1. The experiment aims to perform the assay of Ibuprofen as per Indian Pharmacopoeia. 2. Ibuprofen is titrated with 0.1M sodium hydroxide solution using phenolphthalein as indicator. 3. The percentage purity of Ibuprofen is calculated based on the titration results.

1. 1. Experiment name: Preparation of Benzimidazole.
Aim: To synthesize Benzimidazole from o-phenylenediamine.
References:https://labmonk.com/synthesis-Benzimidazole-from-o-
phenylenediamine.
Requirements:
Chemicals: o-phenylenediamine, formic acid, sodium hydroxide.
Apparatus: Beaker, Round bottom flask, Buchner funnel, measuring cylinder,
filter paper.
Procedure:
Dissolve 27gm of o-phenylenediamine in a round bottomed flask of 250ml and
add 17.5gm of formic acid. Heat the mixture on a water bath at 100◦c for 2hrs.
Cooland add 10% sodium hydroxide solution slowely, with constant rotation of
the flask, until the mixture is just alkaline to litmus. Filter off the synthesized
crude benzimidazole byusing the pump, wash with ice cold water, drain well and
wash again with 25ml of cold water.
Recrystallization with dissolve the synthesized productin 400ml ofboiling water,
add 2gm of decolorizing carbon and digest for 15min. filter rapidly through a
preheated Buchner funnel and a flask at the pump. Coolthe filtrate to about 10◦c,
filter off the benzimidazole, wash with 25ml of cold water and dry at 100◦c. The
yield of pure benzimidazole, m.p. 171-172◦c is 25gm.
Principle:
The two carbon-nitrogen bonds in benzimidazole when disconnected give o-
phenylenediamine and formic acid. Therefore, synthesis of benzimidazole is
affected by simply heating the o-phenylenediamine and formic acid together
(condensation type of reaction)
Reaction:
I. Preparation of drugs/intermediates

2. Mechanism:
Conclusion:Benzimidazole was synthesized and the percentage yield was found
to be __________%.

3. 2. Experiment name: Preparation of Benzotriazole
Aim: To prepare benzotriazole from o-phenylenediamine.
References: https://labmonk.com/synthesis-of-benzotriazole
Requirements:
Chemicals: o-phenylenediamine, glacial acetic acid, sodium nitrite
Apparatus: Beaker, Buchner funnel, measuring cylinder, filter paper.
Procedure:Dissolve 10.8 g of o-phenylenediamine in a mixture of 12 g ofglacial
acetic acid and 30 ml of water contained in a 250 ml beaker; slight warming may
be necessary. Cool the clear solution to 15 °C, stir magnetically and then add a
solution of 7.5 g of sodium nitrite in 15 ml of water in one portion. The mixture
gets warm and reaches a temperature of about 85 °C within 2-3 min and then
becomecoolwhile the colourofthe mixture changes from deep red to pale brown.
Continue stirring for 15 min, by which the temperature will have dropped to 35-
40 °C, and then thoroughly chill in an ice-water bath for 30 min. Collect the
product by vacuum filtration of the pale brown solid which separates and wash
with three 30 ml portions of ice-cold water.
Recrystallization: Dissolve the solid in about 130 ml of boiling water, add
decolourising charcoal, filter and allow the filtrate to cool about 50 °C before
adding a few crystals of the synthesized product (benzotriazole) which have been
retained for seeding. Allow the mixture to retain room temperature slowly (to
avoid the separation of material as an oil) and then thoroughly chill in ice and
collect the benzotriazole which separates as pale straw-coloured needles, m.p. 99-
100 °C. A second crop may be obtained by concentrating the filtrate. The yield is
about 8 g. The benzotriazole crystallises much more readily from benzene (55
ml) but the material is still slightly coloured. A pure white product can be
obtained by sublimation at 90-95 °C at 0.2 mmHg.
Principle: Benzotriazole can be prepared by treating o-phenylene diamine with
nitrous acid (liberated during the reaction between sodium nitrite and acetic acid)
to form mono diazonium salt that follows spontaneous intramolecular cyclization
reaction to produce benzotriazole.

4. Reaction:
Mechanism:
Conclusion: Benzotriazole was synthesized and the percentage yield was found
to be __________%

5. 3. Experiment name: Preparationof Benzocaine
Aim: To synthesize Ethyl p-amino benzoate (benzocaine) from p-amino
benzoic acid.
References:https://labmonk.com/synthesis-of-benzocaine
Requirements:
Chemicals: p-amino benzoic acid, conc.H2SO4 , Sodium carbonate, rectified
spirit, charcoal.
Apparatus: Thermometer, conical flask, round bottom flask, refluxes condenser,
Buchner funnel, funnel, stirrer, and beaker.
Procedure:
Place 4gm of p-Amino benzoic acid, 27ml of absolute alcohol and 5ml of
conc.H2SO4 in a dry 100ml round bottom flask fitted with a reflux condenser.
Reflux for 2 hours on a water bath till it becomes a clear solution. Pour the hot
solution in 80ml of water. If no solid separates, then add little decolourizing
carbon, stir and filter. To the filtrate in 250ml beaker add slowely solid sodium
carbonate till it is neutral to litmus. Cool and filter the product under suction.
Recrystallize the product from 2:1 ethanol-water mixture. Dry the productin air
and determine yield and melting point.
Principle:
Benzocaine is synthesized by Fisher Esterification reaction, which converts
carboxylic acid and alcohol directly to ester by an acid catalyzed nucleophilic
acyl substitution reaction. The interaction between a carboxylic acid and an
alcohol is a reversible process and proceeds very slowely. Equilibrium is only
attained after refluxing for several days. If about 3% of either conc. sulphuric acid
or a dry hydrogen chloride is added to a mixture, the same point of equilibrium
can be reached after few hours. When equilibrium quantities of acid and alcohol
are employed, only two-third theoretically possible yield of ester is obtained.
According to law ofmass action, the equilibrium may be displaced in ester by the
use of excess of the components. It is frequently convenient to use an excess of
the acid, but if the acid is expensive a large excess of alcohol is generally
employed. Since sulfuric acid is used in esterification, benzocaine exists as
sulphate salt. To release free ethyl-4-amino benzoate, sodium carbonate is added.
Excess of sodium carbonate if added can cause a base catalyzed hydrolysis of
ester. So it should be added just to make the pH neutral.

6. Reaction:
Mechanism:
Conclusion: Benzocaine was synthesized and the percentage yield was found to
be __________%.

7. 4. Experiment name: Preparation of phenytoin.
Aim: To prepare phenytoin from benzil and urea.
References: https://labmonk.com/synthesis- from-benzil-and-urea.
Requirements:
Chemicals: Benzil, Urea, sodium hydroxide, ethanol, concentrated hydrochloric
acid
Apparatus: Round bottom flask, reflux condenser, crystallizing dish-500ml,
heating mantle, stirrer,
Procedure:
Place 5.3gm of benzil, 3gm of urea, and 15ml of aqueous sodium hydroxide
solution and 75ml of ethanol in round bottom flask of 100 ml capacity. Set up a
reflux condenser with the flask and boil using an electric heating mantle for at
least 2 hrs. Cool to room temperature, pour the reaction mixture into 125ml of
water and mix carefully. Allow the reaction mixture to stand for 15 min and then
filter the product under suction to remove an insoluble by-product. Render the
filtrate strongly acidic with concentrated hydrochloric acid, coolin ice-water and
immediately filter off precipitated product under suction. Recrystallise at least
once from industrial spirit to obtain about 2.8gm of pure5,5-diphenylhydantoin,
m.p.297-298◦c.
Principle:
Base catalyzed reaction between benzyl and urea is used for synthesis of
phenytoin. The reaction is proceeding via intramolecular cyclization to form an
intermediate heterocyclic pinacol, which on acidification yield hydantoin as a
result of 1,2-diphenyl shift in pinacol rearrangement reaction.
Reaction:

8. Mechanism:
Conclusion: Phenytoin was synthesized and the percentage yield was found to
be __________%.

9. 5. Experiment name: Preparation of Phenothiazine
Aim: To prepare phenothiazine from diphenylamine.
Reference: http://www.prepchem.com/synthesis-of-phenothiazine/
Requirement:
Chemicals: Diphenylamine, Sulphur, anhydrous calcium chloride, alcohol.
Apparatus: Beaker, Buchner funnel, measuring cylinder, filter paper.
Procedure:
22 g of diphenylamine, 8.2 g of sulphur and 3.2 g of anhydrous calcium chloride
are melted together. The reaction sets 140-150 °C with the rapid evolution of
hydrogen sulphide; by lowering the temperature, a few degrees the reaction can
be slackened. When the reaction has moderated, the temperature is raised to 160
°C for a time. The melt, when cool, is ground up and extracted, first with water
and then with dilute alcohol. The residue consists of almost pure phenothiazine.
It can be recrystallised from alcohol. Yield 93%, yellowish leaflets; m.p. 180 °C.
Principle:
Phenothiazine is prepared by fusing diphenylamine with sulphur with rapid
evolution of hydrogen sulphide.
Reaction:
Conclusion: Phenothiazine was synthesized and the percentage yield was found
to be __________%.

10. 6. Experiment name: Preparation of Barbituric acid
Aim: To prepare barbituric acid from urea and diethyl malonate.
References: https://labmonk.com/synthesis-of-barbituric-acid-from-urea-and-
dimethyl-malonate
Requirements:
Chemicals: Sodium metal, Ethanol, Diethyl malonate, Urea, Calcium chloride,
Concentrated hydrochloric acid
Apparatus: Round bottom flask – 2000 ml, Reflux condenser, Beaker, Buchner
funnel, Measuring cylinder, filter paper
Procedure:
Assemble a double surface reflux condenser with a 2 litre round bottomed flask,
place 11.5g of clean sodium. Mix 250 ml of absolute ethanol in a portion and if
the reaction is unduly vigorous, immerse the flask within ice. When all the sodium
has completed reaction, add diethyl malonate 80 g (76 ml), followed by a solution
of dry urea 30 g in 250 ml of hot (70 °C) absolute ethanol. Shake the mixture
thoroughly, attach a calcium chloride guard tube to the top of the condenser, start
reflux of the mixture for 7 h in an oil bath and heat to 110 °C. A white solid will
be separated. Treat the reaction mixture with hot (50 °C) water 450 ml and then
with concentrated hydrochloric acid, with constantstirring, until the solution will
be acid (about 45 ml). Filter the resulting almost clear solution and leave it in the
refrigerator overnight. Filter the solid at the pump, wash it with 25 ml of cold
water, drain well and then dry at 100 °C for 4 hours. The yield of barbituric acid
is 50 g. It melts with decomposition at 245 °C.
Principle:
The synthesis of barbituric acid is affected by condensation of diethyl malonate
with urea in the presence of sodium ethoxide which may be prepared by reacting
Na metal with ethanol and it undergo cyclization reaction with diethyl malonate.
Reaction:

11. Mechanism:
Conclusion: Barbituric acid was synthesized and the percentage yield was found
to be __________%

12. 1. Chlorpromazine HCl
Aim:
To perform assay of chlorpromazine HCl.
References:
1) Indian Pharmacopoeia vol – II page no.1599
Requirements:
1) Chemicals: Acetone, 0.1 MPerchloric acid, Methyl orange etc.
2) Apparatus: Beaker, Pipette, Burette, measuring cylinder, conical flask etc.
Procedure:
Weigh accurately about 0.6 g, dissolve in 200 ml of acetone and add 15 ml of mercuric
acetate solution. Titrate with 0.1 M perchloric acid, using a saturated solution of methyl
orange in acetone as indicator. Carry out a blank titration.
1 ml of 0.1 M perchloric acid is equivalent to 0.03553 g of chlorpromazine hydrochloride.
Principle Theory:
The assay of chlorpromazine HCl can be carried out by using non-aqueous titration. In
the assay of chlorpromazine methyl orange used as indicator.
Reaction:
N
S
N
CH3
CH3
Cl
HClO4
N
S
NH
ClO4
Result: The % purity of chlorpromazine HCl was found to be---------
Conclusion:
II. Assay of Drugs

13. 2. Phenobarbitone
Aim: To perform assay of Phenobarbitone.
References:
1) IndianPharmacopoeiavol –IIIpage no.2900
Requirements:
1) Chemicals: Acetone, 0.1 MPerchloric acid, Methyl orange etc.
2) Apparatus: Beaker, Pipette, Burette, measuring cylinder, conical flask etc.
Procedure:
Dissolve 0.1g in5 ml of pyridine,add0.25 ml of thymolphthalein solutionand10 ml of silver
nitrate-pyridine reagentandtitrate with 0.1 M ethanolicsodiumhydroxide until apure blue
colour is obtained. Repeat the operation without the substance under examination. The
difference between the titration represents the amount of sodium hydroxide required.
1 ml of .0.1 Methanolic sodium hydroxide is equivalent to 0.01161 g of Phenobarbitone
PrincipleTheory:
Result: The % purity of phenobarbitone was found to be---------
Conclusion:

14. 3. Atropine sulphate
Aim:
References:
1) Indian Pharmacopoeia vol-II page no 1298
Requirements:
1) Chemicals: Acetone, 0.1 MPerchloric acid, Methyl orange etc.
2) Apparatus: Beaker,Pipette,Burette,measuringcylinder,conical flasketc.
Procedure:
Weigh 0.5 g, dissolve in 30 ml of anhydrous glacial acetic acid. Titrate with
0.1 M perchloric acid, determining the end-point potentiometrically. Carry
outa blanktitration.1ml of 0.1M perchloric acidisequivalentto0.06768 g of
atropine sulphate
Principle Theory: The assay of atropine sulphate was carried out by using end-
point potentiometry. The 0.1 M perchloric acid used for titration.
Result: The % purity of atropine sulphate was found to be---------
Conclusion:

15. 4. Ibuprofen
AIM:-
To perform ibuprofen including assay as per IP
REFERENCES
1. Tyagi S. A novel concept for enhancement of solubilization and bioavailability of poorly water
soluble drugs: hydrotropy: a review. Int J Pharm Res Biosci 2013;2:372-81.
2. Kapadiya N, Singhvi I, Mehta K, Karwani G, Dhrubo JS. Hydrotropy: a promising tool for solubility
enhancement: a review. Int J Drug Dev Res 2011;3:26-33.
3. Maheshwari RK, Rajput MS, Sinha S. Ecofriendly spectro photometric estimation of tinidazole in
tablet using Lignocaine hydrochloride as hydrotropic solubilizing agent. Asian J Pharm
2009;3(4):319-21.
4. Maheshwari RK, Rail N, Sharma S, Rajput MS, Soni S. New titrimetric analysis Fursemide in bulk
and tablet using mixed hydrotropy concept. Drug Invent Today 2010;2(4):223-5.
APPARATUS
Apparatus
1) 250ml Flask (3)
2) 50ml burettes (2)
3) 600ml beaker
4) Burette clamp
5) Water bath
MATERIALS AND METHODS
All chemicals & solvents used were of analytical grade. A Shimadzu UV/VIS Spectrophotometer with 1
cm matched silica cells was employed for spectrophotometric analysis.
Preliminary solubility study of Ibuprofen
Solubility of selected bulk drug ibuprofen was determined in distilled water and in 8M urea solution at
28±1 °. An excess amount of the drug was added to screw capped 30 ml glass vials containing distilled
water and 8M urea solution. The vials were shaken mechanically for 12 hr at 28±1 °, in an orbital shaker.
These solutions were allowed to equilibrate for next 24hr and then centrifuged for 5 min at 2000 rpm.
Supernatant of each vial was filtered through Whatman filter paper No.41. and filtrates were diluted
suitably and analyzed spectrophotometrically against the solvent blank.

16. Analysis of bulk sample of Ibuprofen by proposed method
For analysis ofibuprofen byproposedmethod(PM),accurately weighed quantityofibuprofen sample (0.2 gm) was
solubilized in 50 ml of 8M urea solution. The resultant solution was titrated with 0.1M sodium hydroxide solution
using 0.1 ml phenolphthalein as an indicator.Necessarycorrection was made by conducting blank determination
and the amount of ibuprofen drug was calculated.
Analysis of ibuprofen by Indian pharmacopeial method [13]
For analysis ofibuprofen byIndian Pharmacopeial method(IPM), accurately weighed quantityofibuprofen sample
(0.2 gm) was solubilized in 50 ml of ethanol (95%).The resultantsolution was titrated with 0.1M sodium hydroxide
solution using 0.1 ml phenolphthalein as an indicator. Necessary correction was made by conducting blank
determination and the amount of ibuprofen drug was calculated.
Table 1: Results of titrimetric analysis of ibuprofen bulk drug sample (n=3)
Method Percent drug estimated (mean±SD) % coefficient Variation Standard error
IPM 98.56±0.495 0.502 0.285
PM 98.67±0.640 0.648 0.369
STRUTURE OF IBUPROFEN
RESULTS AND DISCUSSION
From solubility study, it was found that there was more than 10 fold enhancement in solubility of
ibuprofen in 8M urea solution as compared to solubility in distilled water.
As evident from table no.1, the mean per cent estimated in the bulk drug sample of ibuprofen by I. P.
and proposed method was 98.56% and 98.67% respectively. The results of analysis by the proposed
method were very close to the results of analysis by standard Indian Pharmacopoeial method. This
confirms the accuracy of the proposed method.
The accuracy of the proposed method was validated statistically by low values of standard deviation,
% coefficient of variation and standard error.
CONCLUSION
Thus, it may be concluded that the proposed method of analysis is new, rapid, simple, cost‐effective,
environmentally friendly, safe, accurate and reproducible. This method can be successfully employed
in the routine analysis of ibuprofen in bulk drug sample. There is good scope for other poorly water
soluble drug which may be tried to get solublized by suitable hydrotropic agent to carry out their
titrimetric analysis excluding the use of costlier, unsafe, volatile, pollution causing organic solvents.

17. Procedures
1) 5.0g of the aspirinpreparedinthe previousexperimentwasweighintoaclean, dry250ml
Erlenmeyerflask.
2) 25ml of ethyl alcohol wasaddedtothe flaskandthe flaskwasswirledtodissolvethe aspirin.
Two dropsof phenolphthaleinwere added.
3) The sample with0.1M of NaOH was titratedtoa faintpinkendpoint.The volume of NaOH
usedwasrecorded.Thisvolume of base correspondstothatwhichisrequiredtoneutralize
all acidspresentinthe sample,impuritiesaswell asthe acetylsalicylicacid.
4) 15ml of the volume of base requiredinthe previoustitrationwasadded.Aboutthisvolume
of NaOHwas addedto the Erlenmeyerflaskfromthe burette.
5) The mixture washeatedina waterbath at temperature 90°Cto 95°C for 15 minutesto
hydrolyze the aspirin.The flaskwasswirledoccasionally.
6) The flaskwas cooledtoroom temperature byrunningitwithcoldtapwater.Two more
dropsof phenolphthaleinshouldbe addedif the solutionisnotpink.
7) The initial volume of HCl wasrecordedandthe excessbase wastitratedusingHCl until the
pinkcolordisappears.The volume of HCl usedwasrecorded.
PRINCIPLE:-
1) Acid-base titration
2) Back titration
THEORY:-
Acetyle salicylicacidundergoeshydrolysiswhentreatedwithwormsolutionof sodiumhydroxide
producingsodiumethanoate tofollowingreaction
Result
Molarityof NaOH=___ 0.1 _____M
Molarityof HCl =_____0.1_______
M Mass of aspirin=_____0.5_______g
 Volume of NaOHrequiredtoneutralizeall acidmaterial
Final reading =__________ml

18. Initial reading =__________ml
Volume of NaOH =_________ml
Milimoles of NaOH =_________
 Volume of NaOHusedinhydrolysis
Final reading =_________ml
Initial reading =_________ml
Volume of NaOH =_________ml
Milimolesof NaOH
 Volume of HCl inback titration
Final reading =__________ml
Initial reading =__________ml
Volume of HCl =__________ml
Milimolesof HCl =__________
Milimolesof acetylsalicylicacid =__________
Grams of acetylsalicylicacidinsample =__________
Purityof aspirin(%) =__________
Sample calculation
Calculationof milimolesofacetylsalicylicacid
Milimolesof acetylsalicylicacid=milimolesof NaOHusedinhydrolysis-milimolesof HCl usedinback
titration
Calculationof grams ofacetylsalicylicacid in sample
Grams of acetylsalicylicacidinsample
=molecularweightof acetylsalicylicacidx molesof acetylsalicylicacid
1000
Calculationof purity of acetylsalicylicacid
Purity=gramsof acetylsalicylicacid x100%
Mass of aspirin
Conclusion
In conclusion,the experimentwas___________ because the resultsobtaineddeviatesfarfromthe
ideal resultswe expected.Percentage purityof the aspirinsample is________. However,we have
carriedout the titrationandback-titrationsuccessfully/unsuccessfully.The colourchangesinthe

19. solutionindicatesthere isanreactionoccurred/notoccurredwiththe base andacidusedfor
titration
5. Furosemide
Aim:-
To performfurosemideassayasperIP
References
1. DelgadoJN & RemersWA (Eds),WilsonandGirvold’sTextBookof Organicand Medicinal
and Pharmaceutical Chemistry,9thedn(JB LippincottCo.,Philadelphia,PA),1991, 525.
2. Foye W O (Ed),Principlesof Medicinal Chemistry,3rdedn(Lea& Febiger,Philadelphia,PA),
1989, 408.
3. Gaitonde CD & Jayade P P,IndianDrugs,28 (1991) 242. 4 Anapure SA,Khanna S & Dighe V
S, East Pharm,32 (1989) 193.
4. Stoberski P,Zakrezewski Z&Szulic A,Farm Pol,44 (1988) 398.
5. K Basavaiah*,U Chandrashekar&P Nagegowda IndianJournal of Chemical TechnologyVol.
12, March 2005, pp.149-155.
Apparatus and Material
6) 50ml burettes(2)
7) 600ml beaker
8) Burette clamp
9) Water bath
Experimental Procedure
Titrimetry
All chemicalsusedwere of analytical reagentgrade anddoubledistilledwaterwasusedtoprepare all
solutions. A bromate-bromide mixture (5 mMKBrO3- 50 mM KBr) was prepared by dissolving 0.835
of KBrO3 and6 g of KBr in wateranddilutingto1 L in a volumetricflaskandusedfortitrimetricwork.
Methyl orange indicator (0.5 %) was prepared by dissolving 50 mg of dye in 10 mL of water.
Hydrochloricacid(2 M) was preparedbydiluting177 mL of concentratedacid(S.d. Fine Chem.India,
sp. gr. 1.18) to 1 L with water.
Titrimetric assay
A 10 mL aliquotof pure drugsolutioncontaining 2-20mg of FRU wasaccuratelytransferredintoa100
mL titrationflask,10 mL of 2 M HCl was addedand titratedwithbromate-bromide mixture (5mMw.
r. t. KBrO3) using2 drops of methyl orange indicatortill the disappearance of the indicatorcolour.A
blanktitrationwasperformedandthe volumeof titrantwassubtractedfromthe volumerequiredfor
drug solution titration.
The amount of FRU in the measured aliquot was calculated from:
Amount (mg) = VMwR 0.333

20. Where V = volume of bromate-bromide consumed, mL
Mw = relative molecular mass of drug R = molarity of bromate-bromide mixture w. r. t.
KBrO3.
REACTION
Results and Discussion Optimisation of reaction conditions
Titrimetry
The quantitative nature of the reactionbetweenFRUand in situ generatedbromine wascheckedby
titrating2-20mgof drugtoamethyl orange endpoint.Inthe rangestudied,thereactionstoichiometry
was found to be 3:1 (FRU: KBrO3) which can be representedby scheme 1. The reaction was carried
out in HCl mediumandthe reactionstoichiometrywasfoundto be unaffected when 5-20 mL of 2 M
HCl was usedinatotal volume of 30-40 mL.The linearrelationshipbetweenthe drugamountandthe
titrationendpointisapparentfromthe calculatedcorrelationcoefficientof -------obtainedbythe best
fit line via least squares treatment.

21. Aim: To determine 1-octanol/water partition coefficients of ofloxacin, norfloxacin, lomefloxacin,
ciprofloxacin, pefloxacin and pipemidic acid from 293.15 K to 323.15 K by shake-flask method.
References
1. ZhangC,Yan W. DeterminationandCorrelationof 1-Octanol /WaterPartitionCoefficientsfor
Six Quinolones from 293 . 15 K to 323 . 15 K. Chem Res Chinese Univ. 2010;26 (4):636-639.
2. CongliangZ,YanW,FuanW. Determinationandtemperaturedependence of n-octanol/water
partitioncoefficientsforsevensulfonamidesfrom(298.15to333.15) K. Bull Korean ChemSoc.
2007;28(7):1183-1186. doi:10.5012/bkcs.2007.28.7.1183.
Principle
If a solute / drug is added to two immiscible liquids such as oil (organic phase) and water (aqueous
phase) incontact witheach other,the solute /drug distributesitself betweenthe twoliquidsandan
equilibriumissetup betweenthe solute moleculesinoil and solute moleculesinwater.The ratio of
the concentration of the solute in the two liquids is known as distribution coefficient or partition
coefficient.
Partition Coefficient = [Concentration of drug in oil or organic phase] /
[Concentration of drug in water or aqueous phase]
PartitionCoefficientof adrug is a measure of how well a substance distributesorpartitionsbetween
a lipid(oil) andwater.Highpartitioncoefficientmeansmore tendencytodistribute inlipidsandless
partition coefficient means less tendency to distribute. Partition Coefficient in the range of 1 to 2 is
supposed to predict passive absorption of drug across lipidic membranes. High partition coefficient
usually do not result in more absorption as high lipid solubility and less water solubility may cause
precipitationof drug in the intestinal fluid. For optimum absorption, a drug should have sufficient
aqueous solubility to dissolve in the intestinal fluid at the absorption site and lipid solubility high
enough to facilitate partitioning of the drug in the lipoidal membrane into blood vessels.
Requirements
Chemicals
1. Quinolones:ofloxacin,norfloxacin,lomefloxacin,ciprofloxacin,pefloxacinandpipemidicacid.
2. Double distilled Water
Apparatus
1. Mechanical shaker, water bath , glass flasks
2. UV absorbance, mass balance etc.
Procedure
1. 1-Octanol/water partition coefficient was measured by a shake-flask method. Both the
solvents were mutually saturated before performing the experiments.
2. Solutions of about 5×10–5 mol/L quinolones were prepared in aqueous buffer solutions.
3. Then 10.0 mL of 1-octanol was added to 10.0 mL of the aqueous quinolone solutionin glass
flasks.
III Determination of Partition coefficient of any two drugs

22. 4. The mixtureswerethenstirredina mechanical shakerfor1h.Sampleswereleftinwaterbath
and kept at the appropriate temperature (±0.02 K) for at least 72 h.
5. After that, the aqueous phases were isolated and the concentrations were determined by
measuring the UV absorbance.
6. The partition coefficients were calculated by mass balance. All the partitioning experiments
were performed in at least triplicate. 1-Octanol/water partition coefficients of ciprofloxacin
and sulfamethazine listed in Table 1 were measured, respectively, to complete the data
reported in the literature [1, 2].
Table 1 Measurement and references values for 1-octanol/ water partition coefficients (lgKow) of
some substances at 298.15 K
Substance lgKow exp lgKow ref
Ciprofloxacin 1.0825 1.0800
Kow=co/cw
where , Kow is 1-octanol/water partition coefficient of quinolone,
co is the concentration of quinolone in 1-octanol phase at equilibrium,
cw is the concentration of quinolone in aqueous phase at equilibrium.
Kow is actually the phase equilibrium constant for quinolone partitioned in 1-octanol phase and
aqueous phase saturated with each other at some temperature.
Observation and result
Substance ‘ co ‘ concentration of
quinolone in 1-octanol
phase
‘cw ‘ concentration
of quinolone in
aqueous phase
Partition
coefficient
Kow
Ciprofloxacin
Log p (K) = C1/C2
Where , K=Partition co-efficient,
C1 & C2=Concentration of solute in two immiscible liquids.
Conclusions
The results show that 1-octanol/water partition coefficient of each quinolone increases with the
increase of temperature. Based on the fluid phase equilibrium theory, the thermodynamic
relationship of 1-octanol/water partition coefficient depending on the temperature was proposed,
and the changes of enthalpy, entropy, and Gibbs free energy for quinolones partitioning in 1-
octanol/water were determined, respectively.

23. Aim: To determine 1-octanol/water partition coefficients of Sulfamethazine, sulfamethoxazole from
293.15 K to 323.15 K by shake-flask method.
References
1. CongliangZ,YanW,FuanW. Determinationandtemperaturedependence of n-octanol/water
partitioncoefficientsforsevensulfonamidesfrom(298.15to333.15) K. Bull Korean ChemSoc.
2007;28(7):1183-1186. doi:10.5012/bkcs.2007.28.7.1183.
Principle
If a solute / drug is added to two immiscible liquids such as oil (organic phase) and water (aqueous
phase) incontact witheach other,the solute / drug distributesitself betweenthe twoliquidsandan
equilibriumissetup betweenthe solute moleculesinoil and solute moleculesinwater.The ratio of
the concentration of the solute in the two liquids is known as distribution coefficient or partition
coefficient.
Partition Coefficient = [Concentration of drug in oil or organic phase] /
[Concentration of drug in water or aqueous phase]
PartitionCoefficientof adrug is a measure of how well a substance distributesorpartitionsbetween
a lipid(oil) andwater.Highpartitioncoefficientmeansmore tendencytodistribute inlipidsandless
partition coefficient means less tendency to distribute. Partition Coefficient in the range of 1 to 2 is
supposed to predict passive absorption of drug across lipidic membranes. High partition coefficient
usually do not result in more absorption as high lipid solubility and less water solubility may cause
precipitationof drug in the intestinal fluid. For optimum absorption, a drug should have sufficient
aqueous solubility to dissolve in the intestinal fluid at the absorption site and lipid solubility high
enough to facilitate partitioning of the drug in the lipoidal membrane into blood vessels.
Requirements
Chemicals
1 Sulfonamides -Sulfamethazine, sulfamethoxazole,
2 Double distilled Water.
Apparatus
3 Mechanical shaker, water bath , glass flasks
4 UV absorbance, mass balance etc.
Procedure
2. 1-Octanol/water partition coefficient was measured by a shake-flask method. Both the
solvents were mutually saturated before performing the experiments.
3. Solutionsof about 5×10–5 mol/Lsulfonamides were prepared in aqueous buffer solutions.
4. Then10.0 mL of 1-octanol wasaddedto10.0mL of the aqueous sulfonamides solutioninglass
flasks.
5. The mixtureswerethenstirredina mechanical shakerfor1h.Sampleswereleftinwaterbath
and kept at the appropriate temperature (±0.02 K) for at least 72 h.
6. After that, the aqueous phases were isolated and the concentrations were determined by
measuring the UV absorbance.

24. 7. The partition coefficients were calculated by mass balance. All the partitioning experiments
were performedinatleasttriplicate.1-Octanol/waterpartitioncoefficientsof sulfamethazine
listedinTable 1 were measured,respectively,tocomplete the datareportedinthe literature
[1].
Table 1 Measurement and references values for 1-octanol/ water partition coefficients (lgKow) of
some substances at 298.15 K
Substance lgKow exp lgKow ref
Sulfamethazine 0.2598 0.2579[
sulfamethoxazole 0.8869 0.9000
Kow=co/cw
where , Kow is 1-octanol/water partition coefficient of sulfonamides,
co is the concentration of sulfonamides in 1-octanol phase at equilibrium,
cw is the concentration of sulfonamides in aqueous phase at equilibrium.
Kowis actuallythe phase equilibriumconstantfor sulfonamides partitioned in 1-octanol phase and
aqueous phase saturated with each other at some temperature.
Observation and result
Substance ‘ co ‘ concentration of
sulfonamides in 1-
octanol phase
‘cw ‘ concentration
of sulfonamides in
aqueous phase
Partition
coefficient
Kow
Sulfamethazine
sulfamethoxazole
Log p (K) = C1/C2
Where , K=Partition co-efficient,
C1 & C2=Concentration of solute in two immiscible liquids.
Conclusions
The results show that 1-octanol/water partition coefficient of each sulfonamides increaseswith the
increase of temperature. Based on the fluid phase equilibrium theory, the thermodynamic
relationship of 1-octanol/water partition coefficient depending on the temperature was proposed,
and the changes of enthalpy, entropy, and Gibbs free energy for sulfonamides partitioning in 1-
octanol/water were determined, respectively.