Alkaline hydrolysis pathway of 2,4-dinitroanisole verified by ¹⁸O tracer experiment

The environmental fate of insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), has drawn increasing attention because of their growing use in military activities. One of the main attenuation mechanisms of DNAN degradation in aqueous environments is alkaline hydrolysis. We investigated the pathway for alkaline hydrolysis of DNAN at pH 12 by a combined approach of experiment and theory. An experiment using ¹⁸O-labeled water was performed to verify the reaction pathway. Calculated free energies for two putative reaction pathways by density-functional theory optimized at the SMD(Pauling)/M06-2X/6-311++G(2d,2p) level including explicit solvation of DNAN by 10 H₂O molecules and one OH^- ion gave a prediction in agreement with the experimental result. The verified reaction pathway for alkaline hydrolysis of DNAN is a S_N2Ar nucleophilic aromatic substitution with a methoxy leaving group (OCH₃) at the C1 site.