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Synthesis of five and six-membered cyclic glycerilic carbonates bearing exocyclic urethane functions

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Abstract

Five (5CGC) and six (6CGC) membered cyclic glycerilic carbonates having exocyclic urethane functions, as potential monomers for polyurethanes and polycarbonates, were prepared by two different routes: “two-steps” and the “one-pot” synthesis. For the “two-steps” route, based on the consecutive aminolysis and transesterification reactions, a catalyst screening has been performed. Phosphazene showed the best catalytic activity and provided 5CGC and 6CGC in appreciable amounts whereas the other catalysts favored 5CGC formation. An increase in molar ratio of dimethyl carbonate (DMC) increased the yield and the conversion. In the “one-pot” synthesis, where aminolysis and transesterification were simultaneous, a competition between products formation was demonstrated. In addition to the formation of mono-hydroxyurethanes and glycerilic cyclic carbonates (5CGC and 6CGC), the fast aminolysis of 6CGC and the slower aminolysis of 5CGC was responsible for a partial di-hydroxyurethanes production. The controlled and combined effects of catalyst and DMC excess acting as solvent and reagent allowed to selectively controlling the aminolysis and the transesterification reactions. The same reaction conditions were used for the synthesis of bicyclic carbonates. These new molecules enriched with urethane functions, provided novel and more environmentally friendly synthons for the synthesis of polyurethanes without the use of phosgene or isocyanate.

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