Nitrous acid quinones

The nature and concentration of the dopant are important factors in controlling the physiochemical and mechanical properties of the polymer and its conductivity and long-term stability (54). Several dopants have been proposed, including bromine, iodine, lithium perchlorate, ferric chloride, cupric chloride, hydrogen peroxide, lead dioxide, nitrous acid, quinones, ozone (55), as well as 2-naphthalenesulfonate and p-toluenesulfonate (56). Some of these have been studied by Myers (47), who found that ferric chloride under anhydrous conditions yields the most conductive polypyrrole, with electrical conductivity as high as 45 S/cm. Park and Ruckenstein (21) also reported that ferric chloride provides the best performance as an oxidant. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

On the other hand, there is at least one case of an aromatic amine without a hydroxy group in the 2-position, namely 1-aminophenazine (2.29) which, after the initial diazotization, is oxidized within minutes by air or additional nitrous acid to the quinone diazide 2.31 (Olson, 1977). 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3) so-called neutral diazotization or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. 

The potassium chlorate both oxidises and chlorinates. If chromic acid, or even weaker oxidising agents, is employed the dichloro-quinone is obtained. The oxidation of aminophenols is illustrated in the following, in which nitrous acid serves as oxidising agent. 

The nitrous acid is usually generated by the action of sodium nitrite on an acid solution. The nitrosophenols are identical with the quinone monoximes, formed by acting on quinone with hydroxylamine. 

C10H14Oj) C,H. An alternate route leading from 2,3-xylenol to this diether via nitrogen-containing intermediates was explored. The sequence involved the reaction of 2,3-xylenol with nitrous acid (4-nitroso product, mp 184 °C dec.), reduction with sodium dithionite (4-amino product, mp about 175 °C), oxidation with nitric acid (benzoquinone, mp 5 8 °C), reduction with sodium dithionite (hydro-quinone) and final methylation with methyl iodide. The yields were inferior with this process. 

Amino naphtho Is, such as l-amino-2-naphthol and several 1-aminonaphthol-sulfonic acids, such as l-amino-2-naphthol-4-sulfonic acid, are oxidized to the respective quinone by nitrous acid. Diazotization can, however, take place under normal conditions in the presence of catalytic quantities of metal salts, such as copper or zinc salts. 

Along with nitration processes, isomerization processes may take place which in turn may lead to various fairly complex reactions. As a result such products as C02, CO, NH3 are formed. Such reactions are particularly notable in the nitration of phenols. Their mechanism has been explained by Seyevetz [81] in the following way. A phenol undergoes nitrosation under the influence of nitrous acid present in the nitrating acid. Nitrosophenol isomerizes to quinone oxime, which oxidizes at the double bonds to form mesoxalic acid and its oxime ... 

None of the methods mentioned gives satisfactory diazotization of 1,2- and 2,1-aminonaphthols or their sulfonic acid and other derivatives, all of which are readily oxidized to quinones by nitrous acid in acid solution. Diazotization of these compounds can be carried out successfully by using just enough acid to make the aminonaphthol salt, or, in the case of the sulfo derivatives, to make the compound containing one free sulfo group, and treating with nitrite in the presence of one equivalent of a zinc salt or a small amount of a copper salt. If a copper salt is used, the copper must be removed when diazotization is complete, but the presence of zinc in a diazo solution usually does no harm. 

Pyrrole blacks are obtained by other oxidizing reagents, which were tested mainly on unsubstituted pyrrole. Among these are nitrous acid," lead dioxide,112 ferric chloride,101,102 quinones,89, 61,113 115 diazonium salts,116 and ozone.107... 

Nitroso-d-naphthol has been made by the action of hydroxyl-amine hydrochloride on /3-naphtho-quinone-chlorimide 1 by the action of sulfuric acid upon a solution of potassium or sodium nitrite and the sodium salt of /3-naphthol 2 by the action of sodium nitrite upon an alcoholic solution of zinc chloride and /3-naphthol 3 by the action of sodium nitrite upon /3-naphthol suspended in zinc sulfate solution 4 by the action of nitrous acid on /3-dinaphthol methane 5 and by the action of nitrosyl sulfate upon the sodium salt of /3-naphthol.6... 

Oxidation (with such reagents as iron(III) chloride, potassium dichromate, silver oxide or nitrous acid) of 4,7-, 6,7-, and 5,6-dihydroxy-, and 5,6-dimethoxy-benzimidazoles gives the corresponding quinones. A 5-methyl group is oxidized by permanganate to carboxy (74CRV279). In the presence of copper(II)-piperidine or -dimethylamine complexes oxygen... 

Nitration takes place easily and again there is a tendency for polysubstitution. Phenols are readily nitrosated by nitrous acid. The resultant nitrosophenols are tautomeric with the corresponding quinone monoximes (Scheme 4.16). 

Quinone Oximes.—The most interesting of the derivatives of quinones are the oximes. As stated in the discussion of the ketone structure for quinones one of the proofs for this constitution is the fact that benzoquinone forms both a mono-and a di-oxime when treated with hydroxyl-amine. The mono- oxime of benzoquinone would have the structure as written below and as given on page 638. Now as previously mentioned, (p. 628), para-nitroso phenol, which is made by the action of nitrous acid upon phenol and the constitution of which is established by other methods of synthesis, (p. 627), proves to be one and the same compound with this mono-oxine of para-benzoquinone, the constitution of which is likewise established by the above reaction of hydroxyl amine upon quinone. This is explained by a rearrangement as shown in the following ,... 

Nitrous acid, HNOj, is stable only at low temperatures. It is prepared in situ from sodium or potassium nitrite and dilute sulfuric or hydrochloric acid. This reagent is used for the oxidation of p-aminophenols to quinones... 

Nitrosoresorcinol illustrates the preparation and properties of the nitroso dyes. The action of nitrous acid on the hydroxy compound gives the dye. These nitrosophenols are isomeric with the quinone oximes, which may also be prepared by the action of hydroxylamine on the quinones. 

These compounds are obtained by action of nitrous acid on phenols, and were formerly regarded as nitrosophenols but this assumption has gradually been abandoned. They may also be obtained by action of hydroxylamine on quinones, and yield dioximes on further treatment with this reagent. It is therefore more probable that the nitrosophenols are really oximes of quinones, i. e.j quinones in which one oxygen atom is replaced by the divalent group = IN —OH. 

This dihydronaphthohydroquinone is dissolved in hot acetic acid, the solution is let cool to about 100°, and an aqueous solution of sodium nitrite is run in rapidly with swirling. Nitrous acid effects smooth oxidation to 5,8-dihydro-l,4-naphtho-quinone (4, which can be isolated in 91-97% yield). The temperature is adjusted to 65°, and a warm (65°) solution of sodium dichromate containing a little sulfuric acid is added. The temperature is checked at 65-70° for 15 min., and after 45 min. addition of ice and water precipitates bright yellow naphthoquinone, m.p. 124-125°. 

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... 

Sulphanilic acid, like other para compounds, is converted by chromic acid into quinone. With nitrous acid it yields a diazo compound, which is used in the preparation of valuable dyes. It forms well characterized salts with bases, but does not form salts with acids on account of the presence of the strongly negative sulphonic acid group. 

Liebermann discovered the reaction between nitrous acid and phenols and secondary amines named after him. He prepared amino-naphthols from nitro-naphthols, synthesised the dihydroxyanthraquinones anthrarufin and chrysazin, and studied the reduction of anthraquinone. Another dihydroxy-anthraquinone, quinizarin, was discovered by F. Grimm by heating hydro-quinone with phthalic anhydride. 

Shaw and Wilkinson described a colorimetric estimation of proflavine hemisulphate. A purple colour is developed with nitrous acid but it is not stable if, however, excess of nitrous acid is removed and the quinone-imine is coupled in acid solution with AT-(l-naphthyl)ethylenediamine dihydrochloride a stable purple colour is obtained which is more intense than that of the corresponding uncoupled quinone-imine. 

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