Kinetics of inhibition by phenols and amines

Bolland and ten Haave [151] found that the oxidation of ethyl linoleate inhibited by hydroquinone was described by the relation 

A similar relation was found by Howard and Ingold [162] for the oxidation of styrene inhibited by a variety of phenols. Both of these systems apparently involve some combination of reactions (229) and (230), but their relative importance is indistinguishable on the basis of the kinetic relationship alone except for the stoichiometric ratio of R02- consumed for each AH. Thus the steady-state concentration of R02- in the inhibited system is 

In the oxidations of neat styrene, n = 2 for a variety of phenols, indicating that the probable mechanism for inhibition is 

Hammond and coworkers [159] also found values of n 2 for a variety of amines and phenols in the inhibited oxidation of cumene. However, since the kinetics showed a half-order dependence on cumene and no isotope effect was found in the inhibited oxidation using A-deuterated amines, they proposed a more complex mechanism to account for their findings. Howard and Ingold [162] showed that by using added D20 to maintain the A- or O-deuteration, large isotope effects are found in the inhibited oxidation. Moreover, Mahoney and Ferris [163] showed that the unusual kinetic dependence on hydrocarbon found by Hammond and 

Equation (239) also accounts adequately for some unusual results noted by Thomas [164] and Thomas and Tolman [165] for oxidations of cumene inhibited by phenol, diphenylamine, and trimethylamine. 

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