Trifluoroacetyl fluoride

Formation from tetrafluoroethylene and oxygen may be explosive. It rearranges to trifluoroacetyl fluoride above its b.p., —63.5°C. 

FIGURE 4.64 P450-catalyzed oxidation of HCFC-123 to trifluoroacetyl fluoride and the structures of other HCFCs. 

George, C J. Y. Saison, J. L. Ponche, and P. Mirabel, Kinetics of Mass Transfer of Carbonyl Fluoride, Trifluoroacetyl Fluoride, and Trifluoroacetyl Chloride at the Air/Water Interface, J. Phys. Chem., 98, 10857-10862 (1994b). 

A tertiary radical can be formed by elimination during AF of ter/-butyl methyl and ethyl ethers thus, isolation of the respective perfluoro-/erf-butyl ethers, e.g. 1, occurs in only 36 and 42% yield.28 Significant quantities of perfluoro(2-methylpropane) (2) are also isolated. The longer alkyl chains (ethyl and larger) appear to be slightly less prone to scission than the methyl group. Apparently, carbonyl fluoride is more readily eliminated than trifluoroacetyl fluoride, a phenomenon observed during AF of esters.29 Elimination becomes most serious in the special class of polyethers called ortho esters, e.g. 3-5.30 Cyclic ortho esters, acetals and ketals are much less affected than acyclics. 

Perfluoroacy fluorides are obtained by electrochemical perfluorination of alkoxycarboxylic acids (nickel electrodes electrolyte anhyd HF voltage 6.5 V current density 0.01 — 0.02Acm 2 temperature 10"C) with yields of ca. 5 to 15%.42 Hence the products of the perfluorination of 3-mcthoxypropanoic acid are perfluoro(3-methoxypropanoyl fluoride) (7 %), pentafluoropropanoyl fluoride (19%), and trifluoroacetyl fluoride (52%). 

However, hexafluoroacetone is broken down almost completely87 over potassium tetrafluoro-cobaltate(III) at 250°C only traces of trifluoroacetyl fluoride are detected, the rest being carbon tetrafluoride and carbonyl difluoride. This shows that even if perfluoro ketones are formed in fluorination processes, they will break down, thus demonstrating that transition metal fluoride fluorination will not produce polyfluoro ketones. 

Photolysis of trifluoroacetyl fluoride and chloride results in cleavage of the carbon-halogen bond. The UV absorption band of CF3C(0)C1 starts at 315 nm, with a maximum at 260 nm, while that for CF3C(0)F is blue shifted97 this may suggest that photolysis of the chloride is more important in the troposphere, while photolysis of the fluoride occurs in the stratosphere. 

Bis[trifluoromethyl] lellurium difluoride and excess trifluoroacetic anhydride reacted at 20° to liberate gaseous trifluoroacetyl fluoride and produce bis[trifluoromethyl tellurium bis[trifluoroacetate]. In acetonitrile as reaction medium the exchange of fluoride for trifluoroacctale did not go to completion2. 

At the temperature of 180-200°C, perfluoropropylene oxide ejects diflu-orocarbene and forms N, trifluoroacetyl fluoride (general method for the preparation of difluorocarbene). Difluorocarbene adds to 1,2-dichlorodi-fluoroethylene and yields 0,1,2-dichloroperfluorocyclopropane [121]. 

Trifluoroacetyl fluoride and hexafluoroacctone have been made commercially by reaction of their pcrchloro analogs with hydrogen fluoride and chromium oxide catalysLs. 

Pyrolysis of the cyclic sulfite. 5-(penlafiuoroethyl)-l,3,2,4-dioxathiazole 2-oxide (5). however, gives a mixture of isocyanate, pentafluoropropanonitrile and trifluoroacetyl fluoride. 

Hexafluoropropene oxide (HFPO) [67] fragments exclusively by a reversible process at high temperature to give trifluoroacetyl fluoride and difluorocarbene only [68] (Figure 6.47). 

By reaction oftrimethyl(trifluoromethyl)silane with difluorophosgene or trifluoroacetyl fluoride in the presence of a compound possessing an active halogen, the O-anion thus generated reacts further to give the product of the substitution of this halogen, c.g. 19.Dl-53 58 6t> 104 105... 

The decomposition of hexafluoroacetone was investigated by Batey and Tren-with using a steel reaction vessel at 550-628 °C. Below 570 °C, hexafluoroethane and carbon monoxide are produced by a first-order process which appears to be unimolecular the rate coefficient is expressible as. A = 4 x 10 exp ( —50,900/Rr) sec . Above 570 °C, there is also first-order decomposition to trifluoroacetyl fluoride and (presumably) difluorocarbene which associates to perfluoroethylene and octafluoroisobutene Arrhenius parameters are., 4 = 1.6x10 sec , E = 79,100 cal.mole". Subsequent decomposition of the trifluoroacetyl fluoride... 

The decomposition of trifluoroacetyl fluoride is interesting in that it involves the rupture of the O-F bond. The products are tetrafluoromethane and carbon dioxide. Stewart and Cady found the reaction to be an essentially homogeneous, second-order process in a glass vessel coated with aluminium phosphate. For decomposition at 30-80 °C in the pressure range 1.5 to 3 torr, the rate coefficient was expressible as, A = 8.6x10 exp ( —11,200/lir) l.mole. sec. The following mechanism was proposed... 

Trifluoroacetic acid at 300-390 °C produces mainly carbon dioxide, difluoro-methyl trifluoroacetate, carbon monoxide and trifluoroacetyl fluoride. Blake and Pritchard propose that the decomposition proceeds through the elimination of hydrogen fluoride, followed by the formation of difluorocarbene which largely adds to trifluoroacetic acid to form the difluoromethyl ester. The kinetic order is about 0.5 and the overall activation energy for the formation of carbon dioxide and the difluoromethyl ester is about 45 kcal.mole" ... 

Perfluoroacetic anhydride decomposes at 216-320 °C to carbon monoxide, carbon dioxide and trifluoroacetyl fluoride above 320 °C tetrafluoroethylene and polytetrafluoroethylene are also produced. Corbett and Whittle observed an apparent kinetic order between 0.2 and 0.6, depending upon the reaction conditions. 

The thermal stability of polytetrafluoroethylene oxide and PTFE have been compared under the same conditions by Donato et al. [263] between 450 and 600°C. The decomposition rate has a maximum at 628°C for the oxide and at 568°C for PTFE. The activation energy for the first-order degradations are 98 kcal mole"1 between 8.5 and 85% for the oxide polymer and 85 kcal mole-1 between 523 and 571°C for PTFE. The rate of weight loss is less than 1.2% per min for both polymers below T = 550°C for the oxide and T = 590°C for PTFE. The oxide, however, loses weight below 390° C whereas PTFE does not. The main components of the volatile material are trifluoroacetyl fluoride, carbonyl fluoride and tetrafluoroethylene. An end-initiated thermal degradation with small zip length is proposed. 

HFPO (1) is an excellent source of difluorocarbene, superior to hexafluorocyclopro-pane because it decomposes at lower temperatures. It fragments into the carbene and trifluoroacetyl fluoride with a half-life of 169 min at 190°C, as determined by gas-phase NMR. In the absence of a carbene trap, hexafluorocyclopropane and the acyl fluoride are the main products of HFPO decomposition at 200°C. ... 

The reaction has been shown to be reversible. When trifluoroacetyl fluoride is heated at 130°C with difluorotris(trifluoromethyl)phosphorane (23), a lower temperature source of difluorocarbene, HFPO is formed. " ... 

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