Photolysis of imazapyr (AC 243997) herbicide in aqueous media

Arsenal herbicide, the active ingredient of which is imazapyr [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], is an imidazolinone type of herbicide. Photodegradation of imazapyr 14C labeled at the carboxyl and 5-oxocarbon positions was carried out separately under borosilicate-filtered xenon arc light at 25 degrees C in aqueous media. Imazapyr was shown to photodegrade rapidly and extensively in aqueous solution. The decline of imazapyr concentration in the solution followed first-order kinetics. The half-lives were calculated as 1.9-2.3 days in distilled water, 2.7 days in pH 5 buffer, and 2.3 days in pH 9 buffer. The predominant photolysis products derived from carboxyl-14C-labeled imazapyr were 7-hydroxyfuro[3,4-b]pyridin-5(7H)-one and 2,3-pyridinedicarboxylic acid. Decarboxylation was evident as a minor photodecomposition product of carboxyl-14C-labeled imazapyr. Two cyclized compounds, 2,3-pyridinedicarboximide and furo[3,4b]pyridin-5(7H)-one, were also detected as minor degradates. The one major photolysis product of the 5-oxo-14C-labeled imazapyr was the volatile 14CO2