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BASIC METHODS Diazotisation Non-aqueous Bromination Argentometric


DIAZOTISATION Diazotization is commonly used for the determination of aromatic amino groups in industry. PRINCIPLE: When aromatic primary amines with nuclear –NH 2 groups can be determined quantitavely by standard sodium nitrite solution required to convert them into diazonium salts. Since the formation of diazonium compounds by diazotisation reaction,these method is called Diazotisation titration. CHEMICAL REACTION: C 6 H 5 NH 2 +NaNO 2 +HCl C 6 H 5 N 2 Cl+NaCl+2H 2 0 NaNO 2 +HCl HNO 2 +NaCl KI+HCl HI+KCl 2HI+HNO 2 I 2 +2NO+2H 2 O The iodine liberated reacts with starch to form a blue colour


DETERMINATION OF SULFADIAZINE REAGENTS: Sodium Nitrite (0.1M): 6.9g in 1000ml of water. Starch Indicator: 750mg KI +5ml water 100ml hot water + 2g of ZnCl 2 i n 10ml water + 5g of starch in30ml water ∆ 2min cooled

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PROCEDURE: 1gm of sulphadiazine +40ml of HCl +100ml H 2 O + starch iodide indicator Titrated with 0.1M NaNO 2 End point (Blue colour ) The blank titration should be taken between NaNO 2 and HCl

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CALCULATION: V1-V2) ×M× E.W W× 10 V 1 = vol of the NaNO 2 used in blank titration V 2 = vol of the NaNO 2 used for sample M = Molarity of NaNO 2 E.W=Equivalent weight of the sample W =Weight of the sample %Sulfadiazine =


NON-AQUEOUS Non-Aqueous titration are used for determination of weak acids and weak bases TYPES OF NON-AQUEOUS TITRATION : Acidimetry in non –aqueous titration Alkalimetry in non –aqueous titration The sulfanamides containing weak acid group,so we are using alkalimetry in non –aqueous titration. In these titration: Titrants used :Sodium methoxide,potassium methoxide,Lithium methoxide . Solvents: a. Strong base solvents: n-butyl amine , Morpholine b. Weak base solvents: DMF,Anhydrous pyridine Indicators: Azoviolet,O-nitroaniline,Thymolphthalein,p-hydroxy azobenzene


DETERMINATION OF SULPHATHIOZOLE REAGENTS: 0.1N alkali methoxide.Ex:CH 3 ONa: 40ml of methanol+50ml of toulene in a dry flask Add the sodium metal After complete dissolution add absolute methanol+add50ml of toulene Alternatively add methanol and toulene to get one litre of solution 2.Thymol blue: 0.3g of thymol blue+100ml of absolute methanol


PROCEDURE STANDARDISATION : Sodium methoxide Vs Benzoic acid 200-300mg benzoic acid+25ml DMF+2 drops thymol blue Direct the a stream of nitrogen passed into the flask Titrate with sodium methoxide solution Blue colour (End point) Perform the blank titration

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CALCULATION: MORALITY= W×1000 E.W×(A-B) A= Volume of titrant used for the blank sample B= Volume for titrant used for the benzoic acid E.W= Equivalent weight W= Weight of the benzoic acid

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ASSAY OF SULPHATHIOZOLE TABLETS: Weigh 20 tablets and grind it 1-2 Meq of sulphathiozole+25ml DMF+2 drops thymol blue Tritrate with sodium methoxide Blue colur (End point) Perform the blank titration.

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CALCULATION: % Sulphathiozole =(V 1 -V 2 )×M× E.W W× 10 V 1 = Volume of the titrant used for the blank solution V 2 = Volume of the titrant used for the sample solution M= Molarity of titrant E.W= Equivalent weight of the sample W= Weight taken .


BROMINATION PRINCIPLE: The sulfonamides reacts with bromine which will substitute on the benzene moiety The reaction is H 2 NC 6 H 4 SO 2 NHR+2HBr 2 H 2 NC 6 H 2 Br 2 SO 2 NHR+2HBr Br 2 +2KI 2KBr+I 2 I 2 +2Na 2 S 2 O 3 2NaI+Na 2 S 4 O 6

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METHODS FOR BROMINATION: Excess Method of Wojhan Direct Titration Method of Wojhan Excess Method of Conway Direct Method of Conway

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EXCESS METHOD OF WOJHAN: PROCEDURE: 0.2-0.3g of sulfadiazine+3gm of KBr+25% HCl slowly add 0.1N KB r O 3 untill yellow colour persists Add 1g of KI+starch (Indicator) Titrate with 0.1N Na 2 S 2 O 3 End point(Blue colour ) DIRECT TITRATION METHOD OF WOJHAN: Similar method except the indicator is changed (methyl red) and then titrated with 0.1N KBrO 3 and end point gives the disappearence of red colour

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EXCESS METHOD OF CONWAY: PROCEDURE: 0.25-0.35g of sulfadiazine in 2%NaOH in glass stopered flask Add 0.1N KBrO 3 -KBr(1-2ml)+80ml glacial acetic acid+5ml of conc HCl Shake the flask in 30sec and allowed to stand exactly in 1.5 min The excess bromine is titrated with 0.1N Arsenite Untill bromine colour is discharged DIRECT METHOD OF CONWAY: The sample prepartion is as above.Five drops of alcoholic methyl red are added.The solution is titrated with Bromate -Bromide to the disappearence of red colour .


ARGENTOMETRIC TITRATION PRINCIPLE: Argentometric titration is otherwise known as Precipitation titration Argentimetry involves the use of the standard solution of silver nitrate as the titrant for estimation of the hallides ( chlorides,bromides&iodides ) The hallides are estimated by titration against silver nitrate in two ways 1.MOHR’S METHOD 2.VOLHARDS METHOD

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MOHR’S METHOD : Neutral solution of hallides can be determined by this method PRINCIPLE: The neutral solution of hallide is titrated against the standard silver nitrate,the potassium chromate is used as indicator As the all hallides has been precipitated as silver hallide,then it combines with the potassium chromate to produce silver chromate. End point is the red colour CHEMICAL REACTION: NaCl+AgNO 3 AgCl+NaNO 3 ExcessAgNO 3 AgCr 2 O 7

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VOLHARD’S METHOD: Volhards method can be useful to determine the acid solutions of hallides . This method is used because the silver chromate which is formed in the end point of mohr’s method is dissolved in the acid. PRINCIPLE: In this method excess standard silver nitrate solution is added to the chloride in the conical flask,then silver chloride precipitated is formed. Then it is titrated against the standard ammonium thiocyanate . Ferric ammonium sulphate is used as the indicator Appearance of permanent red colour is formed. AgNO 3 +NaCl AgCl+NaNO 3 ExcessAgNO 3 +NH 4 SCN NH 4 NO 3 +AgSCN


REFERENCES K.A Connors :Text book of Pharmaceutical Analysis,Third edition,Page no:(62-63) Higuchi,Beckmman&Hassan :Pharmaceutical Analysis,second editiom,Page no:(137-157) V.N Rajasekharan,Text book of Pharmaceutical In Organic Chemistry,Page no (126-128)

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