Pendimethalin decomposed readily when irradiated in methanol at wavelengths λ ≥ 250 nm to form a number of products. In addition to the N-dealkylated intermediates, the principal products were 2-methyl-4,6-dinitro-5-[(1-ethylpropyl)amino]benzaldehyde and 2-methyl-4,6-dinitro-5-[(1-ethylpropyl)amino]benzyl alcohol. The decomposition at sunlight wavelengths (λ ≥ 290 nm) in methanol is relatively slower and also leads to N-dealkylation and arylmethyl oxidation. Neither acid nor alkali has an effect on the rate of disappearance of pendimethalin (...)