Nitrosation—oxidation

Nitrosation of phenolic substrates usually uses nitrous acid prepared in situ from a dilute mineral acid and an alkali metal nitrite. In general, for every phenolic group present in a substrate an equal number of nitroso groups can be introduced into the aromatic ring phenol, resorcinol and phloroglucinol react with nitrous acid to form 4-nitrosophenol, 2,4-dinitrosoresorcinol and 2,4,6-trinitrosophloroglucinol respectively. 

Resorcinol (22) is readily converted to 2,4-dinitrosoresorcinol (23) in quantitative yield by slowly adding an aqueous solution containing two mole equivalents of sodium nitrite to a solution of resorcinol that has been acidified with two mole equivalents of sulfuric acid. The 2,4-dinitrosresorcinol (23) from this process can be oxidized to 2,4-dinitroresorcinol (24) with a binary phase system of toluene and dilute nitric acid at -5 Treatment of either 2,4- 

Both 2,4-dinitrosoresorcinol (23) and 2,4-dinitroresorcinol (24) are important in the explosives industry. The lead salt of 2,4-dinitrosoresorcinol has a low ignition temperature and finds use in priming compositions and in electrical igniters. The lead salt of 2,4-dinitroresorcinol is a weak initiator but is found to exhibit high sensitivity to friction and stab action without being highly sensitive to impact, and as such, this compound has found use in primers. 

6-Trinitrophloroglucinol has been synthesized via the nitrosation of phloroglucinol followed by nitric acid oxidation. The direct nitration of phloroglucinol must be conducted at subambient temperature to avoid excessive oxidation, and even then, the yield rarely exceeds 70 

Some phenolic substrates are readily nitrated with nitric acid of 5 % concentration or lower. Such reactions are catalyzed by nitrous acid either already present in the nitric acid or from initial oxidation of the phenolic substrate. Reaction of the substrate with nitrous acid 

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Many reactions, nitration, nitrosation, oxidation, etc are then possible. Titov s generalized scheme is... 

The nitration of phenols can result in anomalous and large differences in product isomer ratios, showing a high dependence on both nitrating agent and reaction medium. Here the situation is complicated by the intervention of an alternative nitration mechanism - that of nitrous acid catalyzed nitration, which proceeds via in situ nitrosation-oxidation (see Section 4.4). 

Data have been presented on the kinetics of nitration of acetanilide in mixtures of nitric and sulfuric acids.29 A review discusses the several mechanisms operative in the nitration of phenol including /> / -sclective nitrosation-oxidation and mechanisms involving phenoxy radical-nitrogen dioxide reaction yielding a 55 45 ortho para nitration ratio.30 The kinetics of mononitration of biphenyl-2-carboxylic acid have been investigated in several solvents. The maximum ortho para product ratio of 8.4 is observed in tetrachloromethane.31 Nitration products were not formed in the presence of dioxane.31,32 Quantum-chemical AMI calculations were performed and the predominant formation of the ortho-nitro product is accounted for by stabilization of the cr-complex by the carboxyl group.33... 

Nitration, suggested to involve nitrosation/oxidation, occurs during diazotization of some substituted 2-amino-1,8-naphthyridine derivatives (15).41 The selectivity of this process was contrasted with that of the nitronium ion reaction. 

Because of Oxone s acidic nature, (V-nitrosation of secondary amines is possible with the use of sodium nitrite in the presence of wet Si02 (eq 55). Nitrophenols can be obtained via nitrosation-oxidation of phenols under similar conditions (eq 56). Although acidic, the use of Oxone for these reactions eliminates the need for strong acids to generate NO+ unlike traditional methods. Nitrosoarenes can also be prepared by oxidation of anilines with Oxone (eq 57). ... 

Electrochemically inactive organic compounds can be converted into an electrochemically active state by nitration, nitrosation, oxidation, hydrolysis, or some other preliminary chemical reaction, and can then be determined polarographically or voltammetrically. Examples of this are polarographic determinations of alkylbenzenesulfonates in natural water samples after extraction and nitration of the aromatic ring [77] and determinations of beta-receptor blocking agents in tablets after conversion to the corresponding V-nitroso derivatives [78]. 

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