Studies on the antioxidants. XVI. Synergistic reaction between butylated hydroxyanisole and butylated hydroxytoluene in hydrogen donation to 2,2-diphenyl-1-picrylhydrazyl.

Abstract

Hydrogen-donating processes of combined antioxidants, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), were followed by using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) as the hydrogen acceptor, and their relation to the synergism is discussed. The hydrogen donation to DPPH by BHA was almost complete in 10 min. DPPH and BHA were regenerated from this reaction mixture by addition of DPPH·H in the molar ratio of 2 : 1, and BHA and 2, 6-di-tert-butylquinone methide (QM) were formed by addition of BHT in the molar ratio of 1 : 1. The phenoxy radical formed from BHA was lost upon further addition of DPPH. These results suggest the formation of a stable intermediate which accepts two hydrogens from BHT to regenerate BHA, and the possible reaction processes of BHA and BHT with DPPH are shown as Chart 1 ; BHA reacts with DPPH to form the stable intermediate via its phenoxy radical, and this intermediate reacts with BHT to regenerate BHA with the enhanced oxidation of BHT to QM via its phenoxy radical. These processes may be associated with the synergism between BHA and BHT in hydrogen donation to DPPH. The amount of loss of DPPH was in fair agreement with the sum of two hydrogens donated by BHT in the enhanced oxidation to QM and hydrogens donated by BHA. The rate of decrease in DPPH concentration by BHA was about 450 times that by BHT.