ORGANIC SYNTHESIS AND INDUSTRIAL ORGANIC CHEMISTRY Inhibiting Effect of Sulfur-Containing Alkylphenols on Oxidation of Vaseline Oil

A comparative study was made of antioxidative properties of sulfur-containing 2,6-di-tert-butyl- phenol derivatives in a model reaction of autooxidation of Vaseline oil. Sulfur-containing derivatives of sterically hindered phenols occupy a prominent place among antioxidants used today to prevent oxidative degradation of various organic materials (polymers, fuels, lubricating oils, plastics, fibers) (1, 2). The high antioxidant activity (AOA) of such compounds is due to the presence of two active fragments: phenolic and sulfur-containing, which show a synergistic effect (3, 4). The relation- ship between the structure and antioxidative per- formance of sulfur-containing phenolic antioxidants (SPAOs) is complex, because the inhibiting properties of these compounds are governed by the structure of phenolic and sulfur-containing fragments, their num- ber and mutual arrangement, and also by the proper- ties of the substrate and oxidation conditions (5). At the same time, elucidation of this relatioship is very important for theory and practice, as it would allow directed synthesis of more effective antioxidants. In this work we studied the antioxidative activity of sulfur-containing alkylphenols I XVII in a model reaction of autooxidation of Vaseline oil (see table) and analyzed the structure activity relationship for these inhibitors. The inhibiting effect exerted by sul- fur-containing alkylphenols on oxidation of Vaseline oil was evaluated by the induction period . As refer- ence antioxidants we used Ionol, Probucol, TB-3, and SO-3. We found that all the sulfur-containing alkylphen- ols I XVII exhibit pronounced antioxidative activity, increasing the induction period of Vaseline oil oxida- tion by a factor of 5 30. A certain correlation is re- vealed between the structure of the antioxidant mole- cule (length of the alkyl chain separating the phenolic and sulfur-containing fragments; structure of substitu- ent at the S atom; number of sulfide and phenolic fragments) and its inhibiting effect. In the series of unsymmetrical sulfides I III with different length of the p-alkyl chain, AOA grows with increasing number of methylene units separating the phenolic and sulfide fragments. This may be associ- ated with changes in the antiradical activity (6). The antioxidative activity of unsymmetrical sul- fides II and IV IX varies depending on the length and extent of branching of the aliphatic substituent at Induction periods of Vaseline oil oxidation inhibited with antioxidants. Antioxidant concentration c a =2 mol g 1 ,