Perfluorinated Epoxides

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Perfluorinated epoxides, which are generally susceptible to C-O cleavage during nucleophihc attack, are cleaved by lithium alummum hydnde Of the available examples, reduction of epoxides from two types of internal olefm to give alcohols IS shown [4S] (equations 37a and 37b)... 

Imine formation is also possible when a fluorine atom is in a geminal position to a suitable leaving group (e.g., halogen38 or O-substituents). Reaction of perfluorinated epoxides (e.g.. 

Again, difluorohalomethyl,50,58 aminodifluoromethyl59 or difluoro(sulfonyloxy)methyl derivatives (e.g., 8)58,60-63 Can be aminolyzed in a similar manner to yield amidines59,63 or amides.50 58,60-62 In the latter process the intermediacy of acid fluorides (see Section 6.1.2.) has been proposed. By analogy, reaction of monoalkylated perfluorinated epoxides with amines leads to a-functionalizcd amides.64 65 In the presence of fluoride ions, perfluorinated epoxides can rearrange to acid fluorides which can be further elaborated with amines to provide the respective amides.63... 

Oxidation of the corresponding olefins by oxygen in the presence of initiators in an inert solvent at elevated temperatures leads to the formation of perfluorinated epoxides (00RP2157805). The initiators are either halogens, trifluoromethylhypofluorite, and tetrafluoroethylene in amounts of 1.0-15.0 v/o% or free-radical producers (94ZOR309). 

Other perfluorinated epoxides give rearrangement" or fragmentation upon treatment... 

Examples of fluoride-ion-initiated reactions involving perfluorinated epoxides are shown in Figure 8.47 [155-158]. Hexafluoropropene oxide (HFPO) and tetrafluoroethene oxide will polymerise under certain conditions in the presence of fluoride ion. The process involves an extending alkoxide and it is terminated by elimination of fluoride ion to give... 

Under SbCls catalysis oxygen-bromine exchange between benzaldehyde and o-chlorobenzal bromide proceeds at 100 °C to give benzal bromide and o-chlorobenzaldehyde in moderate yields [88]. Isomeric transformation of perfluorinated epoxides to the corresponding carbonyl compounds occurs in the presence of SbFs [89]. Isomerization of polyfluorinated olefins, cyclohexadienes, and cyclopropanes is also promoted by the action of SbFs [90]. 

Other perfluorinated epoxides give rearrangement117 119 or fragmentation119 upon treatment with cesium fluoride. 

Perfluorinated oxanes can be synthesized by ECF of oxanes. Perfluorinated epoxides and oxetanes, however, are obtained with difficulty because of cationoid polymerization of the initial three- and four-membered heterocycles in anhydrous HF. Perfluorinated oxolanes are obtained with good yields from oxolanes (Table 20) (94M30, 75ZPK2206). 

Preparation. The preparation of tetrafluoroethylene has been described previously. Perfluorovinyl ethers (4—7) are prepared by the following steps. Hexafluoropropylene [116-15-4] (HEP) is oxidized to an epoxide HEPO [428-59-1] (5) which, on reaction with perfluorinated acyl fluorides, gives an alkoxyacyl fluoride. 

Fluoride ion can also initiate ring opening of hexafluoropropylene oxide to give a heptafluoropropoxide, which can react in turn with the epoxide to give dimers or higher oligomers that are precursors to perfluorinated stable fluids [277, 27S, 279] (equation 61). 

Polyfluoroalkyl- andperfluoroalkyl-substituted CO and CN multiple bonds as dipolarophiles. Dmzo alkanes are well known to react with carbonyl compounds, usually under very mild conditions, to give oxiranes and ketones The reaction has been interpreted as a nucleophilic attack of the diazo alkane on the carbonyl group to yield diazonium betaines or 1,2,3 oxadiazol 2 ines as reaction intermediates, which generally are too unstable to be isolated Aromatic diazo compounds react readily with partially fluorinated and perfluorinated ketones to give l,3,4-oxadiazol-3-ines m high yield At 25 °C and above, the aryloxa-diazolines lose nitrogen to give epoxides [111]... 

Selenium-catalysed epoxidations have been carried out using a perfluo-roalkylated phenylselenide together with hydrogen peroxide, as shown in Scheme 9.6 [13]. The catalyst could be recycled 10 times with no loss of activity, with the toxic selenide immobilized in the perfluorinated solvent. 

SCHEME 85. Epoxidation of alkenes and alkenols with a perfluorinated quaternary ammonium salt of a polyoxometalate catalyst... 

Type II (slow homodimerization) Styrene, allylstannanes" Styrene, 2° allylic alcohols, vinyl dioxolanes, vinyl boronates Styrenes (large ortho substit.) " " 2° allylic alcohols, vinyl epoxides, unprotected 3° allylic alcohols, acrylates, acrylamides, acrylic acid, acrolein, vinyl ketones, vinyl boronates perfluorinated alkane olefins ... 

Alkaline hydrogen peroxide oxidation52 has been extended to higher perfluorinated alk-1-enes, perfluorinated cycloalkenes and certain alkenes with internal C = C bonds.52 57 A convenient reagent for the preparation of perfluoroalkene epoxides is sodium hypochlorite in a mixture with aqueous acetonitrile or another aprotic solvent. Several cis- and traw.s-perfluoroalkenes are oxidized to 32 with retention of configuration (Table 4).58-63... 

Perfluorobicyclo[4.4.0]dec-1 (6)-ene is readily converted into the corresponding epoxide by the same methodology as perfluorinated cycloalkenes75 using sodium hypochlorite. 

A series of functionalized alkenes has been subjected to selective epoxidation reactions. Oxidation of perfluorinated vinyl polyethers by bubbling oxygen through the liquid that contains a catalytic amount of a Lewis acid, e.g. antimony(V) fluoride, results in the formation of acid fluorides together with a smaller amount of C = C bond cleavage.76 Perfluorinated pentaaIkyI-2.3-dihydrofuran 38, an example of an unsaturated cyclic ether that is quite stable owing to perfluoroalkylation. is epoxidized by hypochlorite to the product 39 at 45 C.62... 

Epoxidation of various acyclic and cyclic perfluorinated dienes is accomplished with an aqueous hypohalogenitc and acetonitrile as a cosolvent. The reactivity of a C = C bond toward this reagent is enhanced by the presence of the trifluoromethyl group. This activating effect is nicely illustrated by perfluoro(l-methylcyclohexa-l,4-diene), which reacts smoothly with sodium hypochlorite to give a diepoxide 11 in 58% yield,73 while the oxidation system failed for perfluorocyclohexadienes. Nonconjugated perfluorocyclohepta-1,4-diene (12) is oxidized to the corresponding diepoxide 13 by sodium hypobromite.74... 

Under the conditions of an epoxidation reaction, perfluorinated ketenes behave as unsaturated ketones to give epoxides. Thus, perfluorinated ketene 11 is epoxidized by sodium hypochlorite to afford a stable a-lactone.198... 

Both the C — S single bond and C = C bond are oxidized in perfluorinated (pentafluorosul-fanyl)ethene by ozone or air under pressure.3 4 The reaction fails to give the epoxide (tide supra), but results in the insertion of oxygen into the C —S bond and the formation of the acid fluoride 25 probably by a rearrangement of the initially formed epoxide.214... 

The subject has been covered in various discussions [1,78-84] previously but a striking example in this group of reactions is the occurrence of nucleophilic epoxidation. These reactions emphasise the frequently stressed mirror-image relationship of the chemistry of alkenes and their perfluorinated analogues that we have emphasised earlier. Bleaching powder has proved to be... 

Several methods of condensation were used and each of them consisted of binding the perfluorinated chain to a molecule which exhibited two hydroxy groups or a forerunner of the diol (e.g. epoxide-alcohol or diepoxide). 

The second method [176] consists of hydrolizing the epoxide into the diol over a resin of sulfonated polystyrene. Cambon [177] performed the same reactions and showed that the longer the length of the perfluorinated chain, the greater the yields of the diols 60, 64 and 75% for C4F9, C6F13 and C8F17, respectively. 

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