Iron reaction with nitrous acid

Baeyer confirmed his results by the total synthesis of oxindole, isatin and indole. Nitration ofphenylacetic acid, isolation of the o-nitro isomer, and reduction of the latter followed by ring closure gave oxindole. Reaction with nitrous acid ( .e. potassium nitrate and sulfuric acid) gave isatin oxime, from which by reduction, dehydrogenation with iron(lll) chloride and final hydrolysis, isatin itself was obtained. 

Other reported syntheses include the Reimer-Tiemann reaction, in which carbon tetrachloride is condensed with phenol in the presence of potassium hydroxide. A mixture of the ortho- and para-isomers is obtained the para-isomer predominates. -Hydroxybenzoic acid can be synthesized from phenol, carbon monoxide, and an alkali carbonate (52). It can also be obtained by heating alkali salts of -cresol at high temperatures (260—270°C) over metallic oxides, eg, lead dioxide, manganese dioxide, iron oxide, or copper oxide, or with mixed alkali and a copper catalyst (53). Heating potassium salicylate at 240°C for 1—1.5 h results in a 70—80% yield of -hydroxybenzoic acid (54). When the dipotassium salt of salicylic acid is heated in an atmosphere of carbon dioxide, an almost complete conversion to -hydroxybenzoic acid results. They>-aminobenzoic acid can be converted to the diazo acid with nitrous acid followed by hydrolysis. Finally, the sulfo- and halogenobenzoic acids can be fused with alkali. 

Substitution and oxidation can often both be involved in reactions of tris(diimine)-iron(II) complexes with oxidizing agents. Thus, for example, reaction with hydrogen peroxide involves rate-determining dissociation as the first step. Similarly, initial dissociation seems to be the first step in the predominant pathway for superoxide oxidation of the [Fe(phen)3] cation. Dissociation may also be involved in reactions of diimine-iron(II) complexes with nitrous acid. Here and elsewhere it is recognized that these complexes react with nitric acid—in the initial stages aquation may be the only important path, but autocatalytic redox processes usually become dominant before aquation is complete, especially for the more easily oxidizable ligands and complexes. ... 

Kinetic data for the reaction of Cr(VI) with HNO2 have been interpreted in terms of a prior formation of a nitrito complex of Cr(VI), [Cr030N0] , which undergoes redox recomposition either in a unimolecular process or via reaction with a second mole of HNO2. The reaction of Pu(VI) with nitrous acid " exhibits a rate law somewhat similar to that for the iron(III) cyano complexes. In this... 

Thus, antioxidant effects of nitrite in cured meats appear to be due to the formation of NO. Kanner et al. (1991) also demonstrated antioxidant effects of NO in systems where reactive hydroxyl radicals ( OH) are produced by the iron-catalyzed decomposition of hydrogen peroxide (Fenton reaction). Hydroxyl radical formation was measured as the rate of benzoate hydtoxylation to salicylic acid. Benzoate hydtoxylation catalyzed by cysteine-Fe +, ascorbate - EDTA-Fe, or Fe was significantly decreased by flushing of the reaction mixture with NO. They proposed that NO liganded to ferrous complexes reacted with H2O2 to form nitrous acid, hydroxyl ion, and ferric iron complexes, preventing generation of hydroxyl radicals. 

Moderate yields of thiadiazoles (255) also have been obtained by the thermolysis of mixtures of thioamides (253) and A-sulfinylsulfonamides (259 Scheme 91) (62AG135). The manner in which the proposed intermediate (260) is converted into (255) has not been discussed and the mechanism of this reaction deserves further study. TV-Arylthioureas (261) form 1,2,4-thiadiazole derivatives (73) ( Hector s bases ) in good yields when oxidized with acidic hydrogen peroxide or other oxidizing agents (nitrous acid, iron(III) chloride) as indicated in Scheme 92 (65AHC(5)119). Evidence for the intermediate formation of dithio-... 

On reducing the density of the acid to 1 30, nitrous oxide is formed in amount equivalent to 7 per cent, of the iron dissolved. With acid of density 1 25, the reaction is further complicated, nitrogen and ammonia being produced the former gas reaches a maximum in the case of acid of density 1-15, and then falling, whilst the ammonia reaches a maximum with acid of density 1-05.3... 

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