Preparation perfluoroalkenes

Ultraviolet irradiation of perfluorocarbons in the presence of (C5Me5)2Fe and Li03SCF3 as a fluoride acceptor provides an exceptionally mild system [80] to prepare perfluoroalkenes from perfluoroalkanes and the chemistry can be made catalytic with respect to iron by using zinc to reduce [(C5Me5)2Fe]+(Scheme 6). 

In contrast to carbon-fluorine activation reactions of alkenes or aromatics, the conversion of fluorinated alkanes and cycloalkanes to alkenes and aromatics is well documented. For instance, Grabtree and Burdeniuc discovered metal-based photochemical systems which are useful for the defluorination of perfluorocarbons. " Irradiation of per-fluoromethylcyclohexane or perfluoroisopentane in the presence of decamethylferrocene and LiOTf provides a route to prepare perfluoroalkenes (Scheme 14). These reactions conform to the general equation (vi)a (Scheme 4) with... 

The reaction of perfluoroalkenes with alkaline hydrogen peroxide is a good general method for the preparation of the corresponding epoxides with the exception of the most reactive of the series, TFEO (eq. 6). 

Reaction of perfluoroaLkenes and hypochlorites has been shown to be a general synthesis of perfluoroepoxides (32) (eq. 7). This appears to be the method of choice for the preparation of epoxides from internal fluoroalkenes (38). Excellent yields of HFPO from hexafluoropropylene and sodium hypochlorite using phase-transfer conditions are claimed (34). 

A convenient agent for the preparation of perfluoroalkene epoxides is sodium hypochlorite in a mixture with aqueous acetonitrile or another aprotic solvent cis-and tr<3 5-perfluoroalkenes are oxidized with retention of configuration [9, 10, 11, 12 13] (equation 7, Table 1)... 

Due to their industrial applications, tetrafluorooxirane and perfluoro(2-methyloxirane) are the most frequently mentioned epoxides in the literature, and a number of methods have been developed for their synthesis. Although the epoxidation of perfluoroalkenes with hydrogen peroxide in alkaline media appears to be the most general method for the synthesis of per-fluorinated epoxides, it cannot be used in the preparation of tetrafluorooxirane due to the hydrolytic decomposition of the alkene. 

Normally, the dehydrofluorination process is a 1,2-elimination, but an unusual 1,4-elimination of hydrogen fluoride is also observed in the formation of 15.38 However, the elimination is not concerted, but proceeds via an enolate in a multistep reaction. A second example involves the preparation of polyfluoroalkene(phenyl)diazenes 16a and b.39-40 Interestingly, for the derivative with Rf = C3F7, a 1,2-climination to the perfluoroalkene(phcnyl)hydrazone 16c is observed with phenylhydrazine as base rather than the 1,4-elimination to 16a and b found with triethylaminc.39... 

Preparation of nitronitroso dimers from a variety of straight chain alkenes has been patented. " The reactions of nitric oxide with alkenes are extremely complex (e.g. isobutylene) and are rarely usefiil. Perfluoroalkenes add nitric oxide at room temperature in the da tetraflucMoethylene gives ONCF2CF2NO (68%) the reaction with perfluoropropene is more complex. ... 

Insertion of alkynes and perfluoroalkenes into the Re-H bond of (31) allows the preparation of /3-hydrogen-substituted vinyl and fluoroalkyl derivatives, Re C(CF3)=CH(CF3) (CO)5 and Re(CF2CHF2)(CO)s. 

Several perfluoroalkene derivatives have been made and used successfully in synthesis. Trifluorovinylmagnesium bromide and the lithium derivative may be obtained [39 1] from bromotrifluoroethene but preparation from HFC 134a, which involves metallation of trifluoroethene generated in situ, is now the more accessible route (see Section lA). However, direct metallation of fluorinated alkenes and fluorinated cycloalkenes has also been reported [26, 28] (Figure 10.9). 

Calcium atoms are particularly reactive with organohalides, and the preparation of several RCaX species by codeposition at — 196°C of RX with Ca atoms on macroscale has been reported. Similarly, deposition with perfluoroalkenes gave high yields of oxidative-addition product. ... 

Silver fluoride adds to electron deficient alkenes. The reaction of l,l-dichloro-2,2-dicyanoethylene with AgF, for example, does not produce the expected 1,1-difluoro derivative. Instead, this reaction yields the silver salt of trifluoromethylmalononitrile, presumably through the 1,1-difluoro derivative by subsequent addition of AgF to the strongly electrophilic double bond. Perfluo-roalkylsilver compounds can be prepared by the addition of AgF to perfluoroalkenes. The fluorination of tetrabromo-2,3-diaza-1,3-butadiene affords the tetrafluoro derivative. 

Oleophilic/oleophobic fluorinated surfactants without a hydrophile, designed for use in hydrocarbon systems, are in a structural sense also nonionic fluorinated surfactants (see Section 1.8) for example, the semifluorinated alkanes [266-270], block polyethylene-polypropylene glycol ethers prepared with perfluoroalkene trimers [271], surfactants featuring an oligo(hexafluoropropene oxide) chain [272], and carboxamides and sulfonamides derived from A -(perfluorooctanesul-fonyl)piperazine [273]. 

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