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190
Viva Voce in
Pharmaceutical Chemistry
Q 951 How is Baker-Mulliken test for nitro compounds different
from Tollen’s test for aldehydes?
Ans: Aldehydes, themselves have capacity to reduce the Tollen’s
reagent while nitro compounds are first reduced to corres-
ponding hydroxylamine and this hydroxylamine reduces
Tollen’s reagent.
Q 952 Give the chemistry of ferrous hydroxide test for nitro
compounds.
Ans: To a nitro compound add ferrous ammonium sulphate solution
and then add 6 N sulphuric acid followed by 2 drops of 2 N
potassium hydroxide solution in methanol. The blue green
ferrous hydroxide formed (in situ) reduces the nitrobenzene to
aniline and in process gets oxidized to ferric hydroxide which
is brown. This indicates presence of nitro group.
Q 953 Which compound would be formed after nitration of
nitrobenzene?
Ans: m-dinitrobenzene is formed after nitration of nitrobenzene.
Systematic Qualitative Analysis 191
Q 954 How will you carry out nitration of nitrobenzene?
Ans: For nitration of nitrobenzene fuming nitric acid and conc.
H
2
SO
4
are used. The process should be carried out in fuming
cupboard or condenser must be used. The reaction mixture
should be cooled in cold water bath if excess brown fumes
are evolved during nitration.
Q 955 Which crystalline derivatives can be prepared from nitro
compounds?
Ans: Nitro compounds are first reduced to corresponding amine
and then benzoyl derivative of amine can be prepared.
SPECIAL REAGENTS
Q 956 What is Luca’s reagent?
Ans: Luca’s reagent contains 136 g of anhydrous zinc chloride
dissolved in 105 g conc. hydrochloric acid with cooling.
Q 957 Where is Luca’s reagent used?
Ans: Luca’s reagent is used to differentiate primary, secondary and
tertiary alcohols.
Q 958 What is Schiff’s reagent? Where is it used?
Ans: Schiff s reagent contains 0.001% aqueous solution of fuchsin
and sulphurous acid.
It is used to detect the presence of an aldehyde.
It should never be warmed or treated with alkaline
substances, otherwise the pink colour would be restored in
absence of aldehyde or ketones.
Q 959 What is Fehling’s solution? Where is it used?
Ans: Fehling’s solution is prepared by mixing equal amounts of
Fehling’s solution A and Fehling’s solution B.
Fehling’s Solution A
Dissolve 17.320 g of crystalline copper sulphate (CuSO
4
· 5H
2
O)
in water and make the solution up to 250 ml.
Fehling’s Solution B
Dissolve 86.5 g of crystalline sodium potassium tartrate
(Rochelle salt) in warm water. Dissolve 30 g of pure sodium
hydroxide in water. Mix the tartrate and hydroxide solutions,
cool and make up to 250 ml.
192
Viva Voce in
Pharmaceutical Chemistry
Fehling’s solution is used in the detection of aldehyde
group. Fehling’ s solution is reduced to red cuprous oxide by
the aldehyde .
Q 960 What is Tollen’s reagent? Where is it used?
Ans: Tollen’s reagent is ammonical silver nitrate solution.
Dissolve 3.0 g of silver nitrate in 30 ml of water (solution A)
and 3.0 g of sodium hydroxide in 30 ml water (solution B).
When the reagent is required, mix equal volumes of A and B,
add dilute solution of ammonia drop by drop until the
precipitated silver oxide just dissolves. This reagent must not
be heated. This reagent is used in detection of aldehyde and
nitro group.
Q 961 What is Benedict’s reagent? What is its use?
Ans: Benedict’s reagent contains sodium citrate and copper
sulphate.
Dissolve 86.5 g of crystallized sodium citrate and 50 g of
anhydrous sodium carbonate in about 350 ml of water. Filter,
add a solution of 8.65 g of crystallized copper sulphate in
50 ml of water with constant stirring. Dilute to 500 ml with
water, filter.
Benedict’s solution is modification of Fehling’s solution and
it is single solution which does not deteriorate on standing. It
is used to detect the presence of aldehyde group.
Systematic Qualitative Analysis 193
1. Indian Pharmacopoeia 2022.
2. Indian Pharmacopoeia 2018.
3. Indian Pharmacopoea 2014.
4. Indian Pharmacopoeia 2010.
5. Indian Pharmacopoeia 2007.
6. Indian Pharmacopoeia 1996.
7. Indian Pharmacopoeia 1985.
8. Vogel’s Textbook of Quantitative Practical Organic Chemistry.
9. Vogel’s Textbook of Quantitative Chemical Analysis.
10. Vogel’s Qualitative Inorganic Analysis.
11. Bentley and Driver’s Textbook of Pharmaceutical Chemistry.
12. Practical Pharmaceutical Chemistry by A. H. Beckett and J. B.
Stenlake.
13. Practical Pharmaceutical Chemistry by Harkishan Singh and
V. K. Kapoor.
14. Pharmaceutical Chemistry I Laboratory Manual by Amrita
Parle.
15. Pharmacutical Chemistry II Laboratory manual by Amrita Parle.
16. Viva Voice In-organic Chemistry by Amrita Parle.
17. Viva Voice in Organic Chemistry by Amrita Parle.
18. Pharmaceutical Chemistry Laboratory Manual, second edition,
2023.
19. A Laboratory Manual for Pharmaceutical Chemistry I
Maharashtra State BTE, Mumbai.
Bibliography and
Further Reading
193
