Molecular rearrangements of the Hofmann type

The general procedure of treating carboxylic acid amides with alkaline 

For the preparation of anthranilic acid the starting material is phthalimide, the cyclic imide ring of which is opened by alkaline hydrolysis in the first step of the reaction to give the sodium salt of phthalimidic acid (the half amide of phthalic acid). The intermediate undergoes the Hofmann reaction in the manner outlined on p. 783 yielding o-aminobenzoic acid (anthranilic acid). 

The conversion of a carboxylic acid into an amine by treatment with hydrazoic acid in concentrated sulphuric acid is known as the Schmidt reaction or rearrangement, which often gives higher yields than the related Hofmann rearrangement procedure 

The use of the toxic and hazardous hydrazoic acid is avoided by generating it in situ by adding sodium azide gradually to the carboxylic acid in the presence of concentrated sulphuric acid and chloroform (eg.. 3,5-dinitroaniline, Expt 6.54). The reaction involves the hydrolysis of an intermediate isocyanate (RNCO), which is formed by a mechanistic pathway analogous to that involved in the Hofmann reaction. 

It should be noted that amines may be formed by hydrolysis of amides arising from the intramolecular Beckmann rearrangement of ketoximes (p. 1047) this rearrangement is a further example of the migration of a nucleophilic carbon species from a carbon to an electron-deficient nitrogen. 

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