Addition of hydrogen cyanide to benzylideneanilines. Oxidation products

Abstract

Substituted p-nitrobenzylideneanilines (I) react with hydrogen cyanide in methanol by consuming an equivalent amount of oxygen to give the corresponding α-phenylimino-p-nitrobenzyl cyanides (III) in ca. 50% yields viaα-anilino-p-nitrobenzyl cyanides (II). The other substituted benzylideneanilines give α-anilinobenzyl cyanides, but no dehydrogenation product was obtained. The reaction proceeds by consecutive pseudo-first-order steps (I)+ HCN →(II); (II)+ O₂→(III). For the first step the polar effect is expressed as a ρ value of –1·60. The second step involves base-catalysed dehydrogenation by atmospheric oxygen with a ρ⁺ value of –0·36. These results suggest a mechanism involving a hydrogen abstraction or an electron transfer from the conjugate base of (II).