Heterogeneous synthesis of dimethylhexane-1,6-dicarbamate from 1,6-hexanediamine and methyl carbonate in methanol over a CeO2 catalyst

The efficient synthesis of dimethylhexane-1,6-dicarbamate (HDC) from 1,6-hexanediamine (HDA) and methyl carbonate over a series of heterogeneous catalysts (e.g., MgO, Fe2O3, Mo2O3, and CeO2) was investigated. The reaction pathway was confirmed as an alcoholysis reaction through a series of designed experiments. Under optimized conditions, 100% HDA conversion with 83.1% HDCtotal and 16.9% polyurea was obtained using a one-step with high temperature procedure with CeO2 as the catalyst. A new two-step with variable temperature technology was developed based on the reaction pathway to reduce the polyurea yield. Using the proposed method, the HDCtotal yield reached 95.2%, whereas the polyurea yield decreased to 4.8%. The CeO2 catalyst showed high stability and did not exhibit any observable decrease in the HDC yield or any structural changes after four recycling periods.

Graphical AbstractA non-phosgene route was proposed for the synthesis of HDC via reaction between HDA and MC. CeO2 was found to exhibit high catalytic activity. The pathway was confirmed to be an alcoholysis reaction followed with minimal transesterification reaction. The alcoholysis reaction mechanism is proposed as that the amino group of HDA attacks the carbonyl group of MC, and that 1,6-hexanediurea (HDU) is generated by delivering the methoxy group. Methanol then attacks the amino group of HDU to finally form carbamate. A new two-step, variable-temperature technology was developed based on the reaction pathway to reduce the polyurea yield.Figure optionsDownload as PowerPoint slide