The reaction with oxygen of cyanisopropyl free radicals generated by the polymerization catalyst 2,2′-azobisisobutyronitrile has been investigated. In xylene, or benzene, as solvent at 55° the products identified are: (1) a new compound, 2-cyano-2-propyl hydroperoxide; (2) acetone cyanohydrin; (3) hydrogen cyanide; (4) cyanogen; (5) acetone; (6) p-methyl benzaldehyde (in xylene only); and (7) tetramethylsuccinodinitrile. The hydroperoxide is surprisingly stable; its physical constants are: b.p. 37 °C at 1 mm Hg; m.p. −9 to −8°; [Formula: see text] 1.4138; d20 1.013 g/ml. In benzene under the same experimental conditions, only a very small amount of the hydroperoxide is obtained, the principal product being acetone cyanohydrin. A free-radical mechanism is proposed. The induced decomposition of the hydroperoxide, which is important in benzene, is almost completely inhibited in the presence of xylene. The new hydroperoxide can be used as a polymerization catalyst at moderately elevated temperatures.

The extent of the abnormal recombination of cyanisopropyl radicals to yield the Icetenirnine intermediate has becn irlvestigated a t 80' C. in toluene. I t is fo~ind that 54.47% of the radicals recombine this way. This value is 757; highcr than that reported previously. 'l h~s result rnakes it possible to csti~uate a better value for thc molar extinction of interlnecliate, and suggests the possibility that in the decompositior~ of the latter both free-radical and n~olecular processes are co-operati\.e.

Evidence is presented that the ketenimine intermediate formed in the thermal decomposition of azo-bis-isobutyronitrile (AIBN) rearranges q~lantitatively to tetramethyls~lccinodinitrile (TMSDN), mainly by a molecular mechanism. Interpretation of experimental data 011 the basis of a reaction scheme consistent with the nature of the main products and the features of the kinetics of the decomposition permits estimation, by means of a simple diagram, of the extent of disproportionation, as well as that of the normal and abnormal recombination of cyanisopropyl radicals. The result obtained for the latter is in good agreement with that determined previously by an alternative method. The analysis does not esclude absolutely the possibility of side reactions in which the azo-compound partly decomposes by a molecular process, and the intermediate decomposes into free radicals. Monrever, it is concluded that these side reactions, if any, must be of minor importance.A recent work: by the present authors (7) has show11 that as much as 55% of the initial recombination of cya~lisopropyl radicals is to dirnethylketenecyanisopropylimine, an unstable intermediate detected by . On the other hand, Bickel and Waters (3) have isolated amounts of the normal dirner, TivISDN, which correspond to a n 84% radical recombination. These two results would be coinpatible only if part of the dinitrile is a transformation product of the intermediate. There are other observatioils which support this conclusion: The oily fraction, isolated by Tal2t-Erben and Bywater (6), which contained the kete~~imine in a high concentration, slowly deposited T M S D N crystals when left standing, and ill an attempt to purify the oil by chromatography, using alu~niiluin oxide as absorbent, these authors obtained a high yield of dinitrile, and none of ketenimine. Moreover, the slope of the experimental curve reported by Bevington (1) for the formation of T M S D N as a functio~l of conversio~l is not constant during decomposition as would be expected for a product forming solely a t the expense of the free radicals; instead, the curve presents a nzarked convexity towards the conversion axis, which lllust indicate that a iloticeable fraction of the dinitrile is produced from a precursor other than the free radicals." Therefore, it would be of interest to reconsider the reaction schelne proposed in reference (6), in which the stable products of decompositioll of the intermediate would now have to be specified as TMSDN. T h e reaction schelne under consideration is the following:

As an extension of the results previously reported for two first-order consecutive reactions, the expressions k1·tmax and [B]max/[A]0 are studied as functions of temperature and initial parent concentration for uni-bi-, bi-uni-, and bi-bimolecular consecutive reactions.

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