4-Nitrosophenol

It can act either as a nitrosophenol or as a quinone monoxime. Coloured derivatives, e.g. the sodium salt, are derived from the quinone form. Direct methylation gives a coloured compound which has been shown to be quino-nemethoxime OlCeH4tNOCH3 p-nitrosoani-sole CH30 C6H4 N0 has been obtained by another route and is colourless. 

The colorations produced in this reaction arise from the action of nitrous acid on the phenol, giving />-nitrosophenol (I) which then reacts with excess of phenol to form an indophenol (II) which is an acid-base indicator ... 

The theory that the catalysed nitration proceeds through nitrosation was supported by the isolation of some />-nitrosophenol from the interrupted nitration of phenol, and from the observation that the ortho.-para ratio (9 91) of strongly catalysed nitration under aqueous conditions was very similar to the corresponding ratio of formation of nitrosophenols in the absence of nitric acid. ... 

Condensation of an o-nitrosophenol with an amine hydrochloride in acetic acid (10) Nile Blue [2381-85-3] is formed from the hydrochloride of 1-naphthyl amine. 

Nitroso dyes are metal-complex derivatives of o-nitrosophenols or naphthols. Tautomerism is possible in the metal-free precursor between the nitrosohydroxy tautomer (76) and the quinoneoxime tautomer (77). 

The presence of a nitmso-coinpound may be detected as follows. Melt together a niiniite quantity of nitrosophenol and a few crystals of [ilienol. Add ahout 2 c.c. concentrated sulphuric acid and waiin ciy gently. A blue solution is obtained, which changes to red on dilution with water, and back to blue on adding alkali (Liebermann s nitioso reaction sec Reaction, p. 180). Sec AppL Hiiix, ]). 280. 

Benzofuroxan may be obtained by oxidation of o-quinone dioxime. The first benzofuroxan derivative, 1,2-naphthofuroxan, was obtained by this method. Suitable oxidizing agents include alkaline ferri-cyanide, bromine water, chlorine, and nitric acid. The method is of practical value only when the o-quinone or its monooxime (o-nitrosophenol) is readily available, and since this is not generally the case, other routes, e.g., the oxidation of o-nitroanilines and the thermal decomposition of o-nitrophenyl azides/ are more commonly used. 

The reaction of 2-nitrosophenols with aminoguanidine nitrate in the presence of nitric acid yields 3-amino-1,2,4-benzotiiazine 4-oxides 154 (75KGS1571). 

Recently it has been claimed (Ref 42) that PA may be prepd by nitrosating phenol with Na nitrate and Oxidizing the resulting nitrosophenols with nitric acid,... 

It has already been pointed out that nitrosation is probably the first step in diazotization. Ingold (1952) describes the reaction as N-nitrosation and classifies it as an electrophilic substitution, together with related processes such as the formation of 4-nitrosophenol, an example of a C-nitrosation. It was probably Adamson and Kenner (1934) who first applied these ideas to diazotization and realized that in aniline itself the electron density at the nitrogen atom is greater than in the anilinium ion, so that the base is more reactive. On the other hand, the nitrosoacidium ion (3.1), the addition product of nitrous acid and a proton, is a more powerful electrophilic reagent than the HN02 molecule. They therefore represented the first step of diazotization as in Scheme 3-5. 

Smoking. The effects of smoking on the formation of N-nitros-amines in bacon has been investigated recently by Bharucha et al. ( ). They reported that unsmoked bacon samples generally tended to contain more N-nitrosamines, presumably because of their higher nitrite content at the time of frying. Sink and Hsu (55) showed a lowering of residual nitrite in a liquid smoke dip process for frankfurters when the pH also was lowered. The effects of smoke seem to be a combination of pH decrease and direct C-nitrosation of phenolic compounds to lower the residual nitrite in the product (56). This is an area which requires further study since certain C-nitrosophenols have been shown to catalytically transnitrosate amines in model systems (57). 

Very little is known about the parent benzoxazine analogue,1 due to difficulties in the preparation of o-nitrosophenol. Synthetic procedures and practical application of spironaphthooxazines can be found in the patent literature and have been reviewed.72... 

The nitrosophenol (10), which may be isolated, is oxidised very rapidly by nitric acid to yield the p-nitrophenol (11) and nitrous acid more nitrous acid is produced thereby and the process is progressively speeded up. No nitrous acid need be present initially in the nitric acid for a little of the latter attacks phenol oxidatively to yield HN02. The rate-determining step is again believed to be the formation of the intermediate (9). Some direct nitration of such reactive aromatic compounds by N02 also takes place simultaneously, the relative amount by the two routes depending on the conditions. 

Arylbenzoxazoles have been prepared in moderate yields by allowing aromatic aldehydes to react with copper complexes of o-nitrosophenols (Scheme 108).172 The role of the copper in reactions of this type is unclear but it may be noted that the uncomplexed nitrosophenols are relatively labile.173 Copper complexes of o-nitrosophenols have also been used for the synthesis of benzoxazines (see Section V,D). 

Readily available copper(II) complexes derived from o-nitrosophenols react with dimethyl acetylenedicarbonxylate to give the 1,4-benzoxazine products that would be expected from formal [4 + 2] cycloaddition across the diheterodiene system (Scheme 168).239 No such reaction is observed in blank experiments with uncomplexed tautomeric nitrosophenols hence the copper may cause sufficient electronic perturbation within the heterodiene complex to allow reaction to occur. 

Nitrosoarenes are readily formed by the oxidation of primary N-hydroxy arylamines and several mechanisms appear to be involved. These include 1) the metal-catalyzed oxidation/reduction to nitrosoarenes, azoxyarenes and arylamines (144) 2) the 02-dependent, metal-catalyzed oxidation to nitrosoarenes (145) 3) the 02-dependent, hemoglobin-mediated co-oxidation to nitrosoarenes and methe-moglobin (146) and 4) the 0 2-dependent conversion of N-hydroxy arylamines to nitrosoarenes, nitrosophenols and nitroarenes (147,148). Each of these processes can involve intermediate nitroxide radicals, superoxide anion radicals, hydrogen peroxide and hydroxyl radicals, all of which have been observed in model systems (149,151). Although these radicals are electrophilic and have been suggested to result in DNA damage (151,152), a causal relationship has not yet been established. Nitrosoarenes, on the other hand, are readily formed in in vitro metabolic incubations (2,153) and have been shown to react covalently with lipids (154), proteins (28,155) and GSH (17,156-159). Nitrosoarenes are also readily reduced to N-hydroxy arylamines by ascorbic acid (17,160) and by reduced pyridine nucleotides (9,161). 

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

Cobalt Complexation with 2-ethyl-amino-5-nitrosophenol, extraction with dichloroethane Spectrophotometry at 402 nm < 0.07 jxg/1 [224]... 

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