Methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to dimethylhexane-1,6-dicarbamate over Zn/SiO2 catalyst

Abstract

The heterogeneous Zn/SiO₂ catalysts for the synthesis of dimethylhexane-1,6-dicarbamate (HDC) from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC) were prepared by incipient impregnation. The catalysts were characterized by BET, TG, FT-IR, TEM and XPS, and the results revealed that the activated Zn(OAc)₂ in catalysts was responsible for the main active sites for the reaction. The Zn/SiO₂(300) catalyst exhibited the best catalytic performance with HDA conversion of 96.0% and HDC yield of 68.5% owing to the most amount of activated Zn(OAc)₂ and the highest binding energy of Zn 2p_3/2. No obvious deactivation on the catalyst was found after 5 recycles due to the appropriate interaction between Zn(OAc)₂ and SiO₂. In addition, the results of in situ FT-IR experiments revealed that DMC was activated by the catalyst to form a stable intermediate that was then attacked by HDA with a typical nucleophilic addition–elimination reaction to produce HDC.