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Contrasting effect of guanidinium salts on kinetics of the Diels–Alder reaction
Author(s) -
Kumar Anil,
Phalgune Usha D.,
Pawar Sanjay S.
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.463
Subject(s) - chemistry , salting out , perchlorate , bromide , solubility , allyl bromide , salt (chemistry) , aqueous solution , inorganic chemistry , organic chemistry , ion
Aqueous solutions of guanidinium perchlorate (GnClO 4 ), bromide (GnBr), chloride (GnCl) and acetate (CH 3 COOGn) inhibit the reaction rates and endo products for the cyclopentadiene–methyl acrylate (CPMA) reaction, whereas that of guanidinium sulfate (Gn 2 SO 4 ) 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 Gn 2 SO 4 on the kinetic profiles of the Diels–Alder reactions reported for the first time can be attributed to the dominant role of SO 4 2− 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.