Medicinal chemistry i_lab_manual

EXPERIMENT NO: MEDICINAL CHEMISTRY I BNPCW
SYNTHESIS OF BARBITUTRIC ACID FROM DIETHYL MALONATE
AIM: To prepare and submit barbituric acid from diethyl malonate.
APPARATUS: Round bottom flask, Reflux condenser, Beaker, Glass rod, Buchner funnel,
Filtration apparatus.
CHEMICALS REQUIRED: Sodium, Ethyl malonate, Urea, Absolute alcohol, Hydrochloric
acid, Distilled water.
PRINCIPLE: Barbituric acid is based on a pyrimidine heterocyclic skeleton. Barbituric acid is
also called as 6-hydrouracil. It is odourless and soluble in water. It undergoes Knovenagel
condensation reaction. It is a nucleophilic addition of an active hydrogen compound to a
carbonyl group followed by dehydration reaction in which a molecule of water is eliminated.
Thus the catalyst is usually a weakly basic amine.
PROCEDURE:
STEP-1: In a 2 lit RBF fitted with a double surface reflux condenser place, 11.5gm (0.5gm
atom) of clean sodium and it is dissolved in 250ml of absolute alcohol. To this solution add
80gm (0.5mole of ethyl malonate) followed by 30gm (0.5mole of dry urea) dissolved in 250ml
of ethanol.
STEP-2: After being shaken well for some time, the mixture is refluxed for 7hrs on an oil bath
heated to 110˚. A white solid separates rapidly. After the reaction is completed 500ml of hot
water is added and then enough Hcl is added to make the solution acidic.
STEP-3: The clear solution is filtered and cooled in an ice bath overnight. The white product is
collected in Buchner funnel, washed with 50ml of cold water and then dried in an oven at 105-
100˚ for 3-4hrs. The yield of barbituric acid is 50gm (78%). It melts with decomposition at
254°C.
CATEGORY: Sedatives and Hypnotics.
DOSE: Over doses can cause respiratory problems and death.
USES: CNS Depressant, It is one of the four ingredients to make riboflavin.
REPORT:
1

SYNTHESIS OF PHENYTOIN FROM BENZOIN OR BENZIL.
AIM: To prepare and submit 5, 5 diphenyl hydantoin (phenytoin).
CHEMICALS REQUIRED: Benzil, Urea, Sodium hydroxide, Benzoin, Ethanol, Conc. Nitric
acid, Conc. Hydrochloric acid
PRINCIPLE: The method of synthesis consists of phenytoin in the base catalyzed condensation
of benzil. Phenytoin is synthesized by condensing benzil (1, 2 diketone with urea) intermediate.
Heterocyclic Pinacol undergoes rearrangement to give 5, 5 diphenyl hydantoin .This
rearrangement is called Pinacol Pinacolone rearrangement. This base catalyzed reaction sequence
is thought to be proceed via an intermediate heterocyclic pinacol, which on acidification yields
the required hydantoin. This procedure is generally applicable to all diaryl 1, 2- diketones. So all
diaryl 1,2 diketones are derivatives of hydantoin.
PROCEDURE:
STEP1: PREPARATION OF BENZIL
 Place 20g (0.099 moles) of crude benzoin and 100 ml of conc. Nitric acid in a 250 ml
round bottom flask.
 Heat on a boiling water bath with occasional shaking until the evolution of oxides of
nitrogen gas is ceased.
 Pour the reaction mixture into 300-400 ml of water contained in a beaker. Stir well until
the oil crystallizes as a yellow solid.
 Filter the crude benzil at the pump and wash it thoroughly with water to remove Nitric
acid. Recrystallize from ethanol or rectified spirit.
STEP2: SYNTHESIS OF PHENYTOIN
 Place 5.3g (0.025 moles) benzil, 3g of urea, and 15ml of 30% Sodium hydroxide in 75%
ethanol in a 250 ml round bottom flask.
 Attach the reflux condenser and boil under reflux using an electric heating mantle for
atleast 2 hours. Cool at room temperature and pour the reaction product into 125ml of
water and mix thoroughly.
 Allow to stand for 15minutes and filter under suction to remove insoluble byproducts.
Render the filtrate strong acidity with conc.Hydrochloric acid.
 Cool under ice bath and immediately filter off the precipitate under suction. Recrystallize
from rectified spirit. Melting point of phenytoin- 296°C
BRAND NAME: Dilantin
2

CATEGORY: Anticonvulsant drug
DOSE: Adults-300mg/day, children-5mg/kg/day
USES: Phenytoin is an anti-seizure medication. Used to treat patients suffering from epilepsy.
Useful for the prevention of tonic- clonic seizures, partial seizures.
ADVERSE REACTIONS: Enlargement of gums, nausea, vomiting, liver problems
REPORT:
3

SYNTHESIS OF PARACETAMOL FROM PARA-AMINO PHENOL
AIM: To prepare and submit paracetamol (acetyl para amino phenol).
APPARATUS REQUIRED: Conical flask, Beaker and Filtration apparatus.
CHEMICALS REQUIRED: Para amino phenol, Acetic anhydride, Ethanol and Distilled water.
PRINCIPLE: The synthesis of paracetamol is an acetylation reaction involving acetylation of
free primary amino group to acetamide group. Acetic anhydride undergoes rearrangement to give
an active acetylating species, ketone and acetic acid. Acetylation of para amino phenol involves 2
steps:
STEP 1: A fast step.STEP 2: Slow and is a rate determining step and involves the addition of
nucleophile.
Primary amino group are acetylated extremely, readily and hence it is possible to acetylate this
group selectively in compounds containing both an amino and hydroxyl group. Ex: P-amino
phenol.
PROCEDURE:
 Suspend 11gm (0.1M) of para amino phenol in 30ml of water contained in a 250ml
beaker in conical flask and add 12ml (0.127M) of acetic anhydride.
 Stir or shake the mixture vigorously and warm on water bath.
 After 10min, cool it, filter the solid acetyl derivative at the pump and wash with the
little cold water.
 Recrystallise from hot water (about 75ml) and dry upon filter paper in air.
 The melting point of paracetamol is 169 °C
BRAND NAME: Tylenol, Panadol.
CATEGORY: Antipyretic, Analgesic, Anti-inflammatory.
DOSE: 500mg to 1000mg (adult)
USES: It is used in fever, pain, osteoarthritis, low back pain, head ache, post operative pain etc.
ADVERSE EFFECTS:
 High doses of paracetamol causes liver damage, skin reactions, asthma.
 Paracetamol when taken recreationally with opioids cause loss of hearing.
 Over dose causes paracetamol toxicity. Its symptoms are vomiting, nausea, sweating, lose
consciousness.
REPORT:
4

SYNTHESIS OF 1,4-DIHYDRO PYRIDINE FROM ETHYL
ACETOACETATE
AIM: To prepare and submit 1, 4-dihydropyridine from ethyl acetoacetate.
CHEMICALS REQUIRED: ethyl acetoacetate, formaldehyde, diethylamine, rectified spirit,
ammonia, anhydrous calcium chloride.
PRINCIPLE: A 1,4-dihydropyridine dicarboxylate is also called a 1,4-DHP compound or a
Hantzsch compound.1,4-dihydropyridine is a six membered aromatic ring containing N at 1st
position, which is saturated at1 and 4th position are 1,4-DHP.The Hantzsch pyridine synthesis or
Hantzsch dihydropyridine synthesis is a multi-component organic reaction between aldehyde
such as formaldehyde, 2 equivalents of a β-keto ester such as ethyl acetoacetate and a nitrogen
donor such as ammonium acetate or ammonia.The initial reaction product is a dihydropyridine
which can be oxidized in a subsequent step to a pyridine. The driving force for this second
reaction step is aromatization.
PROCEDURE:
 Cool 52g (51 ml, 0.4mol) of ethyl acetoacetate to 0°c and add 15ml (0.2mol) of 40%
aqueous formaldehyde solution, followed by a few drops of diethylamine as a catalyst.
 Keep the mixture at 0°c for 6hrs and then at room temperature for 40hrs.
 Separate the lower organic layer, extract the aqueous phase with ether and dry the
combined organic fractions over anhydrous calcium chloride.
 Remove the ether under reduced pressure (rotary evaporator) and transfer the residue
together with an equal volume of ethanol to a stout reagent bottle cooled in an ice bath.
 Pass a steady stream of ammonium gas(from a cylinder) into the solution held at 0°c for
1hr,close the bottle with a bung securely attached with a wire and set the bottle and
contents aside at room temp for 40hrs.
 Filter the resulting yellow solution to remove a small quantity of almost colourless
material and heat the filtrate on a boiling waterbath in an evaporating dish until most of
the ethanol has been removed, and then cool and crystallize the residue from about 400
ml of rectified spirit.
 The yield of the pale yellow crystalline dihydropyridine derivative is 36g (71%).MP-181
to 183°c.
CATEGORY: Antihypertensive.
DOSE: Overdoses can cause heart failure and death.
USES: Used in the treatment of congestive heart failure, Cardiovascular diseases.
REPORT:
5

QUINAZOLINONE FROM ANTHRANILIC ACID (BENZOXAZINONE)
AIM: To prepare and submit anthranilic acid from benzoxazinone
APPARATUS: Beaker, measuring cylinder, round bottom flask, glass rod , measuring cylinder.
CHMECIALS: Anthranilic acid, benzoyl chloride,pyridine,N2H4.H2O.
PRINCIPLE: 2-phenyl-4(3H)-3, 1-benzoxazinone was synthesized from benzoylation with
simultaneous cyclization of anthranilic acid and benzyl chloride. Compound 1 was treated with
hydrazine hydrate to yield 3-amino-2-phenyl-4(3H)-quinazolinone. Reaction of compound 2
with aromatic aldehydes/ketones resulted Schiff bases.
PROCEDURE:
Synthesis of 2-phenyl-4(3H)-3,1-benzoxa-zinone (1)
 To a stirred solution of anthranilic acid (0.05 mol) in pyridine (25 ml), benzoyl chloride
(0.05 mol) was added dropwise, maintaining the temperature near 0-5 ˚C for 1h. The
reaction mixture was stirred for another 2h at room temperature until a solid product was
formed.
 The reaction mixture was neutralized with saturated sodium bicarbonate solution and the
pale yellow solid which separated was filtered, washed with water and recrystallized
from ethanol. M.P. 113-115 ˚C, Yield 83%.
Synthesis of 3-amino-2-phenyl-4(3H)-quina-zolinone (2)
 To a stirred solution of 1 (0.05mol) in pyridine (20ml), 80% N2H4.H2O (0.15mol) was
added.
 The reaction mixture was stirred and refluxed for 2h at 117 ˚C. After cooling, the crude
product was obtained by filtration and the crude product was recrystallized from ethanol
to afford 2 as a white product. M.P. 177-178 ˚C, Yield 88%.
Report:
6

SYNTHESIS OF FINOFIBRATE
AIM: To prepare and submit fenofibrate
CHEMICALS REQUIRED: 4-chloro-4′-hydroxybenzophenone, potassium carbonate, isopropanol,
Distilled water, isopropyl 2-bromo-2-methylpropanoate
PRINCIPLE: Synthetic method for obtaining an ester starting from a carboxylic acid which involve the
reaction of an alkyl halide with a metal salt of carboxylic acid.Fenofibrate is preferably obtained with a
good yield by reaction of 4-chloro-4′-hydroxybenzophenone with isopropyl 2-bromo-2-methylpropanoate
in the absence of solvent and in the presence of an alkaline agent, such as, in particular, potassium
bicarbonate.
PROCEDURE:
Step1: 200 g of 4-chloro-4-hydroxybenzofenone, potassium bicarbonate (156 g), 360 g of
isopropyl α-bromo isobutyrate and isopropanol (400 ml) were charged in a round bottom flask.
The mixture was heated to reflux temperature for 48 hours, with stirring.
Step2: After reaction completion, the reaction mixture was cooled at about 60°C, and isopropanol (560
ml), acetone (240 ml), and a decolorizing agent (4.5 g of activated carbon) were added.
Step3: The suspension was further cooled to about 40°C, and stirring was continued for about 30
minutes. The suspension was filtered, and the solid was washed on the filter with a mixture of isopropanol
and acetone. The filtrate was let to stand overnight at room temperature, and then stirred for additional 3-
4 hours at 0-5°C. Precipitated pure fenofibrate was filtered, washed on the filter with isopropanol and
water.
Step4: The compound was collected from the filter and dried at about 60° for 12 hours, to yield 220 g of
pure fenofibrate.Melting point is 79-83 °C
BRAND NAME: Fenoglide,tricor,lipofen.
DOSE: 145mg orally once a day
CATEGORY: Hypercholesteremic drug
USES: Fenofibrate is used to treat high cholesterol and high triglyceride levels and
cardiovascular diseases
ADVERSE EFFECTS: Nausea, headache, backpain, myalgia, nasopharyngitis
7

REPORT:
SYNTHESIS OF ISONIAZID FROM GAMMA PICOLINE
AIM: To prepare and submit Isoniazid from gamma picoline
CHEMICALS REQUIRED: Gamma picoline, sulphuric acid, potassium permanganate, and
hydrazine.
PRINCIPLE: Isoniazid is hydrazide of isonicotinic acid. It is derived from pure gamma
picoline which upon oxidation with potassium permanganate gives carboxylicacid derivative
(isonicotinicacid) which is later converted to ethyl ester upon treating with concentrated
sulphuric acid and methanol by esterification. Later by condensation, hydrazine (Isoniazid) is
obtained from hydrazine.
PROCEDURE:
Step 1: Use 100g (1.08mol) of 4-methyl pyridine (98%purity) and oxidize it with 450 g (2.84
mol) of potassium permanganate. Filter it and evaporate the combined filtrate and washings to
about 1500 ml and add concentrated hydrochloric acid until isonicotinic acid precipitates. Allow
the mixture to crystallize slowly. Collect the crude isonicotinic acid by suction filtration, wash
well with water and dry at 100° C
Recrystallise from hot water ,the resulting isonicotinic acid is pure.
Step 2: The above mixture is filtered. To the filtrate add 15 ml of alcohol and 2% of concentrated
sulphuric acid and add 8g hydrazine.The resultant Isoniazid is obtained.
CATEGORY: Antituberculer drug.
USES: Used to treat tuberculosis, it is used as antibiotic.
DOSE: 300mg orally once a week.
ADVERSE EFFECTS: Swollen joints, increased thirst, increased urination, tingling of arms.
BRAND NAME: Nydrazid.
REPORT:
8

SYNTHESIS OF ANTIPYRINE
AIM: To prepare and submit 3methyl 1phenyl pyrazole5one.
APPARATUS: Conical flask, Beaker, glass rod, Round bottomed flask,Reflux condenser,
Filtering funnel and Tripod stand.
CHEMICALS: Ethyl ester aceate, Phenyl hydrazine, Ether,Distilled water and Ethanol.
PRINCIPLE: The 3methyl 1phenyl pyrazole 5one is prepared by addition and crystallization of
the ethyl acetonadate and phenyl hydrazine. It is complete cyclo addition reaction.
PROCEDURE:
STEP1:
 Synthesis of 3methyl 1phenyl pyrazole
 Mix together 50grams [49moles, 0.389moles] of redistilled ethyl acetoacetate and
40grams [36.5ml, 0.37 moles] of phenyl hydrozene in a large evaporating dish.
 Heat the mixture on boiling under water bath in a fume cupboard for two hours and stir
with glass rod time to time.
 Allow the heavy reddish syrup and cool.
 Add about 100ml of ether and insoluble ether will solidify with in 15min.
 Filter the mixture solid at the pump and wash it thoroughly.
 Recrystallize it form hot water or from a mixture of equal volumes of ethanol and water.
Step 2:
 Synthesis of 2,3 – Dimethyl 1 – phenyl Pyrazole 5 one in a 500ml 3 necked flask eqiped
with a dropping funnel.
 A sealed stirrer unit and double surface condenser and set up in a frame cup board.
 Place a solution of 10 grams of NaOH in a small volume of water and a solution of 43.5
grams [0.25 moles of 3 methyl 1 – phenyl pyrazole 5 – one] in 20ml of methanol.
 Warm the mixture on a water bath and add 336 grams (27ml), 0.285ml of dimethyl
sulphate reflux the mixture for 1 hour and allow to cool with continuous stirring distell of
the methanol.
 Recrystallize the crude product from benzene (or) benzene like petroleum (or) hot water
with addition of little decolorizing carbon.
REPORT:
9

SYNTHESIS OF BENZOCAINE
AIM: To prepare and submit benzocaine.
CHEMICAL REQUIRED: p-nitrobenzoic acid,tin,conc.HCL,NH3, HCL-saturated
ethanol.
PRINCIPLE: Synthesis of ethyl p-amino benzoate [benzocaine] from p-nitro benzoic acid
involved 2 steps.
First step involves reduction with tin & HCL .secound step involves esterification.
Prior esterification of the carbonyl group yield a nitro-ester which cannot be reducted by a metal
acid reducing system, owing to possibility of hydrolytic cleavage of ester grouping.
So the conversion of the nitro group in to a amino group in this cases catalytic hydrogenation
acids. So catalyst reduction is followed by esterfication.metal acid reduction of nitro group yields
the acid reduction in which the final mixture requires carefully basification to effect preparation
of product , which is then esterified.
PROCEDURE:
Synthesis of p-amino benzene:
Place 15gm (o.09gm) of p-nitro benzoic acid in a 1 hour round bottomed flask fitted with a
reflux condenser. Introduce 35gm(o.295 M) of powdered tin and 75 ml of concentrated HCL.
Heat the mixture gently until the reaction commences & remove the flame. Shake the flask
frequently n take care that the insoluble acid adhering to the side of the flask is transferred to the
reaction mixture occasional gently warming may be necessary.After about 20 minutes most of
the tin will have reacted & a clear solution remains.Allow to cool some what & decant the liquid
in to the 1 liter beaker wash the residual tin by decantation with 15 ml of water & add. the
washing to the contents of the beaker add con. NH3 solution (d-0.88) until the solution is just
alkaline to litmus & digest the suspension of ppt hydrate tinoxide on a steam bath for 20mints
add 10gm of filter &steam bath stir well &filter add the pump & wash with hot water , transfer
the filter cake to the beaker, heat on water bath with 200ml of water to insure , extraction of the
produt & refilter con. the combined filtrate & washing until the vol. has been reduce to 175-
200ml filter of any solid with separate, acidify the liquid to litmus with CH3COOH & evaporate
on a waterbath until crystal commence to separate than cooliniser filter the crystal at the pump &
dry in a steam oventhe yield of p-aminobenzoic acid melting point=192 C,9.5gm(7.7%).
STEP 1: SYNTHESIS OF PABA(ESTERFICATION OF PABA)
Place 80ml of absolue ethanol in 250 ml of two necked fflask equipped with double surface
reflex condenser & gas inlet tube. Pass dry HCL throught the alcohol until saturated the increase
10

in weight is amino benzoate acid & heat mixture set to a solid mass of HCL of ethyl p-amino
benzoate. It is better however to pour the hot solution in to 300ml of water( no HCL separate )
add solid carbonate . carefully to the clear solution until it is neutral to litmus filter of the ppt
ester add pump n dry in air the yield of ethyl p-amino benzoate meliting point 91 C is 10 gm
(69%) recrystalization from rectified spirit does not effect the melting point
REPORT:
11

QUALITATIVE ESTIMATION OF HALOGENS[STEPNOW’s METHOD]
AIM: To estimate the number of halogens present in the given sample [stepnow’s method]
APPARATUS: RBF, Conical flask, beaker, reflux condensor, filtering funnel, glass rod.
REQUIREMENTS: Sample, sodium metal, mono ethanolamine, dioxan, silver nitrate, nitric
acid.
PROCEDURE: [PRINCIPLE]- A known weight of the given sample is reduced with sodium
and ethanol. The form sodium phthalate is acidified and precipitated as ether halide by adding
silver nitrate. Then the weight of silver halide is determined and % of halogens is calculated.
For this method but if not good for aryl halides and poly halogens compounds in a modification
of the method, a mixture of mono ethanolamine and dioxan is used instead mixture of
ethanol,mono ethanolamine has a hight boiling point[171 c] and gives satisfactory results.
PROCEDURE [STEPNOW’S METHOD]
 An accurately weighed amount of given sample [20-30mg] is placed in a RBF, fitted with
a reflux condenser.
 Freshly distilled mono ethanolamine [5ml], halogen free dioxan[5ml] and sodium metal
0.9g are added into the flask and warm till the vigorous reaction subside.
 Then the solution is reflux gently an hour with occasional shaking. Additional sodium
metal may be added .if whole of the sodium has disappeared, the flask is then cooled and
excess of sodium is destroyed by adding distilled water (2-3ml) .carefully through the
condenser followed by more water (5ml).
 Flask is washed with distilled water 2-3 times and the washings are collected in the same
beaker a dilute solution of silver nitrate is added drop by drop till the precipitation of
silver halide is completed .The ppt is filtered, washed with water, dried weighed.
REPORT:
12

QUALITATIVE ESTIMATION OF HYDROXYL GROUP
[ACETYLATION METHOD]
AIM: To estimate the number of hydroxyl group present in given sample (Acetylation method).
APPARATUS: RBF, reflux condenser, beaker, glass rod, conical flask.
REAGENT: Acetylation mixture, acetic anhydride, dry pyridine one mixed with the mixture is
transferred to a clean dry bottle and calcium chloride, guard tube is inserted into top of
burette.NaoH solution, phenolphthalein indicator, standardized with std. oxalic solution.
PRINCIPLE:
The acetylation method involves the replacement of hydrogen in an hydroxyl group in
alcohol,phenols by acetylation method by heating with a definite volume by a mixture of acetic
anhydride is hydrolysed by water the total free acetic acid is then estimated by titration with std.
NaoH using phenolphthalein as indicator.
The difference in a volume of NaoH solutions require in two experiment is equivalent to acetic
acid consumed in acetylation to the sample. By knowing the molecular weight of the compound
the no. of hydroxyl group can be calculated.
PROCEDURE:
 Two RBF (100ml) fitted with a reflux water condenser are taken and marked as A and B.
 An accurately weighed amount of sample [0.5g] is placed in a flask A and the mixture of
acetic anhydride and pyridine [10ml] is also added to the blank flask B.
 The flask are heated on a water bath for about one hour and then cooled .
 Distilled water[20ml] is added to each of flask through the condenser by shake it gently
for few min the flask are refluxed again for 2-5min cooled and allowed to stand for
10min.
 Finally, the contents of the flask are titrated with NaoH solution (1N) using phenapthaline
as indicator.
REPORT:-
13

QUALITATIVE ESTIMATION OF METHOXYL GROUP (ZIESEL’s
METHOD)
AIM: To estimate the number of methoxyl group present in the given sample(ziesel’s
method)
APPARARTUS: Round bottom flask, Reflux condenser, Beaker, conical flask, Glass rod.
REQUIREMENTS: Sample (given), hydrogen iodoide , phenol, propionic (or) acetic
anhydride, sodium acetate ,glacial acetic acid (20%) , bromine solution, aqueos sodium
antimony tartarate, sodium thiosulphate (0.05N), formic acid(98%), H2SO4(10%), dilute
HCL (1:1), marble chips, potaasium iodide, starch solution(indicator).
PRINCIPLE: A known weight of the substance is decomposed by heating with constant boiling
hcl.The evolved volatile methyl iodide can be estimated either gravimetrically (or)
volumetrically.
GRAVIMETRIC METHOD:The methyl iodide is removed from the boiling reaction mixture
by a slow stream of co2 and transfer to an absorption vessel containing 4% alcoholic solution of
silver nitrate. Silver iodide is precipitated, filtered and washed with dilute HNO3 and water ,
dried and finally weighed.
VOLUMETRIC METHOD
In this method, in a current of CO2 is transferred to an absorption vessel containing a mixture
of sodium acetate, aceti acid in a bromine solution. Iododine monobromide is first form, which is
oxidized to loric acid,
The iodic acid is then determined iodometrically byadding sodium acetate solution and formic
acid. (To desteroy the excess of bromine) followed by dilute H2SO4 and K2SO4 solution. The
liberated Iodine is treated with the sodium thiosulphate solution.
PROCEDURE:(ZEISEL’S METHOD)
 The given sample is weighed [5-10mg accurately in a small tin foil cup and close tightly
folding it]
 The sample is introduced in to the reaction flask and acetic or propionic anhydride [3-4
drops] is added followed by phenol [5-6 drops]to dissolve the sample .
 Freshly distilled HI [5ml] is then added in to reaction flask and CO2 gas is passed
through the reaction mixture at the rate of 1or 2 bubbles per second.
 The flask is gently heated at 125-130 degree centigrade for an hour .
 Then the absorption vessel is removed and tube is washed with distilled water ,then with
aqueous sodium acetate solution.
14

 The washings are collected in a clean iodide flask and the contents of absorption vessel
are also transferred in the same iodine flask.
 The excess bromine is then destroyed by addition of formic acid by drop by drop
 The complete removal of bromine is tested by the adding methyl red as indicator, the
colour of indicator persist when bromine is completely destroyed.
 The flask is shaken and allowed to stand for 2-3 mins.
 The KI [1g] is added followed by H2SO4 [10%, 10ml] the flask is stoppered, skaken and
allowed to stand for 5-10 mins.
 The liberated iodine is then titrated with NA thiosulphate solution using starch as an
indicator.
 The blank experiment is also performed simultaneously if all reagents is expect the
sample.
REPORT:
15

QUALITATIVE ANALYSIS OF CARBOXYL GROUP [SILVER SALT
GROUP]
AIM: To estimate the no of carboxyl group in the sample.
APPRATUS: Beaker, Round bottom flask, Glass rod, Measuring cylinder, Crucible.
CHEMICALS: Sample containing carboxyl group, 5% AgNO3,NH4OH solution.
PRINCIPLE: The silver salts of carboxylic acid can be easily prepared by treatment of
ammonium salt of carboxylic acid with AgNO3 solution. The silver salts of most of carboxylic
acid are insoluble or sparingly soluble in cold water. A silver salt on ignition decomposes and
gives a qualitative yield of metallic silver which can be determined.
Many silver salts are sensitive to light .Therefore drying of salts should be done under minimum
exposure to light. Further, this method is not used for acids containing halogens and sulphur due
to formation of silver halides and silver sulphides containing silver sulphate on ignition.
PRODURE:
 A weighed quantity of 0.5 g sample is dissolved in distilled water [25-30ml] in 250ml
beaker and ammonium hydroxide solution is added drop wise with continuous stirring till
solution gives a smell of ammonia.
 The solution is boiled gently to remove excess ammonia [check the ammonia vapours
with red litmus]. It is cooled and 5%AgNO3 solution is added with stirring until the
precipitate of silver salt is completed.
 The precipitate is filtered,washed thoroughly with water to remove excess AgNO3 and
drained well by passing the solvent with glass stopper .
 The ppt is transferred on a porous plate, dried in a desiccators and covered with a brown
paper to protect the ppt from light.The dried silver salt [0.3-0.4] is placed in a deied and
preweighed silicon crucible with a lid and weighed accurately .
 The crucible with a Bunsen burner from its upper portion is heated. The heated is
extended to the base of crucible slowly after 5min of low heating and then it is strongly
heated for 15-20 mins.
 Then cool it in a descicator and weigh.The heating process and weighing is repeated to
attain a constant weight.
REPORT:
16

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