1

NON AQUEOUES TITRATION

BYDr. Suman PattanayakAssociate ProfessorDepartment of Pharma Analysis & QA.

Vijaya Institute of Pharmaceutical Sciences for Women

M. Pharm/ I SemAdvance Pharmaceutical Analysis

CONTENT Introduction Types Of Solvents 1. Aprotic solvents 2. Protophilic solvents 3. Protogenic solvents 4. Amphiprotic solvents Non Aqueous Titration Of Weak Acids Non Aqueous Titration Of Weak Bases

INTRODUCTIONDefinition Non aqueous titration are those in

which titration of weakly acidic or basic substances are carried out using non aqueous solvents so as to get sharp end point.

Non aqueous solvents the disadvantages of poor solubility and weak reactivity.

Moisture and corbondioxide should be avoided using non aqueous procedures.

Moisture should be held to less than 0.05%. Standerdisation &titration should be carried out

as far as possible at the same temperature.

In non aueous solvents the acidity is decreases in the following order

HCIO4> HBr>H2SO4>HCI>HNO3o HCl in water…….strongly acidico HCl in acetic acid……weakly acidico Acetic acid in water……weakly acidico Acetic acid in ammonia….strongly acidic

Types of solvents

The solvents are divided into 4 groups 1. Aprotic solvents

2. Protophilic solvents 3. Protogenic solvents

4. Amphiprotic solvents

Aprotic solvents(inert solvents) Aprotic solvents are neutral, chemically inert

substances such as benzene and chloroform. They have a low dielectric constant, do not react with

either acids or bases and therefore do not favor ionization.

The picric acid gives a colorless solution in benzene or toluene which becomes yellow on adding aniline shows that picric acid is not dissociated in benzene or toluene solution.

This type of solvents neither accept or donate protons

Ex:-Benzene , dioxan , chlprobenene,chloroform,ethyl acetate, carbon tetra chloride.

Protophilic solvent Basic in character and react with acids to form

solvated proton HB + Sol. ⇌ Sol.H+ + B- Acid + Basic solvent ⇌ Solvated proton + Conjugate base of

acid A weakly basic solvent has less tendency than a

strongly basic one to accept a proton. Similarly a weak acid has less tendency to donate

protons than a strong acid. As a result a strong acid such as perchloric acid

exhibits more strongly acidic properties than a weak acid such as acetic acid when dissolved in a weakly basic solvent.

Ex:-acetone , eheres, pyridine ,liquid ammonia

Protogenic solvents

Acidic in nature and donte protonsEx:- sulphuric acid , formic acid, propionoic

acid ,acetic anhydride etc.They have high dielectric constant and

ionisedBecause of their strength and ability to

donate protons.

Amphiprotic solvents

Have both protophilic and protogenic properties. This can acept or donate protons.Ex:-water , alcohols, acetic acid CH3COOH ⇌ H+ + CH3COO-

Here the acetic acid is functioning as an acid. If a very strong acid such as perchloric acid is dissolved

in acetic acid, the latter can function as a base and combine with protons donated by the perchloric acid to form protonated acetic acid., an onium ion”

HClO4 ⇌ H+ + ClO4-

CH3COOH + H+ ⇌ CH3COOH2+ (onium ion)

Since the CH3COOH2+ ion readily donates its proton to a

base, a solution of perchloric acid in glacial acetic acid functions as a strongly acidic solution.

When a weak base, such as pyridine is dissolved in acetic acid, equivalent amount of acetate ions are produced which have more tendency to acept protons.

Therefore, to titrate a solution of a weak base in acetic acid with perchloric acid in acetic acid, and obtain a sharp endpoint.

HClO4 + CH3COOH ⇌ CH3COOH2+ + ClO4

- onium ion

C5H5N + CH3COOH ⇌ C5H5NH+ + CH3COO- Acetate

ionCH3COOH2

+ + CH3COO- ⇌ 2CH3COOH Burette conical flask

Adding HClO4 + C5H5N ⇌ C5H5NH+ + ClO4-

DETERMINING END POINT

A. Potentiometric titrationB. Indicator method

C. Potentiometric titration : potentiometric method for the detection of the

equivalence point The end point is determined by using indictor

electrode(glass electrode) and reference electrode(saturated calomel electrode)

Indicator method:

Crystal violet (0.5 per cent in glacial acetic acid)

violet blue-green yellowis

h-greenα-Naphtholbenzein (0.2 per cent in glacial acetic acid)

blue or blue-green orange dark-

green

Oracet Blue B (0.5 per cent in glacial acetic acid)

blue purple pink

Quinaldine Red (0.1 per cent in methanol) magenta -------

almost colour less

Indictor Basic Neutral Acidic

Color changes

Thymol Blue yellow blue

Non Aqueous Titration of weak Bases

Solvents used in the titration of weak bases; Neutral solvents : Ex: -

alcohol,chloroform,benzene,chlorobenzene Acidic solvents: Ex:-formic acid,glacial acetic acid,propionic

acids Titrant used in the titration of weak basess: Ex:-Perchloric acid Indicatores used in the titration of weak bases Ex:-oracat blue ,crystal violet,1-

naphtholbenzein(weak bases) methyl red,methyl orange & thymol blue(stronger bases)

Many weakly acidic substances (aicohol or aprotic solvent)can be titrated in an appropiate non aqueous solvents with a sharp end point .

Ex:- acidic halides, acids,amino acids, enols(barbiturates,xanthines), phenols, pyrroles sulphonamides etc,.

1) Solvents used in the titration of weak acids: Ex:-Ethylenediamine,n-butylamine,morpholine

2) Titrant used in the titration of weak acids: Ex:-sodium methoxide, lithium methoxide, potasium

methoxide ,tetrabutyl ammonium hydroxide etc.

3) Indicatores used in the titration of weak acids Ex:-azo violet.thymol blue,thymolphthalein.,O-Nitro

aniline

Non Aqueous titration Of weak acids

REFERENCES:

Textbook of QUANTITATIVE CHEMICAL ANALYSIS : VOGEL’S

PHARMACEUTICAL TITRIMETRIC ANALYSIS:

A.A NAPOLEON

THAN

K YOU