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In the presence of a suitable nitroxide, 2-(t-butylazo)prop-2-yl hydroperoxide (la) decomposes cleanly into hydroxyl and t-butyl radicals; the rate constant for its disappearance in cyclohexane is given by: k = 9.58 x lO14exp.(-1.47 x lO4/T)s-I.In order to pursue our investigations into the reactions of free radicals with polymerizable alkenes,' we required a clean, thermal source of hydroxyl radicals in organic solution. In this communication we describe the use of 2-( t-butylazo)prop-2-y1 hydroperoxide (la), in conjunction with a nitroxide as a free-radical trap,* to study the reactions of hydroxyl radicals with organic substrates. The role of the nitroxide in this reaction is to scavenge t-butyl radicals generated from (la), as well as to trap the radicals produced from the reactions of hydroxyl radicals with the substrate.?Azohydroperoxide (la) has been shown to initiate free radical polymerization of several alkenes.5 It can be readily prepared by oxygenation of acetone t-butylhydrazone,6 and is a colourless oil which is stable for several months at -20 "C.When a degassed solution of (la) (0.034 M) and nitroxide (2) (0.14 M) in cyclohexane (10.0 ml) was heated at 70 "C for 17 h, the major products were acetone (loo%), 2-methyl-

The reactions of tert-butoxyl radicals with a-methylstyrene and with isopropenyl acetate were examined. Allylic hydrogen abstraction was shown to compete with addition to the double bond at the CH2 group. The proportion of abstraction relative to addition increases with increasing solvent polarity, however, this effect is more pronounced in the reactions of isopropenyl acetate than in those of a-methylstyrene.

Die aus der Thermolyse von 2‐(tert.‐Butylazo)‐propyl‐(2)‐hydroperoxid hervorgehenden OH′‐Radikale reagieren mit den Olefinen (I) und in Gegenwart eines Radikalfängers überwiegend unter Schwanz‐Addukt‐Bildung, während die ebenfalls mögliche, sterisch kontrollierte Kopfaddition zu (III) deutlich langsamer ist (Geschwindigkeitskonstante k = (4.8‐ 13)‐ I08 gegenüber (47‐ l43)‐ 1031/ mol ‐ s).