Solvent polarity and organic reactivity in mixed solvents: evidence using a reactive molecular probe to assess the role of preferential solvation in aqueous alcohols.
Product selectivities [S = ([ester product]/[acid product]) x ([water]/[alcohol solvent])] are reported for solvolyses of p-methoxybenzoyl chloride (2) in aqueous methanol, ethanol, 2,2,2-trifluoroethanol, n-propyl alcohol, isopropyl alcohol, and tert-butyl alcohol at 25, 35, and 45 degrees C. S values are small and depend significantly on the alcohol cosolvent, varying from 1.3 in methanol to 0.1 in tert-butyl alcohol, but S depends only slightly on the solvent composition, and on the temperature. As S adjusts the product ratios for changes in bulk solvent compositions, it is suggested that preferential solvation by either alcohol or water at the reaction site is not a major factor influencing rates or products. Logarithms of rates of solvolyses of 2 correlate well with Kosower Z values (based on solvatochromism). In contrast, another solvatochromic polarity index, E(T)(30), shows "dispersion" in correlations with the solvent ionizing power parameter, Y(OTs), probably due to aromatic ring and other solvation effects.
Bentley
T William
TW
Department of Chemistry, University of Wales, Swansea, Singleton Park, Swansea, SA2 8PP, Wales, United Kingdom. cmsolvol@swansea.ac.uk
Ebdon
David N
DN
Kim
Eun-Ju
EJ
Koo
In Sun
IS
D000438:Alcohols / Q000737:chemistry*; D001565:Benzoates / Q000737:chemistry*; D006868:Hydrolysis; D015335:Molecular Probes / Q000737:chemistry*; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D000438:Alcohols; D001565:Benzoates; D015335:Molecular Probes; D012997:Solvents; D014867:Water; C013409:benzoyl chloride