NON AQUEOUS TITRATION.pptx
- 1. 1 Mrs. Prajakta B. Kothawade Assistant Professor, PES Modern College of Pharmacy, for ladies, Moshi, Pune
- 2. NON AQUEOUS TITRATION The non-aqueous titrations has replaced the aqueous titrations for many substances which are either too weakly acidic or too weakly basic. The principle and technique of this method is simple. It is based on the Bronsted-Lowrey and Lewis theory of acids and bases and, the nature and influence of levelling effect of non- aqueous solvents on substances. 2
- 3. NON AQUEOUS TITRATION The chemical reaction of acid HA with base B in aqueous solution is represented as HA------ H+ +A B + H2O ------- BH+ + OH 3
- 4. NON AQUEOUS TITRATION The non-aqueous solvents which are useful in analytical work can be classified into four classes: 1. Protogenic Solvents: These are acidic solvents and they enhance the basicity, of weak bases e. g. H2SO4,Formic acid. 2. Protophillic Solvents: These solvents are basic in nature and they enhance acidity of weak acids e. g. pyridine, n-butylamine, 4
- 5. NON AQUEOUS TITRATION 3. Amphiprotic Solvents: This category of solvents behave as acid or base depending upon the substance dissolved in it. They accept or donate protons and have levelling effect on the intrinsic strength of drugs. Glacial acetic acid dioxane. 4. Aprotic Solvents : solvents like benzene, carbon tretrachloride etc. are neutral in nature. These solvents do not accept or donate- protons. These are useful in dissolving- substances thus act as solvent and are useful for diluting solutions. 5
- 6. NON AQUEOUS TITRATION LEVELLING EFFECT Levelling Solvents: In general, strongly protophilic solvents are important toforce equilibrium equation to the right. CH3COOH + HClO4 CH3COOH2+ + ClO4 This effect is so powerful that, in strongly protophillic solvents,all acids act as of similar strength. HB B- + H+ The converse occurs with strongly protogenic solvents, whichcause all bases to act as they were of similar strength. Solvents, which act in this way, are known as LevellingSolvents. If the solvent is to be used for a differentiating titration it should be neither strongly acidic nor strongly basic to avoid "LEVELING" effects. 6
- 7. NON AQUEOUS TITRATION The non-aqueous titrations can be categorized mainly in two classes (a) Substances which behave as base under the condition of titrations. (b) Substances which behave as acid under the conditions of titrations.. 7
- 8. NON AQUEOUS TITRATION Thus substances which have both acidic and basic functional group like amino acid can be titrated as acid or base under appropriate conditions of titration. For determination of basic substances a solution of perchloric acid in glacial acetic acid in most commonly used as titrant. For determination of acidic substances a solution of tetrabutyl ammonium hydroxide in four volume of anhydrous toluene and one volume of anhydrous methanol is most commonly used as titrant. 8
- 9. NON AQUEOUS TITRATION Number of Indicator solutions have tried for detection of end point. Following indicator solutions have been found satisfactory. 1. Crystal violet 0.5 percent in glacial acetic acid. Color change is from violet to' blue green. 2. Quinaldine red - 0.1 percent in methanol. Color changes from pink to' colorless. 3. alpha-naphthal benzene- 0.2 per cent in glacial acetic acid Color changes from blue green to orange. 4. Oracet Blue B - 0.5 per cent in glacial acetic acid. Color changes from blue to' purple. 9
- 10. References Vogels Text Book of Quantitative Chemical Analysis, 6/Ed., Pearson Education, page no:41-50 and 363-383. Practical Pharmaceutical Chemistry Part-I by Beckett A H & Stanlake J B, 4/Ed., CBS Publisher & Distributors, page no:137-157 and 165. Pharmaceutical Analysis Vol. I & K. R. Mahadik, S.G. Wadodkar, H. N, I. More, Nirali Prakashan page no: 52-84. 10