A novel method for the green synthesis of biobased hexamethylene-1,6-dicarbamate

Abstract

The synthesis of polyurethane from renewable biomass is crucial for pursuing a sustainable future and a bio-based economy. The traditional production process of hexamethylene-1,6-diisocyanate (HDI) involves highly toxic phosgene, environmental pollution, and unsustainable raw materials. This work proposes a new green and intrinsically safe method for synthesizing HDI. The biomass-based platform molecule 5-hydroxymethylfurfural (5-HMF) is used as the raw material to synthesize HDI through 2,5-bis(aminomethyl)furan (BAF), methyl furan-2,5-dimethylene dicarbamate (FDC), and hexamethylene-1,6-dicarbamate (HDC). This approach opens a new pathway for preparing HDI using sustainable raw materials. Among them, the efficient ring-opening and deoxidation of FDC while retaining methyl carbamate functional groups is attractive and extremely challenging. In this work, we report the process of selectively converting FDC to HDC and screen the active metals, supports, metal loadings of the catalyst, and solvents. In the H₂O-ethanol system, the conversion of FDC over 7 wt% Pt/Nb₂O₅ was higher than 99.9%, and the yields of 2-hydroxy-hexamethylene-1,6-dicarbamate (HHDC) and HDC were 61.0% and 12.5%, respectively. The structure–activity relationship of supported platinum-based catalysts was studied. In addition, it was found that H₂O can significantly promote the formation of HDC. The catalytic reaction path and mechanism of the reaction were proposed by combining experiments with DFT theoretical calculations.