Thermal Degradation of Phenolic Antioxidants

Abstract

Chemical decomposition of 2-tert-butyl-hydroxy-anisol, 2-tert-butyl-hydroxytoluene and 2-tert-butylhydroquinone at 175±5°C in the absence of hydroperoxy or alkylperoxy radicals was studied. 2-tert-butylbenzoquinone was identified as the primary and major oxidation product of TBHQ. Interconversion between TBHQ and TBBQ was observed to play the most important role in antioxidant effectiveness and carry through effect of TBHQ. 3,3'5,5'-tetra-bis-Itert-butyl)-4,4'-dihydroxyl-1.2-diphenylethane from BHT and 3,3'-bis-(1.1-dimethyl ethyl)-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diol and its ethylene glycol type of isomer from BHA were determined as major decomposed products. 2.6-d9-tert-butyl-4-hydroperoxy-4-methylcyclohexa-2.3-dienone was thermolized at frying temperature to simulate and simplify the real system containing BHT and lipid. The products included BHT, 2.6-di-tert-butyl-4-hydroxy-4-methylcyclohexa-2.5-dione, 3.5-di-tert-butyl-4-hydroxybenzaldehyde, 2.6-di-tert-butyl-4-hydroxymethylphenol and unidentified compounds having M.W. 414,442,274 and 278. Trace amounts of 2.6-di-tertbutylbenzoquinone and quinone methide were detected. In the model system containing palmitic acid (16;0) and linoleic acid (18;2), the order of antioxidant effectiveness was TBHQ>BHA>BHT.