A DFT study of the hydrolytic degradation mechanisms of iprovalicarb and iprodione: implications in environmental safety

Abstract

Context

Iprovalicarb and iprodione represent two popular carboxylic acid amide-type (CAA) fungicides which have found wide spread application in the protection of various crops. However, though useful, excessive usage of these compounds could have deleterious effects on human health and environmental safety. Hence, a thorough DFT investigation of the degradation thermodynamics and mechanism for these two compounds was carried out, revealing a multi-step hydrolytic transformation process in the gas phase via overall exergonic processes where the rate limiting steps are calculated at ca. 197 and 235 kJ mol⁻¹, for iprodione and iprovalicarb, respectively. However, in aqueous media, whereas for iprodione the hydrolysis mechanism is identical to that in the gas phase, for iprovalicarb, the endergonic solution phase mechanism is different. Overall, both compounds undergo very slow hydrolysis at neutral pH but, of the two, iprodione offers the shortest residence time. 

Methods

All calculations were carried out at the 6–311 +  + G(d,p)/CAM-B3LYP level of theory, as implemented in the Gaussian-16 software suite. Solution phase calculations were carried out via the well-regarded C-PCM model, an implicit solvation model, known to be efficient and effective at predicting solvation effects.