Regeneration of aromatic amines in alcohol oxidation

With hydrocarbons, two chains are normally terminated by one molecule of the inhibitor (of phenol or aromatic amine), i.e. the stoichiometric coefficient of the inhibitor is f = 2 [1]. With cyclohexanol, multiple termination of chains takes place with the same molecule of the inhibitor, as found for a-naphthylamine [76], This was observed for many aromatic amines in primary as well as in secondary alcohols [77,78], To the first approximation, the mechanism of inhibitor regeneration consists of reaction of the alcohol hydroxyperoxy radical with the radical In, reducing to InH with simultaneous termination of the chain [79], viz. 

Reduction of In by the hydroxyperoxy radical was established in the following way [79]. Tetraphenylhydrazine added to cyclohexanol in the presence of an initiator decomposed to diphenylnitrogen radicals which were reduced to diphenylamine. No reduction was observed in the absence 

Each of these radicals react with In by two routes, reduction of In- to InH and addition to In- (resulting in the disappearance of InH). For example 

The stoichiometric coefficient f- 2(1 + kln/k lnn) and naturally depends on the kind of radical with which In- reacts. As found in experiments on the oxidation of cyclohexanol with a-naphthylamine (120° C, Wi = 1.86 X 1CT6 mole l-1 s-1), f increases with oxygen pressure from 16.6 (Pq2 = 0) to 48 (Pq2 = 760 torr). It follows that the degree of amine regeneration by reaction with hydroxyperoxy radicals is higher than that for hydroxyalkyl 

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