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Association of Hydrotropes in Aqueous Solution Studied by Reaction Kinetics
Author(s) -
Buurma Niklaas J.,
Blandamer Michael J.,
Engberts Jan B. F. N.
Publication year - 2002
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/1615-4169(200206)344:3/4<413::aid-adsc413>3.0.co;2-b
Subject(s) - chemistry , aqueous solution , bromide , sodium , hydrophobic effect , kinetics , hydrolysis , inorganic chemistry , photochemistry , polymer chemistry , organic chemistry , physics , quantum mechanics
The effect of added hydrotropes on the rates of neutral hydrolysis for 1‐benzoyl‐3‐phenyl‐1,2,4‐triazole 1 has been studied, together with the concentration dependence of the 1 H NMR spectra of the hydrotropes in aqueous solution. Hydrotropes include sodium 4‐alkylbenzenesulfonates 2a−e , sodium 4‐methoxybenzenesulfonate 2f , sodium 4‐hydroxybenzenesulfonate 2g , cesium benzenesulfonate 3 , benzamidinium chloride 4 , phenyltrimethylammonium bromide 5a , and benzyltrimethylammonium bromide 5b . All hydrotropes, except 2g , induce strong rate‐retarding effects, indicative of strong interactions with 1 and of remarkably strong hydrophobic interactions between aromatic moieties. Most hydrotropes show neither spectroscopic nor kinetic evidence for cooperative aggregation in the concentration range studied, i.e., from 0 to 1.4 mol kg −1 . Cooperative aggregation is absent because the hydrophobic moieties are too small for hydrophobic interactions to overcome electrostatic repulsion. Lack of aggregation results in high availability of hydrophobic binding sites, thereby accounting for the high solubilizing power characteristic for hydrotropes. However, sodium 4 ‐n‐ propylbenzenesulfonate 2d and sodium 4 ‐n‐ butylbenzenesulfonate 2e show cooperative self‐association forming highly dynamic loose micellar‐type structures.