Diazonium salts quinones

Almost all dyes are quinones or azaquinones of compound 2. The majority are used for thermal transfer processes a recent example is compound 306 (98USP5792587). The second major class are azo dyes, prepared either from aromatic diazonium salts as in compound 307 (95GEP4319296) or from a triazolopyridine 3-diazonium salt as in 308 (81BRP2054630). 

This technique is used to diazotise anilines carrying two or more electron-withdrawing substituents, such as 2,4-dinitro- and 2-cyano-4-nitro-aniline, as well as aminoanthra-quinones and heteroaromatic amines [4]. Some diazonium salts prepared by this technique, such as those from 6-halogeno-2,4-dinitroanilines, are unstable in water and have to be added directly to the coupling component solution. 

The other two dihydric phenols, benzene-1,2-diol (catechol) and benzene-1,4-diol (hydroquinone) are of little interest in this context since they reduce diazonium salts on attempted coupling, being themselves oxidised to the corresponding quinones. 

Stannous chloride is used most frequently for the reduction of nitro compounds [177, 178, 179] and of quinones [180, 181], It is also suitable for conversion of imidoyl chlorides [182] and of nitriles [183] to aldehydes, for transformations of diazonium salts to hydrazines [184], for reduction of oximes [f[Pg.30]

In a 4-1. beaker, equipped with a high-speed stirrer (Note 3), are placed 20 g. (0.185 mole) of quinone (Note 4), 34 g. (0.4 mole) of sodium bicarbonate, 50 g. of chopped ice, and 500 ml. of water. About 10 ml. of the above diazonium salt solution is added (Note 5). After the frothing has subsided (Note 6), the diazonium salt solution is added in 10- to 20-ml. portions over a period of about an hour (Note 7). The temperature of the reaction mixture is kept below 15° during this period by the addition of ice. After the diazonium salt solution has been added, the mixture is allowed to warm up to room temperature, and the stirring is continued for an additional hour. The precipitate of 2-/>-acetyl-phenylquinone is collected on a Buchner funnel and washed thoroughly with approximately 11. of water. The yield of crude yellow-brown solid is 40-41 g. (96-98%). The melting point ranges from 125-135° to 134-136° (Note 8). 

The Balz-Schiemann synthesis can be applied not only to substituted anilines but also to aminobiphcnyls1,131 or amino-substituted fused polyaromatic compounds, such as naphthalene,1114,119,129 anthracene,136 phenanthrene,1135 acenaphthene,133 fluorene,1,131,134 benzanthracene,130 136 pyrene,136 chrysene,136 fluoranthene,131 fluorenone,1,131 anthra-quinone,1,137,139,140 benzanthrone,1,117,118 phenanthraquinone,138 or xanthone.132 Fluorinated pyridines,1,141"146 methylpyridincs,126,147 149 pyridinecarboxylic acids,150 quinolines,1,151 isoquinolines,152 quinazolone,1 thiazoles,153,154 isothiazoles,156 benzothiazoles,157 thiadiazoles,155 and thiophenes154 can also be obtained from the corresponding aminated heterocycles. Modified Balz-Schiemann methods are recommended for amino nitrogen-containing heterocycles, the diazonium salts of which are rather water-soluble and unstable (a violent explosion was reported for pyridine-3-diazonium tetrafluoroborate).159 These new techniques have also been specially adapted for pyrazol-, imidazol-, or triazolamines which fail to react under classical conditions.158... 

Hydroxybenzenediazonium tetrafluoroborates constitute a special case the meta-isomer has the structure of a true diazonium salt, while the ortho- and para-isomers are in ready equilibrium with the corresponding quinone-diazide dimers which have been isolated as com-... 

A fairly general procedure for the synthesis of o- and p-quinones consists in coupling a phenol with a diazonium salt and reducing the resulting azo compound to an aminophenol with sodium dithionite. Mild oxidation with, for example, iron(m) chloride results in the formation of the corresponding quinone (e.g. the preparation of 1,2-naphthoquinone described and formulated in Expt 6.131). 

Reaction of Diazonium Salts with Quinones and with Phenols.239... 

Reaction of Diazonium Salts with Quinones and with Phenols. Aryl-diazonium salts couple with quinones in the presence of sodium acetate to... 

Heating a diazonium salt, sometimes in the presence of copper salts (hydro-quinone from p-aminophenol, or guaiacol from o-anisidine). 

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... 

Morphol-9 10-quinon has been synthesized together with the 2 3-dihydroxy-isomer [xxvi] from 3-hydroxyphenanthrene-9 10-quin-one by nitration, reduction, and conversion of the isomeric amino-compounds to the hydroxy-compounds through the diazonium salts [37]. 

The diazotization products of 2- and 4-aminophenols, -naphthols (etc.), possess a mesomeric (zwitterionic) phenolate-diazonium and quinone-diazide structure. We discussed these structures in the context of aromatic diazotization (Zollinger, 1994 Sect. 2.4) because the synthetic methods used are closely related to those used for aromatic diazonium salts. This is also the case for the diazotization of amino-di-, tri- and tetrazoles, which, in their neutral form, contain a heterocyclic NH group in the )8-position to the amino group. After diazotization, the NH group is very acidic. Following deprotonation the product corresponds to a heterocyclic diazoalkane. Similarly, the diazotization product of 4-(dicyano)methylaniline ((4-amino-phenyl)malonitrile) may lose the CH proton. This compound is, therefore, sometimes called a vinylene homolog of diazomalonitrile (Regitz and Maas, 1986, p. 205). 

Anthraquinone-2-diazonium tetrafluoroborate has been adsorbed onto an edge plane pyrolytic graphite electrode to form a thin unreacted submonolayer film. After transfer to a buffer solution containing no diazonium salt, the adsorbed material was thermally decomposed at room temperature and a grafted anthra-quinone film was obtained with a surface coverage rs ,f < 2 x 10 ° mol car [240]. Nitroazobenzene submonolayers have been obtained by spontaneous modification of PPF surfaces. The apparent thickness was th = 0.6 nm and Raman spectra confirmed the structure of the flhn [241]. On gold, 0.06 was found,... 

Another reaction of diazonium carboxylate is presented in Figure 3.67. By heating the internal carboxylate diazonium salt, a diradical is obtained that reacts with carbon black. Transformation of the dimethoxybenzene group to o-quinone provides a modified carbon surface that can be used as a pseudocapacitance along the quinone/ hydroquinone couple [415]. 

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