ANTIOXIDANT ACTION OF ORGANIC SULFITES .1. ESTERS OF SULFUROUS ACID AS SECONDARY ANTIOXIDANTS

The efficiency of esters of sulphurous acid as secondary antioxidants has been studied. Several aliphatic as well as aromatic open-chain and cyclic sulphites were synthesized and reacted with tert-butyl-, cumen e- and alpha-tetralin hydroperoxides. All sulphites investigated decom pose hydroperoxides in a nonradical way. This reaction proceeds in two steps: in a slow redox reaction and a rapid catalytic decomposition o f the hydroperoxides. The open-chain alkyl sulphites and the cyclic su lphite of 2,2'-thiobis-(6-tert-butyl-4-methylphenol) show especially h igh efficiency. In comparison with trivalent phosphorus compounds, est ers of sulphurous acid react more slowly in the stoichiometric reactio n step, but are also able to decompose hydroperoxides catalytically. B esides these sulphuric acid esters. SO2 SO3, and H2SO4 also take part as catalysts in the reaction. Finally, the rate constants of the reduc tive and catalytic step of the hydroperoxide decomposition were determ ined. (C) 1997 Elsevier Science Limited.