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Nitrosation kinetics of phenolic components of foods and beverages
Author(s) -
FernándezLiencres M. Paz,
Calle Emilio,
GonzálezMancebo Samuel,
Casado Julio,
Quintero Bartolomé
Publication year - 1997
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/(sici)1097-4601(1997)29:2<119::aid-kin5>3.0.co;2-x
Subject(s) - chemistry , nitrosation , p cresol , catalysis , phenol , cresol , reactivity (psychology) , kinetics , inorganic chemistry , medicinal chemistry , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
The kinetics of the reactions between sodium nitrite and phenol or m ‐, o ‐, or p ‐cresol in potassium hydrogen phthalate buffers of pH 2.5–5.7 were determined by integration of the monitored absorbance of the C‐nitroso reaction products. At pH > 3, the dominant reaction was C‐nitrosation through a mechanism that appears to consist of a diffusion‐controlled attack on the nitrosatable substrate by NO + /NO 2 H 2 + ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities ( o ‐cresol ≈ m ‐cresol > phenol ≫ p ‐cresol) is explained by the hyperconjugative effect of the methyl group in o ‐ and m ‐cresol, and by its blocking the para position in p ‐cresol. Analysis of a plot of ΔH # against ΔS # shows that the reaction with p ‐cresol differs from those with o ‐ and m ‐cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO + /NO 2 H 2 + . © 1997 John Wiley & Sons, Inc.