With an Appendix on the Spectroscopic Determination of the Structure of the Reaction Products. By C. LA LAU.)Several types of alkylperoxy-radicals (RO*O*) were prepared both by cobalt-catalysed decompositions of the corresponding hydroperoxides (RO-OH) and by addition of alkyl radicals (R-) to oxygen. Their reactions with a number of 2 : 4 : 6-trialkylphenols (AH) have been investigated. The main products appeared to be peroxides (RO*Oh) having the structure of alkylperoxy-2 : 4 : 6-trialkylcyclohexadienones. If a P-methyl group was present in the phenol, stilbenequinones were also formed. The results are discussed in relation to the inhibitory activity of phenols in autoxidation.FOR most liquid-phase autoxidations of hydrocarbons the propagation sequence generally accepted is :Termination may occur by interaction of the chain-carrying radicals (Re and RO.0.) or by reaction with an inhibitor (Bolland, Quart. Reviews, 1949, 3, 1). The amounts of inhibitor required to suppress oxygen absorption are generally very small-often as little as 0-01%-probably as a result of the large overall kinetic chain lengths. In consequence, the amounts of products formed from the inhibitor are too small for a detailed study, which seriously handicaps investigations into the mode of action of antioxidants.Abundant evidence is available (Bolland, loc. cit.) as regards the predominating part played by alkylperoxy-radicals (RO-0.) in autoxidation. Since the concentration of alkyl radicals (Re) is generally low as a result of their rapid reaction with oxygen to form alkylperoxy-radicals, it seems plausible to assume the inhibitor to operate mainly by reactions with RO-0.. In order to investigate the latter reactions by isolation of products, methods are required for the preparation of alkylperoxy-radicals on a sufficient scale while avoiding the simultaneous oxidation of an excess of other products. Recent literature has dealt to some extent with methods of this kind. Cosgrove and Waters (J., 1951, 388)

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The relative reactivities of a number of polycyclic aromatic hydrocarbons have been determined by measuring their retarding effects on the benzoyl peroxide initiated addition of carbon tetrachloride to hexadecene-1 and/or of bromotrichloromethane to styrene. The results could be satisfactorily represented by kinetic expressions, which yielded the rate constants of the interaction of trichloromethyl radicals with the aromatics, relative to that for addition to the olefin. The inhibitory effects are attributed to addition of the chain-carrying CC13 radicals to the aromatics.The scale of reactivities thus obtained extended from benzene to 3 : 4-benzopyrene, the latter being over 100, OOO times more reactive than the former. A close parallel appeared to exist between reactivity towards free radicals and the highest free valence numbers as well as the corresponding polarization energies calculated for each molecule by means of the molecular orbital method. The significance of these correlations is discussed. * CBrC13 interferes with the iodometric peroxide determinations. Dehydrogenation of dihydroanthracene by thiyl radicals was found by Bickel and Kooyman to produce some anthracene besides a large amount of 9 : 10 : 9' : 10'tetrahydro-dianthranyl (to be published shortly).

A lkylfieroxy-radicals. Part I I I . 2217 426. Alkylperoxy-radicals. Part III? Kinetics of Autoxidations Retarded by A r m t i c Arnines.

By use of a competitive method involving reactions of alkylperoxyradicals either with a 2 : 4 : 6-trialkylphenol (AH) or with a standard hydrocarbon (RH = 9 : 10-dihydroanthracene), the relative reactivities a t 60" of various phenols were determined by measuring initial rates of oxidation. Alkylperoxy-radicals were generated by the dissociation of 2 : 2 : 3 : 3-tetraphenylbutane and reaction of the resulting radicals with oxygen.Three types of kinetics were found to occur, depending on the phenol investigated, and were interpreted on the basis of three different reaction mechanisms.It appeared that phenolic antioxidants can be characterized (1) by the antioxidant efficiency, i.e., the ratio of the rates of hydrogen abstraction by alkylperoxy-radicals from the phenol and from the hydrocarbon respectively, and (2) by the rate of the chain-transfer reaction A* + RH --b AH + R-. All phenolic antioxidants reacted much faster than the standard hydrocarbon, differing among themselves by a factor of about 20. The rate of the chain-transfer reaction decreased with increasing size of orthosubstituents. The presence of two o-tert.-butyl groups completely prevented the starting of new oxidation chains by transfer.