Iminyl radicals in gas-phase synthesis. I. Generation of nitriles by pyrolysis of aryl azines

Low-pressure gas-phase pyrolysis of aryl aldehyde azines leads to formation of the corresponding aryl cyanides in varying yield, together with small amounts of the corresponding stilbenes. In the case of benzaldehyde azine, stilbene formation is shown to be an intermolecular reaction. Certain substituent groups show some thermal decomposition, but this can be avoided by the use of the wines of alkyl aryl ketones; excellent nitrile yields are then obtained. The reaction is postulated as proceeding by unimolecular decomposition of the iminyl radicals formed by cleavage of the central N-N bond; thermochemical estimates are discussed. Azines from furan- and thiophen-2-carbaldehydes produce 1,2-di(2-furyl)ethylene-and 1,2-di(2- thienyl)ethylene respectively as well as the expected nitriles. As in the azines of alkyl aryl ketones, however, no alkenes are formed on pyrolysis of the azines from 2-acetylfuran and 2-acetylthiophen.