Vapor-phase fluorination

Heterogeneous vapor-phase fluorination of a chlorocarbon or chlorohydrocarbon with HP over a supported metal catalyst is an alternative to the hquid phase process. Salts of chromium, nickel, cobalt or iron on an A1P. support are considered viable catalysts in pellet or fluidized powder form. This process can be used to manufacture CPC-11 and CPC-12, but is hampered by the formation of over-fluorinated by-products with Httle to no commercial value. The most effective appHcation for vapor-phase fluorination is where all the halogens are to be replaced by fluorine, as in manufacture of 3,3,3-trifluoropropene [677-21 ] (14) for use in polyfluorosiHcones. 

Heterogeneous reaction, 25 728-729 Heterogeneous reactors, 27 568 Heterogeneous stereospecific polymerization, 20 410-411 Heterogeneous vapor-phase fluorination, 22 863... 

Fukuhara and Bigelow reported two significant vapor-phase fluorinations. Acetone afforded hexafluoroacetone. 1-fluoroacetone, trifluoroacctyl fluoride, oxalyl difluoride, fluorocar-... 

Fluorination of benzene with manganese(III) fluoride at 300"C gives62 a mixture of at least 18 compounds, some of which are common with those from the cobalt(III) fluoride vapor-phase fluorination, but many are unsaturated, the major ones being 1 //,4//-octafluorocyclo-hexene (8, 16%) and 1 //,2//,3f/-hcptafluorocyclohexene (9, 8%). 

Vapor-phase fluorinations are very attractive industrially. Reactions can be conducted continuously at modest pressures (10 atm), with appropriate recycle streams as necessary. However, since an excess of hydrogen fluoride is usually employed, downstream purification involving CFC-HF azeotropes may cause difficulties. 

In an alternative approach, volatile organic substrates were fluorinated in the gas phase on contact with a copper mesh. This work was pioneered by Fredenhagen and Cadenbach in the early 1930s [5] and then continued by Bigelow and Fukuhara [6] as a part of the Manhattan Project (Figure 2.1). Vapor phase fluorination finally enabled the preparation of (relatively) defined polyfluorination products from aliphatic hydrocarbons, benzene, or acetone. 

Vapor-phase fluorination using hydrogen fluoride and, for example, a chromium or aluminum oxide/fluoride catalyst (i.e., the procedures used for manufacture of fluorochloroalkanes16) has also been applied (Eq. 7).17... 

Bauer CF, Andren AW. 1985. Emissions of vapor-phase fluorine and ammonia from the Columbia coal-fired power plant. Environ Sci Technol 19 1099-1103. 

Inorganic fluorides such as cobaltic fluoride have also commonly been used for the vapor-phase fluorination of organic compounds, e.g.,... 

Reactions of replacement of SMe [79], trichloromethyl [97] or trifluoromethyl groups represent effective approaches for modifications of trifluoromethyl containing 1,3,5-triazines. Direct vapor-phase fluorination of tris-(trifluoromethyl)-s-triazine 74 has been studied and was found that the perfluoroalkyl groups of 74 were progressively replaced by fluorine to give mixture of 2,4-difluoro-6-trifluoromethyl-s-triazine 156 and 2,4-bis-(trifluoromethyl)-6-fluoro-s-triazine 157 (Scheme 66) [98]. Photoirradiation of tris-(trifluoromethyl)-i-triazine in cyclohexane leads to a mixture of adduct 158 and dihydrocompound 159 (Scheme 66) [99]. 

The halocarbon gases such as pentafluoroethane (HFC-125), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) and 2H-heptafluoropropane (HFC-227ea) are manufactured by either vapor phase or liquid phase catalytic fluorination pathways in continuous mode of operation. The successful catalysts for vapor phase fluorination processes are usually chromium (111) oxide (preactivated with HF) and/or aluminum compoimds doped with Lewis acids such as Co, Ni or Zn. Similarly, antimony (V) chlorofluoride (SbCl Fp/HF is preferred as catalyst in liquid phase fluorination of chlorinated starting compounds. Some of the methods practiced for obtaining individual halocarbons are listed here. 

As stated in Section 11.2.4, HFC-125 is industrially produced by heterogeneous continuous vapor phase fluorination of tetrachloroethylene over chromium oxyfluoride and allied catalysts at elevated temperature [72], Chromium oxyfluoride is generated by treating chromium (III) oxide with AHF. Cr... 

In the first step, chloroform is converted into chlorodifluoromethane by catalytic vapor phase fluorination reaction with anhydrous hydrogen fluoride and in the second step, chlorodifluoromethane is subjected to a noncatalytic gas phase pyrolysis at temperature 590-900°C and at atmospheric or subat-mospheric pressures to obtain tetrafluoroethylene in about 95% yield. 

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