Tetralin autoxidation initiators

Aqueous dispersions of charged copolymer latexes are active supports of cobalt catalysts for autoxidations of tetralin by cobalt-pyridine complexes and of 2,6-di-rm-butylphenol and 1-decanethiol by CoPcTs. Since these reactants are insoluble in water, a simple explanation of the catalytic activity is that the organic polymer serves to solubilize the reactants in the phase that contains the cobalt catalyst. All three reactions have initial rates that are independent of substrate concentration, as determined by absorption of dioxygen from a gas buret. All three reactions appear to proceed by different mechanisms. Tetralin autoxidation is a free radical chain process promoted by the CoPy complex, whereas the CoPcTs reactions are not free radical chain processes. The thiol autoxidation is reported to involve hydrogen peroxide, whereas the 2,6-di-re/t-butylphenol autoxidation apparently does not. 

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]. 

The present paper reports the results of a kinetic study of the inhibition of the azobisisobutyronitrile-initiated autoxidation of cumene at 60 °C. and of Tetralin at 70 °C. by zinc diisopropyl dithiophosphate, undertaken to test the validity of the chain-breaking inhibition mechanism proposed above. In addition, the effectiveness of several metal dialkyl dithiophosphates as antioxidants in the autoxidation of squalane... 

Small but significant effects of solvent polarity were found in the autoxidation of a variety of alkenes and aralkyl hydrocarbons [216-220] (styrene [216, 218, 219], ethyl methyl ketone [217], cyclohexene [218], cumene [218, 219], tetralin [219], etc.). An extensive study on solvent effects in the azobisisobutyronitrile (AIBN)-initiated oxidation of tetralin in a great variety of solvents and binary solvent mixtures was made by Kamiya et al. [220],... 

Thus, 1 seems to be a true catalyst rather then a new kind of free radical initiator. This behavior is in contrast to the behavior of related manganese complexes. For example, Mn(II) carboxylates are known to decompose CHP during autoxidation of cumene l dinuclear Mn(III) complexes decompose tetralin hydroperoxide during oxidation of tetralin (an inner-sphere Mn-alkyl hydroperoxide intermediate has been proposed) trinuclear, carboxylate and oxo-bridged complexes containing Mn(II) were found to decompose CHP during the catalyzed oxidation of cumene. 

The known examples of catalytic oxygenations involve substrates that undergo relatively facile autoxidation to hydroperoxides often even without an added catalyst. For example tetraline is converted to a-tetralone in the presence of ClFeTPP at 25 °C [96]. CoTTP catalyzes the oxidation of 2,5-dihydrofuran to 2-hydrofuran-5-one and 2-hydrofuran-5-ol in ethyl acetate at 30 C [97]. Furan and 2,3-dihydrofuran were also oxidized but the products were not determined. Tetraline and cumene did not react. The kinetics of autoxidation were interpreted in terms of chain initiation by the dioxygen adduct of CoTTP ... 

This chapter describes our initial investigations of cobalt complexes bound to colloidal polymers for the autoxidations (in which dioxygen is the stoichiometric oxidant) of tetralin, 2,6-di-r rr-butylphenol, and 1-decanethiol. The reactions of these water-insoluble organic compounds proceed faster in the colloids that they do with the same cobalt complexes as catalysts in aqueous solution. Autoxidations have been chosen because of their potential for low cost use for the decontamination of water and for chemical manufacturing processes. 

A complete mechanism for the autoxidation of alkylaromatic hydrocarbons by cobalt(n) in acetic acid has not been established,25 6 although a complex rate law has been determined for tetralin. 22 The reaction most likely proceeds by a fiiee radical chain mechanism in which the purpose of the cobalt ions is to provide a hi h steady state concentration of free radicals by catalysis of the decomposition of THP. The free radical nature of the autoxidation of tettalin with the colloidal CoPy catalysts is supported by experiments which showed inhibition of the reaction by 2,6-di-rerr-butylphenol and 2,6-di-rm-butyl-4-methylphenol, and by a shortening of the induction period and increase of the reaction rate when azobis(isobut nitrile) was added to the reaction mixture as a free radical initiator. 

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