Hexafluoroacetone epoxidation

Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Hexafluoroacetone and hydrogen peroxide in buffered aqueous solution can epoxidize alkenes and allylic alcohols.101 N, Af-Dialkylpiperidin-4-one salts are also good catalysts for epoxidation.102 The polar effect of the quaternary nitrogen enhances the... 

SCHEME 53. Epoxidation of olefins with hexafluoroacetone/H202... 

Highly enantioselective epoxidation of unfunctionalized alkenes was developed by using chiral metalloporphyrin catalysts.1214-1218 Remarkable anion axial ligand effects were observed with [Fe(TPFPP)X] complexes (X = triflate, perchlorate, nitrate).1219 Hexafluoroacetone was found to be an efficient cocatalyst with H202,1220 and alkenes could be epoxidized by ozone at ambient temperature.1221... 

Fluorinated epoxides are very important synthetically. Perfluoroalkenes can be oxidized by numerous means to the corresponding epoxides. The most commonly encormtered epoxide is hexafluoropropene oxide (HFPO), which is made from hexafluoropropene and is used in the synthesis of oligomers and as a source of difluorocarbene. HFPO is a colorless, nonflammable gas, boiling at -27.4 °C it can be ring-opened easily by nncleophiles or electrophiles imder a variety of conditions. HFPO can be rearranged by flnoride ion to perfluoropropionyl flnoride and by Lewis acids snch as UO2 to hexafluoroacetone (HFA). Nncleophiles typically attack the most substituted carbon of the epoxide, freeing the oxyanion to lose fluoride or act as a nucleophile itself Some examples of HFPO reactivity are shown in Scheme 3. 

Copolymers are obtained by free-radical copolymerisation of hexafluoroacetone with, for example, alkenes, tetrafluoroethene and epoxides. 

Recent literature refers to the stereoselective and asymmetric epoxidation of allylic alcohols with organoaluminium peroxides. PhaSiOOH epoxidizes olefins with a stereoselectivity similar to that with peracid. Reports have been made of a-substituted hydroperoxides (acids, esters, ketones, amides, and nitriles) as effective epoxidizing reagents and the application of hexachloroacetone, tetrachloracetone, and hexafluoroacetone hydroperoxide, as well as the HaOa-Vilsmeier reagent system. ... 

M. C. A. van Vliet, I. W. C. E. Arends, R. A. Sheldon, Hexafluoroacetone in hexafluoro-2-propanol A highly active medium for epoxidation with aqueous hydrogen peroxide, Synlett (2001) 1305. 

W. A. Adam, H.-G. Degen, C. R. Saha-Moller, Regio- and diastereoselective catalytic epoxidation of chiral allylic alcohols with hexafluoroacetone perhydrate. Hydroxy-group directivity through hydrogen bonding, J. Org. Chem. 64 (1999) 1274. 

The group of Masui first attempted the direct epoxidation of olefins by using oxygen and NHPI with metalloporphyrins, but they obtained poor results [15]. Ishii and coworkers proposed two different methods. In the first protocol [16,17], the epoxidizing agent is obtained in situ by the aerobic oxidation of a suitable alcoholic (benzhydrol) compound in the presence of catalytic amounts of NHPI. The resulting oxidant, which is not able to promote the epoxidation by itself, is then activated in the presence of an olefin by catalytic amounts of hexafluoroacetone (HFA) (Scheme 6.1). 

SCHEME 6.1 Mechanism for the epoxidation of alkenes catalyzed by N-hydroxyphthalimide (NHPI) in the presence of alcohols and hexafluoroacetone (HFA). 

T. Iwahama, S. Sakaguchi, Y. Ishii, Epoxidation of alkenes using dioxygen in the presence of an alcohol catalyzed by N-hydroxyphthalimide and hexafluoroacetone without any metal catalyst, Chem. Commun. (1999) TS. 

The epoxides (81) themselves have been synthesized by treatment of 4,7-dihydro-1,3-dioxepins (77) withp-nitro- <75BSF1763> or w-chloroperbenzoic acid <75TL2643> or HOCI/H2O2 <8IEUP33426). Alternatively, hexafluoroacetone/hydrogen peroxide in disodium hydrogen phosphate buffered... 

Trifluoromethyl perfluorohexylethyl ketone is an efficient alternative catalyst for the epoxidation reactions of alkenes. Such reactions were carried out using 1-5 mol% of this fluorous ketone as a catalyst and 1.5 equivalents of the oxone in a mixture of hexafluoroisopropanol and water. Thus, the new procedure circumvents the need for volatile fluorine compounds such as trifluoroacetone and hexafluoroacetone. 

Epoxidations with 60 % H2O2 in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), catalyzed by hexafluoroacetone - yield [%], reaction time -... 

At ambient temperature and pressure, hexafluoroacetone is a (toxic) gas, and catalyst recovery is impractical. As a nonvolatile alternative, Sheldon et cd. employed perfluoroheptadecan-9-one. After completion of the epoxidation, this catalyst can be recovered from halogenated solvents such as dichloroethane or TFE by simple cooling of the reaction mixture [39]. Furthermore, this long-chain perfluorinated ketone has the potential for immobilization in fluorous phases. When appHed to epoxidation with perfluoroheptadecan-9-one as catalyst, TFE gave yields of epoxide comparable to those obtained in dichloroethane. However, to achieve good yields of add-sensitive epoxides, buffering by Na2HP04 was necessary. 

Oxirans.— Epoxides are readily available from the catalytic oxidation of alkenes with 2-hydroperoxyhexafluoropropan-2-ol (HPHI) (1), which itself is easily prepared from hexafluoroacetone hydrate (2) and hydrogen peroxide (Scheme 1). HPHI is claimed to have similarities to the natural flavin hydroperoxides which are implicated in epoxidations and hydroxylations by external flavoprotein mono-oxygenases. Yields are typically in the range 77—92%. 

Closely related to this, other olefins were tested in epoxidation reactions. The heterogeneous epoxidation of cyclooctene with H2O2 in scC02 using a manganese porphyrinate catalyst in the presence of hexafluoroacetone hydrate as the co-catalyst at 40" C and 200 bar, leads to complete transformation into cyclooctene oxide. The co-catalyst forms perhydrates and thereby helps to stabilise the porphyrine catalyst and to solubilise H2O2 in SCCO2. 

Campestrini, S. and ToneUato, U. (2002). Catalytic olefin epoxidation with H2O2 in supercritical CO2. Synergic effect by hexafluoroacetone and manganese-porphyrins, Adv. Synth. Catal., 343, pp. 819-825. 

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