Synthesis of Dimethyl\nHexane-1,6-dicarbamate with\nMethyl Carbamate as Carbonyl Source over MCM-41 Catalyst

Dimethyl hexane-1,6-dicarbamate (HDC), the vital intermediate\nfor\nnonphosgene production of hexamethylene-diisocyanate (HDI), was effectively\nsynthesized via carbonylation of 1,6-hexanediamine (HDA) using methyl\ncarbamate (MC) as a carbonyl source over a silanol-rich MCM-41 catalyst.\nThe effects of reaction conditions, including the reaction temperature,\nmolar ratio of raw materials, methanol dosage, catalyst dosage, and\nreaction time, on the HDC yield were evaluated. Under the reaction\nconditions with a reaction temperature of 190 °C, a molar ratio\nof HDA, MC, and methanol of 1:6:50, a catalyst dosage of 10 wt %,\nand a reaction time of 3 h, the yield of HDC can reach as high as\n92.6% with 100% HDA converted. Characterizations based on N<sub>2</sub> physical adsorption/desorption, scanning electron microscopy (SEM),\nX-ray diffractometry (XRD), NH<sub>3</sub>-temperature-programmed\ndesorption (TPD), Fourier transform infrared spectroscopy (FTIR),\nand <sup>1</sup>H magic-angle spinning (MAS) NMR indicated that the\nabundance of silanol groups on the surface of MCM-41 probably resulted\nin the good performance of MCM-41. After five cycles of MCM-41, the\nHDC yield decreased from 92.6 to 67.9%, probably due to the loss of\nsurface silanol groups and the carbon deposition on the catalyst as\nwell as the particle agglomeration. The study on the substrate scope\nsuggested that MCM-41 shows good-to-excellent catalytic performance\nin the synthesis of a variety of aliphatic and alicyclic dicarbamates.