Abstract
AbstractAqueous solutions of guanidinium perchlorate (GnClO4), bromide (GnBr), chloride (GnCl) and acetate (CH3COOGn) inhibit the reaction rates and endo products for the cyclopentadiene–methyl acrylate (CPMA) reaction, whereas that of guanidinium sulfate (Gn2SO4) accelerates them. These contrasting results obtained for the guanidinium salts are interpreted in terms of the salting‐in and ‐out phenomena and by salting coefficients computed from the scaled particle theory. The contrasting effect of Gn2SO4 on the kinetic profiles of the Diels–Alder reactions reported for the first time can be attributed to the dominant role of SO42− over Gn+ ion. It is also shown how the salting‐out effect of NaCl can be neutralized by the salting‐in effect of GnCl in the above reaction. This effect can also be explained in terms of mixing of hydrophilic with hydrophobic cationic species. The effects of the guanidinium salts are also supported by experimental data on solubility, surface tension, volume, compressibility and activation volume. The activation volume of the CPMA reaction calculated from the experimental volumetric data is shown to be salt dependent. Copyright © 2002 John Wiley & Sons, Ltd.
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