Influence of the Solvent Effect on the Cleavage of Dimethyl Methylcyclohexyl-2,4-dicarbamate: The Role of the Hydrogen Bond between the Electron-Donor Solvents and the Reaction Substrate

The cleavage of dimethyl methylcyclohexyl-2,4-dicarbamate (HTDC) is a critical step in the nonphosgene route to the synthesis of methylcyclohexyl-2,4-diisocyanate (HTDI). Understanding the solvent effects is essential for selecting suitable solvents and catalysts for the cleavage of HTDC. In this work, the electronic properties of five high-boiling-point ester solvents (aliphatic and aromatic esters) and the influence on the cleavage of HTDC were investigated using a combined approach of multiscale theoretical simulations and experimental characterization. The results indicate that the electron-donating ability of the solvent and its polarization effect on HTDC are the key factors influencing solvent performance. The reactivity of HTDC and HTDI is influenced by solvent polarization, exhibiting an inverse relationship with the solvent polarity. The electron-donating ability of the solvent influences its interactions with HTDC and the ZnO catalyst via hydrogen bonding, thereby altering both the reactivity of HTDC and its adsorption process on the ZnO surface. Above all, the solvent effect in the carbamate cleavage reaction is systematically investigated. These conclusions will facilitate the design and selection of high-performance solvents for the carbamate cleavage reactions.