Antioxidant synergism between butylated hydroxyanisole and butylated hydroxytoluene

Abstract

Decay of the 2, -radical] in the presence of butylated hydroxyanisole (BHA) was investigated in 1,2dimethoxyethane with or without triethylamine. BHT-radical was conveniently generated by dissociation of its unstable dimer in solution. The products were BHT, 3,3'-di-tert-buty [-5,5'-dimethoxy-2,2'-dihydroxybiphenyl (BHA-dimer), 2,6-ditert-butyl-p-quinone methide (QM), 1,2-bis(3,5-di-tert-butyl-4hydroxyphenyl)ethane, and 3, 3",5,5'-tetra-tert-butyl-4,4"-stil-benequinone. The reaction without added triethylamine gave larger quantities of the last two products and BHA (recovery), whereas the reaction with it provided larger quantities of the first two products. The marked difference in the product distribution can be accounted for by a series of reactions including re -~ versible dehydrogenation of BHA with BHT-radical, which generates 2-tert-butyl-4-methoxyphenoxy radical (BHA-radical) and BHT, reversible dimerization of BHA-radical, which affords an intermediary bis(cyclohexadienone), and spontaneous and base-catalyzed prototropic rearrangement of the intermediate into BHA-dimer. Products of coupling between BHT-radical and BHA-radical were not obtained. BHA was found to undergo facile ac!d-catalyzed addition to QM, providing two isomeric bis(hydroxyphenyl)methanes. The results help to elucidate the mechanism of antioxidant synergism between BHA and BHT and may suggest that the synergism can be affected by base or acid.]AOCS 72, 1565-1.570 (1995).KEY WORDS: Antioxidant synergism, butylated hydroxyanisole, butylated hydroxytoluene, effect of acid, effect of base, fate of phenoxy radicals involved. EXPERIMENTAL PROCEDURESIH (90 MHz) and 13C (22.6 MHz) nuclear magnetic resonance (NMR) spectra were obtained in chloroform-d on a Hitachi (Tokyo, Japan) R-1900 spectrometer. Infrared (IR) spectra were taken in chloroform with a Hitachi EPI-G3 spectrophotometer. Column chromatography was conducted on

Antioxidantes utilizados em óleos, gorduras e alimentos gordurosos

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Thermal oxidation of rice bran oil during oven test and microwave heating

“…Antioxidants either in combination or singly are commonly added to oils and fats to retard oxidation changes (Omura 1995). Among the commonly used antioxidants, tertiary-butylhydroquinone (TBHQ) gave adequate protection, whereas butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) were relatively ineffective (Asap and Augustine 1986;Augustin and Berry 1983).…”

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