The chemistry of nitroso-compounds. Part VII. The first ‘fast’ proton transfer for an aromatic nitrosation

derstood [3]. The nitrosation of certain aromatics is nevertheless of considerable biomedical interest in view of the proven carcinogenic or mutagenic properties of the resulting products. This is the case of phenol and its derivatives [4-7]: the phenol derivative tyramine, which occurs in cheese, meat extract, beer, and soybean products [8-10] has been identified as one of the precursors largely responsible for the mutagenic activity of certain Japanese soy sauces treated with nitrite [11,12]; and bamethan [1-(4-hydroxyphenyl)-2-butylaminoethan-ol], a phenolic drug used for long-term oral treatment of cardiovascular disease, is both nitrosatable and a directly acting mutagen [13]. In view of their status as nitrosatable pre

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Section: Resultssupporting

confidence: 80%

Nitrosation kinetics of phenolic components of foods and beverages

Fernández‐Liencres¹,

Calle²,

González‐Mancebo³

et al. 1997

Int. J. Chem. Kinet.

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“…3) yields the value k a K NO ϩ ϭ 661 Ϯ 48 M Ϫ2 s Ϫ1 and k Ϫa /Kk b ϭ 63.183 Ϯ 5.000 M Ϫ1 . Similar pH dependence has been reported for the nitrosation of 2-naphtol [21] (those experiments were carried out in dilute HClO 4 , but since ClO 4 Ϫ does not catalyze the reaction, the observed pH dependence is comparable with the pH dependence of k 2H 2 O in our work).…”

Section: Resultssupporting

confidence: 90%

Nitrosation kinetics of phenolic components of foods and beverages

Fernández‐Liencres

Calle

González‐Mancebo

et al. 1997

Int. J. Chem. Kinet.

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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.

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“…We have not investigated bromide ion catalysis at other acidities, but in the nitrosation of phenol and 2-naphthol by nitrous acid both limiting cases have been identified experimentally. [18][19][20] The value of K for the hydrolysis of IPN has not been measured, but it expected to be close to 0.83 mol dm-3, which is the value measured directly for the structurally similar ethyl nitrite.21 Thus, in any one experiment K %-[ROH] and k' should be constant throughout the experiment, as we find. However, the addition of 1 mol dm-3 ROH produces a significant reduction as expected.…”

mentioning

confidence: 59%

Nitrosation by alkyl nitrites. Part 7. Comparison with thionitrites: reactions with phenols

Oh¹,

Williams²

1991

J. Chem. Soc., Perkin Trans. 2

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Both isopentyl nitrite (IPN) and S-nitroso-N-acetylpenicillamine (SNAP) react with phenol in the pH range 2-9 to give overwhelmingly 4-nitrosophenol. For IPN the reaction is first order in both IPN and phenol and the measured rate constant is much reduced by the addition of isopentyl alcohol, suggesting that reaction occurs by prior hydrolysis of IPN to nitrous acid. When allowance is made for the nitrous acid ionisation we find no acid catalysis in the pH range 3.62-5.25 but acid catalysis at higher acidities. The corrected rate constant also increases with pH at pH values greater than 6. There is no bromide ion catalysis at pH 4 but a substantial kinetic primary hydrogen isotope effect (using [*H,]phenol) of 4.0 at pH 2.55 which decreases towards 1 as the pH is increased. All of these results are consistent with rapid and reversible hydrolysis of IPN, and phenol nitrosation results from the nitrous acid produced. All of the experimental features parallel those found in the nitrous acid nitrosation of phenol. The kinetic pattern for the reaction of SNAP with phenol is quite different, showing autocatalytic features. We have obtained an EPR spectrum from the photolysis of SNAP, characteristic of RS', and for the phenoxy radical derived from the reaction mixture of SNAP with 2,6-di-tert-butyl-4-methylphenol at pH 7. We propose a radical mechanism for the reaction of SNAP with phenol involving hydrogen-atom abstraction by the RS' radical and subsequent reaction of the phenoxy radical with nitric oxide formed by homolysis of SNAP.

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The chemistry of nitroso-compounds. Part VII. The first ‘fast’ proton transfer for an aromatic nitrosation

Abstract: relative rates of subsequent steps on the reaction path.( I 1 limiting step for reactivity controlled reactions is determined by the of the k-a and kb steps.

Cited by 24 publications

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Nitrosation kinetics of phenolic components of foods and beverages

Nitrosation kinetics of phenolic components of foods and beverages

Nitrosation kinetics of phenolic components of foods and beverages

Nitrosation by alkyl nitrites. Part 7. Comparison with thionitrites: reactions with phenols

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