Carbon Dioxide, a Solvent and Synthon for Green Chemistry

Carbon dioxide is a renewable resource of carbon when we consider the reuse of existing CO2 as a carbon source for producing chemicals. The development of new applications is of major interest from the point of view of carbon dioxide sequestration and within the scope of green chemistry. For example, using CO2 instead of CO or COCl2 for chemical synthesis constitutes an attractive alternative avoiding hazardous and toxic reactants. However, it has the lowest chemical reactivity, which is a serious drawback for its transformation. Supercritical CO2 as a reaction medium offers the opportunity to replace conventional organic solvents. Its benign nature, easy handling and availability, non volatile emitting, and the relatively low critical point (Pc = 73.8 bar, Tc = 31 °C) are particularly interesting for catalytic applications in chemical synthesis, over a wide range of temperatures and pressures. The benefits of coupling catalysis and supercritical fluids are both environmental and commercial: less waste and VOCs emission, improved separation and recycling, and enhanced productivity and selectivity. The case study described in this paper concerns the reaction of carbon dioxide with alcohols to afford dialkyl carbonates with special emphasis on dimethyl carbonate. It is of significant interest because the industrial production of this class of compounds, including polycarbonates, carbamates, and polyurethanes, involves phosgene with strong concerns on environmental impact, transport, safety and waste elimination. The future of carbon dioxide in green chemistry, including supercritical applications, is highly linked to the development of basic knowledge, know-how, and tools for the design of catalyst precursors and reactors

EXAFS STUDY OF SOLUBLE DINITROSYL IRON AND COBALT COMPLEXES CATALYSING SPECIFIC TRANSFORMATIONS OF OLEFINS

La spectroscopie EXAFS a permis de caractériser en solution la structure des complexes cationiques dinitrosyles de fer/cobalt, utilisés comme catalyseurs de la polymérisation des oléfines. Les spectres EXAFS de leurs précurseurs neutres et ceux de composés modèles : Fe(NO)2[PΦ3]Cl, Fe(NO)2[PΦ3]2 ont aussi été enregistrés. Pour le complexe cationique de fer, les résultats suggèrent une coordination du fer de type bipyramide à base trigonale impliquant trois molécules non équivalentes de solvant. Dans ce système comme dans son précurseur, les groupes nitrosyles devraient être légèrement coudés.EXAFS spectroscopy has been used in order to characterize in solution the structure of dinitrosyl iron/cobalt cationic complexes catalysing the polymerisation of olefins. EXAFS spectra were also recorded on the inactive precursors of these systems and on relevant model compounds : Fe(NO)2[PΦ3]Cl, Fe(NO)2[PΦ3]2. For the cationic iron species, the results are quite consistent with a trigonal bipyramidal coordination of iron implying three non equivalent solvent molecules. In this system as in its precursor, the nitrosyl groups are found slightly bent

Isolation and structural determination of two derivatives of the elusive carbamic acid

ABSTRACT The dibenzyl-substituted carbamic acid (PhCH2)(2)NC(O)OH (1), its deprotonation product [(PhCH2)(2)NH2]- [(PhCH2)(2)NCO2] (2) and CoCl(NO)(2)[PhP(OCH2CH2)(2)NC(O)OH]. 2MeCOMe(3 . 2MeCOMe) are reported, the diffractometric study showing the carbamic acids 1 and 3 to be paired through hydrogen bonds

A bridge from CO2 to methanol : News and Views

International audienc