Acid-Base Equilibria of Aliphatic Diazo Compounds

4 Acid-Base Equilibria of Aliphatic Diazo Compounds 

The vast majority of diazoalkane reactions are based on the ambident nucleophilic character of diazoalkanes, as shown by the mesomeric structures of diazomethane 4.32 a and 4.32 b. Bronsted and Lewis acids can be added at the C- and the N()8)-atoms. The reaction with Bronsted acids is particularly important. Alkanediazonium ions are obtained by proton addition at the C-atom giving rise to dediazoniation and various reactions of carbocations (see Chapt. 7). 

The mesomeric structures with electron sextets at the N(J3)- (4.32 c and 4.32 d) and the C-atom (4.32 e) are the basis for understanding that diazoalkanes also have the properties of Lewis acids, and may react at these centers (see Sect. 9.2). 

Dediazoniation of diazoalkanes also takes place, however, without primary addition of a Bronsted or Lewis acid at the C-atom. Carbenes are obtained thermally, photolytically, and by transition-metal catalysis (Chapt. 8). 

Reactions with radicals were hardly known when Huisgen published his review in 1955 and, even today, homolytic processes involving diazoalkanes are not numerous. 

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