ANTIOXIDANT ACTION OF ORGANIC SULFITES - II - ESTERS OF SULFUROUS ACID AS PRIMARY ANTIOXIDANTS

The effect of esters of sulfurous acid as primary antioxidants was exa mined. Different aliphatic, aromatic, open-chain and cyclic sulfites w ere synthesized. The reactions of organic sulfites with RO2 and RO rad icals, the chain carriers of the autoxidation of hydrocarbons and poly mers, were simulated by means of the thermal decomposition of azobisis obutyronitrile (AIBN) in the presence of oxygen and of di-tert-butylpe roxalate (DTBPO). The reactivity of organic sulfites with 2-cyanoisopr opylperoxyl radicals is low. Only aromatic sulfites are able to trap p eroxyl radicals; however, they are not very effective primary antioxid ants. The reactions of the organic sulfites with tert-butoxyl radicals generally lead to an increase in the rate of decomposition of DTBPO, as determined from rate constants measured at 50 degrees C. A decompos ition of DTBPO induced by liberated tert-butyl radicals in the presenc e of alkyl sulfites is very probable. Alkyl sulfites and aromatic sulf ites with aliphatic groups act mainly as hydrogen donors in reactions with alkoxyl and peroxyl radicals. (C) 1998 Elsevier Science Limited. All rights reserved.