Vapor-phase catalytic methylation of 1,1,1,3,3,3-hexafluoroisopropanol for the mass production of 1,1,1,3,3,3-hexafluoroisopropyl methyl ether

With the phasing-out of chlorofluorocarbons and hydrochlorofluorocarbons required by the Montreal and Kyoto Protocols, hydrofluoroethers (HFEs) are now considered to be promising alternatives due to their zero ozone-depletion and low global-warming potentials, and their significant capacities for use in heat-pump and cleaning-agent applications. However, the pollution-free and large-scale synthesis of HFEs has been a long-standing challenge. To address the issue, we previously reported a novel synthetic method for the large-scale production of 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFE-356mmz), a representative HFE, through the vapor-phase methylation of 1,1,1,3,3,3-hexafluoroisopropanol using metal fluorides as catalysts. In this work, mixed oxides of Mg and Al with various Mg/Al₂ ratios were employed as alternative catalysts; their abilities to promote the reaction were determined and the methylation mechanism was explored. All Mg-Al mixed oxides promoted the production of HFE-356mmz, albeit with different efficiencies, which were found to be determined by the surface acid-base properties of the catalysts. The results agree well with those obtained using metal fluorides as catalysts and provide new mechanistic evidence. Our study not only offers further evidence of the reaction mechanism, but also affords a more universal and operable process that uses more-common and less-expensive catalysts.