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RESEARCH PRODUCT

CO2 as a C1-Building Block for Dialkyl Carbonate Synthesis

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Carbon dioxide, one of the major man-made greenhouse gas, is a renewable resource of carbon which can be viewed as a C1 synthon to build valuable chemicals. The development of new applications is of major interest considering CO2 conversion and environmentally friendly reactions. As chemical catalysis offers interesting options, we are studying the molecular design of catalysts for the formation of dialkyl carbonates from alcohols and CO2. This paper reports results on the mechanistic approach for dialkyl carbonate formation with alkoxybutyl tin(IV) compounds. The insertion of CO2 into Sn-OR bonds (R = Me, 1Pr) occurs at atmospheric pressure and room temperature leading to alkylcarbonato tin fragments, Sn-OCO2R. For dialkoxy derivatives, only one Sn-OR bond reacts with CO2 due to a dimerization pathway. Preliminary DFT calculations confirm that the dimer is more stable than the corresponding monocarbonated and dicarbonated monomers. Under catalytic conditions, n-Bu2Sn(OMe)2 gives dimethyl carbonate (selectivity = 100%). Pressure and temperature effects as well as reaction time were studied. The best yield in dimethyl carbonate is obtained under supercritical CO2 conditions (200 bar, 145 °C). The carbonated distannoxane, (n-Bu2SnOMe)(n-Bu2Sn(OCO2Me)O, has ben identified as an intermediate. The relevance of this species for dimethyl carbonate synthesis is discussed.