Ethers fluonnation

Partly Fluonnated Ether Perfluonnaicd Ether Yield (%) Hy-produci Yield m Ref... 

Replacement of hydrogen with halogen can be carried out in the alpha position of fluonnated ethers, amines, aldehydes, or nitriles In 2,2,3,4,4,4 hexafluoro-butyl methyl ether, chlorination occurs predominantly at the methyl, however, bromination occurs mostly at the internal position of the fluorobutyl group 13[Pg.372]

The reactions of some fluonnated ethers may result in the elimination of alkyl fluorides In the case of 2-methoxyperfluoro-2-butene, treatment with antimony pentafluonde gives perfluoro-3-buten-2-one and methylfluoride [7071 By reacting 2-chloro-l,l,2-trifluorodiethyl ether with boron trifluonde etherate or with aluminum chloride, chlorofluoroacetyl fluonde can be obtained with the elimination of ethyl fluonde [108] (equations 76 and 77)... 

Selective fluonnation in polar solvents has proved commercially successful in the synthesis of 5 fluorouracil and its pyrimidine relatives, an extensive subject that will be discussed in another section Selective fluonnation of enolates [47], enols [48], and silyl enol ethers [49] resulted in preparation of a/phn-fluoro ketones, fieto-diketones, heta-ketoesters, and aldehydes The reactions of fluorine with these functionalities is most probably an addition to the ene followed by elimination of fluonde ion or hydrogen fluoride rather than a simple substitution In a similar vein, selective fluonnation of pyridmes to give 2-fluoropyridines was shown to proceed through pyridine difluondes [50]... 

Electrochemical fluonnation ot N,N dialkylammo-substituted carboxylic acids as their methyl esters produces the analogous perfluonnated tertiary amine carboxylic acid derivatives in 18-30% yields as well as cyclic amine ethers [JOO]... 

Systems usually fluonnated by electropositive fluorine reagents include acti-vated alkenes (enol ethers, enol acetates, silyl enol ethers, and enamines), activated aromatic systems, certain slightly activated carbon-hydrogen bonds, and selected organometallics. 

Silyl enol ethers are fluonnated in high yields with xenon difluoride [62 93, 94 95] Applications of this reaction to the preparation of fluonnated... 

Benzyl and alkyl tnalkylsilyl ethers undergo clean fluonnation to give good yields of benzyl and alkyl fluorides, respectively, when reacted with a combination of d quaternary ammonium fluoride and methanesulfonyl orp- toluenesulfonyl fluoride. The reactions are applicable strictly to a primary carbon-oxygen bond, secondary and tertiary alkyl silyl ethers remain intact or, under forcing conditions, aie dehydrated to olefins [29] (equation 22)... 

The mixture was kept at 40-50 C for 3 h and then overnight at room temperature Dibenzyl ether (25%) was isolated Nitrobenzyl fluorides are obtained by adding the alcohol to an excess of the fluonnating agent When hexafluoropropyldiethylamine is added to the alcohol, dibenzyl ethers are formed exclusively ... 

Dehydration to olefins, which sometimes accompanies the reaction of alcohols with DAST [95, 108], is seldom as extensive as with a-fluoroamines (FAR and 1,1,2,3,3,3 hexafluoropropyldiethylamine) but occurs in a few cases to the exclusion of fluonnation, thus, 9a-fluoro-11-hydroxysteroids give 9a fluoro-A -steroids [127, 128] Dehydration accompanied by Wagner-Meerwein rearrangement occurs during the fluonnation of testosterone [129] Intermolecular dehydration to form ethers in addition to fluorides is observed in the reaction of benzhydryl alcohols [104] (Table 6)... 

Diphenylperfluoropentan-l, 5-dione, m contrast to its shorter chain homo-logue, which gives the normal fluonnation product, on treatment with sulfur tetrafluoride and hydrogen fluoride torms a cyclic ether as the only product [178] (equation 90)... 

Electrochemical oxidation of alkyl aryl ethers results m oxidative dealkylation and coupling of the intermediate radicals ElectrooxidaUon m the presence of hydrogen fluonde salt leads to fluonnated dienones [66] (equation 58)... 

Terminally unsaturated fluonnated alkenoic acids can be obtained from poly-fluorocycloalkenes by reaction with potassium hydroxide m rert-butyl alcohol [24] (equation 26) The use of a tertiary alcohol is critical because primary and secondar y alcohols lead to ethers of the cycloalkenes The use of a polar aprotic solvent such as diglyme generates enols of diketones [26] (equation 27) The compound where... 

Fluonnated allylic ethers are prepared under phase-transfer catalysis (PTC) in the presence of tetrabutylammonium hydrogen sulfate (TBAH) fJ] (equation 2)... 

In the presence of dicyclohexyl-18-crown-6 ether, potassium fluoride converts fluonnated vinylic iodides to acetylenes [2] (equation 2)... 

In the Schmidt reaction of fluonnated dicarboxyhc acids, the appropnate amides can be obtained in fairly good yield [48] Complications arise from possible cychzation if the fluorine atom is in the 8 position relative to the newly formed amino group [/] Fluonnated aromatic ethers, upon heating in dimethylformamide, undergo Smiles rearrangement to give diarylamines [49, 50] (equation 11)... 

Covalent fluondes of group 3 and group 5 elements (boron, tin, phosphorus, antimony, etc ) are widely used m organic synthesis as strong Lewis acids Boron trifluoride etherate is one of the most common reagents used to catalyze many organic reactions. A representative example is its recent application as a catalyst in the cycloadditions of 2-aza-l,3-dienes with different dienophiles [14] Boron trifluoride etherate and other fluonnated Lewis acids are effective activators of the... 

The basicities of amines, ethers, and carbonyl compounds are invariably decreased by fluonnation. 2,2,2-Tnfluoroethylamine (p f = 3.3 [61]) and C 5NH2 = -0.36 [62]) are about 10 times less basic than CH3CH2NH2 and CgH5NH2, respectively, and (CF3)2CHNH2 (p j, = 1 22 [71]) is over 10 times less basic than 1-C3H2NH2. The relative gas-phase acidities in Table 15 illustrate the large effect of fluonnation. Perfluoro-rerf-amines (R )3N and ethers R Rf have no basic character m solution [, 74], and CF3COCF3 is not protonated by superacids [72]. 

The high thermal and chemical stability of fluorocarbons, combined with their very weak intermolecular interactions, makes them ideal stationary phases for the separation of a wide variety of organic compounds, including both hydrocarbons and fluorine-containing molecules Fluonnated stationary phases include per-fluoroalkanes, fluorocarbon surfactants, poly(chlorotrifluoroethylene), polyfper-fluoroalkyl) ethers, and other functionalized perfluoro compounds The applications of fluonnated compounds as stationary phases in gas-liquid chroma... 

A fluonnated dimethyl ether is assigned the same number as the corresponding Cj alkane prefixed with an "E , a nomenclature recently adopted by the National Institute of Science and Technology (NIST) in the United States... 

The word fluorocarbon has been used here in a generic way to indicate completely fluonnated liquids, including ethers and amines, rather than in its stricter meaning of having only carbon and fluorine atoms The definition of the word perfluori-nated is somewhat vague, because it can include compounds that retain double bonds or protons... 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluonnation of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluonnation of octanoyl chloride results in perfluonnated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73], Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-AIkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

Values in parentheses arc yields of fluonnated cyclic ethers without pendant ether group (OR f)... 

Cyclic ethers having perfluorinated side chains or perfluorinated rings attached in the a-position with respect to oxygen are remarkably stable toward cobalt trifluoride and can be successfully fluonnated to perfluoro ethers at 440 °C without being cleaved to a considerable extent at the oxygen [16, 77]. Selected examples are shown in Table 4. 

Acyl hypofluorites react readily with enols, enol acetates, vinyl ethers, and enolates [39, 40, 41] (Table 2, entries 1-7) Steroidal enol acetates are also fluonnated smoothly [39] (equations 17-19)... 

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