Aliphatic ethers, fluorination

Fluorination of aliphatic ethers at gentle conditions with cobalt trifluoride or potassium tetrafluorocobaltate do not give perfluorinated products and cause only negligible cleavage of the ether bond. Complex mixtures are formed from ethyl methyl ether and from diethyl ether [9] (equations 16 and 17)... 

Torlon-type polymers are unaffected by aliphatic, aromatic, chlorinated and fluorinated hydrocarbons, dilute acids, aldehydes, ketones, ethers and esters. Resistance to alkalis is poor. They have excellent resistance to radiation. If a total of 10 Mrad is absorbed at a radiation dosage of 1 Mrad/h the tensile strength decreases by only 5%. 

Fluorosilicones consist of PDMS backbones with some degree of fluoro-aliphatic side chains. The fluorinated group can be trifluoropropyl, nonafluorohexylmethyl, or fluorinated ether side group [78,28,79]. These polymers differ not only in substituent group, but also in the amount of fluoro-substitution relative to PDMS, the overall molecular weight and crosslink density, and the amount of branching. In most commercially available cases, these polymers are addition cure systems and the reactions are those discussed previously for silicone networks. 

Production and Uses of Aliphatic Compounds II Ether, Epoxide and Pnlyeiher, Carboxylic Acids and Their Denvatives, Sulfonic Acids, Toxicological Data of Aliphatic Fluorine Compounds (Ger) Liebig, H, Ulm, K Chem Ztg 100 3-14 270... 

Itnino ethers are converted into difluoroamino derivatives, e.g. 9, which are also formed in the reactions with aliphatic amines, but in much lower yields. The yields of N —F product increase when 4-fluorophenylsulfonamide derivatives, e.g. 10, are fluorinated.9... 

The products of the electrochemical perfluorination of aliphatic or cyclic ethers are the corresponding perfluorinated ethers. Byproducts are perfluorinated ethers with shorter carbon chains, perfluoroalkanes, perfluorocarboxylic acid fluorides and oxygen difluoride. Cyclic perfluorinated ethers can be produced by electrochemical fluorination of alcohols,32 aliphatic carboxylic acids33 or of their acid halides34 containing not less than four carbon atoms in the chain. 

The result of the reaction of sulfur tetrafluoride with alcohols strongly depends on the structure of the alcohol. Simple aliphatic alcohols, such as methanol, ethanol and propan-2-ol, give alkyl ethers as the main product with only small amounts of fluoroalkanes.41 42 Yields of fluorinated products increase with increasing acidity of the hydroxy group and, in general, the reaction is only synthetically useful with alcohols equally or more acidic than tropolone (p K, = 6.42). 

Aliphatic a-hydroxy ketones react with sulfur tetrafluoride, generally to provide trifluoroal-kanes. However, under carefully chosen conditions the carbonyl group in hydroxy ketones remains intact while the hydroxy group undergoes selective substitution by fluorine. Thus, 5-hydroxyoctan-4-one reacts with sulfur tetrafluoride (20°C, 3 h) to give a 1 1 mixture of 5-fluorooctan-4-one(l b) and 2-oxo-l-propylpentyl fluorosulfite.63 a-Fluoro ketones 1 are formed in high yield and as the sole product when diethyl ether is used as solvent.64... 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

Investigation of the reaction of xenon difluoride and difluoroiodobenzene with aliphatic 1,3-dienes in the presence of boron trifluoride-diethyl ether complex has shown that under mild conditions this reaction proceeds with kinetic control, to form mainly the products of 1,2-addition of fluorine atoms. The ratio of product is reported in Table 5. 

A large number of synthetic pyrethroids with a variety of aromatic and aliphatic fluorine substituents have been commercialized, and will be discussed in the sections on fluorinated ether, aromatic fluorine, and fluorinated aliphatic groups, respectively. Fluvalinate (Mavrik ) [50] is a trifluoromethylphenyl pyrethroid, initially introduced by Zoecon (later Zandos Ag) and later replaced by tau-fluvalin-ate, which contains two of the four isomers of fluvalinate. Tau-fluvalinate (Apistan ) is a synthetic pyrethroid used for the topical treatment of honeybees against the parasitic mite Varroa jacobsoni. Mite resistance to tau-fluvalinate has been reported [51],... 

Simons process — Electrochemical polyfluorination reactions of organic compounds are the only efficient way to industrial production of perfluorinated compounds. The reaction proceeds in the solution of KF in liquid HF (b.p. 19.5 °C), where the starting substances as alcohols, amines, ethers, esters, aliphatic hydrocarbons and halo-hydrocarbons, aromatic and heterocyclic compounds, sulfo- or carboxylic acids are dissolved. During anodic oxidation, splitting of the C-H bonds and saturation of the C=C bonds occur and fluorine atoms are introduced. 

The difluoromethylation of aliphatic alcohols is also possible, in principle, but the resulting difluoroethers often tend to undergo acid-catalyzed hydrolysis to the corresponding formates. They are only stable if the corresponding alcohol is sufficiently acidic, i. e. if it carries electron-withdrawing substituents. O-Difluoro-methylated carbohydrates have been reported [7]. In contrast, some highly fluorinated alkyl difluoromethyl ethers can be synthesized under quite drastic conditions (Scheme 2.168), and because of their extreme stability they can be used as inhalation anesthetics [3, 8]. 

Scheme 2.173 Synthesis of aromatic and aliphatic perfluoroalkyl ethers via the fluorination of the corresponding perfluoro-alkanoates with SF4 [18a, 19a].

The very strong deshielding effect of the oxygen linkage of the ethers is second only to that of fluorine in the chemical shifts observed for adjacent carbon nuclei. The aliphatic additivity constants for several ether groups are ... 

Sulfur tetrafluoride was among the first reagents to be used for the direct substitution of hydroxy groups by fluorine. Good yields are only achieved with relatively acidic alcohols, such as nitro alcohols, polyhalo alcohols and hydroxy carbonyl compounds. The fluorination of simple aliphatic alcohols with sulfur tetrafluoride results in side reactions, such as formation of ethers, hence fluorination using other methods (vide infra) is preferred. Moreover, sulfur tetrafluoride cannot be handled without special pressure apparatus and requires precautions to be taken due to its physical and toxicological properties, hence it is, nowadays, frequently replaced by other reagents, but it is still in use for relatively inert substrates (see Vol.ElOa, p 321 ff, also Houben-Weyl. Vol. 5/3. pp 84-86). 

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