P- Nitrosophenol

Tautomerism exists in the case of o- and p-nitrosophenols and naphthols which exist mainly as the quinone oximes, and which also give high field shifts. The values for the oxime groups in the 1,2-naphthoquinones, for example, were 229 and 265 ppm for the 1-oxime and the 2-oxime respectively. 

The experimental model used to illustrate the ECE mechanism was the reduction of p-nitrosophenol at a mercury electrode, in which the chemical step is dehydration [54]. The experimental data have been analyzed by best-fitting curve pro-... 

In reactions of A,A-dimethylaniline, care must be taken in the final isolation of the free p-nitrosoamine from its salt, since prolonged treatment with excessive alkali leads to the formation of p-nitrosophenol [21a]. By the way, the initial proof that the product of nitrosation is the para isomer was simply based on the observation that, after prolonged add hydrolysis of p-nitrosophenol, a product formed which had an odor that resembled that of 1,4-benzoquinone. It is to be hoped that more substantial structure proofs are used today. 

The nitrosation of phenols proceeds in a manner similar to that of tertiary amines. For example, l-nitroso-2-naphthol has been prepared from the sodium salt of /9-naphthol by treatment with sodium nitrite and sulfuric acid near 0°C [29], This general procedure, suitably modified, has been used to prepare other nitrosophenols such as p-nitrosophenol (m.p. 135°-136°C) [30]. 

Animation of p-nitrosophenol ethers with primary aromatic amines [28] (Eq. 58). 

Many nitroso compounds are reported to melt with decomposition. For example, p-nitrosophenol is unstable, and may ignite at elevated temperatures [18]. Some nitroso compounds are reported to have disagreeable odors, some are lachrymators, and some nitrosophenols may cause rashes [18]. 

Methylphenylnitrosoamine E thylpheny Ln itrosoamine Nitrosobenzene o-Nitrosotoluene. m-Nitrosotoluene. p-Nitrosotoluene. a-Nitrosonaphthalene. p-Nitrosophenol. a-Nitroso-P-naphthol. 4-Nitroso- a-naphthol pNitrosoNNdimethylaniline p-Nitroso -NN diethylani line. p-Nitroso-N-methylaniline p-Nitroso-Nethylaniline p-Nitrosodiphenylamine... 

This reaction is frequently applied to the preparation of dialkylamines. The dimethylamine evolved in the above reaction may be absorbed by leading through hydrochloric acid from the latter solution the hydrochloride is obtained by evaporation. p-Nitrosophenol, it is to be noted, is tautomeric, in some reactions behaving as quinone monoxime. 

Phenol may be converted into a mixture of o- and p-nitrophenols (Expt 6.102) by reaction with dilute nitric acid the yield of p-nitrophenol is increased if a mixture of sodium nitrate and dilute sulphuric acid is employed. Upon steam distillation of the mixture of nitrophenols, the ortho isomer passes over in a substantially pure form the para isomer remains in the distillation flask, and can be readily isolated by extraction with hot 2 per cent hydrochloric acid. The mechanism of the substitution probably involves an electrophilic attack (cf. Section 6.2.1, p. 851) by a nitrosonium ion at a position either ortho or para to the activating hydroxyl group, to yield a mixture of o- and p-nitrosophenols, which are then oxidised by the nitric acid to the corresponding nitrophenols. The reaction depends upon the presence in the nitric acid of traces of nitrous acid which serve as the source of the nitrosonium ion. 

The formation of Af-nitrosamines which usually separate as orange-yellow oils or low melting solids indicates the presence of a secondary amine. Confirm the formation of the nitrosamine by the Liebermann nitroso reaction. This consists in warming the nitrosamine with phenol and concentrated sulphuric acid. The sulphuric acid liberates nitrous acid from the nitrosamine, and the nitrous acid reacts with the phenol to form p-nitrosophenol, which then combines with another molecule of phenol to give red indophenol. In alkaline solution the red indophenol yields a blue indophenol anion. 

Examples of this mechanism are the reduction of o-nitrophenol, p-nitrosophenol, uranium complexes, and tocopherols, among many others [55], and also proteins containing two redox sites including the possibility of an intramolecular electron transfer [35]. 

Technical grade of p-nitrosophenol may explode on storage.1 o-Nitrosophenol explodes on heating while p-nitrosophenol may ignite spontaneously if nitrates were present in the sodium nitrite used for its preparation. 

From diazotized aniline and p-nitrosophenol Borsche 88 obtained 2-hy-droxy-5-nitrosobiphenyl (XXIII) in 8% yield, and with 2-methyl-4-ni-trosophenol he obtained 2-hydroxy-3-methyl-5-nitrosobiphenyl (XXIV). 

It has been shown that the addition of nitrous acid lowers the initiation temperature of the reaction the addition of p- nitrosophenol affects the reaction in a similar way. The addition of urea to nitric acid results in lowering the reaction rate. A similar nitration scheme was given by Veibel [150],... 

Pure p- nitrophenol may also be prepared by nitrosation of phenol, followed by oxidation of p- nitrosophenol with dilute nitric acid. The m- isomer is usually prepared by diazotization of m- nitroaniline. 

Such reaction pathways are common for many systems, e.g., isomerizations, couplings, and homogeneous disproportionation, studied mainly in nonaqueous media [i-iii]. The reduction of p-nitrosophenol is a typical example [ii] ... 

Nitrophenols, alkylation, 148 o-Nitrophenol-p-sulfonic add, 107 p-Nitrophenyloxamic add, 93 o-NitrophenyBiydrazine, 97 p-NitrophenyDiydrazine, 95 Nitrophenylpyrazolones, 97 Nitrosobenzene, 78 p-Nitrosodiediylaniline, 309 p-Nitrosodimediylaniline, 308, 311 reduction, 78, 312 Nitroso- -naphthol, 80, 201 p-Nitrosophenol, 85 Nitrosylsulfuric add, 9, 247 o-Nitrotoluene, 53, 160 m-Nitrotoluene, 51 Nitrotoluenes, 3... 

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