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180
Viva Voce in
Pharmaceutical Chemistry
Q 902 State whether esters are acidic, basic or neutral.
Ans: Esters are neutral compounds.
Q 903 How would you judge the possibility of ester presence from
preliminary tests?
Ans: Esters have characteristic odours, e.g. ethyl acetate has fruity
odour while methyl salicylate has odour of oil of wintergreen.
Q 904 State one medicinal use of ester.
Ans: Local anesthetics have ester function, e. g. benzocaine,
procaine.
Q 905 State the qualitative tests of esters.
Ans: Qualitative tests for detecting presence of esters are
hydroxamic acid test and phenolphthalein test.
Q 906 Describe hydroxamic acid test and phenolphthalein test.
Give chemistry.
Ans: Heat ester with hydroxylamine hydrochloride in presence of
sodium hydroxide, for 1–2 minutes. Cool and acidify with
dilute HCl and then add FeCl
3
solution. A violet or deep red-
brown colouration/ppt develops immediately.
Systematic Qualitative Analysis 181
Q 907 Describe phenolphthalein test for esters.
Ans: To an ester, add dilute sodium hydroxide solution and
phenolphthalein solution. A pink colour is produced due to
alkaline medium. Heat. When pink colour is discharged or
reduced in intensity, it indicates presence of an ester.
Esters are hydrolysed into an acid and an alcohol. The acid
neutralises the sodium hydroxide and pink colour is
discharged.
Q 908 Amides and esters, both give positive hydroxamic acid test.
How would you differentiate the two?
Ans:
l. Amides when heated with sodium hydroxide, evolve
ammonia which can be detected by smell. This test is negative
for esters.
2. During hydroxamic acid test also amides evolve ammonia
while esters do not.
3. Esters have fruity/characteristic smell while amides like
acetamide have mouse like odour.
Q 909 Which crystalline derivatives can be prepared from esters?
Ans: Benzylamides or 3, 5-dinitro-benzoates can be prepared easily
from esters. They are crystalline in nature.
AMIDES
Q 910 What are amides?
Ans: Amides are organic compounds containing –CONH
2
group
attached to an alkyl or aryl group.
Q 911 Are amides acidic, basic or neutral?
Ans: Amides are neutral in nature.
Q 912 Which two functional groups are involved in the formation
of amides?
Ans: Amides are prepared by reacting ammonia with acid chlorides
or acid anhydrides. The two functional groups involved in
the formation of amides are carboxy and amine.
Q 913 Name five amides.
Ans: Urea, formamide, acetamide, benzamide and thiourea.
182
Viva Voce in
Pharmaceutical Chemistry
Q 914 What are the general properties of amides?
Ans: Amides are colourless solids with exception of formamide
which is a liquid. Amides are odourless except acetamide
which has mouse-like odour. Formamide, acetamide and urea
are readily soluble in water, thiourea is moderately soluble,
oxamide, benzamide and salicylamide are almost insoluble
in water.
Q 915 Which is the functional group present in urea?
Ans: Urea has amide functional group.
Q 916 What happens when urea is heated in a dry test tube?
Ans: When urea is heated in a dry test tube, it melts forming biurette
and ammonia gas is evolved.
Q 917 What is Beilstein’s test? Is it positive for amides? If yes,
explain why?
Ans: Beilstein’s test is performed to detect the presence of halide.
The hot copper oxide from the copper wire decomposes the
organic compound containing halide to form copper halide,
which is volatile at high temperatures and gives the usual
green copper colouration.
Beilstein’s test is positive for amides. When copper oxide
reacts with amides like urea and thiourea, it gives volatile
cuprous cyanide and therefore also gives green colouration.
Though green colouration is given by amides, this test does
not indicate the presence of halide in amides.
Q 918 Give a common test for amides.
Ans: When amides are heated with an alkali like sodium hydroxide,
it hydrolyses and ammonia gas is evolved.
Q 919 Describe hydroxamic acid test for amides.
Ans: When an amide is heated with hydroxyl amine hydrochloride
in an alkaline medium, corresponding hydroxamic acid is
formed. The enol form of this acid reacts with ferric chloride
to give corresponding ferric hydroxamate which is reddish
brown.
Fundamentals of Volumetric Analysis 183
Q 920 What is biuret test? Which compound gives this test?
Ans: Biuret test is given by urea. When urea is gently heated in dry
test tube, the compound melts and ammonia gas is evolved.
After 1–2 minutes, the liquid suddenly solidifies with the
formation of biuret.
Dissolve the residue in a few ml of warm NaOH solution,
cool and add 1 drop of copper sulphate solution. A purple or
rose-pink colouration is produced.
Q 921 Describe urea nitrate test.
Ans: When a few drops of concentrated HNO
3
are added to
concentrated aqueous solution of urea, a white crystalline urea
nitrate, precipitates out.
Q 922 An organic compound on being strongly heated with 10%
sodium hydroxide solution evolves ammonia. What is the
inference?
Ans: The compound may be an amide.
184
Viva Voce in
Pharmaceutical Chemistry
Q 923 Which two functional groups are prone to easy hydrolysis?
Ans: Esters and amides are prone to hydrolysis. Amides when
heated with aqueous NaOH solution, yield ammonia and the
sodium salt of corresponding acid.
Esters hydrolyse to give corresponding alcohol and sodium
salt of the acid.
Q 924 Which crystalline derivative can be prepared from amides?
Ans: On hydrolysis crystalline acid can be obtained if the amide
has aromatic group.
N-benzylamides can be easily formed by reacting amides
with benzyl amines.
AMINES
Q 925 What are amines?
Ans: Amines are the organic compounds having NH
2
group. This
group is attached to an alkyl or aryl group.
Q 926 Whether amines are acidic/basic or neutral? Why?
Ans: Amines are basic in nature. Amines have NH
2
group. The
nitrogen group has lone pair of electrons and the alkyl group
(which is electron pushing group) makes the pair of electron
more available for sharing with an acid. Aromatic amines are
less basic than aliphatic amines as the aromatic ring is
stabilized due to formation of Kekule structure.
Q 927 What are the types of amines?
Ans: Amines are classified as
• Primary amines R — NH
2
e.g. aniline, methyl amine.
R
1
• Secondary amines N—H
R
2
e.g. diphenyl amine, monomethyl aniline
R
1
• Tertiary amines N—R
3
R
2
e.g. triethyl amine, triphenyl amine
Systematic Qualitative Analysis 185
Q 928 Describe the physical properties of primary aromatic amines.
Ans: These are mostly liquids except p-toluidine and 1- and 2-
naphthylamine. All are colourless when pure, but rapidly
darken on exposure to light and air. These compounds are
sparingly soluble in water but dissolve readily in dilute
mineral acids.
Q 929 What is the solubility of amines in water, sodium hydroxide
and dilute hydrochloric acid?
Ans: Amines are soluble in water when they contain less than 4
carbon atoms. They are soluble in dilute hydrochloric acid
(due to their basicity) but insoluble in sodium hydroxide
solution.
Q 930 What is the difference between amides and amines?
Ans: Amines have the structure R—NH
2
while amides have the
structure R—CONH
2
Q 931 What are the elements present in amines?
Ans: Amines contain carbon, hydrogen and nitrogen elements.
Q 932 Give example of an aromatic amine.
Ans: Aniline is a primary aromatic amine.
Q 933 What are the general reactions of primary aromatic amines?
Ans: Primary aromatic amines give
1. Isocyanide or carbylamine reaction,
2. Benzoyl and toluene p-sulphonyl derivatives
3. Form diazonium compounds which react with alkaline
-naphthol to give red dyes.
Q 934 Explain carbylamine test and write chemical reaction
involved.
Ans: To an amine add chloroform and ethanolic solution of sodium
hydroxide. Heat. An offensive odour of carbylamine/
isocyanide indicates the presence of primary amine.
Q 935 Describe diazotization test for the detection of aromatic
primary amines.
Ans: Take three test tubes. In first test tube, dissolve the primary
aromatic amine in conc. HCl and water. In second test tube,
186
Viva Voce in
Pharmaceutical Chemistry
take 2 ml of 10% solution of sodium nitrite. In third test tube,
dissolve 0.l g of -naphthol in 2 ml of 10% NaOH. Cool the
solutions in ice cold water at 0–5°C. Add sodium nitrite
solution to primary amine solution followed by addition of
-naphthol solution. Formation of orange-red dye confirms a
primary aromatic amine . This test is given only by primary
aromatic amines.
Q 936 Explain the chemistry and utility of p-toluene sulphonyl
chloride test for detection of amines.
Ans: p-toluene sulphonyl chloride test can also be performed using
benzene sulphonyl chloride. This test is known as Hinsberg
test. This test is performed to differentiate the primary,
secondary and tertiary amines.
To the substance/amine, add p-toluene sulphonyl chloride
and 10% sodium hydroxide solution with vigorous shaking
and observe the formation of precipitate of benzene sulphonyl
derivative. If no reaction occurs, heat the contents on a water
bath for 2–3 minutes and then cool in ice.
1. If the precipitate appears after acidification with hydrochloric
acid, it indicates the presence of primary amine.
2. If the precipitate appears in alkaline medium, it indicates the
presence of secondary amine.
3. Tertiary amines do not react.
Systematic Qualitative Analysis 187
For Primary Amines
For Secondary Amines
Q 937 How would you differentiate primary amine, secondary
amine and tertiary amine?
Ans: Primary amines give carbylamine test, azo dye test and gives
ppt in acidic media in p-toluene sulphonyl chloride test.
Secondary amines do not give carbylamine test, azo dye test
and gives ppt in alkaline media in p-toluene sulphonyl
chloride test. Secondary amines give positive nitrosamine test
while primary amines do not give this test.
188
Viva Voce in
Pharmaceutical Chemistry
Tertiary amines do not give carbylamine test, azo dye test
and p-toluene sulphonyl chloride test. Tertiary amines readily
react with methyl iodide to form methiodide salts which
crystalise out.
Q 938 Describe nitrosamine test for secondary amines.
Ans: In this test, in situ nitrous acid is formed by reaction between
hydrochloric acid and sodium nitrite. This nitrous acid
(HNO
2
) reacts with secondary amine to give the nitrosamine
(R
2
.N.NO).
Q 939 Which is the characteristic test for tertiary amines?
Ans: Tertiary amines give crystalline methiodides when they react
with methyl iodide.
Q 940 Which crystalline derivatives can be prepared from amines?
Ans: Amines can form picrates, benzene sulphonyl derivative,
p-toluene sulphonyl derivative, benzoyl derivative which are
crystalline solids.
Q 941 Why is azo dye test performed at low temperature?
Ans: Diazonium chloride which is formed in the reaction during
dye test, is unstable and explosive at higher temperature. To
avoid explosion it is performed at low temperature.
Q 942 How will you differentiate between aliphatic and aromatic
primary amines?
Ans: Aromatic primary amines give azo dye test while aliphatic
primary amines do not give this test.
Q 943 How can obnoxious odour of carbylamine be neutralised/
controlled?
Ans: After performing the carbylamine test, excess of conc. HCl is
added to the isocyanide/carbylamine formed in the test. The
isocyanide would hydrolyse to the odourless amine.
Systematic Qualitative Analysis 189
NITRO GROUP
Q 944 Give five examples of nitro compounds.
Ans: Nitrobenzene, p-nitrotoluene, m-dinitrobenzene, o- and
p-nitrophenols, o-, m-, p-nitro anilines.
Q 945 Describe the physical properties of nitrobenzene.
Ans: Nirobenzene is a pale yellow liquid, insoluble in water and
heavier than water. It has characteristic odour of bitter
almonds.
Q 946 What is the colour of nitro compound?
Ans: Nitro compounds are pale yellow to yellow in colour.
Q 947 Odour of nitrobenzene, resembles which compound’s
odour?
Ans: Odour of nitrobenzene is similar to bitter almonds. It
resembles the odour of benzaldehyde and benzonitrile.
Q 948 What are the general reactions of nitro compounds?
Ans:
l. Nitro compounds are reduced in acid solutions to primary
amines and these amines can be detected using different tests
like carbylamine test.
2. Nitro compounds give positive Baker-Mulliken test/Tollen’s
test.
3. Nitro compounds oxidize the blue green ferrous hydroxide
to brown ferric hydroxide.
Q 949 Describe the Baker-Mulliken test/Tollen’s test for nitro
compounds.
Ans: This test is also known as Tollen’s reagent test.
Prepare solution of the nitro compound in ethanol and to it
add ammonium chloride and zinc dust with shaking. Boil for
five minutes on water bath, cool and filter. To the filtrate, add
Tollen’s reagent and heat on water bath for 5 minutes without
disturbing the test tube. Development of black grey precipitate
or silver mirror indicates the presence of nitro group.
Q 950 Give the chemistry of Baker-Mulliken test.
Ans: Nitro compounds are reduced by zinc and ammonium
chloride solution to the corresponding hydroxylamine. This
hydroxylamine is capable of reducing the Tollen’s reagent
producing black grey precipitate or silver mirror.