Extreme solvent effects on reaction rate constants at supercritical fluid conditions

The reaction rate constant was adjusted continuously over two orders of magnitude for the unimolecular decomposition of α‐chlorobenzyl methyl ether using the supercritical fluid solvent 1, 1 diffluoroethane. Activation volumes were observed as low as −6,000 cm 3 /mol, which is about an order of magnitude more negative than those reported previously in the literature for a homogeneous reaction. Spectral shift (solvatochromic) data were measured for phenol blue in the same fluid in order to interpret the rate data. A method is presented to predict solvent effects on rate constants at supercritical fluid conditions.