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Nucleophilicities of Para‐Substituted Phenoxide Ions in Water and Correlation Analysis
Author(s) -
GABSI W.,
BOUBAKER T.,
GOUMONT R.
Publication year - 2014
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.20846
Subject(s) - nucleophile , chemistry , electrophile , aryl , benzotriazole , reaction rate constant , ion , aqueous solution , medicinal chemistry , reactivity (psychology) , linear correlation , computational chemistry , stereochemistry , organic chemistry , kinetics , alkyl , catalysis , mathematics , medicine , physics , alternative medicine , statistics , pathology , quantum mechanics
Second‐order rate constants for the reactions of 2‐aryl‐4,6‐dinitrobenzotriazole 1‐oxides 1a‐d with some 4‐X‐substituted phenoxide ions 2a‐d (X = OCH 3 , H, Cl, and CN) have been measured in aqueous solution at 20°C. The p K a values for the σ‐complexation processes of a series of benzotriazole 1a‐d measured in water have been used to determine their electrophilicity parameters E according to the correlation E = –3.20 – 0.662 p K a (F. Terrier, S. Lakhdar, T. Boubaker, and R. Goumont, J Org Chem, 2005 , 70, 6242–6253). For these reactions, plots of log k versus the electrophilicity parameters E of the benzotriazoles 1a‐d were linear, allowing to derive the nucleophilicity parameters N and s for phenoxide ions as defined by the Mayr equation log k 1 (20°C) = s ( E + N ) (H. Mayr, M. Patz. Angew Chem, Int Ed Engl 1994 , 33, 938–957). The N values are found to cover a range of nucleophilicity from 6.85 to 10.22, going from 4‐cyanophenoxide 2d for the least reactive ion to 4‐methoxyphenoxide 2a for the most reactive nucleophile. Good linear correlations were found between the nucleophilicity parameters N of phenoxide ions 2a‐d and the p K a values of their conjugate acids ( N = –3.05 + 1.25 p K a ) and the constants of the substituents X ( N = 9.21 – 2.51).