Peroxy acids and other oxidants

Piesnicar, B. Oxidations with peroxy acids and other peroxides, in Oxidation in Organic Chemistry (ed. Trahanovsky, W. S.), 5, 211 -294 (Academic Press, New York, 1978). 

Primary amines are oxidized to hydroxlyamines, which in turn are oxidized to ni-troso compounds, which are oxidized to nitro compounds. Hydrogen peroxide, peroxy-acids, and other common oxidizing agents are used to oxidize amines. The oxidation reactions generally take place by mechanisms that involve radicals, so they are not well characterized. 

R0)2P-S—S—P(0R)2. A number of these products and others from reactions of dithiophosphoric acids with oxidants are listed in Table 2 since they are some of the impurities to be anticipated. Thiophosphoryl (P=S) compounds are rapidly, quantitatively, and stereospecifically converted to phosphoryl (P=0) compounds by organic peroxy acids under mild conditions. The reactions of peroxy acids and dithiophosphoric acids and salts have apparently not been characterized. 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

Methods for the oxidation of azo to azoxy compounds have been reviewed.Typical oxidants are MCPBA and other peroxy acids and hydrogen peroxide. r-Butyl hydroperoxide is also an effective oxidant for azobenzenes in the presence of molybdenum hexacarbonyl. Trifluoroperacetic acid has been used to oxidize perfluoroazobenzene and other fluorinated azobenzenes to the azoxy compounds in high yield It is also capable of oxidizing azoxyarenes, such as compound (47), to the di-A(-oxides. 4... 

Derivatives of phosphonic acids, RP==O(0H)2, can be prepared by several different oxidative methods. Primary phosphines RPH2 are oxidized to phosphonic acids by hydrogen peroxide or by sulfur dioxide thus, phenylphosphine gave benzenephosphonic acid (96%) on reaction with sulfur dioxide at room temperature in a sealed tube. Phosphinic acids, RI sO(OH)H, can also be oxidized to the corresponding phosphonic acids with hydrogen peroxide. Ozone oxidized the dioxaphosphorane (54) to the phosphonic ester in 73% yield. Ozone is also capable of stereospecific oxidation of phosphite esters to phosphates. For example, the cyclic phosphite (SS) was oxidized to the phosphate (56) with retention of configuration. Peroxy acids and selenium dioxide are other common oxidants for phosphite esters. 

The scope of peroxytrifluoroacetic acid oxidations resembles that of peroxyacetic acid and other peracids, although sometimes the outcome may be different [285]. The advantage of peroxytrifluoroacetic acid is that it reacts faster than the other peroxy acids peroxyacetic acid, peroxyben-zoic acid, w-chloroperoxybenzoic acid [286], and peroxyformic acid [285]. 

The oxidation reagents used most frequently for the conversion of sulfides into sulfoxides and sulfones are hydrogen peroxide, peroxy acids, and periodates. Periodates usually do not oxidize sulfoxides to sulfones [770 771, 772, 776, 775], In addition, many other, even rather exotic, oxidants have been used especially for chemoselective oxidations of sulfides containing functional groups vulnerable to attack by peroxy compounds, such as double bonds and carbonyl groups. 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

The previous section amply demonstrates the advantages of dimethyldioxirane as an oxygen transfer agent for preparative oxidation chemistry compared to other oxidants such as peroxy acids and alkaline hydrogen peroxide the synthetic applications are literally endless. Nonetheless, the mechanistic details of the oxygen transfer are to date still inadequately understood. Presently available experimental data [3] such as sterochemistry, kinetics, activation parameters, isotope effects, reactivity patterns, etc. are consistent with the complex butterfly transition state A, initially proposed for peroxy acids as oxygen atom donors, and the novel diradical-like transition state B (Scheme 9). 

Sulphines are formed by the oxidation of thiones with peroxy-acids, but they then react further, albeit much more slowly, to give the ketone, sulphur, and sulphur dioxide. This latter reaction is kinetically similar to many other oxidations with peroxy-acids, and the results are consistent with electrophilic attack of the peroxy-acid on the C=S double bond to give a cyclic sulphinate ester (4), which rapidly decomposes to give the ketone and sulphur monoxide. In contrast, oxidation of thiobenzanilide 5-oxide with m-chloroperoxybenzoic acid gives products derived from the sulphene PhC(NHPh)=SOa. Further examples of the reaction between diarylsulphines and aryldiazomethanes to give epi-sulphoxides have been reported. ... 

Oxygen donors like peroxy acids, ozone, and pyridine IV-oxides cause carbon-carbon cleavage, perhaps by formation of a perepoxide (43 Scheme 30) (81JCS(P1)1871). Other oxidants have also been reported to react with oxiranes (64HC( 19-1)228). 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Treatment of 51 with an excess of sodium benzoate in DMF resulted in substitution and elimination, to yield the cyclohexene derivative (228, 36%). The yield was low, but 228 was later shown to be a useful compound for synthesis of carba-oligosaccharides. <9-Deacylation of228 and successive benzylidenation and acetylation gave the alkene 229, which was oxidized with a peroxy acid to give a single epoxide (230) in 60% yield. Treatment of 230 with sodium azide and ammonium chloride in aqueous 2-methoxyeth-anol gave the azide (231,55%) as the major product this was converted into a hydroxyvalidamine derivative in the usual manner. On the other hand, an elimination reaction of the methanesulfonate of 231 with DBU in toluene gave the protected precursor (232, 87%) of 203. 

The rate of epoxidation of alkenes is increased by alkyl groups and other ERG substituents and the reactivity of the peroxy acids is increased by EWG substituents.72 These structure-reactivity relationships demonstrate that the peroxyacid acts as an electrophile in the reaction. Decreased reactivity is exhibited by double bonds that are conjugated with strongly electron-attracting substituents, and more reactive peroxyacids, such as trifluoroperoxyacetic acid, are required for oxidation of such compounds.73 Electron-poor alkenes can also be epoxidized by alkaline solutions of... 

Vacuum evaporation of the product of untreated conversion of the pyridine to its N--oxide with 5% excess of the peroxy acid in chloroform gave a residue which decomposed violently [1], This was attributed to the relative stability of the peroxy acid in the cold pure state, which when concentrated and finally heated with other materials underwent accelerating decomposition [2],... 

---