Fluorine with hydrocarbons

A promising and extremely interesting new area of research is the synthesis of perfluoropolyethers by the reaction of elemental fluorine with hydrocarbon polyethers (34, 35). An extensive recent research program at the University of Texas at Austin has succeeded in establishing the generality of this approach. In the initial study, polyethylene oxide was reacted with elemental fluorine under... 

In view of the extremely exothermic nature of the reaction of elemental fluorine with hydrocarbons, inorganic hydrides, and so on, it might seem obvious that there should be little or no selectivity in the reactions of molecular or atomic fluorine. 

The threshold energy or activation energy for the reaction of atomic fluorine with hydrocarbons (79, 80) or hydrogen (81) is near zero, and these reactions, in fact, produce a similar set of HF molecules in excited vibrational states. In a variety of studies by various techniques, the reactions of F and F2 with such species are generally reported to have activation energies of... 

Indeed, there is apparently no selectivity in the reactions of fluorine with hydrocarbons at room temperature. However, at room temperature the reaction of fluorine with a molecule such as benzene initially may show a slight steric preference for reactions with the it system due only to the higher probability of a collision occurring there in preference to a proton site. 

Attempts to synthesize CF4 and C2F6 were made quite early nearly at the same time when elemental fluorine was isolated by Moissan in 1886 [1], Moissan attempted the reaction of fluorine with hydrocarbons, however, this resulted in violent explosions. In 1926, the first fluoride of carbon was obtained by P. Lebeau and A. Damien who succeeded in synthesis and isolation of CF4 by combustion of carbon in fluorine [2]. 

This reaction has often reached explosive proportions in the laboratory. Several methods were devised for controlling it between 1940 and 1965. For fluorination of hydrocarbons of low (1—6 carbon atoms) molecular weight at room temperature or below by these methods, yields as high as 80% of perfluorinated products were reported together with partially fluorinated species (9—11). However, fluorination reactions in that eta involving elemental fluorine with complex hydrocarbons at elevated temperatures led to appreciable cleavage of the carbon—carbon bonds and the yields invariably were only a few percent. 

Materials similar ia high temperature properties to the Du Pont material with better low temperature properties have been synthesized usiag direct fluofination. The first was produced by reaction of fluorine with iaexpensive hydrocarbon polyethers such as poly(ethylene oxide). In the simplest case, poly(ethylene oxide) is converted to the perfluoroethylene oxide polymer ... 

Carbonyl sulfonyl fluorides of the formula FC0(CF2) S02F have been prepared by electrochemical fluorination of hydrocarbon sultones (41,42). More commonly in a technology pioneered by Du Pont, perfluoroalkanecarbonyl sulfonyl fluorides are prepared by addition of SO to tetrafluoroethylene followed by isomerization with a tertiary amine such as triethylamine (43). 

Saturated hydrocarbons such as neopentane, notbomane, and cyclooctane have been converted to the corresponding perfluoro derivatives in 10-20% yield by gas-phase reaction with fluorine gas diluted with helium at —78°C. Simple ethers can be completely fluorinated under similar conditions. Crown polyethers can be fluorinated by passing an Fa/He stream over a solid mixture of sodium fluoride and the crown ether. Liquid-phase fluorination of hydrocarbons has also been observed, but the reaction is believed to be ionic, rather than radical, in character. A variety of milder fluorination agents have been developed for synthetic purposes and will be discussed in Chapter 6 of Part B. 

Fluorinated organic compounds often may seem abnormal m comparison with hydrocarbon or other halocarbon compounds, but their behavior usually is quite intelhgible and predictable when the effects of fluonnation on molecular properties are understood This chapter discusses these charactenstic effects... 

Electrochemical fluorination is an important technique for obtaining saturated perfluoroheterocycles. Incorporation of a partially fluorinated group into hydrocarbon ethers enhances their stability toward fluorination with CoF3 and this approach has been extended toward electrochemical fluorination [89MI1 90JFC(49)409]. Adduct (6) obtained by free radical... 

The reactions of fluorine atoms with hydrocarbons are similar to those of active nitrogen in that they provide an essentially universal response. Fluorine atoms abstract H atoms from hydrocarbons at near-collisional reaction rates. Reactions with fluorine are highly exothermic, forming strong H—F (=570 kJ mol-1) and C—F (=485 kJ mol-1) bonds while breaking much weaker C—H (=414 kJ mor1) and C—C (=368 kJ mol-1) bonds. The hydrogen abstraction reaction... 

Peduoropolyethers, which constitute special class of fluoropolymer, are useful as lubricants,1 elastomers,2 and heat-transfer fluids under demanding conditions. Several commerical products are available, which are generally prepared by ring-opening polymerization of hexafluoropropylene oxide or by the random copolymerization oftetrafluoroethylene and hexafluoropropylene with oxygen under ultraviolet irradiation.3 Direct fluorination of hydrocarbon ethers has been reported4 but must be done very slowly under carefully controlled... 

The Lagow group first entered the perfluoropolyethers field in 1977, by reacting fluorine with inexpensive hydrocarbon polyethers to prepare perfluoropolyethers. In the simplest case (Figure 14.3) poly (ethylene oxide) is converted to perfluoroethylene oxide polymer, a simple reaction chemistry that we first reported in the literature.27 As will be seen later, this direct fluorination technology as well as many new patents from Exfluor Research Corporation have been non-exclusively licensed to the 3M Corporation by the Lagow research group.3 "39... 

We discovered another synthetic technique that involves the conversion by direct fluorination of hydrocarbon polyesters to perfluoropolyesters followed by treatment with sulfur tetrafluoride to produce new perfluoropolyethers.42 The first paper in this area ofreasearch reported that conversion of poly(2,2-dimethyl-1,3-propylene succinate) and poly( 1,4-butylene adipate) by using the direct fluorination to produce novel branched and linear perfluoropolyethers, respectively. The structures are shown in Figure 14.6. The second paper concerns the application of the direct fluorination technology base directed toward oligomers, diacids, diesters, and surfactants.43... 

In contrast to saturated hydrocarbons, the unsaturated hydrocarbons react with atomic fluorine by two pathways, i.e. (atomic fluorine addition at >C=C< double bond and hydrogen substitution by fluorine atoms. The reaction of fluorine with aromatic hydrocarbons proceeds with the formation of F-derivatives and hydrogen atoms break off ... 

The extensive studies of the behavior of mixed monolayers or bilayers of di-acetylenic lipids and other amphiphiles parallel to some degree the studies of dienoyl-substituted amphiphiles. Since the dienoyl lipids do not contain a rigid diacetylenic group in the middle of the hydrophobic chains, they tend to be miscible with other lipids over a wide range of temperatures and compositions. In order to decrease the lipid miscibility of certain dienoyl amphiphiles, Ringsdorf and coworkers utilized the well-known insolubility of hydrocarbons and fluorocarbons. Thus two amphiphiles were prepared, one with hydrocarbon chains and the other with fluorocarbon chains, in order to reduce their ability to mix with one another in the bilayer. Of course it is necessary to demonstrate that the lipids form a mixed lipid bilayer rather than independent structures. Elbert et al. used freeze fracture electron microscopy to demonstrate that a molar mixture of 95% DM PC and 5% of a fluorinated amphiphile formed phase-separated mixed bilayers [39]. Electron micrographs showed extensive regions of the ripple phase (Pb phase) of the DM PC and occasional smooth patches that were attributed to the fluorinated lipid. In some instances it is possible to... 

Like perfluorinated polymers, perfluorinated fluids are both chemically and thermally very stable. Originally developed during the Manhattan Project their commercial application dates from the 1960s. There are two major production methods, cobalt(III) fluoride fluorination of hydrocarbons and electrochemical fluorination. The first route involves the fluorination of a stirred or fluidized bed of cobalt(II) fluoride to cobalt(III) fluoride with elemental fluorine at... 

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