CO2 Coupling with Epoxides Catalysed by One-pot, in situ Activated Zinc Ascorbate under Ambient Conditions

An in situ generated zinc ascorbate pre-catalyst for cyclic carbonates (CCs) synthesis via CO2 coupling with epoxides under ambient conditions was reported. Spectroscopic measurements indicated that CO2 was inserted within the zinc ascorbate complex through the formation of an activated zinc carbonate catalyst upon abstracting the enediol protons with sodium hydride (NaH). The aliphatic diols were not activated under the applied conditions and did not interfere within either the process of cycloaddition or CO2 activation. The catalyst was active against different terminal epoxides, with conversion of 75%, when propylene oxide was used at 20 °C, 1 atm CO2 and 17 h which is considered a good advancement for heterogeneous based catalysis. Moreover, in order to achieve green chemistry principles, to ultimately end up with more ecofriendly approaches for the synthesis of the cyclic carbonates following a simple baloon technique. Yields under mild conditions were up to 88% for stryene carbonate. Herein, we used zinc as a sustainable metal, together with ascorbic acid as a bio-renewable material in addition to CO2 as a renewable feed-stock. Furthermore, waste prevention was attained by using the reaction side product (NaBr) as a co-catalyst.