Highly efficient synthesis of novel bio-based pentamethylene dicarbamate via carbonylation of pentanediamine with ethyl carbamate over well-defined titanium oxide catalysts

Abstract

Carbonylation of pentanediamine (PDA) is a green and effective route for the synthesis of pentamethylene dicarbamate (PDC), an important intermediate compound for the preparation of polyurethanes (PUs) and other chemicals. In this work, TiO₂-101 and TiO₂-110 catalysts with preferential exposure of (101) and (110) facets, respectively, were prepared and studied for the carbonylation of PDA with ethyl carbamate (EC). The catalysts were characterized by various techniques, including XRD, BET, SEM, TEM, XPS, NH₃-TPD, and in situ FTIR. The characterization results indicated that TiO₂ catalysts with exposed (110) and (101) facets were synthesized successfully. The overall results suggested that the (101) facets on the TiO₂ surface provide high amounts of surface Lewis acid sites that played a pivotal role in PDC formation, which gave a conversion and yield both up to 99% under optimized conditions. In situ FTIR spectroscopy clearly revealed that polyurea as an intermediate was formed in the reaction and subsequently converted to PDC catalyzed by the TiO₂ catalyst. Furthermore, the DFT results showed that the conversion of polyurea to PDC over the (101) facets was more prone to occur than the (110) facets due to the lower reaction energy barrier. In addition, the TiO₂-101 catalyst displayed excellent stability without an obvious activity decline after five cycles. Furthermore, this strategy also could be successfully expanded to the efficient syntheses of a series of N-substituted carbamates.