Nitrates of diazonium compounds

8 Nitrates of diazonium compounds Organic pigments, self-heating, 4.2 

There are over 8000 chemicals that exhibit commercially significant optical properties. Some of these are natural products such as indigo, chlorophyll, and cochineal, but the majority are synthesized in a series of steps involving dye intermediates (any of the 3000 or more organic and inorganic chemicals used as raw material precursors to manufactured dyes, the most important of which are benzene and naphthalene). Coal tar dyes refers to the dyestuffs originating from the complex mix of hydrocarbons (benzene, toluene, xylene, pyrene, naphthalene, anthracene, etc.) present in coal tar (8007-45-2). Petroleum has succeeded coal as the dominant source of dye intermediates. Dyes, pigments, and dye intermediates include 

---

Diazonium salts are formed by the diazotization reaction, the action of nitrous acid on primary aromatic amines in the presence of a mineral acid. As salts, these compounds are able to stabilize the reactive azo group in preparation for making dyes and other products. Nitrates of diazonium compounds are diazonium nitrate salts. 

Sodium nitrite is an important reagent in the preparation of diazonium compounds, e.g. reaction 14.106 in which HNO2 is prepared in. situ. Alkali metal nitrates yield the nitrites when heated alone or, better, with Pb (reaction 14.107). 

Benzene and some of its derivatives react with solutions of mercuric nitrate in concentrated nitric acid to give nitrophenols. These reactions, known as oxynitrations may proceed by mercuration followed by nitroso-demercuration the resulting nitroso compound becomes a diazonium compound and then a phenol, which is nitrated. ... 

The formation of 3,3, 4,4 -tetrachloroazobenzene, l,3-bis(3,4-dichlorophenyl)triazine and 3,3, 4,4 -tetrachlorobiphenyl from 3,4-dichloroaniline and nitrate by E. coli plausibly involved intermediate chemical formation of the diazonium compound by reaction of the amine with nitrite (Corke et al. 1979) (Figure 2.2g). 

During nitration of several amino derivatives, diazotisation and oxidation occurred to produce internal diazonium phenoxide compounds. 5-Acetylamino-3-bromobenzo[h ]thiophene unexpectedly underwent hydrolysis, diazotisation and oxidation to the explosive compound below. 

As expected, electrophilic substitution of a compound with a powerful electron-releasing substituent at the 3-position results in the 2-substituted compound. Thus bromination and diazonium coupling of 3-dibenzofuranol occurs at the 2-position, and bromination, chlorination, and nitration ... 

The nitro group does not undergo migration of the naphthalene ring during the usual nitration procedures. Therefore, mono- and polynitration of naphthalene is similar to low temperature sulfonation, The nitronaphthalenes and some of their physical properties arc listed in fable 2. Many of these compounds are not accessible by direct nitration of naphthalene but are made by indirect methods, e.g nitrite displacement of diazonium halide groups in the presence of a copper catalysts, decarboxylation of nitronaphtbalcnccar-boxylic acids, or deamination of nitronaphthalene amines. They are nsed in the manufacture of chemicals, dye intermediates, and colorants for plastics. 

Commercial sodium nitrite contains 1—3% sodium nitrate, the harmful effect of which on diazonium compounds may be obviated by adding to the amine solution or the nitrite solution an amount (1-5—4 5% of the weight of nitrite used) of sodium metabisulphite slightly in excess of that necessary to reduce the nitrate. Diazonium compounds prepared in this way or with pure sodium nitrite are much more stable (J. Soc. Dyers, 41, 275.)... 

Another method of preparing azobisindolizines is by reaction with tosyl or picryl azide.191-193 2-Methylindolizine is converted into the 3,3 -bisazo compound after 2 minutes. The product yields the radical ion 130 (detected by EPR) when treated with 1 mole of silver perchlorate.194,195 The redox characteristics of such compounds have been studied by Hiinig and co-workers.196,197 In view of the instability of aminoindolizines, they have not been used to prepare diazonium salts. 1-Nitrosoindolizines, however, yield diazonium nitrates in good yield when treated with dry nitric oxide.182,198 The products are stable both in... 

The conversion may consist simply in oxidation or be the result of a more complex reaction. For example, nitrosotoluene can be converted into diazonium nitrate under the influence of nitrous acid. Bamberger [132] found in 1918 that nitrosobenzene could be converted into benzenediazonium nitrate under the influence of nitrous acid. According to Bamberger [133] and Nesmeyanov [134], mercury-aromatic compounds also give nitrates of corresponding diazonium compounds under the influence of N203, presumably also through nitroso compounds. 

The present, straightforward, two-step synthesis of 5.6-dimethoxyindazole from 3,5-dimethoxyacetophenone illustrates the usefulness of this amination reaction. With standard chemistry the introduction of a hydrazine group into the acetophenone molecule would have required four steps 1) nitration, 2) reduction of the nitro group to the aniline, 3) diazotization and 4) reduction of the diazonium compound to the hydrazine. 

The diazonium sulfates are preferred to the nitrates or chlorides. Aryl chlorides and nitro compounds are sometimes formed as by-products in the decomposition of diazonium chlorides and nitrates. For example, o-nitro-p-cresol is formed in 69% yield by the hydrolysis of the diazonium nitrate from p-toluidine. ... 

---