Abstract
The oxidative decomposition of t-butylated hydroxyanisole (BHA) and formation of its dimers were investigated during the thermal oxidation of saturated and unsaturated triglycerides.
Glycerol trilinoleate, in which BHA had been dissolved, was oxidized by air at 150°C to obtain two oxidation products of BHA from the reaction mixture by extraction with acetonitrile and silicic acid column chromatography. They were identified as the diphenyl ether type dimer and biphenyl type dimer of BHA by 1H-NMR and mass spectroscopy. The isomers of the BHA dimer and BHA monomer in oxidized triglycerides were determined by HPLC, using LiChrosorb SI-60 as the stationary phase, hexane-diisopropyl ether mixture (9 : 1) as the mobile phase, and a UV monitor (290 nm).
Changes in the concentrations of BHA and its dimers during the thermal oxidation of glycerol trilaurate and glycerol trilinoleate were followed by HPLC. In glycerol trilaurate, BHA was oxidized to give its dimers. The total quantities of BHA and its monomer showed little decrease. It is thus apparent that BHA dimers undergo only slight oxidative decomposition in saturated triglyceride. A considerable decrease in BHA concentration was observed in glycerol trilinoleate, and the total quantities of BHA and its dimers were less within the time tested than those in glycerol trilaurate. In the saturated triglyceride, a diphenyl ether type dimer predominated, but in the unsaturated triglyceride, a biphenyl type dimer was larger, indicating reversal of relative composition.
