Catalysts screening, optimization and mechanism studies of dimethylhexane-1,6-dicarbamate synthesis from 1,6-hexanediamine and dimethyl carbonate over Mn(OAc)(2) catalyst

Abstract The catalytic synthesis of dimethylhexane-1,6-dicarbamate (HDC) from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC) over a series of homogeneous catalysts (e.g., metallic nitrates and acetates) were investigated. Mn(OAc) 2 was found to be the most effective catalyst for this reaction. Under the optimum reaction conditions (reaction temperature of 363 K, DMC-to-HDA molar ratio of 4:1, catalyst concentration of 7 wt% (based on HDA), and reaction time of 5 h), HDC yield can reach as high as 98.0% with HDA totally converted. Online in-situ Fourier Transform Infrared (FTIR) and Density Functional Theory (DFT) calculations were used together to investigate the interactions between Mn(OAc) 2 and substrates. The results indicated that both of HDA and DMC had interactions with Mn(OAc) 2 , but the energy barriers of the transition states (TS) of DMC (DMC-TS) was higher than that of HDA (HDA-TS), which meant that HDA was easier to interact with Mn(OAc) 2 to form new complex than DMC. The whole process can be proposed that, the new species II , which was formed by the interaction of HDA and Mn(OAc) 2 , attacked carbonyl carbon of DMC to generate intermediate HMC and finally to HDC. The experimental data and calculation results are in good agreement with each other.