A computational mechanistic study of the deamination reaction of melamine

Abstract

A detailed computational study of the deamination reaction of melamine by OH–, nH2O/OH–, nH2O (where n = 1, 2, 3), and protonated melamine with H2O, has been carried out using density functional theory and ab initio calculations. All structures were optimized at M06/6-31G(d) level of theory, as well as with the B3LYP functional with each of the basis sets: 6-31G(d), 6-31 + G(d), 6-31G(2df,p), and 6-311++G(3df,3pd). B3LYP, M06, and ωB97XD calculations with 6-31 + G(d,p) have also been performed. All structures were optimized at B3LYP/6-31 + G(d,p) level of theory for deamination simulations in an aqueous medium, using both the polarizable continuum solvation model and the solvation model based on solute electron density. Composite method calculations have been conducted at G4MP2 and CBS-QB3. Fifteen different mechanistic pathways were explored. Most pathways consisted of two key steps: formation of a tetrahedral intermediate and in the final step, an intermediate that dissociates to products via a 1,3-proton shift. The lowest overall activation energy, 111 kJ mol−1 at G4MP2, was obtained for the deamination of melamine with 3H2O/OH−.