Diazonium salts react with strongly activated rings to give azo compounds (Scheme 7). The reaction is called diazo coupling .
Scheme 7
5.11.7 Gabriel Amine Synthesis
Phthalimide forms the phthalimide anion, when the acidic N-H proton is abstracted by potassium hydroxide (Scheme 8). The phthalimide anion is a strong nucleophile that displaces the tosylate ion. Thus, heating the N -alkyl phthalimide with hydrazine gives the primary amine and the phthalimide hydrazide.
Scheme 8
5.11.8 Hofmann Rearrangement
Primary amides react with chlorine or bromine, in the presence of a strong base, to form amines with loss of the carbonyl carbon atom. This reaction, called the Hofmann rearrangement , is used to synthesize primary amines. For example, rearrangement of p -nitrobenzamide gives p -nitroaniline (Scheme 9).
Scheme 9
Step 1 : The first step involves the replacement of one of the hydrogens on nitrogen by a halogen.
Step 2 : The alkyl group migrates to nitrogen with retention of configuration and the leaving group leaves.
Step 3 : Hydroxide ion from water attacks the carbonyl group of the isocyanate and gives a carbamic acid.
Step 4 : Decarboxylation gives the amine.
