Nitrosation of Phenolic Compounds: Effects of Alkyl Substituents and Solvent |
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Authors: | Samuel González-Mancebo Javier Lacadena Yolanda García-Alonso Jesús Hernández-Benito Emilio Calle Julio Casado |
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Institution: | (1) Facultad de Biología, Universidad SEK, E-40003 Segovia, Spain, ES;(2) Departamento de Química Física, Facultad de Química, Universidad de Salamanca, E-37008 Salamanca, Spain, ES |
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Abstract: | Summary. Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of
the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction
was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2
+ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron
donating substituents, and a good Hammett correlation was observed with ρ = −6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH ≈ 3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly
by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.
Received July 13, 2001. Accepted (revised) September 18, 2001 |
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Keywords: | , ,Kinetics, Reaction mechanisms, Nitrosation, Phenolics, |
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