DETERMINATION OF AMINES 1

DETERMINATION OF AMINES : 

DETERMINATION OF AMINES The following general methods may be used: Acetylation method Bromination method Non aqueous method Picrate method

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Acetylation method: The acetic anhydride is reacted with amines and gives acetic amine dervative and acetic acid. The excess of acetic anhydrate is determine by titrate with standard NaoH soln using PHP sol n as indicator ,end point is appearance of pink colour. Blank titration also carried out. Reaction: RNH₂ +(CH₃ CO) ₂ O RNH.COCH₃ +CH₃ COOH (CH₃ CO) ₂ O + H₂O 2CH₃ COOH CH₃ COOH + NaoH CH₃COONa + H₂O Reagents: 1. acetic anhydride in pyridine: acetic anhyride (one volume) + pure dry pyridine(3volumes) ↓ transfer to the semi micro burette, keep the soda lime guard at the top of the burette.

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Mixed indicator solun: Aqueous cresol red (one part of 0.1%) (neutralised with NaoH souln) + Aqeous thymol blue (3 parts of 0.1%) (neutralised with NaoH souln) the colour changes at PH 9.8 Alcholic NaoH souln: NaoH (18N) 20gm dissolved in aldehyde free ethonal (or) methonal in a volumetric flask.

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PROCEDURE: weigh 2mill equivalets amine into 250ml I₂ flask ↓ add 6ml of acetic anhydride-pyridine reagent. ↓ Insert the stopper and allow to stand at room temperature with frequent gentle agitation ↓ Cool flask under tap water. ↓ Add 10ml of water to the cup around the stopper. ↓ Loose the stopper so that water runs down the stoppr and walls of the flask.

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swirl the contents of the flask to ensure through mixing. ↓ Cool the flask under the running water or in ice,with the stopper partially open. ↓ Rince the stopper and walls of the flask with 10 ml of n-butanol. ↓ Add few dropes of mixed indicator. ↓ Titrate immediately with Std 0.5m alcoholic NaoH souln to apperance of blue colour. Prepare the blank titration also.

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Formula: % NH₂ ₌ (V₁ - V₂) X N₁ X 16.03 X 100 w X 1000 V₁ ₌ Blank NaoH solun . V₂ ₌ NaoH used for sample W ₌ Weight of sample N₁ ₌ Normality of NaoH.

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BROMINATION: bromination involves the iodometric titration , when bromine is react with phenol gives 2,4,6 tri bromo phenol and hydrogen bromide. Excess of bromine react with KI gives iodine and KBr. Iodine reacts with sodium thiosulphate gives sodium iodide Reaction : C₆H ₅OH + 2Br₂ 2,4,6 tribromo phenol +3HBr Reagents used: 1.potasium bromate-bromide soln : dissolve 0.2N KBro₃ of 5.567gm and 75 gm of KBr in water ↓ Dissolve to one litre in a volumetric flask. 2. Sodium thio sulphate soln: dissolve 0.1N 2Na ₂ So₃ , 25gm in 1 litre of penta hydrate freshly boiled and cooled distilled water 3.Starch indi cator soln: one gm of strach + 100ml of boiled water Br₂+ 2KI 2KBr +I ₂ I ₂+ 2Na ₂ So₃ 2NaI +Na₂S₄O₆

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↓ Boil the mixture for one minute ↓ Allow to cool and add 3 gm KI ↓ Transfer in to the stoppered bottle KI solution 20%: Dissolve 100 gm of KI in 400 ml of distilled water. Procedure : Weigh accurately about 0.25 gm of amine (eg; aniline ) into 250 ml volumetric flask . ↓ Disslove the sample in min vol of dil Hcl ↓ Make up to 250 ml with distilled water ↓ Pipette out 25 ml of the amine soln in to a 500 ml of iodine flask + 25 ml of bromate –bromide soln + 25 ml of water + 5ml con Hcl and stoppered the flask immeadiately. ↓ Shake the flask for 1 minute to mix the reagents and allow to stand for 10 min

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Coool the flask under tap water ↓ And place the 10 ml of KI soln in the cup arround the stopperd flask ↓ Slightly dislodge the stopper where upon the I₂ soln is drawn in to the flask with no loss of Br₂ ↓ Shake the flask for 30 sec and allow to stand for 5-10 min ↓ Remove the stopper and wash the neck of the flask with water ↓ Titrate the free I₂ with 0.1N sodium thio sulphate using 2ml of the starch indicator. perform blank titration Formula : % purity = ↓ (V₁N₂-V₂N₁) X M X 100 W X 2000 X Z

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NON AQUEOUS: REAGENTS 1.Perchloric acid inglacial acetic acid: mix 0.1N of perchloric acid(72 %) with 500ml glacial acetic acid in a litre volumetric flask ↓ Add 20 ml of pure acetic anhydride ↓ Mix the contents ↓ Dil to litre with glacIal acetic acid ↓ Allow to stand for over night to ensure the complete reaction of the acetic anhydride with the water present. 2.Methyl violet indicater: dissolve 30gm of methyl violet in 100ml of chlorobenzene. 3.crystal violet indicator: dissolve 1gm of crystal violet in 100ml of glacial acetic acid.

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Alfa Naphtho Benzein Indicator: dissolve the 0.5gm of alfa naphtho benzein in 100ml of glacial acetic acid. PROCDURE : dissolve about 0.3g accurately weighed of the amine in 50ml of glaceial acetic acid in 250ml of conical flask. ↓ add 3drops of crystal violet bule → blue green methyl violet violet → green ↓ titrate with per chloric acid Blank titration to done with 50ml of glacial acetic acid.

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Calculation: % purity = V₁ X N₁ X M X 100 w X 1000 V = vol of per acetous chloric acid N = normality of acetous perchloric acid M = molicular weigh amine W = weigh of sample

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PICRATE METHOD: the picrates of amines behaves as bases, when they aer dissolved in glaceial aceitic acid and titrated with acetous per chloric acid. when the salt (BH)+{(NO2)3C6H2O}- OR (BH)+ (PIC)- (BH)+ (PIC)- is dissolved in glaceial acetic acid, the picrate ions is sufficiently basic to to give a moderately satisfactory end point by potentiometric titration. (BH)+ (PIC)- (BH)+ (PIC)-

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PROCEDURE : prepare the picrate of base(eg: pyridine,piperdine,diethenolamine,or diethylamine) recrystalise from alcohol and dry it. ↓ Weigh acceuretely about 0.8gm of picrate and dissolve in50ml of glacial acetic acid. ↓ Add 2drops crystal violet indicator ↓ Titrate with acetous per chloric acid ↓ End point blue-green colour E.Wt = weight of picrate X 1000 vol of acetous per chloric acid X N

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Thank you