Nitrous acid hydroxyl radical reaction

Thus, antioxidant effects of nitrite in cured meats appear to be due to the formation of NO. Kanner et al. (1991) also demonstrated antioxidant effects of NO in systems where reactive hydroxyl radicals ( OH) are produced by the iron-catalyzed decomposition of hydrogen peroxide (Fenton reaction). Hydroxyl radical formation was measured as the rate of benzoate hydtoxylation to salicylic acid. Benzoate hydtoxylation catalyzed by cysteine-Fe +, ascorbate - EDTA-Fe, or Fe was significantly decreased by flushing of the reaction mixture with NO. They proposed that NO liganded to ferrous complexes reacted with H2O2 to form nitrous acid, hydroxyl ion, and ferric iron complexes, preventing generation of hydroxyl radicals. 

The Baudisch reaction295 makes it possible simultaneously to introduce a nitroso and a hydroxyl group in the ortho-position to one another. In this reaction NOH radicals are produced by oxidation of hydroxylamine or reduction of nitrous acid these radicals, in conjunction with an oxidizing agent and in the presence of a copper salt as catalyst attack the aromatic nucleus. Yields are seldom very high, but few o-nitrosophenols are easily prepared in other ways. Cronheim296 has reported the first preparation of fifty mono-and di-substituted n-nitrosophenols by the Baudisch reaction. 

Peroxynitrite is capable of initiating many of the reactions commonly attributed to hydroxyl radical, particularly under acidic conditions. Halfpenny and Robinson (1952a,b) showed that nitrous acid plus hydrogen peroxide in aqueous solutions at pH 2, which generates peroxynitrous acid, initiated the polymerization of methylmethacrylate (the precurser to Plexiglas) as well as the hydrox-ylation, nitration, and polymerization of benzene. 

In a similar way to nitrite, although at a somewhat lower rate, nitrous acid can be oxidised by the hydroxyl radical [35,43], Furthermore, it also undergoes a thermal decomposition process that parallels the photoinduced reaction [53]. 

The first-order reaction rate constant for the isomerization of peroxynitrous acid to nitrate is 4.5 s 1 at 37°C therefore, at pH 7.4 and at 37°C the half-life of the peroxynitrite/peroxynitrous acid couple (let both these species be referred to as peroxynitrite for the sake of brevity) is less than 1 s. The reaction mechanism of peroxynitrite decomposition was a subject of controversy. Primarily proposed was that peroxynitrous acid decomposes by homolysis, producing two strong oxidants hydroxyl radical and nitrous dioxide (B15) ... 

In the previous discussion of O-atom and O3 reactions, the hydroxyl radical is a prominent product. As will be seen later, OH radicals are also produced in the photolyses of aldehydes and nitrous acid. The resulting OH chain mechanism for propylene is summarized below ... 

This shows that the reaction depends upon the two remaining ammonia hydrogens which unite with the non-hydroxyl oxygen of the nitrous acid forming water, leaving the hydroxyl group of the nitrous acid for the alkyl radical. We shall find when we study the primary amines... 

With nitrous acid. The reaction of the aromatic primary amines with nitrous acid is different from that of the aliphatic primary amines with the same reagent, and serves to distinguish the two groups of compounds. When a primary alkyl amine is treated with nitrous acid the hydroxyl compound of the radical is formed and all of the nitrogen of the amine is given off as free nitrogen. The reaction is as follows ... 

Reactions with Nitrous Acid.—With nitrous acid (HO—NO) primary amines, due to the presence of two remaining ammonia hydrogen atoms, react with the oxygen of nitrous acid which is linked directly to the nitrogen alone. In the case of the alkyl amines the reaction does not stop here, but the hydroxyl group of the nitrous acid unites with the alkyl radical forming an alcohol and the nitrogen is set free. 

Peter Griess, 1858.—Diazo compounds were discovered and first prepared by Peter Griess in 1858. The historical method used by him is the same in general as is now used widely in dyestuff manufacture. It has already been described and consists in the action of nitrous acid on an aromatic primary amine, e.g., aniline. When this reaction takes place, at ordinary or slightly raised temperatures, the same products are obtained as with aliphatic primary amines, viz., the hydroxyl compound of the hydrocarbon radical, free nitrogen and water. 

At the present time, it is not possible to identify the exact role of the dihydroxybenzene in this reaction. Two possibilities can be considered first, whether it acts like a reducing agent on the hydrogen peroxide to give the hydroxyl radical, in a similar way to the Fenton reaction [10] or whether, after its oxidation by hydrogen peroxide into quinone, it causes an electron transfer from the phenol to give the phenoxy radical, in a similar role to the nitrosonium cation in the nitrous acid catalysed nitration of phenols [11]. In either case, this peculiar characteristic of the hydroxylation reaction explains the good behaviour... 

Other reactions also produce hydroxyl radical an important example is the photolysis of nitrous acid (HONO) at wavelengths of 290-400 nm ... 

A similar intramolecular oxidation, but for the methyl groups C-18 and C-19 was introduced by D.H.R. Barton (1979). Axial hydroxyl groups are converted to esters of nitrous or hypochlorous acid and irradiated. Oxyl radicals are liberated and selectively attack the neighboring axial methyl groups. Reactions of the methylene radicals formed with nitrosyl or chlorine radicals yield oximes or chlorides. 

X-ray Induced Hydroxylation of Benzoic Acid. It is well known that irradiation of benzoic acid in dilute solutions gives rise to decarboxylation as well as to hydroxylation in the ortho- meta- and para-positions (10, 27). From these investigations it follows that radiation induced formation of hydroxybenzoic acids in neutral aqueous solutions accounts for about 50% of the total degradation. In order to shed more light on the ability of N20 to convert hydrated electrons into oxidizing radicals, it was decided to compare the effect of nitrous oxide with that of hydrogen peroxide under anoxic conditions. If Reaction 1 and 2 occur rapidly, the effect of nitrous oxide would be expected to be similar to that of hydrogen peroxide, except that the latter compound may also convert H atoms into OH radicals. 

---