Perfluorobenzenes

Michaels C A, Lin Z, Mullin A S, Tapalian H C and Flynn G W 1997 Translational and rotational excitation of the C02(00°0) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene evidence for impulsive collisions accompanied by large energy transfers J. Chem. Phys. 106 7055-71... 

Fluorine replacement m perfluorobenzene can be achieved in good yields and high selectivity when heavy metal thiolates are used as nucleophiles [29, 30, 31, 32] (equations 19-21). 

Perfluorobenzene undergoes Sf Ar reactions readily with dimethylarmne, aniline, N methylaniline [AS], piperidine, A/-tnmethylsilyliminotnmcthylphos-phorane [69], and bthinm aniUde [70], but the reactions are often accompanied by sigmficant amounts of di- or polysubstitubon However, with the lithium salt of A -tnmethylsilylanilme, only one fluorine atom in pcrfluorobenzeneis replaced [71] (equation 36)... 

A new thermal preparation ot fluorinated species is copyrolysis Copyrolysis of fluorinated compounds like perfluorobenzene, fluorinated aromatic anhydndes, and fluorinated heteroaromatics with tetrafluoroethylene or other fluonnated olefins is a useful method of preparing fluorinated olefins [88 89], functionalized fluoroaromatics [90 91 92, 93, 94, 95], fluonnated benzocycloalkanes [80, 96, 97, 98, 99, 700], fluorinated heterocycles [80, 93, 101, 102, 103], and fluonnated polycyclic compounds [104] (equations 19 and 20)... 

That charge-transfer effects are not involved follows from the fact that the rate of triplet decay in perfluorobenzene is larger than that in benzene. If the benzophenone triplet were to act as acceptor and the benzene derivative as donor in a charge-transfer complex, the substitution of perfluorobenzene for benzene should render this type of process much less probable due to the strongly electron-withdrawing character of the fluorine atoms. 

Production of pol3rmers through poly-substitution or poly-condensation reactions would be expected to be a natural extension of simple PTC chemistry. To a large extent this is true, but as Percec has shown. Chapter 9, the ability to use two-phase systems for these reactions has enormously extended the chemist s ability to control the structure of the polymers produced. Kellman and co-workers (Chapter 11) have also extensively studied poly-substitution displacements on perfluorobenzene substrate to produce unique polymers. 

Preparation of Bis-1, 4-(disubstituted)perfluorobenzene and Bis-4,4 (disubstituted)perfluorobiphenyl. To a solution of 4.85 mmole of HFB or PFB and 9.65 mmole of 4-isopropylphenol or 4- -butylthiophenol in 20 ml of solvent was added 20.8 mmole of K2CO3 and 1.34 mmole of 18-crown-6 ether. The magnetically stirred heterogeneous mixture was heated to reflux or to 80 with DMAc and maintained under dry N2 for 4-24 hr. For reactions with... 

In any event, 02SbFg and 02AsFg act as very effective one-electron oxidants with regard to aromatic amines, nitrogen- and sulfur-containing heterocyclic compounds (Dinnocenzo and Banach 1986, 1988,1989) as well as to perfluorobenzene, benzotrifiuoride, and perfluoronaphthalene (Richardson et al. 1986). The oxidation proceeds in Freon (CHCIF2) at temperatures from -115 to -145°C, and the formation of the organic cation-radicals has been firmly established. 

The chlorination of CeFjSSCeFg in an inert solvent furnishes the perfluorobenzene sulfenyl chloride 137) ... 

Cesium tetrafluorocobaltate(III) behaves quite differently 12,14 at 250CC it reacts with benzene to give some diene 13 (26%) and several aromatics [fluorobenzene (32%), pentafluorobenzene (9%), perfluorobenzene (4%), and others in lesser amounts]. 

Conjugated perfluorocyclohepta-1,3-dicne gives by the same epoxidation a mixture of monoepoxide 14 and diepoxycyclohcptane 15.74 Dichlorinated perfluorocyclohexa-1,3-diene 16 is selectively epoxidized to 17 by trifluoroperacetic acid in 22% yield.107 A bicyclic diene, synthesized from perfluorobenzene and 1,2-dichloroethene, is monoepoxidized to give 18 by the same oxidizing agent in 20% yield.108... 

A mixture of perfluorobenzene (0.30 mL), H20, d = 1.403. 0 26 mL), and McCN (10 mL) was heated at 140 C in a fused glass ampule for 10 h. The mixture was then filtered, the filtrate was poured into 0.1 M NaflSO, (100 mL), acidified with H2S04, and extracted with Et20. The ethereal solution was dried ( CaCf) and the solvent was removed in vacuo to give the crude product that was purified by TLC (CHC13) ... 

Hexafluorinated Dewar benzene oxide 1 is prepared in 7% yield by the irradiation of hexafluorobenzene in the presence of oxygen,12 research undertaken in the hope of gaining access to the valence isomers perfluorobenzene oxide (3) and perfluorooxepin (4). Even gentle heating of 1 (50 C, 7d), however, leads only to perfluorocyclohexa-2,4-dien-l-one (2). Note that cyclohexadienone 2 is also the only product obtained from the pyrolysis of per-fluorobicyclo[2.2.0]hex-5-en-2-otie hydrate (see Section 5..3.2.1.). 

Takenaka and Lemal subsequently undertook an extensive study of the perfluorobenzene oxide (3)/perfluorooxepin (4) system.13,14 After considerable effort, benzene oxide 3 was successfully prepared by ozonization of tricyclic precursor 5 and photolytic decomposition of the resultant ozonides. Oxepin 4 was not observed directly, but was estimated by NMR computer simulations to be present in small proportion (3 %) at 55"C. The principal reaction of 3 is its rearrangement to cyclohexadienone 2, which occurs at room temperature in polar solvents, by heating in nonpolar solvents, or in the presence of Lewis acids. Photolysis of 3 with benzophenone as triplet sensitizer also produces 2. Furthermore, attempts to trap the oxepin, for example by treatment with bromine in the dark, result in cyclohexadienone 2. 

There is only a small number of reactions known whereby a perfluorinated aromatic compound is formed by thermal disproportionation perfluorotoluene is disproportionated at temperatures above 500 C to form perfluorobenzene and perfluoroxylcnc.42 44 The perfluoroxylene itself can be dismutated at 550°C to yield perfluorotoluene and 1,2.4- and 1,3,5-perfluoro-... 

Electrochemical reduction, though a little-used method, defluorinates aryl fluorides to the corresponding hydrogeno derivatives. 1,3-Difluorobenz.ene is reduced at a mercury cathode to give a mixture of fluorobenzene and benzene,54 while the reduction of perfluorobenzene at an... 

Zirconocene complexed with activated magnesium159 reduces perfluorobenzene to 1.2,4,5-tet-rafluorobenzene (4) (for the procedure159 see Section 2.1.1.1.). The quantitative generation of pentafluorobenzene is observed by l9F NMR spectroscopy prior to the formation of 4 and deuterium incorporation when performed in tetrahydrofuran-r/8. Unlike more reactive substrates. perfluorobenzene does not exhibit any reactivity toward activated magnesium in the absence of zirconocene.159... 

Perfluorocycloalkanes are aromatized forming the corresponding perfluoroaromatics (Table 7), e.g. perfluorocyclohexane was transformed to perfluorobenzene. 

If chlorine or hydrogen are present in the starting compounds, additional polyaromatics are obtained and, in the case of hydrogen, a simultaneous elimination of hydrogen fluoride is observed, e.g. formation of perfluorobenzene (1) and pentafluorobenzene (2).121... 

Pentafluorophenol, when heated in a strong solution of aqueous potassium hydroxide, gives perfluorobenzene-l,3-diol (3).34... 

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