THERMAL CLEAVAGE REACTIONS OF N-CHLOROKETIMINES - BEHAVIOR OF IMINO RADICALS

In contrast to the relatively stable diphenyl N-chloroketimine (1), phenyl benzyl N-chloroketimine (2) in chlorobenzene solution (<0.04 M) undergoes cleavage at 130° to form benzonitrile and benzyl chloride along with small amounts of bibenzyl. The reaction is accelerated by slow addition of benzoyl peroxide and inhibited by oxygen. A radical chain sequence is postulated involving β scission of phenyl benzyl ketimino radical (13) as the key step. The intermediate benzyl radical has been trapped by added 1-octene to form 1-phenyl-3-chlorononane (12) and by added tri-n-butyltin hydride (Bu3SnH) to form toluene. At 35-40°, radical 13 can be partially intercepted by Bu3SnH before cleavage. Phenyl α-methylbenzhydryl N-chloroketimine (3) gives benzonitrile, 1,1-diphenylethylene, and hydrogen chloride on thermolysis, the latter two products apparently derived from 1,1-diphenyl-1-chloroethane (10). In concentrated solution, additional products from the thermolysis of 2 included ammonium chloride and 2,3,4,5-tetraphenylpyrrole (9). The reduction of 1 with Bu3SnH at 50-60° could be inhibited by oxygen and accelerated by di-t-butyl peroxyoxalate as anticipated for a radical chain process. Silver ion catalyzed Beckmann rearrangement of 2 gave N-phenylphenylacetamide (4) free from N-benzylbenzamide (5), so that chlorine appears to be syn to the benzyl group. Similar treatment of 3 gave no amides but only benzonitrile and 1,1-diphenylethylene. Attempts to prepare the N-chloroketimine from phenyl benzhydryl ketimine by the same procedures which were successful for 1, 2, and 3 gave initial chlorination on carbon rather than on nitrogen. © 1969, American Chemical Society. All rights reserved.