Green and efficient cycloaddition of CO2 toward epoxides over thiamine derivatives/GO aerogels under mild and solvent-free conditions

Thiamine derivatives that are cheap, readily available, non-toxic and green are used as heterogeneous catalyst for the generation of cyclic carbonates through cycloaddition of CO2 to epoxides without the need of co-catalyst and solvent. The interaction between thiamine hydrochloride (VB1-Cl) and substrates (CO2 and propylene oxide) was proven by ultraviolet-visible spectroscopy and H-1 nuclear magnetic resonance analysis, and it is deduced that the synergistic action among multi-functional groups (hydroxyl, halide anion and amine) is a favorable factor for cycloaddition reaction. A series of VB1/GO aerogels were facilely prepared through the addition of aqueous VB1 derivatives to a suspension of GO in ethanol at room temperature. It was found that the aerogel generated through the interaction of VB1-Cl with GO shows catalytic activity and stability higher than those of VB1-Cl. It is because the electrostatic interaction between GO and VB1-Cl enhances the nucleophilicity and leaving ability of anion. The effects of reaction temperature, catalyst loading, CO2 pressure and reaction time on CO2 cycloaddition to propylene oxide were thoroughly studied.