Aliphatic radicals, particularly 2,2,6,6-tetramethylpiperidin-l-oxyl, react with alkyl radicals [I]. Nitroxyls containing aromatic substituents at the N atom also react with other types of radicals. For example,4;2',2,3, is an effective scavenger of alkyl, peroxy, and alkoxy radicals [2]. In the reaction with peroxy radicals a quinone-nitrone is formed, which has an intense absorption band in the visible region of the spectrum. This enables the rate of formation of various types of free radicals to be measured from the consumption of the nitroxyl (I) and the formation of the quinone-nitrone.
It was of interest to examine the possibility of using the nitroxyl (I) to study the rate of free-radical formation in reactions for the catalytic decomposition of hydroperoxides. The study of these reactions by the inhibitor method is usually hampered by many amines, phenols, and nitroxyl radicals altering the properties of the catalytic system appreciably in addition to the reaction with radicals [3][4][5]. As a model reaction we chose the muchstudied decomposition of cumyl hydroperoxide catalyzed by Co acetylacetonate [6,7].
EXPERIMENTAL
Cumyl hydroperoxide (CHP) was decomposed in chlorobenzene solution at 50~ in an inert atmosphere. Chlorobenzene and CHP were purified by the methods in [7]. We used nitroxyl radicals kindly provided by A. B. Shapiro; the purity of the nitroxyl was checked chromatographically, the nitroxyl concentration was determined from the EPR spectra (EPR-V spectrometer), and that of CHP was determined iodometrically, account being taken of the liberation of iodine by the nitroxyl and by the products of its conversion. The optical spectra were recorded on a Specord UV-VIS spectrophotometer.