Synthesis of hexamethylene-1,6-dicarbamate by methoxycarbonylation of 1,6-hexamethylene diamine with dimethyl carbonate over bulk and hybrid heteropoly acid catalyst

Synthesis of HDC by methoxycarbonylation of HDA with DMC was carried out over the bulk and hybrid heteropoly acid (HPA) catalyst. The catalysts were systematically characterized by XRD, FTIR, SEM and NH₃-TPD techniques. The by-products produced in the reaction were identified and a possible reaction pathway was proposed based on the by-products analysis. The performances of bulk and hybrid HPA catalysts were evaluated. The H₄[SiW₁₂O₄₀] catalyst revealed high performance compared with other catalysts and its high performance was attributed to its acidic properties. Effects of reaction parameters and reusability of the H₄[SiW₁₂O₄₀] catalyst were also investigated. Under the optimized reaction conditions, HDA conversion reached 93.2% with 64.8% HDC selectivity and only 3.8% by-product selectivity. Moreover, a possible reaction mechanism was proposed for the synthesis of HDC over H₄[SiW₁₂O₄₀] catalyst.