186
Question
(a) Illustrate the following reaction giving suitable example(s) in each case:
(i) hoffmann bromamide degradation reaction
(ii) diazotisation
(iii) gabriel phthalimide synthesis
(b) Distinguish between the following pairs of compounds:
(i) aniline and N-methylaniline
(ii) (CH3)2NH and (CH3)3N
OR
(a) Write the structures of main products when benzene diazonium chloride (C6H5N+2Cl−) reacts with the following reagents:
(i) CuCN/KCN
(ii) H2O
(iii) CH3CH2OH
(b) Arrange the following:
(i) C2H5NH2,C2H5OH,(CH3)3N -in the increasing order of their boiling point
(ii) aniline, p-nitroaniline, p-methyl aniline - in the increasing order of their basic strength
(i) hoffmann bromamide degradation reaction
(ii) diazotisation
(iii) gabriel phthalimide synthesis
(b) Distinguish between the following pairs of compounds:
(i) aniline and N-methylaniline
(ii) (CH3)2NH and (CH3)3N
OR
(a) Write the structures of main products when benzene diazonium chloride (C6H5N+2Cl−) reacts with the following reagents:
(i) CuCN/KCN
(ii) H2O
(iii) CH3CH2OH
(b) Arrange the following:
(i) C2H5NH2,C2H5OH,(CH3)3N -in the increasing order of their boiling point
(ii) aniline, p-nitroaniline, p-methyl aniline - in the increasing order of their basic strength
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Solution
(a)(i) Hoffmann bromamide degradation reaction-Hoffmann developed a method for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.(ii) Diazotisation :-Benzenediazonium chloride is prepared by the reaction of aniline with nitrous acid at 273−278K. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. Theconversion of primary aromatic amines into diazonium salts is knownas diazotisation.(iii) Gabriel phthalimide synthesis - Gabriel synthesis is used for the preparation of primary amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Aromatic primary amines cannot be prepared by this methodbecause aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.(b)(i) Given in image(ii) (CH3)2NH = Secondary amine (CH3)3N = tertiary amine
(i) Hoffmann bromamide degradation reaction-
Hoffmann developed a method for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide.
In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.
(ii) Diazotisation :-Benzenediazonium chloride is prepared by the reaction of aniline with nitrous acid at 273−278K. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The
conversion of primary aromatic amines into diazonium salts is known
as diazotisation.
(iii) Gabriel phthalimide synthesis - Gabriel synthesis is used for the preparation of primary amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Aromatic primary amines cannot be prepared by this method
because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.
(b)
(i) Given in image
(ii) (CH3)2NH = Secondary amine
(CH3)3N = tertiary amine
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