Non-aqueous titration, Introduction, Theory & Principle, Solvents & Types of solvents, Indicator, Types of Non-aqueous titration, Methods of determination of end point, Assay of Sodium benzoate

1. NON-AQEUOUS TITRATION
PRESENTED BY,
GRACE SHAJI CHITTILAPPILLY
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL
CHEMISTRY
KARPAGAM COLLEGE OF PHARMACY,
COIMBATORE-32

2. CONTENTS
• INTRODUCTION
• THEORYAND PRINCIPLE
• SOLVENTS AND TYPES OF SOLVENTS
• INDICATORS
• TYPES OF NON-AQUEOUS TITRATIONS
• METHOD OF DETERMINING END POINT
• ASSAY OF SODIUM BENZOATE

3. INTRODUCTION
• Titrations which are carried out in the absence if aqueous medium are called as
non-aqueous titration.
• These are used for the assay of certain weak acids and weak bases which give
poor end point in aqueous solutions.
• Substance which are insoluble in water but soluble in non-aqueous solvents can
also be titrated by non-aqueous titrations.
• The simplicity, speed, precision and accuracy of Non aqueous titrimetric
methods,

4. are equivalent to those of the classical procedures.
• Moisture is to be avoided in using Nonaqueous procedures, since H2O being weakly
basic, would compete with the weak nitrogen base for the HClO4 and the sharpness of
the endpoint would be lost.
• It has been found that the moisture content in Nonaqueous titrimetry should be held
to less than 0.05% so as not to have any appreciable effect on the end point.
H2O HClO4 H3O+
ClO4
-
RNH2 HClO4 RNH3
+
ClO4
-
+ +
+ +

5. • Greater care in the control of temperature during the standardisation and analysis
procedures is necessary when utilizing Nonaqueous titrimetric.
• Because Non-aqueous solvents in general have greater coefficients of expansion than
water, so that small temperature difference can cause significant errors unless suitable
correction factors are used.
• Standardization and titration should be carried out as far as possible at the same
temperature.
• Volume of titrant may be corrected by applying the following formula,
Vc = V[1 + 0.001(t1 – t2)]

6. Where, Vc – corrected volume of titrant
V – volume of titrant measured
t1 – temperature at which titrant was standardised
t2 – temperature at which titration was carried out.
TYPE OF TITRANT SOLVENTS
Non-aqueous acidic titrants Perchloric acid, Fluorosulphonic acid, p-toluene sulphonic
acid
Non-aqueous basic titrants Sodium methoxide, Potassium methoxide, Lithium
methoxide, Tetra alkyl ammonium hydroxide
Non-aqueous solvents/ vehicles Chloroform, Benzene, Pyridine, Ethylenediamine, Sulphuric
acid.

7. THEORY AND PRINCIPLE
o Non-aqueous titration is based upon Bronsted-Lowry and Lewis theory of acids and
bases,
o According to this theory, acid is a substance which ionizes to give a proton i.e., proton
donor and base is a substance which conjugates with a proton i.e., proton acceptor.
o In Non-aqueous solvents, it frequently become necessary to regard neutralization as a
reaction between weakly protophyllic substances which tend to accept a pair of
electrons and highly protophyllic substances which tend to provide a pair of electrons
in the formation of covalent bonds by coordination, i.e., a reaction btw acids and bases.

8. oAn acid undergoes ionization to give a proton and conjugate base of the acid.
oBase conjugates with a proton to give a conjugate acid of the base.
oTherefore, each acid has its conjugate base and every base has its conjugate acid.
oAccording to Bronsted-Lowry and Lewis theory of acid and bases,
1. Acid is a substance which is either,
a) An electrically neutral molecule (eg: HCl)
HB H+
B-
acid proton conjugated base
of acid
+
B H+
HB
conjugated acid
of base
+
base proton

9. b) A positively charged cation
c) A negatively charged anion
2. Base is a substance which is either,
a) An electrically neutral molecule
b) A negatively charged anion
REASON FOR NON-AQUEOUS TITRATION
 Rapid, accurate and simple to perform.
 Require no elaborate equipment.

10.  Extends the solubility range of certain water-insoluble substances like fats and oils.
 Very weak acids and very weak bases titrated in non-aqueous solvents.
 Mixture of 2 or more acids can be titrated using different solvents with each
individual acid giving separate end point.
Pharmaceutical preparations can be easily and accurately assayed.
 Primary, secondary and tertiary amino acid can be directly titrated.
Physiologically active components of a drug can be selectively titrated.
Mixture of amines can be easily analysed.

11. SOLVENTS USED IN NON-AQUEOUS
TITRATIONS
IDEAL PROPERTIES
It should be pure and non-toxic.
It should be miscible with both the titrant and the solute.
It should not produce any undesirable effects by interacting with the titrant or solute.
It should have high dielectric constant.
It should not interfere with the end point of titration.
It should be readily available and inexpensive.

12. EFFECTS OF SOLVENTS
1. LEVELLING EFFECT OF SOLVENT
The tendency of a strong acid to enhance the basicities of a weak base and that of a strong
base to enhance the acidity of a weak acid is referred as the levelling effect.
The ability of a weakly basic solvent to accept a proton from an acid is relatively less when
compared to that of a strongly basic solvent.
Similarly, ability of a weak acid to donate a proton is very less when compared to that of a
strong acid.
When a strong acid(eg: perchloric acid) is dissolved in a weakly basic solvent, it has more
tendency to donate a proton when compared to that of a weak acid.

13. Alternatively, in the presence of strong basic solvent, the acidic strength of a weak
acid enhanced and it becomes similar or comparable to that of strong acids because
the affinity of strong base to accept a proton is very high.
2. DIFFERENTIATING EFFECT OF SOLVENTS
The tendency or ability of a weak acid in basic solvent to accept a proton is very less.
These solvents have the capacity to accept proton from strong acid but not from weak
acids and are called differentiating solvents.
They have no role in non-aqueous titrations.

14. TYPES OF SOLVENTS
1. APROTIC SOLVENTS
2. PROTOPHILIC SOLVENTS
3. PROTOGENIC SOLVENTS
4. AMPHIPROTIC SOLVENTS

15. 1. APROTIC SOLVENTS
Aprotic solvents are neutral i.e, they neither donate nor accept protons.
They are chemically inert
Virtually unreactive under the conditions employed.
Have low dielectric constant.
They do not undergo ionization because they neither react with acid nor with bases.
Aprotic solvents are added to ionizing solvents in order to sharpen the end point by
depressing the solvolysis of the neutralized product.

16. They are used for the dilution of reaction mixtures.
Do not exert a ‘Levelling effect’.
Act as a medium for the titration.
Eg: Benzene, Chloroform, Carbon tetrachloride, Toluene, Acetonitrile, Ethyl acetate,
Chlorobenzene.
In case of picric acid + toluene colourless solution + aniline
yellow colour solution
Picric acid is not dissociated in toluene soln.

17. Presence of base aniline it functions as an acid.
The development of yellow colour being due to the formation the picrate ion.
O2N NO2
NO2
OH O
–
O2N NO2
NH2
+ C6H6NH3
undissociated
colourless
picrate ion
yellow colour

18. 2. PROTOPHILIC SOLVENTS
Protophilic solvents are basic in nature.
They react with weak acids and form solvated protons, thereby enhancing the acidity
of weak acids.
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, such as perchloric acid, exhibits more strongly acidic properties than a
weak acid, such as acetic acid, when dissolved in a weakly basic solvent.
This solvent exhibits “levelling effect”.

19. Eg: Acetone, Ethers, Pyridine, Dimethyl formamide, n-butyl amine, Ethylene
diamine, Liquid ammonia.
3. PROTOGENIC SOLVENTS
Protogenic solvents are acidic in nature.
They donate protons to enhance the strength of weak bases.
They have high dielectric constants and are ionised.
HB Solvent
basic
Solvent-H+
B-
Solvated
proton
conjugate
base
+ +
weak
acid

20. Because of their strength and ability to donate protons, they enhance the basicity of
weak bases.
Eg: Sulphuric acid, formic acid, hydrochloric acid, hydrogen fluoride, acetic
anhydride.
4. AMPHIPROTIC SOLVENTS
Amphiprotic solvents act as both acids and bases i.e., they accept as well as donate
protons.
Eg: Water, Glacial acetic acid, alcohols, dioxan

21. The capacity of amphiprotic solvents to dissociate is very less.
Acetic acid is generally used for titrating most of the basic substances and it
dissociates.
In abv situation, acetic acid is acting as an acid. When perchloric acid (strong acid) is
dissolved in acetic acid (weak acid), the acetic acid acts as a base and accepts protons
donated by perchloric acid to yield an onium ion or protonated acetic acid.
CH3COOH H+
CH3COO-
acetic acid proton acetate ion
+
HClO4 H+
ClO4
-
perchloric acid proton chlorate ion
+

22. A solution of perchloric acid or perchloric acid solution in glacial acetic acid acts as a
strongly acidic solution because onium ion act as a proton donor.
When pyridine (weak base) is dissolved in acetic acid, the acetic acid enhances the
basic nature of pyridine by exerting its levelling effect.
Hence, to obtain a sharp end point, a weakly basic solution can be titrated in acetic acid
with perchloric acid in acetic acid.
CH3COOH H+
CH3COOH2
+
acetic acid proton onium ion
+

23. HClO4 CH3COOH CH3COOH2
+
ClO4
-
perchloric acid acetic acid onium ion chlorate ion
C5H5N CH3COOH C5H5NH+
CH3COO-
pyridine acetic acid acetate ion
HClO4 C5H5N C5H5NH+
ClO4
-
perchloric acid pyridine chlorate ion
+
+
+
+
+
+

24. SOLVENTS USED IN NON – AQUEOUS TITRATION
1. Glacial Acetic Acid/ Ethanolic Acid
Most common solvent used for Non-aqueous substance.
It contains around 0.1 to 1.0% of water and acetic anhydride is added to prior to its use, to
convert the water content into acid.
Ethanolic acid is used alone or in combination with other solvents like acetic anhydride,
acetonitrile and nitromethane.
2. Acetonitrile
Used in combination with other solvents like chloroform, phenol and acetic acid.
It gives sharp end point when metal acetate are titrated with perchloric acid.

25. 3. Alcohols
Most of the organic acid salts are titrated in solvent mixtures of glycols and alcohols or glycol
and hydrocarbon.
a. Methanol and benzene
b. Ethylene glycol with propan-2-ol with butan-1-ol.
4. Dioxan
Its second solvent of choice after glacial acetic acid.
Used when mixtures are to be quantified.
This solvent does not show levelling effect on acid or base.
It gives separate end point.

26. Dioxan has high water content which limit its usage.
5. Dimethyl Formamide (DMF)
Its protophilic type of solvent and is used for titrating benzoic acid and amides
DMF does not give separate end points.

27. INDICATORS
Sl. no INDICATOR
COLOUR CHANGE
BASIC NEUTRAL ACIDIC
1
Crystal violet
violet Blue-green Yellowish-green
N
C
H3 CH3
N N
C
H3
CH3
CH3
CH3
Cl
–

28. 2
1-Naphtholbenzein
Blue or blue-green orange Dark-green
3
Oracet Blue B
Blue Purple Pink
O
H
O
NH
NH
C
H3
O
O

29. 4
Quinaldine red
Magenta Almost colourless
5
Thymol blue
Yellow Blue
6
Azoviolet
Pink Blue
N
+
N
CH3
CH3
CH3
I
–
O
S
C
H3 CH3
OH
C
H3
C
H3
C
H3
O
H
O
O
CH3

30. TYPES OF NON – AQUEOUS TITRATION
1. NON-AQUEOUS TITRATION OF WEAK BASES (acidimetry)
• Weak bases, Kb value = or > 10-6 to be titrated in water.
• Weak bases which don't meet this requirement cannot be titrated with accuracy in aqu.
system.
Because water competes with basic species in solution for proton of titrant.
Due to Amphiprotic properties(acid or base depending on procedure & expt condition with
regard to proton donation and acceptance)

31. • Most commonly used procedure of titration of organic bases with standard solution of
perchloric acid in acetic acid.
• Perchloric acid is strongest of common acid in acetic acid solution – commonly used
medium.
H2O H+
H3O+
RNH2 H+
RNH3
+
Compete with
+
+
H2O B OH-
BH+
ROH B RO-
BH+
Compete with
+
+
+
+

32. • Addition of acetic anhydride – use to remove water aqueous perchloric acid.
• Weak bases compete very effectively with acetic acid for protons.
1) Solvents used
• Solvents used in acidimetric non-aqueous titrimetric analysis – neutral or acidic in
nature.
• Neutral solvents – Acetonitrile, alcohols, chloroform, benzene, chlorobenzene, dioxan,
ethyl acetate.
• Acidic solvents – formic acid, Glacial acetic acid, propionic acid, acetic anhydride.
• A solvent, acetic acid reacts with base B.

33. • Conjugated base anion = CH3COO- , react with titrant.
 Titrant react with solvent
Titration reaction
Overall reaction
B CH3COOH BH+
CH3COO-
+ +
HClO4 CH3COOH CH3COOH2
+
ClO4
-
+ +
CH3COO-
CH3COOH2
+
2CH3COOH
+
B HClO4 BH+
ClO4
-
+ +

34. 2) Titrant used
• Widely used titrant – perchloric acid in glacial acetic acid or relatively neutral solvent
dioxan.
• Hydrogen bromide and certain organic sulfonic acid.
3) Preparation of 0.1M Perchloric acid
Slowly add 8.5ml of HClO4 to 500ml of anhydrous glacial acetic acid with continuous
mixing.
Add 25ml acetic anhydride, cool

35. Add anhydrous glacial acetic acid to 1000ml and stand for 24 hrs before use for the
excess acetic anhydride to be combined & carry out determination of water.
4) Standardization of 0.1M Perchloric acid
Weigh accurately about 0.35g of potassium hydrogen phthalate (previously powdered
lightly and dried @ 120oC for 2 hrs).
Dissolve it in 50ml anhydrous glacial acetic acid.
Add 0.1ml crystal violet solution [indicator]

36. Titrate with 0.1N Perchloric acid
End point: violet colour change to emerald green
Perform a blank titration
• Each ml of 0.1N perchloric acid = 0.02024g of C8H5KO4.
COOK
COOH
+ HClO4
COOH
COOH
+ KClO4
Potassium hydrogen
phthalate
Perchloric acid
benzene-1,2-dicarboxylic
acid

37. 5) Indicator
oOracet blue
oCrystal violet
oQuinaldine red
o1-Naphtholbenzin
oMalachite green
oMethyl rosaniline chloride
6) Example
• Titration of adrenaline, amino acid and mixture of amines.

38. 2. NON-AQUEOUS TITRATION OF WEAK ACIDS (ALKALIMETRY)
• Many weakly acidic substances can be titrated in an appropriate non-aqueous solvent
with a sharp end-point.
1) Solvents used
• Factor for choosing solvent – solubility of substance for analysis.
• Strong base solvents: Ethylene diamine, n-Butylamine, Morpholine.
• Weak base solvents: DMF, anhydrous pyridine.
2) Titrants used
• Potassium methoxide – stronger titrant but not used because gelatinous reaction prdt.

39. • Sodium methoxide – produce a gelatinous precipitate.
• Lithium methoxide in toluene methanol – is more preferred.
• Alternatively Tetrabutyl ammonium hydroxide in methanol is used to determine the
number of weakly acidic substance.
3) Indicators
INDICATOR SOLVENT OF CHOOSE COLOUR CHANGE
Azo violet n-butylamine Blue
Thymol blue Dimethyl formamide Blue
o-nitro aniline Orange - yellow
Thymolphthalein Colourless to blue
p-hydroxy azobenzene

40. 4) Preparation of 0.1M Sodium Methoxide solution in Toluene – methanol
Cool 150ml of anhydrous methanol in ice water + 2.5g of freshly cut sodium in small
portions.
When metal dissolved, add sufficient toluene, previously dried over sodium wire to
produce 1000ml.
5) Standardisation of 0.1M Sodium methoxide solution
Place dimethyl formamide 80ml in conical flask.
Add 0.15ml of Tymolphthalein solution

41. Immediately add 0.4g of Benzoic acid.
Titrate with 0.1M sodium methoxide solution.
End point: appearance of blue colour. Perform blank titration.
• Each ml of 0.1M sodium methoxide = 0.01221g of C7H6O2.
6) Preparation of 0.1M Lithium Methoxide in Toluene - Methanol
Dissolve 0.7g of freshly cut Lithium in 150ml of anhydrous methanol.
Cool the flask during the addition of metal.
When reaction complete add sufficient Toluene to produce 1000ml

42. 7) Standardisation of 0.1M Lithium methoxide
Weigh accurately 0.25g of benzoic acid dissolve in 25 ml of dimethyl formamide
Titrate with Lithium methoxide solution using Quinaldine red as indicator
Protect solution from atmospheric CO2 throughout titration.
Perform blank titration.
• Each ml of 0.1M Lithium methoxide = 0.01221g of C7H6O2.

43. METHODS OF DETERMINING END POINT
1. COLOUR CHANGE
 Most useful method in which the end point is determined using different
indicators.
2. POTENTIOMETRY
 End point is indicated by a sharp change in the potential across two electrode.
 The end point is also indicated by a change in the resistance or the amount of
current flowing through the solution being titrated.

44. 3. SPECTROPHOTOMETRY
 Determination of end point by photometric titration depends upon changes in the
absorbance of the solution mixture at the end point.
 Here the titration is carried out with or without the indicators and depends upon the
absorption of radiations by test solution.
4. AMPEROMETRY
 Determination of end point depends on changes in the diffusion current due to
change in the concentration of electro-active material in the solution upon reaction
with reagent.

45.  By plotting the values of diffusion current and the volume of titrant, a titration curve
is obtained from which the end point can be determined.
5. CONDUCTOMETRY
 Determination of end point using conductometry depends upon changes in the
conductance of the solution before and after the end point.
 End point can be determined from titration curves which are plotted using
conductance and the volume of reagents.

46. ASSAY OF SODIUM BENZOATE
Weigh accurately the sodium benzoate sample
Dissolve in 50ml of glacial acetic acid
Add 2 drops of 1-naphtholbenzein as indicator
Titrated with 0.1 N perchloric acid
End point: colour changes from blue to green

47. THANK YOU…,
WORK HARD IN SILENCE; LET SUCCESS MAKE THE NOISE.