Question

How can you prepare primary amine by hoffman degradation reaction?

Answer 1

Methods of Preparation of Amines

Hoffmann’s Bromamide Reaction

We can also prepare amines (only primary) by Hoffmann degradation. In this method, the amine will have one carbon atom less than the amide. The reaction proceeds

Mechanism of above reaction is as given below:

Br2 KOH CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen KO—Br HBr

Mechanism

2NaOH Br2 CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen NaOBr NaBr H2O

(a) CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen

(b)CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen

R — NH2 CO2 → R — N = C = O (Isocyanate)

Curtius, Schmidt, and Lossen Rearrangement

These reactions are basically rearrangement reactions in which carbon migrates from carbon to nitrogen with the formation of an isocyanate. In these migration processes i.e., 1, 2 shift, migrating group is an alkyl or aryl group and leaving group may be:

Br in Hoffmann rearrangement

N2 in Curtius and Schmidt rearrangement

CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen

The isocyanate formed on hydrolysis gives amine. Let us now look at these reactions in greater details.

Curtius Reaction: Acid chloride on treatment with sodium azide give acid azides which on pyrolysis gives isocyanates. On further hydrolysis, it

Schmidt Reaction: Carboxylic acid reacts with the hydrazoic acid in the presence of concentrated H2SO4 to give isocyanates.

CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing Nitrogen

Lossen Reaction: Hydroxylamine on treatment with acid chloride gives acyl derivatives of hydroxylamine. The acyl derivatives exist in two tautomeric form keto form called hydroxamic form and enol form called hydroximic acid. The hydroxamic form.CBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing NitrogenCBSE, Class 12, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Amines, Compounds containing NitrogenThe hydroxamic form (keto form) forms O-acyl derivatives of hydroxamic form which on heating with bases forms isocyanates and finally amines upon hydrolysis.