Mn(OAc)2 as an Effective Catalyst for Synthesis of Dimethylhexane-1,6-Dicarbamate (HDC) from 1,6-Hexanediamine(HDA) and Dimethyl Carbonate (DMC)

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 screened as the most effective catalyst for this reaction. The effects of reaction temperature, DMC-to-HDA molar ratio, catalyst concentration and reaction time, were investigated. Under the optimum conditions (reaction temperature of 363K, DMC-to-HDA molar ratio of 4:1, catalyst concentration of 7wt.% (based on HDA), and reaction time of 5 h), HDC yield can reach as high as 98.0% with 100% HDA conversion. Online in situ Fourier transform infrared (FTIR) were used to investigate the interactions between Mn(OAc)₂ and substrate. The results indicated that the new species, which was formed by the reaction of HDA with Mn(OAc)₂, attacked carbonyl carbon of DMC to generate intermediate HMC and finally to HDC, Density Functional Theory (DFT) calculation support the results from FTIR.