Caro acid compounds

Oxidants suitable for the partial oxidation of amines to nitroso compounds are peroxy acids Caro acid, which is prepared in situ from potassium persulfate and sulfuric acid [195, 199 potassium peroxysulfate (Oxone) [295] peroxyacetic acid [i53], and peroxybenzoic add [1186], 3-Nitro-o-toluidine [195] and 5-nitro-o-toluidine [199] in aqueous-alcoholic solutions, when treated with a mixture of potassium persulfate and concentrated sulfuric acid, give 3-nitro-2-nitrosotoluene and 5-nitro-2-nitrosotoluene in respective yields of 60 and 55-66%. Organic peroxy acids convert 2,6-dihaloanilines into 2,6-dihalonitrosobenzenes (equation 497) [753, 1186]. p-Phenylenediamine (1,4-diaminobenzene) is oxidized by Oxone (2KHS05 KHS04 K2S04) in an aqueous suspension at room temperature to p-dinitrosobenzene in a quantitative yield [205]. 

Nitroso compounds are formed selectively via the oxidation of a primary aromatic amine with Caro s acid [7722-86-3] (H2SO ) or Oxone (Du Pont trademark) monopersulfate compound (2KHSO KHSO K SO aniline black [13007-86-8] is obtained if the oxidation is carried out with salts of persulfiiric acid (31). Oxidation of aromatic amines to nitro compounds can be carried out with peroxytrifluoroacetic acid (32). Hydrogen peroxide with acetonitrile converts aniline in a methanol solution to azoxybenzene [495-48-7] (33), perborate in glacial acetic acid yields azobenzene [103-33-3] (34). 

Sulfuric acid, H2SO4, the most important commercial sulfur compound (see Sulfuric acid and sulfur trioxide), and peroxymonosulfuric acid [7722-86-3] (Caro s acid), H2SO, are discussed elsewhere (see Peroxides and peroxide compounds, inorganic). The lower valent sulfur acids are not stable species at ordinary temperatures. Dithionous acid [15959-26-9] H2S2O4, sulfoxyHc acid [20196-46-7] H2SO2, and thiosulfuric acid [13686-28-7] H2S2O2 are unstable species. A discussion of efforts to isolate and characterize the unstable sulfur acids is given (330). 

Aromatic nitroso-compounds can also be obtained by oxidation of primary amines, but only one oxidising agent is known with which the process can satisfactorily be carried out. This reagent is monopersvl-phuric acid (Caro s acid) ... 

Numerous sulfur and phosphorus peroxy compounds such as monopersulfuric acid (Caro s acid, la), monopersulfate (Oxone, Ib), ammonium monopersulfate Ic, tetra n-butyl-ammonium monopersulfate Id, peroxydisulfates 2a and 2b", tetra n-butylammonium peroxydisulfate 2c, symmetrical bissulfonyl peroxide 3 , acyl sulfonyl peroxide 4 , unsymmetrical sulfonyl peroxide 5 , sulfinyl peroxy intermediates 6a, sulfonyl peroxy intermediate 6b, sulfonimidoyl peroxy intermediate 7, bis(diphenyl phosphinyl) peroxide 8 , unsymmetrical phosphorus peroxide 9 and phosphoranyl peroxy intermediate 10" are known. Recently, many researchers have shown interest in the preparation and... 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

As is well known, the oxidation of aniline with various oxidizing agents leads to a variety of products, usually highly colored polymeric materials. However, the reaction with Caro s acid (permonosulfuric acid, H2SOs) with aniline produces nitrosoaniline rapidly [76]. With this reagent, many aromatic amines have been oxidized to the corresponding nitroso compounds, e.g., the three nitronitrosobenzenes were prepared from the corresponding nitroani-lines [77, 78]. The reaction is normally carried out in an aqueous medium. In... 

Pentafluoronitrosobenzene, 363, 410 Pentyl azide, 271 Peracid oxidation of amines, 323, 363,409 of azo compounds, 355-356 of hydrazones, 362 of hydroxylamines, 364,415 of imines, 406 of oxaziranes, 407 Perchloryl fluoride, 336 Perfluoroalkylureas, 162 Perfluoro-2-azopropene, oxidation of, 432 Periodic acid oxidation, 338 Permonosulfuric acid, see Caro s acid Phenazines, 321... 

In some cases in which the Caro s acid oxidation of amines was not satisfactory, the corresponding hydroxylamines have been oxidized with acidified dichromate solutions [42], Both aliphatic and aromatic nitroso compounds have been prepared by this method [17, 42, 82, 90]. Frequently the reaction mixture from the reduction of a nitro compound is treated directly with the oxidizing medium without the isolation of the intermediate hydroxylamine. The method has been called the nitro reduction oxidation technique, [82] a terminology we cannot condone. 

An unstable intermediate peroxygenated compound is also always formed. This gives a blue coloration to fresh guaiacum tincture and is possibly analogous to Caro s acid.2... 

A still more favourable effect upon current efficiency is achieved if certain substances such as fluorides are added, which raise the potential by some hundredths or even tenths of a volt. Other compounds such as chlorides, eyanides (potassium cyanide, ferrocyanide or ferricyanide) or thiocyanates have a double effect on one hand they decompose the Caro s acid and on the other hand they raise the anode potential. Ammonium thiocyanate is almost generally used. It reduces Caro s acid, at first, and changes it into sulphuric acid and hydrogen cyanide, the latter promoting a rise in the anode potential. 

Less forcing conditions with organic peracids or Caro s acid can be used to make nitroso compounds.323 Although, as mentioned earlier, a low excess of oxidant can be used deliberately to give the diazo-coupled material as the major product,324 this can react further to the azoxy compound, but the latter is then hard to oxidize.325 Aliphatic primary amines are more difficult to oxidize compared to the aromatics, but use of peracetic acid in a solvent will lead to the formation of nitro compounds.322... 

Tetroxans ( dimeric ketone or aldehyde peroxides ) (7) are readily obtainable from carbonyl compounds and Caro s acid or hydrogen peroxide and sulfuric acid by the method described by Baeyer and Villiger.28,20 However, aromatic ketones undergo a Baeyer-Villiger rearrangement under these conditions to form esters of carboxylic acids.30... 

Small quantities of ammonium thiocyanate of hydrochloric acid are added to increase the anode potential. The peroxo compound obtained is subsequently hydrolyzed, the hydrolysis proceeding by way of the peroxo-monosulfate. (Caro s acid) ... 

An interesting reaction in which emeraldine is formed was observed by Caro [16]. If aqueous solution of free aniline is oxidised with potassium permanganate, and filtered from the separated manganese dioxide, the filtrate is a yellowish liquid, from which ether takes up a yellow amorphous eompound. This latter is converted into a green salt of emeraldine by mere contact with acids. A substance possessing the properties of emeraldine is formed simultaneously with quinone by oxidation of paramido-diphenylamine. A larger yield is obtained if this base is oxidised with an equivalent of aniline, and in this case quinone is not formed [17]. On further oxidation emeraldine yields a darker coloured compound, but it is doubtful if this is aniline black. The formation of emeraldine from paraphenylenediamine and diphenylamine leads to the supposition that it is a phenylated indamiue of the formula ... 

These comprise a series of weak dyestuffs discovered by Caro and Wittj the type of which is obtained by heating azophenine with concentrated sulphuric acid or with zinc powder. The formation of this compound, which contains two azine rings, may be represented by the following equation —... 

From this time dye research in the German aniline dye industry flourished. Caro later described azo dye research and development as scientific mass production. The most important activity was the invention of key aryl amine intermediate compounds for use in the coupling reaction, and for this endeavor structural studies were essential. Caro extended the range of the new azo dyes into the reds with his invention of fast red AV (19) in July 1877. This was based on his reasoning that two naphthalene-based components in the azo compound would give a red. To achieve this he used diazotized 1-naphthionic acid (4-amino-1-naphthalenesulfonic acid) (20)37. 

Despite the economic importance of rosaniline (aniline red, magenta) (6) and its derivatives during the 1860s and after, there was no clear structural information about aniline-derived colorants, at least until 1878. Then, through the joint work of the cousins Emil and Otto Fischer, the search for the parent compound of 6 was successfully concluded with publication of the modern structures for aniline dyes. The Fischers starting point had been Caro and Wanklyn s work on 6 and rosolic acid (13). 

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