Tuning catalyst solubility in CO₂by changing molar volume

Abstract

Poor-solvating property of supercritical carbon dioxide (scCO 2 ) has been a great challenge, which limits the use of CO 2 as a common ''green'' solvent. The present report describes that by increasing molar volume (v) and lowering the melting temperature, which lowers cohesive energy density or solubility parameter (d), it is possible to increase the solubility of metal-based catalysts in scCO 2 without using costly fluorinated or tailormade CO 2 -philic modifications. We have studied various chlorodistannoxanes (1) and CuÁb-diketonates (2) to support our views. The study of bio-diesel production and transesterification of hindered esters using 1 in scCO 2 shows a 2Á8-folds rate enhancement coupled with an easier catalyst and product separation than that in organic solvents. The methodology, which works at least within the range of Van der Waals sphere of interactions, can be useful to solubilizing the molecules in scCO 2 and carries great opportunity in catalysis as well as in separation science.

Total replacement of solvent in polyurethane synthesis using carbon dioxide soluble 1,3‐dichlorodistannoxane catalysts

“…Differences in the catalytic activity of catalysts in neat CO 2 were observed as shown in Figure 4(a). Effect of various catalysts showed that the catalyst 1a is most effective while catalyst 1b is least effective, inferring the reactivity in order 1a > 1d > 1c > 1b , which was in accordance to the trend of their solubility in CO 2 9…”

“…This is in agreement with our earlier observation regarding the trend of catalytic activity of chlorostannoxanes in sun flower oil methanolysis and ethyl–2,2‐dimethylacetoacetate transesterification with benzyl alcohol in CO 2 , showing 1a and 1d are most and least reactive catalysts, respectively. This implies that the mechanism of reaction is likely to be similar to that of other distannoxane catalyzed reactions 9…”

“…TON increased from about 70 at 10 bars CO 2 to 240 at 60 CO 2 bars pressure. This may be attributed to the increased solubility of the catalysts as the phase trends to go from the gaseous phase to near critical phase 9…”

“…Our continuing effort in solvent replacement for chemical reactions by CO 2 can be applied to the synthesis of polyurethanes 9. However, the extreme insolubility of diisocyanates in most of the solvents makes it very difficult to obtain total solvent replacement during polyurethane synthesis.…”

Determination of Solubility Parameters for the p-Xylene Oxidation Products

“…27 This work inspired us to apply the simple viscosity-based technique for the determination of δ to generate information on the solubility of the PXOX products.…”