Surface Photochemistry: Decomposition of Azobis(isobutyronitrile) on Dry Silica Gel

Article abstract of DOI:10.1021/jo00175a005

The generation of cyanopropyl radical pairs by the photolysis of azobis(isobutyronitrile) (AIBN) adsorbed on dry silica gel-benzene slurries has been investigated.The results require revision of an earlier observation that restrictions on the rotational motion of cyanopropyl radicals at a silica gel-benzene interface prevented the formation of the unsymmetrical coupling product dimethyl-N-(2-cyano-2-propyl)ketenimine.Both tetramethylsuccinodinitrile and the ketenimine were formed on the silica gel surface, even when dry, although the latter was partially hydrolyzed to the corresponding amide.Measurements of geminate recombination of radicals produced by direct photolysis of mixtures of deuterated and nondeuterated AIBN indicated that some radicals could escape, by translational motion, from their original geminate partners.The amount of translational motion was increased for the same cyanopropyl radical pair generated by triplet-sensitized AIBN decomposition.This latter observation supports the view that the triplet-sensitized decomposition of AIBN occurs directly from an exited state rather than by isomerization to a thermally labile cis isomer.