Synthesis, Characterization Of Acid Ionic Liquids And Their Application In Condensation Reaction Of Methyl Phenyl Carbamate With Formaldehyde

The synthesis of methylene diphenyl dimethylcarbamate (4,4'-MDC) from methyl N-phenyl carbamate (MPC) and formaldehyde (HCHO) has been investigated in the presence of several environmentally friendly acidic ionic liquids (ILs) as both the catalyst and the reaction solvent, for the liquid acid catalysts cause corrosion to the equipment and result in environmental pollution while solid acid catalysts not only deactivate rapidly but also need organic solvents for the condensation reaction.Several kinds of ILs with alkyl groups in imidazolium or pyridinium cations were synthesized,and their catalytic and solvent performances were evaluated in the condensation reaction of MPC with HCHO. The result showed that [emim]BF4 ILs modified with H+ had better catalytic activity. The influences of reaction temperature, molar ratio of MPC to HCHO, the amount of ILs and reaction time on 4,4'-MDC synthesis reaction were studied using the [emim]BF4 ILs with the excess of HBF4 of 20% as both the catalyst and the reaction solvent. Under the suitable reaction conditions of 70℃, molar ratio of MPC to HCHO=4/1, mass ratio of ILs to MPC=4/1 and reaction time 1.5 h, the yield and the selectivity of 4,4'-MDC were 71.74% and 71.91%, respectively. The ILs was reused four times after treated by ultrasonic extraction with CHCl3 and no significant activity loss was observed after the second run. In order to understand the relationship between the catalytic activity of [emim]BF4 modified with H+ and its chemical structure, 1 H NMR and traditional experiment method were utilized and the structure of imidazolium cation was proved to be a macromolecular group formed by hydrogen-bonded with H2O(or the mixture of H2O and HBF4 ).Five sulfonic acid-functionalized ionic liquids (SFILs) with 1-(butyl-4-sulfonate) -3- methyl imidazolium ([HSO3-bmim]) as the cation were prepared. The Br?nsted acidity of the SFILs was confirmed by FT-IR using pyridine as a probe molecule and the acid strength of the SFILs was determined by the Hammett method combined with UV-visible spectroscopy. The result showed that the acid strength of SFILs was consistent with their catalytic activity for the synthesis of 4,4'-MDC. Among the SFILs, [HSO3-bmim]CF3SO3 with the highest acid strength showed the best catalytic activity. The influences of reaction conditions on 4,4'-MDC synthesis in the presence of [HSO3-bmim]CF3SO3 were studied. Under the suitable reaction conditions of 70℃, 40 min, molar ratio of (MPC)/(HCHO)=10/1 and mass ratio of (ILs)/(MPC)=4.5/1, the yield and selectivity of 4,4'-MDC were 89.9 % and 74.9 %, respectively. SFILs could be reused four times after the removal of water and no significant loss in the catalytic activity was observed.