Oxidation using peroxytrifluoroacetic acid

The conversion of an amino group into a nitro group can be useful when specific substitution patterns are required. The synthesis of 1,4-dinitrobenzene from 4-nitroaniline is illustrative (Scheme 7.5). Oxidation can be accomplished directly using peroxytrifluoroacetic acid or in two steps using H2SO5 (monoperoxysulfuric acid) and oxidation of the resulting nitroso compound with hydrogen peroxide. Alternatively, the amine can be diazotized in fluoroboric acid and then reacted with sodium nitrite in the presence of copper powder. 

Two different modes of reaction have been reported for steroidal A -3-ketones 20). Potassium persulphate in sulphuric acid gave the 4 0xa"3 ketone (23), considered to arise by an initial Baeyer-Villiger oxidation to the unsaturated lactone (21) as an enol lactone of the C(g)-aldehyde (22) this could suffer further degradation through a second Baeyer-Villiger attack on the aldehyde group [64], Other. workers [6 ] used peroxytrifluoroacetic acid and obtained the 5a-carboxy--4"Oxa 3-ketone (25) and the bridged product (26), apparently derived by an internal aldol condensation of the intermediate lactone-aldehyde (24). 

The Baeyer-Villiger reaction is also effected by biochemical oxidation using the enzyme cyclohexanone oxygenase from Acinetobacter strain NCIB 9871. Cyclohexanone is thus converted into e-caprolactone [1043], and phenylacetone (l-phenyl-2-propanone) is transformed into benzyl acetate. The formation of benzyl acetate from phenylacetone involves the same migration as that in oxidation with peroxytrifluoroacetic acid (equation 387) [1034]. More examples of biochemical Baeyer-Villiger reactions occur in diketones and steroids see equation 397). 

A very common oxidizing reagent is peroxytrifluoroacetic acid, which is usually generated in situ from trifluoroacetic acid [29, 30, 31] or trifluoroacetic anhydride [32, 33, 34] and hydrogen peroxide Peroxytrifluoroacetic acid is one of the most efficient epoxidizing reagents [35] It can be used to prepare epoxides... 

Dichloronitrobenzene has been prepared by deamination of 3,5-dichloro-4-nitroaniline and of 2,4-dichloro-3-nitroaniline. This procedure is an example of the rather general oxidation of anilines to nitrobenzenes with peroxytrifluoroacetic acid. Use of this reagent is frequently the method of choice for carrying out this transformation, and it is particularly suitable for oxidation of negatively substituted aromatic amines. Conversely, those aromatic amines, such as />-anisidine and j8-naphthylamine, whose aromatic nuclei are unusually sensitive to electrophilic attack give intractable mixtures with this reagent. This is not... 

Some substrates show limited solubility in sulfuric acid solutions and this can affect the rate of oxidation. However, the main factor for slow amine oxidation is due to the high concentration of protonated amine under these highly acidic conditions. Under these conditions only weakly basic amines have a high enough concentration of unprotonated form to permit oxidation to occur. As a result, sulfuric acid solutions of peroxydisulfuric acid are only useful for the oxidation of very weakly basic amines. Peroxydisulfuric acid oxidizes trinitrotoluidines to tetranitrotoluenes (Table4.1, Entry 3) but leaves the more basic dinitrotoluidines unaffected. The opposite is true of peroxyacids like peroxytrifluoroacetic acid and so the reagents are very much complementary. 

Peroxytrifluoroacetic acid is used tor numerous oxidations of saturated hydrocarbons and aromatic compounds It oxidizes alkanes, alkanols, and carboxylic acids with formation of hydroxylation products [29] Oxidabon of cyclohexane with peroxytrifluoroacetic acid proceeds at room temperature and leads to cyclohexyl trifluoroacetate in 75% yield, 1-octanol under similar conditions gives a mixture of isomeric octanediols in 59% yield, and palmitic acid gives a mixture of hydroxypalmitic acids in 70% yield [29]... 

Peroxyformic, peroxyacedc and peroxytrifluoroacetic acids are most commonly used to bring about this type of oxidation, but 2-sulfoperoxybenzoic acid, monoperoxysuccinic acid and disuccinoyl peroxide (which is converted to monoperoxysuccinic acid by hydrolysis), also oxidize alkenes to ttiols with the advantage that the free diols are obtained directly. 

It was early reported that perbenzoic acid in chloroform at room temperature quantitatively oxidizes tii-n-butylborane as in equation (37), The reaction with peroxytrifluoroacetic acid has been used analytically but very little in synthesis. 

Chloroperoxybenzoic acid, monoperoxyphthalic acid, peroxymaleic acid, or peroxytrifluoroacetic acid are also used for the preparation of quinoxaline iV-oxides 4 or 5. 

Peroxytrifluoroacetic acid is used for the epoxidation [283, 287] and anti hydroxylation [285, 288] of alkenes the Baeye Villiger oxidation of... 

An important addition to the arsenal of oxidants for the Baeyer-Villiger reaction is peroxytrifluoroacetic add [282, 283, 284]. Although this reagent is less easily accessible than peroxyacetic acid and aromatic peroxy acids, it is more reactive. The yields of esters obtained by oxidation of ketones with peroxytrifluoroacetic acid are high enough to justify the use of this oxidant for the quantitative determination of aldehydes and... 

Dibutyl sulfide is converted into dibutyl sulfoxide with one equivalent of peroxytrifluoroacetic add and into dibutyl sulfone with two equivalents of peroxytrifluoroacetic acid [279]. On the other hand, with manganese dioxide, dibutyl sulfide yields dibutyl sulfoxide exclusively 541], and with chromic acid, it yields dibutyl sulfoxide, even when an excess of the oxidant is used and even when the reaction is carried out at 100 °C 541] (equation 552). 

Further use of this oxidant to produce a number of poly nitro aromatics was reported by Nielsen and co-workers [71] in their remarkable paper. The authors also reviewed work on the other oxidants used to pass from HN to NO Caro acid, peracetic, permaleic, m-chloroperbenzoic and perbenzoic acids. They pointed out that the power of the oxidant is proportional to the acid strength of deoxy peracid. Peracetic and m-chloroperbenzoic acids are suitable for the oxidation of aliphatic primary amines, whereas peracetic, peroxytrifluoroacetic and peroxymaleic acids are best for the oxidation of ring substituted anilines. Potassium persulphate in sulphuric acid was also used successfully [71 ]. 

Oximes derived from (l-oxoalkyl)phosphonic esters have been oxidized to the 1-nitro derivatives in moderate to good yields by means of 3-chloroperoxybenzoic acid in CH2Cl2 The use of peroxytrifluoroacetic acid leads to unwanted side reactions. 

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