Non-aqueous titrations are used for substances that are too weakly acidic or basic to titrate in water. The technique involves dissolving the substance and titrant in a non-aqueous solvent. There are four classes of non-aqueous solvents: protogenic solvents enhance basicity; protophillic solvents enhance acidity; amphiprotic solvents can act as acids or bases; and aprotic solvents are neutral. Common indicators used for non-aqueous titration include crystal violet, quinaldine red, and alpha-naphthal benzene. The substance being titrated can be categorized as behaving as an acid or base under the conditions, and an appropriate titrant

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.
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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
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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,
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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.
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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.
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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..
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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.
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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.
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10. References
 Vogel’s 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.
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