Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by talc and other phyllosilicates
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RESEARCH ARTICLE
BMC Chemistry Open Access
Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by talc and other phyllosilicates Fiona Nakibuule1,2, Steven Allan Nyanzi1, Igor Oshchapovsky2,3, Ola F. Wendt2 and Emmanuel Tebandeke1*
Abstract Naturally occurring phyllosilicate minerals such as talc and vermiculite in conjunction with n-tetra butyl ammonium bromide (TBAB) co-catalyst were found to be efficient in the coupling of C O2 with epoxides to form cyclic carbonates. The reaction was carried out in a pressurized autoclave reactor at moderate pressures of 10–35 bars and temperatures of 100–150 °C. The optimized catalyst system exhibited > 90% conversion of the epoxides and > 90% selectivity for the desired cyclic carbonates, in the presence or absence of a solvent. The selectivity of the catalytic system could be improved with heat pre-treatment of the phyllosilicates albeit this resulted in slightly lower epoxide conversion. The results obtained using the heat treated phyllosilicates strongly support the hydrogen bond assisted mechanism for the cycloaddition of epoxides and CO2. The cycloaddition reaction could also be carried out in the absence of TBAB, although lower cyclic carbonate yields were observed. The phyllosilicate part of the catalyst system is heterogeneous, easy to separate after completion of reactions and reusable a number of runs without loss of activity. Keywords: Carbon dioxide, Cycloaddition, Cyclic carbonates, Epoxides, Talc, Phyllosilicates Introduction Modern societies today are highly dependent on carbonaceous fossil fuels as the primary source of energy [1– 3]. Complete combustion of these fuels produces carbon dioxide (CO2), a gas whose concentration in the atmosphere has increased significantly: and is believed to contribute significantly to global warming [4, 5]. There are increasing concerns for global warming and heightened interest worldwide to reduce CO2 atmospheric emissions. One of the solutions being considered to this problem is converting CO2 into chemical products for which there is significant commercial demand [6–8]. Although the amount of C O2 that can be consumed through chemical production is small compared to the amount *Correspondence: [email protected] 1 Department of Chemistry, College of Natural Sciences, Makerere University, P. O. Box 7062, Kampala, Uganda Full list of author information is available at the end of the article
generated by fossil fuel combustion, its conversion nevertheless would be favorable from the green chemistry perspective. Moreover, if done efficiently, using CO2 as a chemical feedstock, would constitute a net positive contribution towards sustainability [9–11]. Unfortunately, due to the thermodynamic stability of C O2 its activation and insertion into organic molecules still remains a challenge. A promising process in CO2 chemical fixation, is its insertion into epoxides to produce cyclic carbonates (Scheme 1). The CO2 and epoxide cycloaddition reaction, proceeds with 100% atom economy, and thu
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