H+
] 103(mol.dm-3) = 1.25(1);
HOAc-H2O % (v...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
STOICHIOM...
58
Table: IV-1.
Summary: Stoichiometry of the oxidation of Glycolic acid–SeO2
system
[H+
] 103(mol.dm-3) = 1.25(1);
HOAc-H...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
PRODUCTAN...
60
Table: IV-3
Identification of oxidation products by the compared observed melting
points and reported melting points
3....
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
DISCUSSIO...
62
GENERAL FEATURES FOR THE OXIDATION OF GLYCOLIC ACID WITH SeO2
Before elaborating the actual mechanism of the reaction p...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
(6) The p...
64
that for the oxidation of Glycolic acid with SeO2 the mechanism could be
proposed as per following scheme:
Rate Express...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
+
𝒅𝒄
𝒅𝒕
[...
66
+
𝒅𝒄
𝒅𝒕
[ 𝑷𝒓𝒐𝒅𝒖𝒄𝒕] =
𝐤 𝟐 𝐤 𝟏
[ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟐 𝐒𝐞𝐎 𝟑
][ 𝐇+]
{𝐤−𝟏
[ 𝐇 𝟑 𝐎+] + 𝐤 𝟐 }
When,
𝐤 𝟐 ≫ 𝐤−𝟏
The rate of reaction...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
CONCLUSIO...
68
5. This work can better and suitably be utilized some branches of science to
which kinetics is relevant are –
Branch : ...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
Reference...
70
26. A. Simon and R. Paetzold, Zeitschrift Fur Anorg. and Allgeimeine;
Chemie, 303,53 (1960).
27. B. G. Gasanov, M. A. S...
“Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in
aqueous-acid medium”
58. Cleme...
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“Kinetics and mechanism of sulphuric acid oxidation of glycolic (ga) by selenium dioxide in aqueous acid medium”

  1. 1. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” CHAPTER - I INTRODUCTION Research provides one an opportunity to pit's wits with the seminal principles underlying this creation. Since the emergence of nature, everything changes in universe. It is an inescapable fact, which from time to time immemorial, has moved poets, exercised metaphysicists and excited the curiosity of natural philosophers, chemists and scientists towards exploration of nature in search of something a new for their knowledge and purpose. Chemistry has been an integral part of the natural phenomenon. Many reactions move at snail’s pace whereas others occur instantaneously. Chemical kinetics is a branch of chemistry concerned with the velocity of chemical reactions and the mechanism by which chemical reactions occur [1]. It deals with the rates of chemical reactions and how rates depend on factors, such as concentration and temperature. Ideally, a complete reaction mechanism would require the knowledge of all the molecular details of the reaction. In most of the reactions, it is only the disappearance of starting materials and the appearance of final products that can be detected. In general, however, the net reaction is not the whole story, but simply represents a summation of all the changes that occur. The net change may actually consist of several consecutive reactions each of which constitutes a step in the formation of final products [2]. The mathematical models that describe chemical reaction kinetics provide chemists and chemical engineers with tools to better understand and describe chemical processes such as food decomposition, microorganism growth, stratospheric ozone decomposition, and the complex chemistry of biological systems[3]. These models can also be used in the design or modification of chemical reactors to optimize product yield, more efficiently to separate products, and to eliminate environmentally harmful by-products[4]. Kinetics
  2. 2. 2 aims fundamentally at the details of the process in which a system converts from one state to another and the time required for the transformation. Hence, chemical kinetics provides information about the rate of reaction on possible pathways, by which the reactants are transformed into products. Thus, the fundamental of objective of the study of the kinetics of chemical The kinetics of oxidation reactions and the investigation of the reaction mechanisms from the kinetic data have been always the most interesting subjects in chemistry. In any kinetic investigation, one may be interested to arrive at (i) the relationship between the rate and the various factors like concentrations of the reactants, temperature, reaction medium etc., and, (ii) interpretation of the empirical rate laws in the light of the mechanism proposed [5]. The pioneering work engineered by German chemist L.F. Wilhelmy (1812-1864) on the rate of inversion of sucrose [6] has originated a revolution by opening a new chapter of kinetics in chemistry. Since then the significance of chemical kinetics came in existence. Chemical kinetics is a branch of chemistry, which deals with the measurement of the rates of chemical reactions. An ideal theory of chemical kinetics would start with the time dependent equation, which could be solved to predict the rates of such simple physical and chemical processes as change in the energy state of a molecule and energy transfer reactions in which no net chemical changes occur but energy is transferred between molecules. Livingston [7] called the special attention in signifying in the field of reaction mechanism as “No reaction mechanism can be considered to me more than a temporary working hypothesis until it is supported by kinetic data”. The chemical kinetics remains one of the most important tools even this day in finding out the undetermined mechanism of the reaction. Thus due to developments of modern physical techniques viz, n.m.r, i.r, u.v, visible,
  3. 3. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” absorption spectroscopy, mass spectra, epr, thermogravimetry, colorimetric, polarography, chromatography etc. and wide and vast applicability of hi-tech, super-tech, has shed a new light and horizons on reaction mechanism and provide the complete picture of the reactions. The elucidation of reaction mechanism is still one of the most fascinating problems in inorganic and organic chemistry. Chemical Kinetics has furnished a pool of precious wealth of information about the nature and in course of a reaction [8] viz. molecularity, concentration, reaction path, frequency of activated complex, mass, temperature and other properties such as influence of substituent groups and structural alterations, rate equation, salt effect, isotopic effect, activation parameters and various environmental changes etc, like solvent polarity, pH and catalytic changes in a reaction. The above study leads to work at stoichiometry, identification of intermediates and isolation of end- products as an indirect support to reaction mechanism. Modern trends in kinetics Pauling L., Franklin [8] introduced the electron transfer that has created a new era in the field of chemical kinetics. The oxidants based on redox reactions are of considerably academic interest and of technological importance. In 1969, A. Broido developed T.G. techniques and employed to study the kinetics of chemical reaction based on the Arrhenius equation. Recently this valuable phenomenon of kinetics is fully utilized to carry out the reaction exhibiting radioactivity [9] with half-life less than a second does. The radioactive decay of an unstable nucleus is an important example of a process that follows a first-order rate law: 29Cu 64 29Cu 30Zn + 64 , = 12.8 hrs. 64
  4. 4. 4 The laser technology, Flash photolysis, rate of growth of malignancy in cancer, rate of blood circulation in body, and rate of tissues movement in bioplants [10], etc. applied to kinetic measurements within the range of pico second. Yalman[11] applied electro-negativity and well defined oxidation state to kinetics. In 1970, Goldstein[12] (U.S.A.) has utilized molecular orbital theory to provide a strong evidence of changes in order of electro negativities based on redox reactions. During the recent era, it has become interesting to investigate the mechanistic pathway of redox reactions. Originally, this field was little probed as the mechanism often varied greatly with the oxidizing and/or reducing agents employed. Oxidation of organic compounds may be represented as electron transfer, hydride transfer, H atom transfer and addition-elimination and displacement mechanism. Oxidation- Reduction The present study deals with the kinetics of oxidation reactions involving oxidation-reduction. It will be, therefore, necessary to give a brief account in this regard. The process in which there is de-electronation from reacting species is called oxidation and conversely, reduction implies the addition of electrons (electronation) to the reacting species. Oxidant is one which gains electrons and reductant is one which loses electrons. Oxidation- reduction reactions occur simultaneously in solution. Hence in all oxidation-reductions, there will be a reactant undergoing oxidation and one undergoing reduction. In these reactions, electrons are transferred from reductant to the oxidant.
  5. 5. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Selenium Dioxide as an oxidant The potential of selenium dioxide as an oxidizing agent for organic compounds was first realized in the early 1930's by Riley[13]. Since this initial discovery, selenium dioxide has found wide application as a selective reagent in organic synthesis [14]. Selenium dioxide most commonly oxidizes carbon- hydrogen bonds attached to various activating groups such as olefins, aldehydes, ketones, acetylenes, esters, amides, carboxylic acids, anhydrides, and aromatic nuclei. Aldehydes, ketones and olefins are oxidized in good yields under relatively mild conditions. Alcohols, amines, phenols, and mercaptans are oxidized in poor yields under vigorous conditions. Alkanes, ethers, and alkyl halides are usually not attacked by selenium dioxide, and when they are, only under severe reaction conditions. Selenium dioxide is a colorless solid. It exists as one dimensional polymeric chain with alternating selenium and oxygen atoms. It sublimes readily and hence the commercial samples of SeO2 can be purified by sublimation. SeO2 is an acidic oxide and dissolves in water to form selenous acid, H2SeO3. THE SURVEY OF LITERATURE PERTAINING TO THE OXIDATION OF VARIOUS COMPOUNDS BY SELENIUM DIOXIDE In the present work, selenium dioxide has been employed as an oxidant. It has been, therefore, thought worthy to give a brief account regarding the work done with this oxidant.
  6. 6. 6 Oxidation kinetics with Ketones Riley[13] introduced selenium dioxide as an oxidant to oxidize some ketone. They obtained glyoxals as the product of the oxidation of these compounds. They pointed out that the active species of oxidant was selenious acid not the selenium dioxide. They observed that when a mixture of acetone with a little water was added to selenium dioxide in cold, the reddish color due to libration of Se developed more repidly than the case when dry acetone was used. Mel’nikov and Rokitskaya[14] have studied the kinetics of oxidation of some ketones. They have observed that the oxidation by SeO2 is a bi-molecular reaction and the rate is measured based on degree of enolization of the carbonyl group of these compounds. Different types of ketones such as Me2CO, Et2CO, Pr2CO, Bu2CO,(isoPr)2CO, MeCOEt, MeCOPr and methyl hexyl ketones were studied. They have found that the rate of oxidation retards gradually with rising molecular weight of the substrates. Duke[15] studied the kinetics of oxidation of acetone by seleniuos acid in each of the experiment, the reactants concentrations were kept such that only the concentration of seleniuos acid changed. While that of other reactants remained unchanged. The plots of log [H2SeO3] vs. Time were found to be straight lines, the slope being first order in oxidant. The selenium dioxide-catalyzed hydrogen peroxide oxidation of ketones was discovered by Payne and Smith1 in 1957. The reaction involves a migration of an alkyl or aryl substituent, which is to a ketone carbonyl group, to the other available position, with subsequent oxidation of the carbonyl group to a 1 G. B. Payne and C. W. Smith, J. Org.. Chem., 2_2, 1680 (1957).
  7. 7. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” carboxylic acid. For example, cyclopentanone 1 is oxidized to cyclobutanecarboxylic acid 2. The reaction was carried out in tertiary-butyl alcohol for two hours at 80° using equimolar quantities of ketone and hydrogen peroxide. Selenium dioxide was only present in about 2 mole percent. Sonoda and Tsutsumi[16] have oxidized many ketones by the method of Payne and Smith in an attempt to elucidate the mechanism of this novel reaction. Their results have been summarized by White2 and a few examples are shown below. Since selenium dioxide does not promote this rearrangement directly, Sonoda and Tsutsumi have suggested that peroxy selenious acid or some other higher oxidized state of selenious acid attacks the carbonyl group in the same manner as selenious acid. The resulting intermediate rearranges to their proposed 2 N. Sonoda, T. Yamaguchi, and S. Tsutsumi, J. Chem. Soc. Japan, Ind. Chem. Soc., 63, 737 (1960).
  8. 8. 8 intermediate 3, which decomposes as shown to the rearranged carboxylic acid 4. White has followed up the work of Sonoda and Tsutsumi with an investigation of the hydrogen peroxide-selenium dioxide oxidation of desoxybenzoin to diphenylacetic acid. Yields as high as 68% (based on unrecovered desoxybenzoin) were obtained along with small amounts of benzyl benzoate and its hydrolysis products, when 0.1 mole of ketone, 0.2 mole of peroxide, 0.03 mole of selenium dioxide and 0.1 mole of sodium acetate were refluxed in 80% acetic acid for three hours. Obviously the Baeyer-Villiger oxidation is a competing reaction here. When aliphatic ketones were oxidized by his method, White only reported the isolation of tarry products. White[17] also has shown that the reaction is not affected by selenic acid or a combination of selenic acid and hydrogen peroxide and that it may proceed through an enol selenite ester 5, as does the normal selenium dioxide oxidation of ketones. He proposes the following mechanism for the reaction. White concludes that the reaction is catalyzed by acetate ion, and that it may proceed through an enol selenite ester 5, as does the normal selenium dioxide oxidation of ketones. He proposes the following mechanism for the reaction.
  9. 9. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Schaefer[17] also studied the sodium acetate catalyzed kinetics of oxidation of p-nitrobenzyl phemyl ketone and p-methoxy benzyl phenyl ketone by SeO2 in 80-90% acetic acid. The proposed mechanism involved the base catalysed formation of an enol selenite ester, which subsequently rearranged and decomposed to yield α-diketone, se and water. To explain the acetate catalyzed SeO2 oxidation of, it was suggested that acetate plays several conflicting roles, but overall effect was accelerated one. Oxidation kinetics of ketones by selenium dioxide also been studied by Sharpless and Gorden[18]. According to them β-ketoseleninic acid formed by an electrophillic attack of selenious acid on the enol is the key intermediate. They suggested that pummerer like decomposition of this intermediate yield α- diketone.They pointed out that the peroposed mechanism of Corey and Schaefer[19] was widely accepted but it did not involve an organo-selenium
  10. 10. 10 intermediate. The principal objection to the mechanism was the selenium (II)keto esteris hydrolysed very rapidly to alcohol. Through these workers could not isolate such an organo-selenium intermediate, but made an attempt to give experiemntal evidence regarding its formation in the reaction mexture. Singh and Anand[20] have studied the kinetics and mechanistic investigation of cyclic ketones viz. cyclohexanone, cycloheptanone and cyclo- octanone by selenium dioxide in 50% (v/v) acetic acid water miture. Reactions were found to be first order both in [oxidant] and [substrate]. The acid was found to be catalyzed rate of the oxidation odf cyclic ketones. The rate vof reaction further increased with increase in the the concentration of acetic acid in the reaction mixture. Plot of log k1 vs. 1/D was lenear with a positive slope,is suggested that the slow step involved the neutral molecule and positive ion on the basis of solvent isotopic effect; an attack of reaction species of selenium dioxide on the keto form of cyclic ketone was suggested. The mechanism proposed by them involved concerted attack of electrophile RH2SeO3+ and nucleophile, H2O on cyclic ketone to form enol selenium(IV)ester in the acid catalysed oxidation.The enol selenium(IV) ester on internal rearrangement gives selenium(II)ester, which on acid catalysed 1,2-elimination gave the oxidation products. The reported order of reactivity among cyclic ketones were Cyclohexanone > cycloheptanone > Cyclooctanone Valechha and Pradhan [21] have studied the oxidation of acetyl aceton by selenium dioxide in 50% (v/v) acetic acid –water mixture at 500C. The reaction follows first order kinetics with respect to xidant and substrate. The presence of H2SO4 incresed the reaction rate, which was found to further increase with, increases [H2SO4]. These workers studied the solvent polarity on the reaction rate by varying the percentage of composition of acetic acid They observed that the increase in the percentage of acetic acid in reaction mixture decreased the
  11. 11. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” rate of oxidation. Plot of log k1 vs. D-1/2D+1 was found linear, on the basis of this, it was suggested that the reaction is a dipole-diple type. The primary salt effect on the reaction rate was found to be normal retarding. The mechanism proposed for the oxidation process involved an electrophile attack of selenious acid on acetyl acetone to gives enol selenium (IV) ester in slow step. The latter on fast internal rearrangement give selenium (II)keto ester and finally 2,3,4- pentanetrione as the end-product . They ruled out the probability of biselenite ion, HSeO3-, as being the effective oxidizing species. The operative mechanism summarized as below- Sanjay and co-workers[22] have studied kinetics of oxidation of 2- alkanones by selenium dioxide in aqueous acetic acid medium in presence of
  12. 12. 12 perchloric acid. The reactions exhibited first-order dependency in [substrate], [SeO2] and [H+]. The reaction was fully acid catalyzed. Decreasing in the dielectric constant of the medium, slightly accelerating effect. The soichiometric studies revealed 1:1 mole ratio of oxidant and substrate. They have found 2,3- diketoneas oxidation product. Selenium dioxide–ketone system suggested the following mechanism-
  13. 13. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Sewanne[23] has studied the kinetics of oxidation of acetophenone by selenium dioxide in aqueous acetic acid sulphuric acid medium. The reaction follow first order kinetics in [SeO2],[Substrate] and [H+] ion. Reaction is fully acid catalyzed .Primary salt effect was found to be negligible effect on the reaction rate. The solvent polarity on the reaction rate by varying the percentage of composition of acetic acid .Sewanee has observed that the increase in the percentage of acetic acid in reaction mixture increased the rate of oxidation. Plot of log k1 vs. D- 1/2D+1 was found linear, on the basis of this, he was suggested that the reaction is a dipole-diple type. It was observed that the electron with drawing group retard the reaction rate while the electron releasing groups accelerate the reaction rate. The mechanism involving an electrophile attack of seleniuos acid,H2SeO3 on the keto form of substrate in rds. Oxidation ofalcohols The oxidation of alcohols to aldehydes by selenium dioxide has been studied by Mel'nikov and Rokitskaya[24] They investigated a series of saturated, low molecular weight alcohols and proposed that at low temperatures an alkyl acid selenite 7 is formed, and that at higher temperatures 7 can react with more alcohol to form a dialkyl selenite 8, which decomposes at higher temperatures to the aldehyde or ketone, selenium, and water.
  14. 14. 14 The alkyl acid selenites can be obtained as crystalline solids from methanol[25- 26] or ethanol[27,28] solutions of selenium dioxide by dehydration with calcium chloride in a desiccators. They are decomposed by water to the alcohol and selenious acid. The lower dialkyl selenites may be distilled at reduced pressure without decomposition[29]. The yields of these oxidation products were always low and temperatures of 300°C or more were needed to obtain any oxidation at all. Riley and co workers[30]. report 40-50% conversions of benzyl alcohol to benzaldehyde with selenium dioxide at the reflux temperature of the alcohol. No traces of benzoic acid could be detected. Allylic alcohols also show a tendency to be oxidized in fairly good yields to the aldehyde by selenium dioxide. Thus, α- methylallyl alcohol has been oxidized to α -methylacrolein in 62% yield[30] and β-methylallyl alcohol oxidized to crotonaldehyde in 60% yield[30]. Austin[31] et al. also used selenium dioxide as an oxidant in the oxidation kinetics of some alcohols. They have found that aliphatic alcohols reduced selenium dioxide at higher temperature than their boiling points. They have observed that ethyl, propyl and butyl alcohols yield glyoxal on oxidation with selenium dioxide. It was suggested that reactions with much more complex as well as sensitive to temperature changes than the aldehyde and ketone in case of benzyl alcohol, they found that the oxidation occurred but not completely, at the boiling point of the alcohols under investigation. The products of oxidation were corresponding aldehydes. Mel’nikov and Rokiskaya[32] have studied the oxidation of various alcohols with selenium dioxide. They observed that alcohols on reaction with selenium dioxide to form to dialkyl selenites,which on heating decomposed in to corresponding aldehydes, Se, H2O. Valechha and Pandey[33] have also reported the kinetics of oxidation of allyl,crotyl and cinnamic alcohols by selenium dioxide in 80%(v/v) acetic acid – water medium. The order of reaction with respect to each substrate and
  15. 15. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” selenium dioxide was found to be unity. Reactions were fully catalyzed by the mineral acid is reported. The observed reactivity among the alcohols were reported as- Crotyl > allyl > cinnamic alcohols. One scheme of mechanism is proposed as- Allyl alcohol[34] is reported easily oxidized into the correspondig aldehyde by selenium dioxide. Weygand prepared cyclic selenite ester from orthophthal alcohol and decomposed it thermally to ortho phthal aldehyde. Oxidation ofaldehydes Khan[35] et al have investigated the kinetics of oxidation of some aliphatic aldehyde such as acetaldehyde,propanaldehyde, n-butanaldehyde and α- chloroacetaldehyde by selenium dioxide in aqueous acetic acid and sulphuric acid medium. They have found that reaction exhibit first-order kinetics in each [SeO2], [aldehyde] and [H+] ions. The reaction was acid a catalyzed. A positive effect of acetic acid is observed. The stoichimetry of each reaction under investigation has determined by equilibrrating the reaction mixture containing an excess of selenium dioxide over aldehyde in varying ratio at 400oC for 48 hrs.
  16. 16. 16 The stoichimetry studies revealed that 1:1 mole ratio of substrate and oxidant. The oxidation product was glyoxals reported. Single rate expression – d/dt[SeO2]= k1[aldehyde][H+].The application of steady-state treatment with reasonable approximation yields the rate law capable of explaining and justifying the observed kinetic. Oxidation ofsubstitutedparaffin Schaefer and Horvath[36] studied the oxidation of 1,3-diphenyl propane by SeO2 in 99% acetic acid at 115 0C,1,3-diphenyl-2-propane-1-ol acetate was obtained as the product of oxidation under reaction conditions in high yield. N.D. Valechha and A .Pradhan[37] have reported kinetics of oxidation of diphenyl methane by SeO2 in 80% (v/v) dioxane-water mixture in the presence of perchloric acid. The order of reaction with respect to the [SeO2] is one. The
  17. 17. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” reaction pseudo first order constant in [DPM]. They have found benzophenone as the oxidation product. Oxidation studiedof desoxybenzoin Corey and Schaefer[38] have made a most critical study selenium dioxide oxidation. The Oxidation of desoxybenzoin by selenium dioxide carried out in 70% acetic acid –water mixture at 89.2 0C. It was found that the reaction was second order in [desoxybenzoin] and [SeO2]. The added strong acid in the reaction mixture was found to catalyze the reaction rate. They have also observed the oxidation of various p- substituted desoxybenzoin with substituents in benzoyl group moiety. It have been reported that the electron repelling substituents groups in the benzoyl group, increases the rate of
  18. 18. 18 reactions, while the effect in the benzyl groups to decrease the rate. According to them, this fact is expected for an acid catalyzed oxidation of desoxybenzoin by selenium dioxide. Schaefer[39] has also reported the selenium dioxide in 90% of acetic acid. He has suggested that acetate play several conflicting roles but overall effect was accelerated one. With Esters Riley[13] et. al. applied selenium dioxide to oxidized acetone dicarboxylate, ethyl mandelate, ethylmalate,ethyl phenyl ropinate and ethyl acetate etc. Refluxing the compounds with selenium dioxide for 2 to 5 hrs. At temperature120-200 OC. Benerji, Borton and Cookson[40] have investigated a series of sterio isomeric methyl-3,6-dioxoeduues monoates by selenium dioxide. Valechha[41]have reported that the kinetic study of oxidation of ethyl acetoacetate by selenium dioxide in aqueous acetic acid water medium. The reaction is first order in both SeO2 and [EAA]. In presence of sulphuric acid and percloric acid, reaction rate were found catalyzed. Oxidative Degradation of Some α- substituted mandelic The kinetics of oxidation of some substituted mandelic [42] such as mandelic and para-chloro substituted mandelic acid by selenium dioxide in aqueous acetic acid medium in the presence of sulphuric acids has been studied. The reaction follows identical kinetic being first order in each SeO2, substrates and H+ concentrations. The reaction is acid catalyzed. A positive effect of acetic acid is observed. Various thermodynamic parameters have been computed. A single rate expression – d/dt= k1[α-hydroxy acid] [H2SeO3] [H+] and one scheme of
  19. 19. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” mechanism are proposed . H3SeO3+ and AcH2SeO3+ are postulated as the prime profile species. Stoichiometric study revealed 1:2 mole ratio of oxidant and substrate. Where, X stands for –H and –Cl, for mandelic and p-chloromandelic acid respectively. Singh[43] et. al.also studied that the kinetics of oxidation of some α- hydroxy acids such as p-NO2 and p-Br substituted mandelic acids by selenium dioxide in aqueous acetic acid medium in the presence of sulphuric acids has been carried out. The reaction follows identical kinetics being first order in each SeO2, substrates and H+ concentrations. The reaction is acid-catalysed. A positive effect of acetic acid is observed. Various thermodynamic parameters have been computed. A single rate expression kobs = k1 [α-hydroxy acid] [H2SeO3] [H+] and one scheme of mechanism is proposed. H3SeO3+ and AcH2SeO3+ are postulated as the prime profile species. Stoichiometric study revealed 1:2 mol ratio.
  20. 20. 20 Oxidation ofolefins Guillemonat[44] made the first serious attempt to explain the mechanism of olefin oxidation by selenium dioxide. His scheme is outlined in the following three reaction steps. The R group is a radical containing an ethylenic linkage adjacent to the indicated CH2-H. Guillemonat mechanism, although rather general and crude,does explain why one always recovers starting material, why the product is dependent on the solvent, why the occasional formation of dienes results, and why organoselenium compounds are isolated from these reactions. However, this mechanism does not predict the site of predominant attack in the oxidation. Guillemonat studied the selenium dioxide oxidation of a number of branched, straight chain, and cyclic olefins in the C5-C9 range. From this study he formulated a set of empirical rules, which are listed below and illustrated by examples from the literature. These rules are listed as summarized by Trachtenberg[45]. (a) Trisubstituted olefins[46] are oxidized preferentially on the disubstituted side of the double bond, if there is non-bridgehead allylic hydrogen there. For example,
  21. 21. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” (b) Reaction at an endocyclic position in 1-alkyl cyclohexenes is preferred to exocyclic attack[46,47] Thus, carvomenthene yields carvotanacetone as the major product. Phellandral is obtained as a minor product. ' (c) Oxidation never occurs at bridgehead positions in bicyclic systems falling within the limits of Bredt's rule[49]. For example, α-pinene is oxidized only to myrtenol and myrtenal, with no oxidation-taking place in the six-membered ring. α -pinene myrtenol myrtenal (d) When the allylic position favored is tertiary, dienes can result. 2,3- dimethylcyclohexene[50] is oxidized to a mixture of diene and o-xylene which probably results from dehydrogenation due to adjacent activated allylic positions. Olson[51] has studied the oxidation of ethylene with selenium dioxide in acetic acid at 100-125° and 50 psi of ethylene. Compounds 11, 12, and 13 were isolated. When a mineral acid such as hydrochloric or perchloric was added, the
  22. 22. 22 yield of 11 was increased six fold, but without acetic acid present, there was no reaction. When sodium acetate was added, only 12 and 13 were obtained. The increased rate on addition of strong acid is consistent with Schaefer and Horvath's mechanism in which selenium dioxide is converted to its conjugate acid, which is the reacting species. Olson concludes from his study that the reaction is specific acid catalyzed by acetic acid and that acetates are not formed from esterification of alcohols, but is primary reaction products. Oxidation ofamines with selenium dioxide The reaction of amines with selenium dioxide was first investigated by Hinsberg[52-55] in 1889. He found that o-phenylenediamine reacted with selenium dioxide to give a compound, called a piaselenol. A series of these types 46 47 of compounds was investigated, Hinsberg also isolated a compound with structure 7 from reaction of 1,8 diaminonapthalene with selenium dioxide Hinsberg also isolated a compound with structure 8 from reaction of 1,8 diaminonapthalene with selenium dioxide.
  23. 23. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Heterocyclic amines having a tertiary nitrogen atom, such as pyridine or quinoline, may be refluxed with selenium dioxide without change. However, the -N=CH- group in these compounds is comparable in activating ability to the carbonyl group. Thus, 2- and 4-picoline 48 are easily oxidized to the corresponding aldehydes and acids. In addition, the hydroxymethyl pyridines, as discussed above, serve as good examples. Hydroxy groups allylic to an imine function are oxidized to the ketone readily. For example, hydroquinine is oxidized to hydroquinone. Selenious acid combines with aliphatic and aromatic amines at low temperatures to form crystalline, substituted ammonium salts. Alkyl ammonium selenites result when alcoholic solutions of selenium dioxide are added to amines. With increasing temperatures, both aliphatic and aromatic amines are oxidized rapidly to yield resinous or tarry products. The reaction between most amines and selenium dioxide is highly exothermic and usually proceeds with explosive violence. Riley showed that aniline reacted with an equimolar amount of selenium dioxide in methanol, to give a white crystalline substance, C7H11O3NSe, M.P. 56°, that slowly decomposed to a dark violet substance, with a faint odor of nitrobenzene. THE SURVEY OF LITERATURE PERTAINING TO THE OXIDATION OF GLYCOLIC ACID WITH OTHER OXIDANTS By Manganese(III) The kinetics of oxidation of glycolic acid, Glycolic a by manganese (III) in sulfuric acid solutions at 293 K has been studied[56]. A solution of the mild oxidant, Mn(III) sulfate, in aqueous sulfuric acid medium was prepared by a standard elec-trochemical method. The oxidation reaction was monitored by spectrophotometry at a fixed wavelength (λmax = 491 nm), varied temperature,
  24. 24. 24 and varied solution conditions. The Mn(III)-GA reaction stoichiometry of 4:1 was determined and the products were characterized. The experimental rate law is: rate = kobs [Mn(III)][GA]x[H+]y, where x, and y are fractional orders. The effects of varying ionic strength, solvent composition (dielectric constant), acid, and the reduction product, Mn(II), on the rate of the reaction were investigated. Activation parameters evaluated using Arrhenius and Eyring plots suggest the occurrence of an entropy controlled reaction. A mechanism consistent with the observed kinetic data has been proposed. A rate law has been derived based on the mechanism. With acid permanganate The initial oxidation stages of glycolic acid by acid permanganate[57] were investigated. The rate of the induction period was slow and then gradually increased. The kinetics of oxidation were second order, first order with respect to both glycolic acid acid and Mn(VII). The reaction was acid catalyzed. Addition of Mn(II) ions largely increased the rate of the initial stages and decreased the rate of the following stages. The oxidation rate was decreased by the addition of F- or P2O4-4 ions. The Arrhenius equation was valid for the reaction between 16.5 and 34°C. Activation parameters were evaluated and a mechanism consistent with the results obtained was proposed. Glycolic acid acidby pyridinium fluorochromate The kinetics and mechanism of the oxidation of glycolic acid (GA) by pyridinium fluorochromate[58] (PFC) has been studied by spectrophotometric method in 50% acetic acid – 50% water (v/v) medium in a temperature range of 298 K- 313 K. Under the conditions of the pseudo-first order, the reaction follows first order with respect to [GA], [H+] and [PFC]. The reaction is catalysed by perchloric acid. There is no salt effect. The rate increases with increase in the percentage of acetic acid and the plot of log kobs versus 1/D is linear with a positive slope indicating the positive ion – dipole nature of the reaction.
  25. 25. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Activation parameters have been evaluated. Based on the experimental results, a probable reaction mechanism of oxidation was proposed. The recent literature survey also revealed that glycolic acid have been oxidized by various oxidants viz. Pyridinium chlorochromate[59] (PCC), tripropylammonium fluorochromate (TriPAFC)[60] Vanadium (V)[61] and Ce (IV)[62] etc. However, literature survey reveals that no work seen on above topic/entitle, all these facts are inspired to me to explore mechanistic path of this problem. The substrate is chosen for the kinetics and mechanistic investigation is: Glycolic acid
  26. 26. 26 CHAPTER - II MATERIALS AND METHODS In the kinetic investigation of glycolic acid by selenium dioxide acetic acid-water medium in presence of sulphuric acid, different chemicals were used in the form of solutions. The procedure employed for the preparation of these solutions and for the kinetic study is mentioned in the following sections: PREPARATION OF SOLUTIONS AND THEIR STANDARDIZATION A. Preparation of selenium dioxide solution and its standardization Selenium dioxide (Loba) solution was prepared by dissolving a weighed quantity of pure selenium dioxide in distilled water. Solution was standardized iodometrically as 2-ml. of selenium dioxide solution was taken with a graduated pipette in a conical flask, 10ml. of 2N H2SO4 and one gram of solid KI were added. The iodine liberated was titrated against standard sodium thiosulphate solution using starch as an indicator. B. Preparation of substrates solution The stock solution of glycolic acid (sigma 98%) was used to solution, prepared by dissolving a calculated quantity of the glycolic acid in glacial acetic acid. C. Iodine solution 3.32 gram of KI were weighed and transferred to a 500 ml. volumetric flask. About 10 ml. of water was added to it. Now about 5 to 5.2 grams of iodine were weighed and transferred to the sane volumetric flask. When iodine was completely dissolved, the solution was diluted with distilled water and makeup to the mark. The iodine solution thus prepared was standardized as-
  27. 27. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Standard sodium thiosulphate solution was taken with a graduated pipette in a conical flask. To this 10ml. of 4 N HCl and about 2ml. of 1% starch solution were added. This was titrated with iodine solution until light blue color is developed. D. Solution of sulphuric acid Stock solution of H2SO4 (Analar E. Merck) of desired strength was prepared by diluting the calculated volume (from specific gravity) of acid with distilled water and finally its concentration was determined by titrating it against standard NaOH solution using phenolphthalein as an indicator. E. Sodium thiosulphate solution Sodium thiosulphate solution was prepared and standardized by the method prescribed in the literature. F. Starch solution 1% Starch solution was prepared as per procedure given in the literature; this starch solution was used as an indicator. Kinetic measurements Kinetics of oxidation of glycolic acid under study by selenium dioxide in aqueous acetic acid as solvent has been followed iodometrically as follows: The glass stoppered reaction flask made of Pyrex glass containing substrate, acetic acid and other reagents if any, was kept together with a stock solution of selenium dioxide in a thermostat maintained at a desired temperature with an accuracy ±0.1. When the two flasks attained the temperature of thermostat, a required volume of selenium dioxide was pipette and transferred to reaction flask. At the instant half of selenium dioxide solution was added to the reaction flask, zero time was noted. Immediately 2 ml. aliquot was withdrawn into a flask containing 10ml. ice cold water and 10 ml. of 0.01
  28. 28. 28 sodium thiosulphate solution along with 5ml. of 4N HCl. About 2ml of starch solution was added to it and then un-reacted sodium thiosulphate left was titrated against standard 0.01N iodine solution until a light blue color is developed. Aliquots were with drawn at known intervals of time and concentration of selenium dioxide left un-reacted was estimated iodometrically. These readings are the values of (a-x) at time “t”. The experimental data were fed into the integrated form of equation for first-order reactions. The values of pseudo first-order rate constant obtained from the rate equation - Were found fairly constant within the experimental error suggested that each reaction obeys first-order kinetics. In order to study the effect of varying concentration of sulphuric acid on the reaction rate, kinetic runs have been carried out at varying concentration of acid, but at fixed substrate and oxidant concentration, solvent composition and temperature. Effect of temperature The rate of reaction was studied at different temperatures to evaluate various activation parameters such as temperature coefficient, frequency factors, and energy of activation, free energy of activation and enthalpy of activation and entropy of activation. 1. Temperature coefficient The temperature coefficient of the reaction for 50 and 100C rise in temperature was calculated by following expression: k = 2.303 t log a (a-x) k = 2.303 t log a (a-x)
  29. 29. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” 𝑇𝑒𝑚𝑝. 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 = 𝑘2 𝑘1 … … … … .. (1) Where, k1 is rate constant at temperature t and k2 is rate constant at 50 or 100C higher than ‘t’. 2. Energy of activation The effect of temperature on the rate of reaction given by Arrhenius equation – 𝑘 = 𝐴𝑒 − 𝐸𝑎 𝑅𝑇 ……………… …(2) Where, k is rate constant at absolute temperature T, A is frequency factor, Ea is the energy of activation, and R is the gas constant. From equation (2) we obtain- log 𝑘 = log 𝐴 − 𝐸𝑎 2.303𝑅𝑇 … … … … .. (3) Therefore, a plot of log k against inverse of T should be straight line having a- 𝑆𝑙𝑜𝑝𝑒 = − 𝐸𝑎 2.303𝑅 … … … …… … (4) The energy of activation was determined graphically and also by calculating from equation: 𝐸𝑎 = 2.303𝑅𝑇1 𝑇2 𝑇1 − 𝑇2 𝑙𝑜𝑔 𝑘2 𝑘1 … … … . (5) Where k1 and k2 are constant at temperature T1 and T2 respectively. 3. Frequency factor By rearranging equation (3) frequency factor “A” can be obtained as log 𝐴 = log 𝑘 + 𝐸𝑎 2.303𝑅𝑇 … … … … .. (6) The values of frequency factor obtained from equation (6) have been reported.
  30. 30. 30 4. Free energy of activation (G#) The free energy of activation (G#) is obtained using equation- –  𝐺# = 2.303 𝑅𝑇 𝑙𝑜𝑔 𝑘# … … … …… . (7) Where, k# = kr h / KBT Therefore, –  𝑮# = 𝟐. 𝟑𝟎𝟑 𝑹𝑻 𝒍𝒐𝒈 𝒌𝒓𝒉 𝑲 𝑩 𝑻 …… … …(𝟖) 5. Enthalpy of activation (H ) The enthalpy of activation (H ) of the reaction was obtained from the Eyring’s equation by plotting log krh/KBT vs. 1/T graphically. The slope of the plot is H  / 2.303R. 6. Entropy of activation (S#) The entropy of activation (S#) is calculated from the equation G# = H# – TS# --------- (9) Thus the values of the activation parameters viz. Ea, A, H#, G# and S# are calculated for each reaction. (D) Stoichiometry and product analysis The stoichiometry of each reaction understudy was determined under experimental conditions. The oxidation products of the reaction were identified chromatographically[63-64] and by spot test qualitatively[65]. (E) Test for free radicals The formation of free radicals during the course of reaction was tested using the solution of acrylonitrile (monomer) by trapping method[66-67].
  31. 31. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” CHAPTER - III EXPERIMENTAL KINETIC DATA In the chapter III, various experimental kinetic data are recorded in various tables, were computed. Various Graphs were plotted and facts have been made according to experimental data and graphs. SECTION: IIIA TYPICAL KINETIC RUN The preliminary studies reveal that the oxidations of Glycolic acid undertaken are measurable temperature at 308 to 323 K. The results so obtained were used to calculate the rate constant using integrated rate equation. The following typical kinetic runs representing the kinetic findings of the studies are carried out as: a) typical kinetic run for the effect of Selenium dioxide, b) typical kinetic run for the effect of substrates, c) typical kinetic run for the effect of sulphuric acid, d) typical kinetic run for the effect of dielectric constant of the medium, e) typical kinetic run for the effect of temperature.
  32. 32. 32 Fig.IIIA-1
  33. 33. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Table: IIIA-1 TYPICAL KINETIC RUN Effect of selenium dioxide [SeO2] : 2.50X10-3 (mol.dm.-3) [GA] : 2.50X10-2 (mol.dm.-3) [H+] : 1.25X10-3 (mol.dm.-3) HOAc-H2O : 30%(v/V), Temperature : 313 K. S. No. Time (sec.) Vol. of 𝑁 1000 hypo (ml.) 105k1(s-1) 1. 0 5.00 - 2. 1500 4.15 12.42 3. 3000 3.45 12.37 4. 4500 2.90 12.11 5. 6000 2.40 12.23 6. 7500 2.00 12.22 7. 9000 1.65 12.32 8. 10500 1.40 12.12 9. 12000 1.15 12.25 10. 13500 0.95 12.30 Average k1 =12.25X10-5(s-1) Graphical k1 =12.23X10-5(s-1)
  34. 34. 34 Fig.IIIA-2
  35. 35. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Table: IIIA-2 TYPICAL KINETIC RUN Effect of concentration of Glycolic acid [SeO2] : 2.50X10-3 (mol.dm.-3) [GA] : 2.50X10-2 (mol.dm.-3) [H+] : 1.25X10-3 (mol.dm.-3) HOAc-H2O : 30%(v/V), Temperature : 313 K. S. No. Time (sec.) Vol. of 𝑁 1000 hypo (ml.) 105k1(s-1) 1. 0 5.00 - 2. 2100 4.15 8.87 3. 4200 3.50 8.45 4. 6300 2.90 8.65 5. 8400 2.45 8.49 6. 10500 2.00 8.73 7. 12600 1.70 8.56 8. 14700 1.45 8.42 9. 16800 1.20 8.50 10. 18900 0.95 8.79 Average k1 =8.69X10-5(s-1) Graphical k1 =8.64X10-5(s-1)
  36. 36. 36 Fig.IIIA-3
  37. 37. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Table: IIIA-3 TYPICAL KINETIC RUN Effect of concentration of sulphuric acid [SeO2] : 2.50X10-3 (mol.dm.-3) [GA] : 1.25X10-2 (mol.dm.-3) [H+] : 1.00X10-3 (mol.dm.-3) HOAc-H2O : 30%(v/V), Temperature : 313 K. S. No. Time (sec.) Vol. of 𝑁 1000 hypo (ml.) 105k1(s-1) 1. 0 5.00 - 2. 1800 4.15 10.35 3. 3600 3.40 10.71 4. 5400 2.80 10.74 5. 7200 2.30 10.79 6. 9000 1.90 10.75 7. 10800 1.60 10.55 8. 12600 1.30 10.69 9. 14400 1.05 10.84 10. 16200 0.85 10.94 Average k1 =10.68X10-5(s-1) Graphical k1 =10.63X10-5(s-1)
  38. 38. 38 Fig.IIIA-5
  39. 39. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Table: IIIA-4 TYPICAL KINETIC RUN Effect of Dielectric constant of the medium [SeO2] : 2.50X10-3 (mol.dm.-3) [GA] : 1.25X10-2 (mol.dm.-3) [H+] : 1.25X10-3 (mol.dm.-3) HOAc-H2O : 20%(v/V), Temperature : 313 K. S. No. Time (sec.) Vol. of 𝑁 1000 hypo (ml.) 105k1(s-1) 1. 0 5.00 - 2. 1800 4.05 11.71 3. 3600 3.25 11.97 4. 5400 2.6 12.11 5. 7200 2.15 11.72 6. 9000 1.75 11.67 7. 10800 1.35 12.12 8. 12600 1.15 11.67 9. 14400 0.95 11.53 10. 16200 0.80 11.31 Average k1 =11.81X10-5(s-1) Graphical k1 =11.79X10-5(s-1)
  40. 40. 40 Fig.IIIA-6
  41. 41. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Table: IIIA-5 TYPICAL KINETIC RUN Effect of concentration of Temperature From the above tables it is clear that under different conditions the pseudo first order rate constants obtained are constant for Glycolic acid. The plot of log a/ (a-x) against time are obtained linear passing through origin (Fig. IIIA-1 to IIIA - 5). The rate constant evaluated from plot is good agreement with the respective calculated value. Therefore, therefore, It is, concluded that system, under study [SeO2] : 2.50X10-3 (mol.dm.-3) [GA] : 1.25X10-2 (mol.dm.-3) [H+] : 1.25X10-3 (mol.dm.-3) HOAc-H2O : 30%(v/V), Temperature : 323 K. S. No. Time (sec.) Vol. of 𝑁 1000 hypo (ml.) 105k1(s-1) 1. 0 5.00 - 2. 900 4.15 20.70 3. 1800 3.45 20.62 4. 2700 2.90 20.18 5. 3600 2.40 20.39 6. 4500 1.95 20.92 7. 5400 1.75 19.44 8. 6300 1.40 20.21 9. 7200 1.15 20.41 10. 8100 1.00 19.87 Averagek1 =20.30X10-5(s-1) Graphical k1 =20.24X10-5(s-1)
  42. 42. 42 obeys first order kinetics concluded, that each system, under study obeys first- order kinetics. SECTION: III B The experimental studies reveal that the oxidation of Glycolic acid undertaken is measurable temperature at 313 K. The results so obtained were used to calculate the rate constant using integrated rate equation. The following kinetic data i.e. rate constants; recorded and representing the kinetic findings of the studies are carried out as: Section III B-1: Dependence of rate on initial concentrations of SeO2, Section III B-2: Dependence of rate on the variation in the concentrations of Glycolic acid, Section III B-3 Dependence of rate on the variation in the concentrations sulphuric acid, Section III B-4: Dependence of rate on the variation in the % of composition of dielectric constant of the medium, Section III B-5: Dependence of rate on the variation in temperature Section III B-6: Thermodynamics parameters.
  43. 43. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium”
  44. 44. 44 SECTION: III B -1 Dependence of rate of oxidation reaction on the initial concentration of oxidant (SeO2) The dependence of rate on the initial concentration of oxidant was investigated by the varying in the concentrations of oxidant i.e. selenium dioxide (SeO2), while, the concentrations of other reactants are kept constant at their respective temperature. The summarized results recorded in the Table: III B-1 Table: III B-1 Summary: Dependence of rate of oxidation reaction on the initial concentration of oxidant (SeO2) Perusal of Table III B-1 and the plots of log (a-x) vs. time are linear with nearly uniform slope (Fig. III B- 1). Therefore, it is, concluded that the order of reaction is one with respect to oxidant. [SeO2] = 2.50X10-3 (mol.dm.-3) [GA] = 1.25X10-2 (mol.dm.-3) [H+] = 1.25X10-3 (mol.dm.-3) HOAc-H2O = 30%(v/V), Temperature = 313 K. [ SeO2]103 (mol.dm.-3) Glycolic acid 1.00 12.35 1.25 12.22 2.00 12.18 2.50 12.25 4.00 12.22 5.00 12.18
  45. 45. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Fig.IIIB-2
  46. 46. 46 Fig.IIIB-2(a)
  47. 47. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” SECTION: III B -2 Dependence of rate on the variation in the concentrations of Glycolic acid The effect of the concentration of Glycolic acid on the reaction rate was investigated by varying their concentration, while the concentration of other reactants was kept constant on their respective temperature. The results are recorded in the Table III B -2 Table III B -2 [SeO2] = 2.50X103 (mol.dm-3); [H+] = 1.25X102(mol.dm-3); HOAc-H2O = 30% (v/v) Temperature = 313 K . 102[GA](mol.dm.-3) 105k1(s-1) 1.00 8.69 1.25 12.25 2.00 17.77 2.50 22.66 4.00 35.14 5.00 42.53 6.25 53.81 Perusal Tables III B-2 and B-2a that the rate constants are increases with increase in the concentrations of substrate. The plot of k1 versus [LA] is obtained linear passing through origin (Fig.IIIB-2). The double reciprocal plot between 1/k1 and 1/ [substrate] is also obtained linear with passing through origin (fig. III B(2a)). Based on above results it is concluded that-(i) the plot of k1 vs. [substrate] is initially linear
  48. 48. 48 passing through origin, hence, the reaction follows first-order behavior with respect to the concentrations substrate. (ii) This evidence ruled out the formation of a complex during the reaction. Fig.IIIB-3
  49. 49. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” SECTION: IIIB-3 Dependence of rate on the concentration of Sulphuric acid The effect of the concentration of sulphuric acid on the reaction rate was investigated by varying their concentration, while the concentration of other reactants was kept constant on their respective temperature. The results are recorded in the Table III B-3. Table: IIIB-3 Summary: Dependence of rate on the variation of the concentration of sulphuric acid. [SeO2] = 2.50X103 (mol.dm-3); [GA] = 1.25X102(mol.dm-3); HOAc-H2O = 30% (v/v) Temperature = 313 K . Perusal of Table IIIB-3 shows that the first-order rate constant increases with increase in concentration of H2SO4 acid i.e. reactions is fully acid catalyzed. The plot of k1 vs. [H+] and log k1 versus log [H+] was obtained linear with positive slope (Fig. III B-3). [H+]103 (mol.dm-3) 105k1(s-1) 1.00 10.30 1.25 12.25 2.00 15.56 2.50 16.79 4.00 20.36 5.00 21.28 6.25 21.92
  50. 50. 50 Fig. III B-4
  51. 51. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” SECTION: IIIB-4 Dependence of rate on the dielectric constant of the medium In order to study the effect of solvent polarity, on the rate of reaction between Glycolic acid with selenium dioxide, experiments were carried out by taking varying composition of binary mixture of acetic acid water; maintaining the concentration of other reactants constant. The kinetic investigation was made at constant temperature the results are summarized in Table III E. Table: IIIB-4 Summary: Dependence of rate on the variation of the composition of binary solvent polarity. [SeO2] = 2.50 X10-3 (mol.dm-3) [GA] = 1.25 X10-2 (mol.dm-3) [H+] = 1.25 X10-3 (mol.dm-3) Temperature = 313K # Data of Dielectric constant of the medium aretaken fromN. venktasubramanian: J.Sci.,Indian res.,1961, 20 B,542. Perusal of Table IIIB-4, shows that the first-order rate constant increases with increase % of composition of acetic acid i.e. rate increases with increase in dielectric constant of the medium. The plot of log k1 versus 103/D was obtained linear with positive slope (Fig. III B-4). HOAc-H2O % (V/V) 103/D 105k1(s-1) 20 17.17 11.81 30 19.15 12.25 40 21.98 12.53 50 25.64 12.78 60 30.36 13.10 70 38.04 13.35
  52. 52. 52 Fig.IIIB-5
  53. 53. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” Fig.IIIB-6
  54. 54. 54 SECTION: III B-5 Dependence of rate on variation of temperature The dependence of rate on temperature was studied at four different temperatures for Glycolic acid with selenium dioxide while keeping the concentration of other reactants constant. The summarized results are recorded in Table III: B-5. Table: IIIB-5 Summary: Dependence of rate on temperature [SeO2] = 2.50X10-3(mol.dm-3); [H+] = 1.25X10-3(mol.dm-3), HOAc-H2O = 30% (v/v) , Temp. K 308 313 318 325 0C 35 40 45 50 [GA] 102 GLYCOLIC ACID (mol. dm-3) 1.25 8.93 12.25 15.95 20.30 2.00 11.14 15.28 19.61 24.61
  55. 55. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” SECTION: IIIB-6 THERMODYNAMIC PARAMETERS Various activation parameters namely temperature coefficient, energy of activation, frequency factor, free energy, enthalpy of activation and entropy of activation for each reaction are calculated and presented in the following Table. Table: IIIB-6 The Arrhenius plot had drawn between log k1 vs. the reciprocal of absolute temperature (Fig. III B-5). The value of energy of activation (Ea) is calculated from the slope of Arrhenius plot. The frequency factor (A) is calculated using graphical value of Ea. The enthalpy of activation (H#) is evaluated from the slope of the plot between the krh / kBT and 1/T (Fig. B-6). Where, kr is specific rate constant. The value of free energy of activation (G#) and entropy of activation (S#) is calculated by using Erying equation. These parameters are summarized in the (Table III B-7). [SeO2] = 2.50X103(mol.dm-3); [H+] = 1.25X103(mol.dm-3), HOAc-H2O = 30% (v/v) , Temp. Coefficient [GA] 102 GLYCOLIC ACID (mol. dm-3) 1.25 1.371 1.302 1.272 1.786 2.00 1.317 1.452 1.366 1.914
  56. 56. 56 Table: III B-7 THERMODYNAMIC PARAMETERS [SeO2] 103 (mol.dm-3) = 2.50(1-3); [H+ ] 103(mol.dm-3) = 1.25(1); HOAc-H2O % (v/V) = 30(1-3), Temperature K = 313(1-3). Substrate Ea KJ mol-1 A s-1 ∆H# KJ mol-1 ∆G# KJ mol-1 ∆S# JK mol-1 GLYCOLIC ACID 48.03 ±0. 66 2.36x107 ±0.76 49.83 ±0.97 -87.68 ±0.58 -99.45 ±0. 57
  57. 57. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” STOICHIOMETRY AND PRODUCT ANALYSIS The stoichiometry of the reaction of oxidation of Glycolic acid with SeO2 in presence of sulphuric acid, in aqueous-acetic acid medium was determined in duplicate at their experimental temperature by following procedure. In stoichiometric determination, the experiments were planned and designed, in which the oxidant concentration was in excess (10 times) over the concentration of substrate. The binary composition of H2O and CH3COOH were taken similar to their respective runs. The calculation volume of the reactants were mixed and maintained in a thermostat at the experimental condition of temperature, for sufficient time that is until there is no change in SeO2 concentration. The SeO2 un-reacted in each reaction mixture is, then estimated separately, periodically by titrating a definite volume of the reaction mixture iodometrically3. Thus, the quantity of SeO2 used up to oxidize a definite quantity of each substrate understudy completely is calculated. The results are recorded in Table: IV-1. 3 Vogel’s text book of practical organic chemistry,5th edn. pp. 1235, Johon wiley & sons inc., 605,avenue, New York
  58. 58. 58 Table: IV-1. Summary: Stoichiometry of the oxidation of Glycolic acid–SeO2 system [H+ ] 103(mol.dm-3) = 1.25(1); HOAc-H2O % (v/V) = 30(1-3), Temperature K = 313(1-3). From these stoichiometric data, it is found that for complete oxidation of one mole of Glycolic acid, one mole of SeO2 is required. The stoichiometric equations empirically can therefore, represented as: The oxidation product of Glycolic acid presented in Table- IV-2 Table: IV-2 Oxidation products of Glycolic acid- SeO2 system Substrate Mole ratio Substrate SeO2 Products Glycolic acid 2:1 Sr. No. [substrate]103 (mol. dm-3) Initial [SeO2]102 (mol. dm-3) Final [ SeO2]103 (mol. dm-3) Consumed [ SeO2]103 (mol. dm-3) Mole ratio [ SeO2 ] [substrate] Glycolic acid 1. 4.00 4.00 31.89 8.11 2.02 2. 5.00 5.00 39.99 10.01 2.00
  59. 59. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” PRODUCTANALYSIS The final oxidation products of the reactions, under investigation were qualitatively identified by existing conventional methods.4,5,6,7 1. Test of free radicals The reactions of Glycolic acid with SeO2 showed an induction period. The presence of free radicals in the system understudy was tested qualitatively by addition of 1-2 ml of acrylonitrile (monomer) in about 5-6 ml of the reaction mixture employing trapping method. The non-occurrence of turbidity and white precipitate clearly indicates the absence of free radicals in the system8. 2. Identification of oxidation main end-product A 0.25 M solution of 2,4-dinitrophenylhydrazine, may be used for the preparation of derivatives of keto compounds. Dissolve 25 g of 2,4- dintrophenylhydrazine in 300 ml of 85 % perchloric acid in a 600 ml beaker on a stream bath , dilute the solution with 200ml. 95% ethanol, allow to stand and filter through a sintered glass funnel. it must be emphasized that this reagent is not suitable for the routine detection of carbonyl compounds since it also gives a precipitate in cold with certain amine, esters, and other compounds; if, however, a dilute solution of the keto compound in ethyl alcohol is treated with a few drops of the reagent and mixture diluted with water and heated, the precipitate produced with keto compounds generally not dissolves. Collect the crystals of 2,4-dinitrophenylhydrazone of keto and re-crystallized again wash, dried it, then determine the melting points to compare with reported melting points as following Table : IV-3 4 Feigel, F.: "Spot Test in Inorganic Applications", Elsevier, NewYork, Vol. I, 341 (1954). 5 Feigel, F. : "Spot Test in Inorganic Applications", Elsevier, NewYork, 12, 12 (1966). 6 Feigel, F. : Z. anal. Chem., 60, 28 (1921). 7 Feigel, F.: "Spot Test in Inorganic Applications", Elsevier, NewYork, 60, 189 (1966). 8 Gunjan singh : PhD thesis ,central library, A.P.S. University , REWA (M.P.) india (2004)
  60. 60. 60 Table: IV-3 Identification of oxidation products by the compared observed melting points and reported melting points 3. Test for selenium, reduction product of SeO2 Free selenium- The red precipitated selenium formed by the reduction of selenium dioxide in each reaction was tested as a small quantity of red precipitated Se was dissolved in the CS2 . The surface of a piece of silver foil was roughened with fine emery paper. The metal foil was the thoroughly cleaned. A drop of test solution was placed the foil and solvent(CS2) was allowed to evaporate. A gray fleck (of silver selenide) appeared, indicating that the red precipitate obtained was of free selenium9. 9 F. Feigel; “Spot test” Vol. I Inorganic Applications, Elsevier Publishing Co. London, p-341 (1954) Substrate Main oxidation product Melting points of 2,4-dinitrophenylhydrazone derivatives of oxidation products Observed melting point (0C) reported melting point (0C) Glycolic acid Formaldehyde 1550 0C 155.2 0C
  61. 61. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” DISCUSSION AND INTERPRETATION OF RESULTS Preliminary Remarks The problem entitled “Kinetic study on reactions of Glycolic acid with selenium dioxide in water acetic acid medium” deals with the mechanism of oxidation of Glycolic acid suggested that these reactions occur at measurable rate within a range of temperature (35- 50C). The detailed study of rate was switched on at measurable temperature i.e. 400C for respectively. Since there is a little difference between the activity of these compounds and therefore this point will be discussed in subsequent pages. It is found that under the condition [SeO2] << [substrate], is reaction follows first order kinetics in [SeO2], all these reactions are homogeneous and characterized by induction period. The induction period can be accounted in terms of slow approach of steady state. In these subsequent pages, we will give a comparative account of all the reaction studied. Chemical kinetics play very important role and adds valuable and precious wealth of information’s towards its literature as is obvious. The study of mechanism of organic compounds is a subject of major importance to all chemists for not only does it require consideration of the properties and reaction of both organic and inorganic compounds, but above all, it has vast implications in connective with the understanding of the nature of life. “No mechanism is perfect itself until unless is it’s supported by same kinetic data” ...Franklin
  62. 62. 62 GENERAL FEATURES FOR THE OXIDATION OF GLYCOLIC ACID WITH SeO2 Before elaborating the actual mechanism of the reaction path, it would be better at this stage to revisualize the results recorded in chapter III, which leads the following conclusion: (1) The kinetics data have been collected for variant in concentration of oxidant (SeO2) at fixed concentration of other reactants and temperature. The linear plots of log (a-x) vs. Time, suggested that the first order rate dependency with respect to oxidant. (2) Perusal Tables: IIIB (2-2a) that pseudo first-order rate increases with increase in the concentration of substrate. The plot of k1 versus [substrate] are obtained linear passing through origin (Fig.IIIB-2). The double reciprocal plot between 1/k1 and 1/ [substrate] is obtained linear with passing through origin ( Fig.IIIB-2). Based on above results it is concluded that- (a) The plot of k1 vs. [substrate] is initially linear passing through origin and reaction rate increases with increase in the concentration of substrate; hence, the reaction follows first-order behavior with respect to the substrate. (b) This evidence is the ruled out the formation of a complex during the reaction. (3) Reactions are fully acid catalyzed but velocity of the reaction slightly increases with increase the concentration of H2SO4 acid. The plot of k1 vs. [H2SO4] and plot of log k1 vs. log [H2SO4] is obtained linear with the positive unit slope, confirming that the reactions are fully acid catalyzed. (4) The first-order rate constant increases with increase composition of acetic acid i.e. rate accelerated with increase in dielectric constant of the medium. The plot of log k1 versus 103/D were obtained linear with positive slope.
  63. 63. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” (6) The presence of free radicals in the system understudy was tested qualitatively by addition of 1-2 ml of acrylonitrile (monomer) in about 5-6 ml of the reaction mixture employing trapping method. The non-occurrence of turbidity and white precipitate clearly indicates the absence of free radicals in the system. (7) Acetaldehyde was formed as the end-product of oxidation of Glycolic acid, which were identified by the determination of melting points of 2,4- dinitrophenylhydrazone derivatives of oxidation products and existing conventional methods. (8) The stoichiometric determinations have been suggested that 2:1 mole ratio for substrate and oxidant (SeO2). (9) Various activation parameters namely temperature coefficient, energy of activation (Ea), frequency factor (A), enthalpy of activation (ΔH#), free energy of activation (ΔG#), and entropy of activation (ΔS#) for each reaction are calculated for Glycolic acid– SeO2 system and according to the reaction mechanism, rate equation and order of reaction have been discussed. The iso-kinetic and Exner’s have been explained. Based on these results a probable reaction path for this oxidation might be proposed in the following subsequent pages. MECHANISM OF THE OXIDATION The kinetic data as summarized in the beginning of the various section of Chapter III reveal that the reaction velocity follows first-order kinetics. In the oxidation of Glycolic acid with SeO2 it was found that the respective kinetic findings in their finality are similar for substrate. It can, therefore, be concluded
  64. 64. 64 that for the oxidation of Glycolic acid with SeO2 the mechanism could be proposed as per following scheme: Rate Expression Taking into the consideration of various steps involved in the proposed mechanism, the rate equation could be derived as follows- Rate Expression Taking into the consideration of various steps involved in the proposed mechanism, the rate equation could be derived as follows- − 𝐝𝐜 𝐝𝐭 = [ 𝐇 𝟑 𝐒𝐞𝐎 𝟑 ] = 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟑 𝐒𝐞𝐎 𝟑.+ ] − 𝐤−𝟏 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞][ 𝐇 𝟑 𝐎+]… … (𝟔) The rate of formation of the main product cited by
  65. 65. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” + 𝒅𝒄 𝒅𝒕 [ 𝑷𝒓𝒐𝒅𝒖𝒄𝒕] = 𝒌 𝟐 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞] … … … … … … .(𝟕) On the execution of steady – state approximation − 𝐝𝐜 𝐝𝐭 = [ 𝐇 𝟑 𝐒𝐞𝐎 𝟑.+ ] = + 𝒅𝒄 𝒅𝒕 [ 𝑷𝒓𝒐𝒅𝒖𝒄𝒕] … … … … … … … … … … … …… … … … (𝟖) The net rate of formation of acid selenite is given as + 𝒅𝒄 𝒅𝒕 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞] = 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟑 𝐒𝐞𝐎 𝟑 .+ ] − 𝐤−𝟏 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞][ 𝐇 𝟑 𝐎+] − 𝐤 𝟐 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞] … … … … … … … … … … … … … … .(𝟗) At stationary state + 𝒅𝒄 𝒅𝒕 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞] = 𝟎 Therefore, 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟑 𝐒𝐞𝐎 𝟑.+ ] − 𝐤−𝟏 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞][ 𝐇 𝟑 𝐎+] − 𝐤 𝟐 [ 𝐀𝐜𝐢𝐝 𝐬𝐞𝐥𝐞𝐧𝐢𝐭𝐞] = 𝟎 …… … … … … … … …… … … … … … … … .(𝟏𝟎) Since, [ 𝐴𝑐𝑖𝑑 𝑠𝑒𝑙𝑒𝑛𝑖𝑡𝑒] = 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟑 𝐒𝐞𝐎 𝟑.+ ] {𝐤−𝟏 [ 𝐇 𝟑 𝐎+] + 𝐤 𝟐} … … … … … … …… … … … . .(11) Since then, [ 𝐇 𝟑 𝐒𝐞𝐎 𝟑.+ ] ∝ [ 𝐇 𝟐 𝐒𝐞𝐎 𝟑 ][ 𝐇+]… …… … … … … … … … … … … … …… … … (𝟏𝟐) On inserting the value of acid selenite from equation (11) to(6), The Reaction rate of take the form as
  66. 66. 66 + 𝒅𝒄 𝒅𝒕 [ 𝑷𝒓𝒐𝒅𝒖𝒄𝒕] = 𝐤 𝟐 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟐 𝐒𝐞𝐎 𝟑 ][ 𝐇+] {𝐤−𝟏 [ 𝐇 𝟑 𝐎+] + 𝐤 𝟐 } When, 𝐤 𝟐 ≫ 𝐤−𝟏 The rate of reaction becomes 𝒌 𝒐𝒃𝒔. = 𝐤 𝟏 [ 𝐒𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞][ 𝐇 𝟐 𝐒𝐞𝐎 𝟑 ][ 𝐇+]… … … …… . (𝟏𝟑) The derived rate equation (13) explains all the experimental facts, which are in good agreement with our experimental kinetic data i.e. the observed first order kinetic in [substrate], [oxidant] and [H+] ion etc.
  67. 67. “Kinetics and Mechanism of sulphuric acid oxidation of glycolic (GA) by selenium dioxide in aqueous-acid medium” CONCLUSIONS 1. Kinetic studies utilizing selenium dioxide as an oxidant in series of reaction lead us to conclude that the activity of it is much limited and needs to be explored in a Broadway. It possesses vital potentiality with two-electron system and displays interesting behaviors at moderate condition of temperature. 2. SeO2 is mild, economically cheap oxidant, easily available in market and it possesses vital potentiality with two electron systems and displays interesting behaviors at moderate condition of temperature to reduce the cost of the oxidation reactions involved especially in drugs and pharmaceutical industries and also in soft drink or cold drink industries. 3. This study will act as a milestone and will pave the way for future researcher to enlighten the mechanism utilizing SeO2 as an oxidant for some other organic compounds like disulphide, Anthranyl Styryl Ketone, chalcones, aliphatic ketones, amines and amino acids in the similar manners and also can be catalyzed by phosphotungstic acid and micelles like CTAB etc. The contribution and information through kinetic study will enrich chemical literature to a great extent in journals. 4. Its applied aspects may be judged in lather industries10, analytical, chemical separation, and identification of organic compounds and paper and pulp industries11. 10 V. Priya, M. Balasubramaniyan and N. Mathiyalagan: J.Chem.Pharm.Res.,2011, 3(1):522-528 11 S.B.Patwari,S.V.Khansole andY.B.Vibhute : J.Iran.Chem.Soc., Vol.6, No.2, 2009, pp. 399-404.
  68. 68. 68 5. This work can better and suitably be utilized some branches of science to which kinetics is relevant are – Branch : Application of kinetics Biology : Physiological process (e.g. digestion and metabolism), bacterial growth, tissues growth of malignancy. Chemical engineering : Reactor design Electrochemistry : Electrode processes Geology : Flow processes Inorganic chemistry : Reaction mechanism Mechanical Engineering : Physical metallurgy, Crystal dislocation mobility. Organic chemistry : Reaction mechanism Pharmacology : Drug action, pharmacodynamic Physics : Viscosity, diffusion, nuclear processes Psychology : Subjective time, memory.
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