Free radicals trapping reactions with 3,5-di-t-butyl-nitrosobenzene. The alpha-nitrobenzyl free radical

The reactions of sodium and potassium phenylnitrolates (the salts of aci-ph enylnitromethane) with iodine, studied by Nenitzescu in 1929,(1) were reinv estigated in order to detect the cr-nitrobenzyl free radical. In agreement with Nenitzescu we confirmed that only (+/-)-alpha,alpha'-dinitrodibenzyl ( m.p. 150 degrees) resulted on treating the salts with iodine at 0-5 degrees . The meso modification (m.p. 236-237 degrees) does not seem to be formed i n any reaction conditions used either by Nenitzescu or by us in this work. Addition of an iodine crystal to a suspension of sodium phenylnitrolate in dry benzene and immediate recording,of the ESR spectrum allowed the observa tion of a nitrogen free radical (a(N) = 0.458 mT; g = 2.0058), not agreeing with the structure of the simple alpha -nitrobenzyl free radical. Dry pota ssium phenylnitrolate kept hi a dry air atmosphere is transformed in 3,4,5- triphenylisoxazole. Possible structures for the observed radical and the pa thway leading to its formation are discussed in relation to trans-stilbene formation.