Radical-scavenging activity of butylated (BHT) and its metabolites

To clarify the radical-scavenging activity of butylated hydroxytoluene (BHT), a food additive, stoichiometric factors (n) and inhibition rate constants (k(inh)) were determined for 2,6-di-tert-butyl-4-methylphenol (BHT) and its metabolites 2,6-di-tert-butyl-p-benzoquinone (BHT-Q), 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHA-CHO) and 3,5-di-tert-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadiene-1-one (BHT-OOH). Values of n and k(inh) were determined from differential scanning calorimetry (DSC) monitoring of the polymerization of methyl methacrylate (MMA) initiated by 2,2'-azobis(isobutyronitrile) (AIBN) or benzoyl peroxide (BPO) at 70degreesC in the presence or absence of antioxidants (BHT-related compounds). The n values declined in the order BHT (1-2) > BHT-CHO, BHT-OOH (0.1-0.3) > BHT-Q (similar to0). The n value for BHT with AIBN was approximately 1.0. suggesting dimerization of BHT. The k(inh) values declined in the order BHT-Q ((3.5-4.6) x 10(4) M-1 s(-1)) > BHT-OOH (0.7-1.9 x 10(4) M-1 s(-1)) > BHT-CHO ((0.4-1.7) x 10(4) M-1 s(-1)) > BHT ((0.1-0.2) x 10(4) M-1 s(-1)). The k(inh) for metabolites was greater than that for the parent BHT. Growing MMA radicals initiated by BPO were suppressed Much more efficiently by BHT or BHT-Q compared with those initiated by AIBN. BHT was effective as a chain-breaking antioxidant. (C) 2004 Elsevier Ireland Ltd. All rights reserved.