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The reaction kinetics and mechanism of the CO 2 cycloaddition to limonene diepoxide as well as the gas liquid mass transfer of CO 2 as a function of the reaction mixture composition, temperature and pressure were unveiled for the first time. The reaction proceeds via a consecutive-parallel mechanism in the presence of homogeneous catalysts i.e. tetrabutylammonium halides via the formation of a mono-carbonate intermediate. Among the catalysts screened, tetrabutylammonium chloride (TBAC) resulted to be the most active, presenting the best compromise between nucleophilicity, the leaving group ability and the counterion size. The liquid density and viscosity were measured as a function of temperature and chemical composition. The experimental data were fitted to plausive kinetic equations while the kinetic constants and activation energies were estimated by nonlinear regression analysis with the gPROMs software. The final product, i.e. limonene dicarbonate was produced through a solvent-free 100 % atom economy pathway and fully characterized, finding possible application as a building block for the synthesis of isocyanate-free polyurethanes. • Homogeneous catalysts for cycloaddition of CO 2 to limonene epoxide were screened. • The best catalyst was TBAC providing high yields of dicarbonate. • The product distribution was determined by NMR. • Precise kinetic studies and mathematical modelling were carried out. • The work provides a green pathway to future polyurethanes.
Orabona et al. (Mon,) studied this question.