Computational elucidation of mechanisms of alkaline hydrolysis of nitrocellulose: dimer and trimer models with comparison to the corresponding monomer

Density functional theory (DFT) investigation has been undertaken to explore alkaline hydrolysis mechanisms for nitrocellulose in the gas phase and in bulk water solution by considering the dimer and trimer forms of 2,3,6-trinitro-β-d-glucopyranose in the (4)C(1) chair conformation and by comparing the computed results with the monomer. Ground and transition state geometries were optimized using the B3LYP functional and the 6-311G(d,p) basis set both in the gas phase and in the bulk water solution. The nature of respective potential energy surfaces was ascertained through harmonic vibrational frequency analysis. Intrinsic reaction coordinate calculations were performed to ensure that computed transition state connects to the respective reactants and products. Single-point energy calculations were also performed using the recently developed M06-2X functional and the cc-pVTZ basis set using the B3LYP/6-311G(d,p) optimized geometries. Effect of the bulk water solution was modeled using the polarizable continuum model (PCM) approach. It has been suggested that the dimeric form of 2,3,6-trinitro-β-d-glucopyranose can be considered as the smallest model to study the nitrocellulose system regarding the alkaline hydrolysis reaction. It was predicted that the peeling-off reaction will start after the denitration of various sites, which will follow a C3 → C6 → C2 denitration route. Further, it was determined that the peeling-off reaction will be more preferred than the ring cleavage through the ring CO bond.