Recommendations for measuring second‐order rate constants and kinetic solvent isotope effects on acid‐catalyzed reactions
Author(s) -
Jensen James L.,
Carr Michael D.,
Yamaguchi Kenneth S.
Publication year - 1983
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550150304
Subject(s) - chemistry , kinetic isotope effect , solvent , kinetic energy , reaction rate constant , catalysis , acetal , salt (chemistry) , solvent effects , aqueous solution , isotope , analytical chemistry (journal) , kinetics , organic chemistry , deuterium , physics , quantum mechanics
Abstract Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p ‐methoxybenzaldehyde diethyl acetal, k D +/ k H += 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k H +( k D +). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k L +be calculated from a least‐squares fit of data to the equation k obs = k L +[L + ], and that the KSIE be reported as k D +/ k H +. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ℜ20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].