On the photolysis of phthalic acid dimethyl and diethyl ester: a product analysis study

Dimethyl phthalate, DMP, and diethyl phthalate, DEP, are rather photostable (Phi(-phthalate) less than or equal to 0.03). Exposure of neat DMP and DEP in the presence of air to high absorbed doses of UV light yielded a variety of products, many of them identifiable by GC-MS analysis. The products were divided into two fractions by ether extraction. Typical products contained in the ether-soluble fraction of irradiated DMP and DEP are: [GRAPHICS] The ether-insoluble fraction consists of oligomeric compounds (molar mass: several 10(3) g mol(-1)) that are characterized by a high degree of substitution at the aromatic rings and by the existence of conjugated double bonds that act as chromophoric groups absorbing light in the visible wavelength range. Reaction pathways based on the primary cleavage of bonds next to the carbonyl groups and leading to the following radicals are proposed: [GRAPHICS] (C) 1998 Elsevier Science S.A.