Efficient synthesis of dimethyl hexane-1,6-dicarbamate via methoxycarbonylation of 1, 6-hexanediamine with methyl carbamate over acid-base enhanced CeO2

Abstract

The carbonylation of 1,6-hexanediamine (HDA) is an important method for the production of dimethyl hexane-1,6-dicarbamate (HDC), which is of great significance for the non-phosgene synthesis of hexamethylene-diisocyanate. This research focuses on the synthesis of HDC through the methoxycarbonylation of HDA using methyl carbamate as a carbonyl source. The study investigates the utilization of CeO2 catalyst prepared via H2O2assisted precipitation. Various characterization techniques, including N2 physical adsorption and desorption, SEM, TEM, XRD, NH3TPD, CO2TPD, and XPS are employed to analyze the texture and structure of CeO2 catalysts prepared through different methods. In situ FTIR experiments are conducted to monitor the potential process of the carbonylation reaction. The results of the in situ FTIR spectroscopy clearly indicate the formation of polyurea as an intermediate compound, which subsequently converts into HDC. The findings demonstrate that CeO2 prepared using the hydrogen peroxide precipitation method exhibits a larger specific surface area, stronger acid-base properties, and a higher content of surface-adsorbed oxygen. These characteristics are favorable for the carbonylation reaction. Under optimized conditions, the HDC yield reaches 96.0% with complete conversion of HDA. The catalyst's activity essentially maintained throughout ten cycles. Additionally, a substrate versatility study reveals that CeO2 exhibits excellent catalytic properties for synthesizing a range of aliphatic and alicyclic dicarbamates.