Pertrifluoroacetic acid

The great utility of hydrogen peroxide as a reagent for the conversion of sulphoxides to sulphones spurred the investigation of other peroxy-containing compounds. Probably the most commonly used species is peracetic acid which is formed by the reaction of acetic acid with hydrogen peroxide. In addition, other peroxy acids such as pertrifluoroacetic acid and m-chloroperbenzoic acid and hydroperoxides and hydrotrioxides are often used to convert sulphoxides to sulphones. 

In a synthetic sequence involving thietanoprostanoids45, peroxydodecanoic acid was successfully used to oxidize a hydroxysulphoxide to the corresponding hydroxysulphone (equation 14). The use of pertrifluoroacetic acid in this case apparently produced unidentifiable products. 

Iodosobenzene reacts with TMSOTf 20 (or with TMSONf 21) to give the adducts 2026 or 2027, which are transformed by TMSCN 18 to the adduct 2028 [189]. 2028 is also obtained from iodobenzene by treatment with pertrifluoroacetic acid then reaction with TMSOTf 20 and Me3SiCN 18 [190] (Scheme 12.56). The... 

Perphthalic acid <550SC(3)619) is an even milder reagent that works even at —20 to 20 °C. Performic, permaleic and pertrifluoroacetic acids are strong oxidizing agents and they are recommended for AT-oxidation of the least reactive substrates. The last of the three is the most commonly used, especially for the oxidation of highly deactivated substrates (Scheme 16) such as perchloropyridine (electronic deactivation) (74MI20501) and 2,6-dibromopyridine (electronic and steric deactivation) (equation 35). 

Oxidation with Stoichiometric Oxidants. Certain peracids reacting with alkanes yield alcohols. Peracetic acid,68 69 perbenzoic acid,70 m-CPBA,71,72 and nitroper-benzoic acids may be used. Alcohols or an equilibrium mixture of the alcohol and the trifluoroacetate77 are formed on the action of pertrifluoroacetic acid. A high degree of regioselectivity (better than 97%), specifically, preferential attack at the tertiary C—H bonds, is usually observed ... 

Pertrifluoroacetic acid may be prepared by the reaction of hydrogen peroxide with trifluoroacetic acid. The following procedure gives an anhydrous solution of the reagent. Add trifluoroacetic anhydride (25 ml, 0.18 mol) dropwise to a stirred suspension of 86 per cent hydrogen peroxide (4.1 ml, 0.15 mol) in ice-cold dichloromethane (70 ml). On completion of the addition stir at 0°C for a further 10 minutes, dry with anhydrous sodium sulphate and use the solution... 

The oxidation of oximes offers an attractively simple route to nitroalkanes from carbonyl compounds. The most effective reagent is pertrifluoroacetic acid in acetonitrile in the presence of sodium hydrogen carbonate as a buffer. Yields are improved by the addition of small quantities of urea to remove oxides of nitrogen. The reaction is illustrated by the conversion of dipropyl ketoxime into 4-nitroheptane (Expt 5.190). 

CAUTION The reactions involving hydrogen peroxide and pertrifluoroacetic acid should be carried out in a fume cupboard behind a safety screen. Adequate precautions should be observed in handling the hydrogen peroxide solution (1). 

Nitroheptane. Prepare a solution of pertrifluoroacetic acid in acetonitrile as follows. Place 50 ml of acetonitrile in a two-necked, 250-ml round-bottomed flask fitted with a dropping funnel and a reflux condenser. Insert a plastic-covered magnetic stirrer follower bar and cool the flask in an ice bath sited on the stirrer unit. To the cooled and stirred solution add 5.8 ml (0.2 mol) of 85 per cent hydrogen peroxide (1) and then 39.0 ml (58.1 g, 0.24 mol) of trifluoroacetic anhydride. Stir the solution for 5 minutes and then allow to warm to room temperature. In a three-necked, 500-ml round-bottomed flask fitted with a sealed stirrer unit, dropping funnel and reflux condenser place 200 ml of acetonitrile, 47 g (0.56 mol) of sodium hydrogen carbonate, 2g of urea and 12.9g (0.1 mol) of dipropyl ketoxime. Heat the stirred suspension under reflux on the water bath and add dropwise over 90 minutes the prepared solution of pertrifluoroacetic acid. When the addition is complete heat the mixture under reflux for 1 hour. Pour the cooled reaction mixture into 600 ml of cold water and extract with four 100 ml portions of dichloromethane (note the organic layer is the upper layer in the first extraction, but subsequently it is the lower layer). Wash the combined extracts with... 

The epoxidation reaction is achieved most conveniently by employing m-chloroperbenzoic acid (or perbenzoic acid) in a solvent such as chloroform. The use of other peracids, such as peracetic acid or pertrifluoroacetic acid, give lower yields of the oxirane since the oxide may be readily cleaved to form the monoester of the diol (e.g. Section 5.4.5, p. 547). 

One of the most important methods for lactone preparation, and hence of the corresponding hydroxy acids (or halogeno acids, Section 5.14.1 above) is the Baeyer- Villiger rearrangment of cyclic ketones by the action of peracids. A wide variety of peracids have been used in this reaction but currently the reagents of choice are pertrifluoroacetic acid, m-chloroperbenzoic acid, and permaleic acid. The mechanism is formulated below for the conversion of an acyclic ketone into an ester. 

Oxidation of DCC with pertrifluoroacetic acid affords N-trifluoromethyl-N,N -... 

Victorian brown coal occurs in five major lithotypes distinguishable by color index and petrography. Advantage has been taken of a rare 100 m continuous core to compare and contrast chemical variations occurring as a function of lithotype classification. For many parameters there is a much greater contrast between the different lithotypes than there is across the depth profile of (nearly) identical lithotypes. Molecular parameters, such as the distributions of hydrocarbons, fatty acids, triterpenoids and pertrifluoroacetic acid oxidation products, together with gross structural parameters derived from IR and C-NMR spectroscopic data, Rock-Eval and elemental analyses and the yields of specific extractable fractions are compared. 

The lithotype profile was investigated in greater detail with the product composition of the different brown coals being reported in Tables 1 and 2. A distinct decrease in the total concentration of detectable oxidation products occurs with darker lithotypes (Table 1). This result is consistent with increasing aromaticity (Figure 2) and the preferential attack on aromatic structures by the pertrifluoroacetic acid reagent. The total destruction of the tertiary structure within the brown coal lithotypes is evidenced by their low yield of insoluble products (Residue) which is primarily composed of mineral matter. 

Figure 5 Plot of pertrifluoroacetic acid oxidation aliphatic proton yield data derived from P.M.R. and elemental analysis.

Product Composition of Brown Coal Lithotypes Pertrifluoroacetic Acid Oxidation Mixtures... 

Table IL Pertrifluoroacetic Acid Oxidation Product Distribution (—1 0 X 2 C/3 m H > r 1...

Table 5. Proton Population (Area %) in the Pertrifluoroacetic Acid...

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