PHOTODECOMPOSITION OF PYRETHRIN .I. ALLETHRIN PHTHALTHRIN AND DIMETHRIN - MODIFICATIONS IN ACID MOIETY

Pyrethrin I, phthalthrin, allethrin, and dimethrin readily decompose when irradiated by a sun lamp, in air, as thin films on glass, the rate of decomposition decreasing in the order listed and each pyrethroid yielding at least 11 products. Hydrolysis does not appear to be a major photochemical reaction for pyrethroids. Work with pyrethrin I and allethrin indicates that the alcohol moiety of pyrethroids suffers photochemical attack, but the chemical reactions involved are not known. The photochemical changes in the acid moiety of each of the four pyrethroids are the same and they involve stepwise oxidation of the trans-methyl group of the isobutenyl moiety to the respective alcohol, aldehyde, and carboxylic acid derivatives; oxidation of the isobutenyl double bond to a keto derivative; rupture of this double bond to yield esters of trans-caronic acid; and other attacks resulting in at least six additional modifications of the acid rnoietv. © 1969, American Chemical Society. All rights reserved.