Tetralin inhibited oxidation

Aryl phosphites inhibit the initiated oxidation of hydrocarbons and polymers by breaking chains on the reaction with peroxyl radicals (see Table 17.3). The low values of the inhibition coefficient / for aryl phosphites are explained by their capacity for chain autoxidation [14]. Quantitative investigations of the inhibited oxidation of tetralin and cumene at 338 K showed that with increasing concentration of phosphite /rises tending to 1 [27]. 

Several other types of antioxidants can inhibit oxidation by donating a hydrogen atom to a peroxy radical. Howard (15) has described the interesting case of inhibition by a second hydrocarbon or its hydroperoxide. In the particular case he discussed, the inhibition of the oxidation of cumene by Tetralin (TH) or Tetralin hydroperoxide (TOOH) occurs because the tetralylperoxy radical (T02 ) reacts with a cumylperoxy radical (CO2 ) much more rapidly than two cumylperoxy radicals react with one another. The inhibition sequence can be represented by the following reactions. 

The results of a similar study of the inhibited oxidation of Tetralin at 70 °C. are shown in Figures 4 to 6. Again, the initial oxidation rate is... 

Co-oxidation of Cumene and Tetralin. The present method for determining cross-propagation constants is based on Thomas and Tolman s (34) observation that the oxidation of cumene is strongly inhibited by adding low concentrations of Tetralin hydroperoxide. These workers concluded that TOO radicals formed in the transfer reaction ... 

The kinetics of the zinc diisopropyl dithiophosphate-in-hibited oxidation of cumene at 60°C. and Tetralin at 70°C. have been investigated. The results cannot be accounted for solely in terms of chain-breaking inhibition by a simple electrow-transfer mechanism. No complete explanation of the Tetralin kinetics has been found, but the cumene kinetics can be explained in terms of additional reactions involving radical-initiated oxidation of the zinc salt and a chain-transfer step. Proposed mechanisms by which zinc dialkyl dithiophosphates act as peroxide-decomposing antioxidants are discussed. 

Yamamura and coworkers used an oxygen absorption method to study the effects of a series of 46 dihydric phenols on inhibition of azo-initiated oxidation of tetralin . They reported activities in terms of the stoichiometric factor, n, and the rate of oxygen absorption, during induction periods. The 13 catechols studied all showed higher n factors (n = 2.0-2.3) and lower values than any other of the diols. Unfortunately, they were not able to obtain values. 

The reactions of phosphites with peroxy radicals continue to attract attention because of the use of phosphites as anti-oxidants. The autoxidation of a variety of hydrocarbons, e.g. tetralin, cumene, styrene, and cyclohexane, is inhibited by zinc dialkyldithiophosphates (60). In order to assess the reactivity... 

Figure 6. Inhibition of tetralin oxidation by dibenzylhydroxyl amine, AIBN-inhibited.

However, Boozer and Hammond [7] have obtained additional support for the postulated chain termination via reaction (9) as opposed to reaction (5) on the basis of isotopic labelling experiments and from the inhibiting effect of amines not possessing a labile N—H function in their structure [8]. The use of deuterium-labelled methyl aniline and diphenyl-amine as inhibitors in the oxidation of tetralin and cumene did not show the isotope effect which would be expected if reaction (5) was important. Similarly, both AT-dimethylaniline and AT,AP-tetramethyl-p-phenylene-diamine have measurable inhibitory activity despite the fact that neither has a labile hydrogen [8]. However, it has been argued [12] that neither a kinetic isotope effect nor a labile hydrogen is necessary if inhibition results from an electron transfer reaction of the type... 

The maximum achievable conversion of the bulk tetralin is about 35 % due to the formation of higher oxidation products that inhibit the reaction. A similar product-inhibiting effect has been observed in the homogeneous reaction carried out in acetic acid (14) it is believed to arise from product species such as a-naphthol and 1,6-dihydroxynaphthalene. 

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