Synthesis of Dimethyl Hexane-1,6-dicarbamate with Methyl Carbamate as Carbonyl Source over MCM-41 Catalyst

Dimethyl hexane-1,6-dicarbamate (HDC), the vital intermediate for nonphosgene production of hexamethylene-diisocyanate (HDI), was effectively synthesized via carbonylation of 1,6-hexanediamine (HDA) using methyl carbamate (MC) as a carbonyl source over a silanol-rich MCM-41 catalyst. The effects of reaction conditions, including the reaction temperature, molar ratio of raw materials, methanol dosage, catalyst dosage, and reaction time, on the HDC yield were evaluated. Under the reaction conditions with a reaction temperature of 190 °C, a molar ratio of HDA, MC, and methanol of 1:6:50, a catalyst dosage of 10 wt %, and a reaction time of 3 h, the yield of HDC can reach as high as 92.6% with 100% HDA converted. Characterizations based on N₂ physical adsorption/desorption, scanning electron microscopy (SEM), X-ray diffractometry (XRD), NH₃-temperature-programmed desorption (TPD), Fourier transform infrared spectroscopy (FTIR), and ¹H magic-angle spinning (MAS) NMR indicated that the abundance of silanol groups on the surface of MCM-41 probably resulted in the good performance of MCM-41. After five cycles of MCM-41, the HDC yield decreased from 92.6 to 67.9%, probably due to the loss of surface silanol groups and the carbon deposition on the catalyst as well as the particle agglomeration. The study on the substrate scope suggested that MCM-41 shows good-to-excellent catalytic performance in the synthesis of a variety of aliphatic and alicyclic dicarbamates.