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The relative permittivity ( r ) of dimethyl ether (DME) was measured as a function of temperature and pressure in the gaseous, liquid, and supercritical states. The temperature and pressure ranges studied were (303 to 403) K and (0.04 to 33.2) MPa, respectively. The relative permittivity was fitted to the reduced density (F r ) using the function ( r -1)/(2 r + 1), and the apparent dipole moment (µ * ) of the liquid phase was calculated using Kirkwood's theory of molecular polarizability.

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Conventional, unmodified, transition metal catalysts, substrates and reagents have sufficient solubility in sc HFC134a for organic synthesis. Reactivities (100% conversion in 2 h) and enantioselectivities (ca. 90%), comparable to those achievable in conventional organic solvents, are obtained in the asymmetric hydrogenation of a series of substrates in this alternative reaction medium using a rhodium(I)/MonoPhos catalyst.

The solubility of a variety of unsaturated carboxylic acids is determined in supercritical tetrafluoroethane (HFC 134a) at 90 uC using a capacitative method. The solubility is found to decrease in the order crotonic-. 6-methoxytetralone-. methylsuccinic-. a-acetamidocinnamic-. itaconic acid. In all cases the solubility of the acid in HFC 134a was one to two orders of magnitude greater than that in CO 2 under comparable conditions; equivalent to ca. 20 fold reduction in the energy required to compress the gas needed to dissolve one mole of substrate. The solubility of the ternary system HFC 134a, methylsuccinic and itaconic acids was measured as a function of pressure and the dissolution selectivity for the two acids was characterised. The minimum number of stages required to separate methylsuccinic from itaconic acid is determined using equilateral triangle diagrams.