The activities of dimethyl carbonate and dimethyl sulfate as a methylation reagent were studied by density- functional theory （DFT）. B3LYP/6-31G（d, p） methods were used to optimize the structures of dirnethyl carb...The activities of dimethyl carbonate and dimethyl sulfate as a methylation reagent were studied by density- functional theory （DFT）. B3LYP/6-31G（d, p） methods were used to optimize the structures of dirnethyl carbonate and dimethyl sulfate and calculate theirs charge densities. Dimethyl sulfate is easier than dimethyl carbonate to react with a nucleophUic reagent. In dimethyl sulfate, the alkoxy carbons are the only reactive atomic nucleus because of steric hindrance. A nucleophilic reagent is more likely to react with carbonyl carbons than alkoxy carbons of dimethyl carbonate; in the presence of a Lewis acid, the phenyl nucleophilic reagent reacts with the Lewis acid first. Lewis acid increases the negative charge density of a nucleophUic reagent in polar solvent, and also incurs an accretion of steric hindrance. Polar solvent avails to ionize dimethyl carbonate and thus enables the reaction of methylation. The frequencies of transition state calculated by Gaussion 03 confirm the inferred reaction mechanism. The harvest rates of 4-methoxyphenol in the experiments of methylation reactions of hydroquinone with respectively dimethyl carbonate and dimethyl sulfate support the foregoing theortical conclusions.展开更多
文摘The activities of dimethyl carbonate and dimethyl sulfate as a methylation reagent were studied by density- functional theory （DFT）. B3LYP/6-31G（d, p） methods were used to optimize the structures of dirnethyl carbonate and dimethyl sulfate and calculate theirs charge densities. Dimethyl sulfate is easier than dimethyl carbonate to react with a nucleophUic reagent. In dimethyl sulfate, the alkoxy carbons are the only reactive atomic nucleus because of steric hindrance. A nucleophilic reagent is more likely to react with carbonyl carbons than alkoxy carbons of dimethyl carbonate; in the presence of a Lewis acid, the phenyl nucleophilic reagent reacts with the Lewis acid first. Lewis acid increases the negative charge density of a nucleophUic reagent in polar solvent, and also incurs an accretion of steric hindrance. Polar solvent avails to ionize dimethyl carbonate and thus enables the reaction of methylation. The frequencies of transition state calculated by Gaussion 03 confirm the inferred reaction mechanism. The harvest rates of 4-methoxyphenol in the experiments of methylation reactions of hydroquinone with respectively dimethyl carbonate and dimethyl sulfate support the foregoing theortical conclusions.
