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Toward the Design of Halide‐ and Metal‐Free Ionic‐Liquid Catalysts for the Cycloaddition of CO 2 to Epoxides
Author(s) -
Galvan Manuele,
Selva Maurizio,
Perosa Alvise,
Noè Marco
Publication year - 2014
Publication title -
asian journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.846
H-Index - 44
eISSN - 2193-5815
pISSN - 2193-5807
DOI - 10.1002/ajoc.201402044
Subject(s) - chemistry , cycloaddition , phosphonium , nucleophile , ionic liquid , carboxylate , catalysis , epoxide , cyclohexene oxide , inorganic chemistry , halide , carbonate , selectivity , reagent , organic chemistry
Carbonate and carboxylate methyltrioctylphosphonium ionic liquids [P 8881 ][A], made by a totally halide‐ and metal‐free procedure, have been used as new organocatalysts for the cycloaddition of CO 2 to styrene oxide. At 100 °C and ambient pressure, the performance of such compounds, particularly the acetate salts, was quite satisfactory. Even in the presence of catalyst amounts as low as 1–5 mol %, reaction conversions of 35–75 % were achieved with 100 % selectivity towards the expected cyclic carbonate. An analysis on the effect of the catalyst structure and loading, as well as operative parameters including temperature and pressure, demonstrated that anions played a major role on the activity and the stability of the ionic liquids. A parallel transformation of the phosphonium cation into its phosphine oxide was also identified as a consequence of the combined action of epoxide reagents and weakly nucleophilic carbonate and carboxylate species. Accordingly, a reaction mechanism was formulated.