Oxidation of β-Carotene. Site of Initial Attack

The reaction between β-carotene and molecular oxygen in toluene at 60° was investigated. A linear relation was found between the loss in β-carotene and time. The reaction rate increased with increasing temperature. The activation energy, Εa, for the oxidation of β-carotene was found to be 10.2 kcal/mol. Though free-radical initiators caused rate enhancement, the kinetics of the reaction and the light absorption characteristics of the reaction solution were altered. This indicated a difference in the mechanism of the reaction in the presence of free-radical initiators. The rate of loss of β-carotene was increased in the presence of cupric ions and decreased in the presence of diphenylamine. The products of the reaction were β-carotene 5,6-monoepoxide and its isomer, β-carotene 5,6,5′,6′-diepoxide, and β-carotene 5,8-monoepoxide and its isomer, β-carotene 5,8,5′,8′-diepoxide. A reaction mechanism was proposed. © 1970, American Chemical Society. All rights reserved