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Salt and solvent effects on alkaline hydrolysis of N ‐hydroxyphthalimide. Kinetic evidence for ion‐pair formation
Author(s) -
Khan M. Niyaz
Publication year - 1994
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.610070805
Subject(s) - chemistry , reaction rate constant , valence (chemistry) , ion , hydroxide , solvent , salt (chemistry) , inorganic chemistry , hydrolysis , kinetics , organic chemistry , physics , quantum mechanics
The effects of the concentrations of LiCl, NaCl, KCl, CsCl, Na 2 CO 3 and BaCl 2 on the rates of reactions of hydroxide ion with ionized N ‐hydroxyphthalimide (NHP − ) at 30°C and in H 2 O–MeCN solvents containing 10, 50, 60, 66, 70, 76 and 80% (v/v) MeCN reveal the formation of ion‐pair complexes between cations of the salts, which probably exist in solvent‐separated loose ion‐pair forms (M n + ⃛X k − ) and NHP − . An increase in MeCN content from 2 to 76% (v/v) causes an increase in the association constants ( K ) by factors of 40, 21 and 9 for LiCl, NaCl and KCl, respectively, while the respective increase in the rate constants ( k ′ s1 ) for the collapse of the ion‐pair complexes to product is ca two‐fold. The values of k ′ s1 remain almost unchanged whereas the values of K increase 7·5‐fold with an increase in MeCN content from 2 to 70% (v/v) for CsCl. Ion‐pair complex formation was not detected in the presence of Me 4 NCl at 70% (v/v) MeCN. The observed pseudo‐first‐order rate constants are highly sensitive to the valence state of cations and almost insensitive to the valence state of the anions of the salts.