Kinetic studies on free radical reactions : II. The photochemical reaction between DPPH and methylmethacrylate

Abstract

The reaction between α, α'-diphenyl-β-picrylhydrazyl (DPPH) and methylmethacrylate (MMA) in benzene solution induced by UV irradiation was investigated. The change of DPPH concentration was photometrically pursued, and electron spin resonance spectra of the solutions in the course of reaction were observed, where the significant influence of dissolved oxygen was found. In the case of the absence of dissolved oxygen the apparent rate of disappearance of DPPH is of the first order, only corresponding hydrazine being produced. On the other hand, in the presence of dissolved oxygen it is of the zero order and hydrazine, diphenylnitroxide (DPNO) which was identified by ESR spectrum, and a diamagnetic substance which will be produced from the reaction of one DPPH and one peroxy radical, are produced concurrently. In both cases it was interred from the view-point of kinetics that DPPH not only acts as a radical scavenger but also its photo-ecxited molecule participates in the step of radical production from MMA molecule.