CHEMISTRY: Guest in a Green Solvent

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Science  09 Nov 2001:
Vol. 294, Issue 5545, pp. 1243c
DOI: 10.1126/science.294.5545.1243c

Hydrocarbon solvents are used widely in the chemical industry for cleaning and coating and for reaction and separation processes. Environmentally friendly chemical synthesis uses alternative solvents such as ionic liquids, water, and liquid and supercritical carbon dioxide (scCO2). The last is particularly attractive because CO2 is inexpensive and environmentally benign (except as a greenhouse gas). Furthermore, changing the density of scCO2 alters its effectiveness as a solvent, and this can be used to control reaction rates and yields.

Unfortunately, many reactants and catalysts do not dissolve readily in scCO2. Several approaches have been used to overcome this problem. For example, surfactants have been designed that enhance the solubilizing properties of scCO2, and microemulsions of water and scCO2 have been used. Now, Yeung et al. show that Pd nanoparticles encapsulated within poly(propylene imine) dendrimers will catalyze chemical reactions in scCO2. In two reactions, the catalyst produced high yield and selectivity with little degradation.—JU

Chem. Comm. 2001, 2290 (2001).

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