Nitrosation kinetics of phenolic components of foods and beverages

Abstract

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+/NO2H2+ 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+/NO2H2+. © 1997 John Wiley & Sons, Inc.

Characterization of Nitrite-Related Reaction Products in Beer

“…In addition to the study of nitrite reaction products in the complex beer matrix, there was simultaneously paid attention to the substances formed by the nitrite reaction with few compounds previously described in beer. − These substances were 2-ethyl phenol, 2-methoxy phenol (guaiacol), vanillic acid, and amino acids (tyrosine, phenylalanine, and histidine). They were chosen with a criterion to contain a substituted aromatic ring, which is supposed to be favorable to form C -nitroso compounds. − …”

Importance of phenols structure on their activity as antinitrosating agents: A kinetic study

“…Casado et al ,[192223] have shown unambiguously that the reaction with nitrous acid occurs by the first of these mechanisms. However, other nitrosating agents, like nitrososulfonamides[21] and alkyl nitrites,[24] in basic media, present a different behavior.…”

“…This and other N -methyl- N -nitrosobenzenesulfonamides have been used before as nitrosating agents in the study of the transnitrosation of amines[20] and phenols. [21] In addition, we expect to collect more evidence on the mechanism of nitrosophenol formation, as there has been some discussion on whether the reaction occurs directly at the carbon atom[192223] or the previous formation of an O -nitroso intermediate is involved. [2124] The nitrosation of OH-blocked ‘phenols,’ such as anisole, is possible when the mechanism involves the nitrosonium ion polar reaction,[25] but it will not be observed when the reaction follows the oxidative pathway via the phenoxy radicals, because the formation of those are hindered, as observed by Daiber et al .…”