Perfluoro carbonyl fluorides

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. 

In the following procedures, chlorine monofluoride is used as the source of positive chlorine to convert carbonyl fluoride in the presence of cesium fluoride as well as perfluoro-tm-butyl alcohol into the corresponding hypochlorites, because it is much more convenient to handle than the unstable chlorine monoxide. 

The hrst report on the synthesis of fluorinated oxazetidine was published in 1955 by Barr and Haszeldine. They isolated perfluoro-2-methyloxazetidine (79) from reaction of tetrafluoroethylene with trifluoronitrosomethane, along with its polymer. This reaction proceeds even at room temperature, but higher temperature (about 100°C) favors formation of 79. The compound is inert to aqueous base or acid and UV light, but its pyrolysis at 550°C yields equimolar amounts of carbonyl fluoride and perfluoro-2-azapropene (Scheme 2.37). 

Thermal decomposition products of PTFE (up to 500 C) are mainly the monomer, tetrafluoroethylene and some perfluoro compounds (such as, perfluoroisobutylene). Between 500 °C to 800 °C, the decomposition product is mainly carbonyl fluoride, which can hydrolyse easily (to produce toxic and corrosive hydrofluoric acid and carbon dioxide). 

Perfluoro-(2,5-dimethyl-l-oxa-2,5-diazacyclopentane) (57) decomposes slowly at room temperature in the absence of light to give 1 mol. equiv. of perfluoro-2-azapropene and a quantitative yield of a gum possessing an elemental analysis and F n.m.r. spectral characteristics consistent with the polymer [N(CF3)-0-CF2]n presumably homolytlc ring fission at an N—O bond is followed by j3-scission of the resultant biradical (59) [see Scheme 42 . (CF3)2N-0-N(CF3)2 + heat (CFs)2N-0 + (CFs)2N ->-(CF3)2N-N(CF3)2]. Flow pyrolysis of the diazacyclo-pentane at 150—200 °C and ca. 1 mmHg pressure in platinum yields trifluoronitro-somethane, carbonyl fluoride, perfluoro-2-azaiM opene, and traces of a yellow gas that possesses i.r. spectral characteristics identical with those reported for a... 

CFaiN RfCOF + hvRr + COF Rr + CFjiN- -> RpN CFj. Extension of this to the bis-acyl fluorides FOC (CF2)3-COF and FOC-(CF2>4-COF, however, gives low yields of perfluoro-(Af-methylpyirolid-2-one) (15 %) and perfluoro-(A -methylplperidin-2-one) ca. 10%), respectively, instead of the imines CFg N-(CF2) N CF2 (a = 3 or 4), presumably via the sequence of events shown in Scheme 39. Fluoride-initiated (CsF) reactions between the formaldazine and these, and other, acyl fluorides leads to novel heterocyclic carbonyl compounds which suffer decarbonylation when irradiated with u.v. light (see Scheme 40). Carbonyl fluoride and oxalyl fluoride react with the formaldazine in the presence of caesium fluoride to yield the acylic and cyclic product (57) (70%) and (58) (ca. 55%), respectively the latter fragments to trifluoromethyl isocyanate when exposed to u.v. light. 

The development of a new high-performance fluoro-elastomer based on perfluoromethyl perfluorovinyl ether has already been mentioned (see ref. 305 and p. 26). Preparation of the ether involves ring-opening of perfluoro-propene oxide with trifluoromethoxide ion generated in situ from carbonyl fluoride. Similarly, perfluorobut-3-enyl perfluorovinyl ether (58) can be synthesized from perfluoropropene oxide and perfluoroglutaryl difluoride > ... 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

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. 

Perfluoro ketones and perfluoro a-diketones, with a trifluoromethyl group in the -position to the carbonyl, cyclize in the presence of antimony(V) fluoride to give furan derivatives, as reviewed by Krcspan and Petrov.4 Perfluoro(4-methylpentan-2-one) (1) rearranges to per-fluoro(2,4-dimethyltetrahydrofuran) (2) in 84% yield, when heated in the presence of anti-mony(V) fluoride.5... 

In perfluoro a-diketone 7, which lacks a trifluoromethyl group /i to the carbonyl in the 2-position. it is the carbonyl in the 3-position that participates in the cyclization to form per-fluoro(2-acctyltetrahydrofuran) (8), when 7 is heated at 150 C in the presence of antimony(V) fluoride.5 Perfluoro(2-methyltetrahydropyran-3-one) also rearranges to furan derivative 8 in high yield when heated at 100 C in the presence of antimony(V) fluoride for 20 hours.5... 

The mechanism for the cyclization of these perfluoro ketones, proposed by German and coworkers5 and discussed in the review by Krcspan and Petrov.4 involves initial activation of the carbonyl with antimony V) fluoride and a 1.4-fluorine shift from the /1-trifluoromethyl group. The resultant difluoromethylene carbocation then cyclizes with the carbonyl oxygen to give the tetrahydrofuran. 

The reaction of trimethyl(perfluorophenyl)silanc with carbonyl centers occurs under mild reaction conditions, similar to those used for trimethyl(trifluoromethyl)silane. Acetyl fluoride in acetonitrile in the presence of catalytic amounts of potassium fluoride gives l-fluoro-l-(penta-fluoropheny )ethyl acetate (12) in 65% yield. When the bifunctional acid fluoride perfluoro-glutaryl difluoride reacts with trimethyl(perfluorophcnyl)silane in acetonitrile in the presence of potassium fluoride, the perfluorinated diketone perfluoro(l,5-diphenylpcntane-l,5-dione)... 

Synthesis of Perfluoro(4-Carbomethoxybutyl Vinyl Ether). The parent ester was prepared from perfluoroglutaryl fluoride and hexa-fluoropropylene oxide by the reactions shown in Figure 2. This ester had a boiling point of 146 °C, and showed characteristic vinyl ether infrared absorptions at 5.42/, 5.55/. (carbonyl group), and 10.0/. (-OCH3 group). 

Hydrogen fluoride opens oxirane 16 under very vigorous conditions to give perfluoro-t-butanol (17). However, Lewis acids isomerize perfluorooxrranes to carbonyl compounds, as illustrated by the transformation of perfluorocyclopentene oxide (18) into perfluorocyclopentanone (19) over alumina. ... 

A number of perfluoromethacrylic acid derivatives have been obtained by the elimination of alkyl fluoride from alkoxy-derivativesof perfluoro-(2-methyl propene) and related compounds for details describing the preparation and reactions of carbonyl derivatives of fluorinated olefins see Chapter 2, pp. 62—77. Fluoroalkyl acrylates, CH2 CH-C02Rf [Rf = (CF3)2CF, (CF3)(CF2C1)-CF etc.], have been... 

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