Concerning the Role of Supercritical Carbon Dioxide in S 1 Reactions.

A series of S 1-type reactions has been studied under various conditions to clarify the role of supercritical carbon dioxide (scCO ) as reaction medium for this kind of transformations. The application of scCO did not result in higher yields in any of the experiments in comparison to those under neat conditions or in the presence of other inert compressed gases. High-pressure UV/Vis spectroscopic measurements were carried out to quantify the degree of carbocation formation of a highly S 1-active alkyl halide as a function of the applied solvent. No measureable concentration of carbocations could be detected in scCO , just like in other low polarity solvents. Taken together, these results do not support the previously claimed activating effect via enhanced S 1 ionization due to the quadrupolar moment of the supercritical fluid.