Zn 1,3,5-benzenetricarboxylate as an efficient catalyst for the synthesis of cyclic carbonates from CO₂

Development of heterogeneous catalysts for the cycloaddition of CO₂ with epoxides to produce cyclic carbonates is a hot issue in the field of chemical fixation of carbon dioxide. It is fairly promising as production of by-products is quite low. In this study, the [Zn₃(BTC)₂]/n-Bu₄NBr catalytic system was investigated for the solventless cycloaddition of carbon dioxide with epoxides and had an excellent synergetic effect in promoting the reaction. The reaction parameters were moderate i.e. (130 °C and 13 bar CO₂ pressure) and were selected by a study of the catalytic system. Under the optimal reaction conditions, the yield of cyclic carbonate reached 99%. A decrease in the yield of cyclic carbonate was not apparent after [Zn₃(BTC)₂] was reused three times, indicating that [Zn₃(BTC)₂] was stable. At the same time, the catalytic activity of the catalyst for other epoxides was also verified. The acidic and alkaline nature of the [Zn₃(BTC)₂] catalyst did not change obviously after recycling the catalyst three times. In this study it is also verified that the [Zn₃(BTC)₂] catalytic cycloaddition reaction was closely related to the Lewis acid/base distribution. In addition, a plausible mechanism for the synergistic effect of the catalyst (Lewis acid and base properties) and the co-catalyst was suggested.