Synthesis mechanism of dimethylhexane-1,6-dicarbamate from 1,6-hexamethylenediamine, urea and methanol: A molecular scale study based on density functional theory.

This work provides a molecular scale insight into non-phosgene synthesis based on the reaction of dimethylhexane-1,6-dicarbamate from 1,6-hexamethylenediamine, urea and methanol with computational electronic method. By exploring almost all possible reaction modes and comparing the effective barrier of each channel, this work analyzes the optimal reaction mechanism for both non-catalytic and self-catalytic systems. The mechanism without catalysis has a high effective free energy barrier (FEB) of 47.0 kcal mol−1. As for self-catalytic system, after sorting out the reaction pathway network, an effective FEB of 24.6 kcal mol−1 is confirmed which corresponds to dissociation of urea. [Display omitted] • A molecular scale insight into synthesis of carbamate from amine, urea and methanol. • Almost exhaustive potential energy surface exploration. • The optimal pathway involves self-catalysis. • Carbamimidic acid, isomer of urea, has good catalytic effect. • The whole process is determined by dissociation of urea. [ABSTRACT FROM AUTHOR]