Carbon fluorine generation

Pyrolysis of chlorodifluoromethane is a noncatalytic gas-phase reaction carried out in a flow reactor at atmospheric or sub atmospheric pressure yields can be as high as 95% at 590—900°C. The economics of monomer production is highly dependent on the yields of this process. A significant amount of hydrogen chloride waste product is generated during the formation of the carbon—fluorine bonds. 

The process is characterised by the electrofluorination of volatile organic substrates within the matrix of pores of a carbon anode immersed in molten KF 2HF as electrolyte (as in a mid-temperature fluorine generator cell), and depends on the phenomenon that the anodically charged porous carbon is not wetted by the electrolyte. The fluorination probably takes place at the three phase interface of organic vapour, solid carbon, and liquid electrolyte in close proximity to, or at the sites where fluorine is being evolved. 

The preparation of this substance consists in passing gaseous fluorine through a 2 per cent solution of sodium hydroxide.1,2,3 The product obtained is a mixture consisting of approximately 50 per cent OF2 and 50 per cent 02, together with small amounts of fluorides of carbon (from the fluorine generator). 

The reaction of CsF and fluorine with carbon dioxide generates the stable bis-hypofluorite CF2(OF)2. This remarkable, energetic compoimd is presumably formed via the intermediacy of the smallest acyl hypofluorite, FC(0)0F, which can itself be prepared by the photochemical fluorination of difluoroformyl peroxide, FC(0)00C(0)F. 

In contrast to the FVP synthesis of indenocorannulene (98) from phenyl-corannulene, the fluoro-substituted analogue 29 (X=F) turns out to be very efficient [126] (Scheme 28). Catalytic cyclization is initiated by reaction of a silyl cation with an aryl fluoride to generate a phenyl cation and, subsequently, Friedel-Crafts reaction to an intramolecular aryl coupling, flowed by deprotonation, to give 98, The enabling feature of this reaction is the exchange of carbon-fluorine for sihcon-fluoiine bond enthalpies. 

Figure 6.3 A typical, industrial fluorine-generating cell. The electrolysis occurs in a steel pot, which also serves as the negative electrode. The positive electrode is compacted carbon, and a gas separation skirt prevents reaction between the fluorine produced at this electrode and the hydrogen produced at the other. The electrolyte is a blend of one mole of KF per 2 moles of HF, which is liquid above 70 °C. The cell is maintained at 80-100 °C by using a cooling jacket when electrolysis is occurring, and by heating when it is not. The fluorine can be contained within the steel pot because it forms a thin layer of insoluble fluoride, which prevents the bulk of the metal being attacked.

In contrast, additions of fluorine and carbon to fluormated olefins are widely investigated The best known processes involve reactions of olefins with fluoride ion to generate carbanionic intermediates [203] that are trapped in situ by carbon-based electrophiles. 

The addition of perfluoroalkyl iodides to simple olefins has been quite successful under aqueous conditions to synthesize fluorinated hydrocarbons.119 In addition to carbon-based radicals, other radicals such as sulfur-based radicals, generated from RSH-type precursors (R = alkyl, acyl) with AIBN, also smoothly add to a-allylglycines protected at none, one, or both of the amino acid functions (NH2 and/or CO2H). Optimal results were obtained when both the unsaturated amino... 

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