Crystal structure, thermal decomposition mechanism and catalytic performance of hexaaquaaluminum methanesulfonate

摘要

Hexaaquaaluminum methanesulfonate crystals, [Al(H2O)6][CH3SO3]3 were synthesized by a hydrothermal reaction of Al(OH)(3) with methanesulfonic acid. Single-crystal diffraction determination revealed that Al3+ was coordinated by six water molecules in octahedral geometry, while the CH3SO3- anion connected with Al3+ through coordinated water molecules by hydrogen bonds. The six-coordinate environment of Al was also determined by Al-27 MAS NMR measurement. Thermogravimetric analysis and Fourier transform infrared spectroscopy showed that the decomposition intermediate at 265-365 degrees C was Al 2 (mu-OH)(CH3SO3)(5) and the final product was amorphous Al2O3 residue with about 0.8 wt% SO3 at 520-800 degrees C. A pure phase of [Al(H2O)(6)][CH3SO3](3) was confirmed by powder X-ray diffraction analysis. Esterification of n-butyric acid with n-butanol and ketalization of cyclohexanone with glycol catalyzed by [Al(H2O)(6)][CH3SO3](3) and Al-2 (mu-OH)(CH3SO3)(5), respectively, proceeded in 100% yield by continuously removing the produced water. In the case of tetrahydropyranylation of n-butanol at room temperature in dichloromethane, the catalytic activity of [Al(H2O)(6)][CH3SO3](3) was much lower than that of Al-2 (mu-OH)(CH3SO3)(5). Furthermore, both [Al(H2O)(6)][CH3SO3](3) precursor and Al-2 (mu-OH)(CH3SO3)(5) catalysts could be recycled.