Fluorides, acyl oxidation

The oxidation may be carried out with an inert solvent thermally (35), with a sensitizer such as bromine (36), with uv radiation (37), or over a suitable catalyst (38). Principal by-products of all these oxidation processes are the acyl fluoride products derived from oxidative cleavage of the perfluoroaLkene (eq. 

Preparation. The preparation of tetrafluoroethylene has been described previously. Perfluorovinyl ethers (4—7) are prepared by the following steps. Hexafluoropropylene [116-15-4] (HEP) is oxidized to an epoxide HEPO [428-59-1] (5) which, on reaction with perfluorinated acyl fluorides, gives an alkoxyacyl fluoride. 

The perchloryl fluoride [7616-94-6] FCIO, the acyl fluoride of perchloric acid, is a stable compound. Normally a gas having a melting poiat of —147.7° C and a boiling poiat of —46.7°C, it can be prepared by electrolysis of a saturated solution of sodium perchlorate ia anhydrous hydrofluoric acid. Some of its uses are as an effective fluorinating agent, as an oxidant ia rocket fuels, and as a gaseous dielectric for transformers (69). 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Besides acetophenone, this reaction was also applied to p-chloro- andp-methoxyacetophenone, and even to an aliphatic ketone, acetone (although the yield was stated to be only half as large as that obtained from mesityl oxide, i.e., less than 30%, Dorofeenko and co-workers reported a 45% yield of 2,4,6-trimethylpyrylium perchlorate from acetone, acetic anhydride, and perchloric acid), and is the standard method for preparing pyrylium salts with identical substituents in positions 2 and 4. The acylating agent may be an anhydride in the presence of anhydrous or hydrated ferric chloride, or of boron fluoride, or the acid chloride with ferric chloride.Schneider and co-workers ... 

Recently, acylsilanes have been utilized as useful intermediates in organic synthesis [57], For example, treatment of acylsilanes with the fluoride ion generates the corresponding acyl anions which react with electrophiles. On the other hand, by using the electrochemical method, acylsilanes serve as acyl cation equivalents because nucleophiles are introduced at the carbonyl carbon. Chemical oxidation of acylsilanes with hydrogen peroxide which affords the corresponding carboxylic acids has been reported [58], However, the anodic oxidation provides a versatile method for the introduction of various nucleophiles... 

Pd salts and CC14 in the presence of K2CO3,362 or (3) RuH PPluV363 Primary alcohols RCH2OH can be directly oxidized to acyl fluorides RCOF with cesium fluoroxysulfate.364 Lactones can be prepared by oxidizing diols in which at least one OH is primary.365... 

Substituted benzylic alcohols and aromatic aldehydes can be oxidized efficiently to substituted benzaldehydes and benzoic acids, respectively, with F-Teda BF4.101,102 The conversion proceeds via the acid fluoride which enables aldehydes to function as acylating agents in a one-pot procedure. 

Synthetic methods have limited the preparation of saturated perfluoropolyethers. The most successful perfluoropolyether synthetic chemistry has been DuPont s anionic polymerization of perfluoroepoxides, particularly hexafluoro-propylene oxide and tetrafluoroethylene oxide (39). Their synthetic procedure is a three-step scheme for saturated perfluoropolyether production involving oxidation of perfluoroolefins to perfluoroepoxides, anionic polymerization to acyl fluoride terminated perfluoropolyethers, and conversion of acyl fluoride end groups to unreactive end groups by decarboxylation reactions or chaincoupling photolytic decarboxylate reactions. 

The chemistry of perfluoro(2-methyloxirane) (hexafluoropropylene oxide) has been comprehensively reviewed, including its isomerization to hexafluoroacetone or propionyl fluoride.28 The rearrangements of polyfluorooxiranes with Lewis acids have been reviewed by Krespan and Petrov.29 Fluoride ion and other Lewis bases rearrange tetrafluorooxirane and monosubstituted perfluorooxiranes to acyl fluorides, and symmetrically disubstituted perfluorooxiranes to ketones (Scheme 9).30... 

Being an oxidizing agent, CsS04F was used to transform primary alcohols as well as aromatic aldehydes to the corresponding acyl fluorides (equation 180)309. Various N-substituted uracils and barbituric acid derivatives form, in contact with this reagent, 5-fluoro-6-alkoxyuracils accompanied by some 5,5-difluoro derivatives (equation 181)310. 

Cyclization can also occur through halide displacement after initial metalation. For example, acylation of o-lithiofluorobenzenetricarbonylchromium with y-butyrolactone at 25 °C for 24 h is followed by spontaneous fluoride displacement to give complex 36. Oxidation with excess iodine liberates the lactone in 48 % overall yield (Scheme 15) [20]. 

The preparation of the fiuoroalkyl perfluorovinyl ethers, e.g. II, starts from the corresponding acyl fluorides which are decarboxylated by heating up to 300 C in the presence of activators, such as zinc(II) oxide and silica gel, or in the presence of salt-forming agents of the sodium carbonate type." ... 

In similar way pcrfluoroclhanecan be produced from perfluoropropanoyl fluoride. This process has also been applied " to high molecular weight molecules and to acyl fluorides derived from polymcrizalion of tetralluoroethylenc oxide. 

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