Ethers, aryl fluoroalkyl

Applications. Table 12 Hsts crop-protection chemicals and pharmaceuticals containing the aryl fluoroaLkyl ether group. 

Aryl fluoroalkyl ethers have been prepared from the reaction, at room temperature in HMPA, of fluo-ro-substituted alkoxides with activated fluoro-,149 nitro-,149 and, at 150 °C, also chloro-arenes150,151 and some chloro-substituted pyrazines (equation 15), pyrimidines, quinolines,150,152 and pyridines.152 Disubstitution was observed in die presence of comparably activated leaving groups such as in 2,4- and 2,6-di-chloronitro- or cyano-benzenes, whereas regiospecific substitution took place at position 4 in 3,4-dichloronitro- or cyano-benzene and at position 2 in 2-fluoro-6-chlorocyanobenzene.151 Steric hindrance and the number of fluorine substituents in the alkoxide pose limits to the reactivity. Thus, tertiary alkoxides, or alkoxides containing more than four fluorine substituents, displace activated nitro and fluoro, but not chloro substituents.149,150 The secondary hexafluoro-2-propoxide anion does not react even with the more reactive nitro and fluoro derivatives.149... 

Sheppard WA (1964) a-Fluorinated ethers. I. Aryl fluoroalkyl ethers. J Org Chem 29 1-11. doi 10.1021/jo01024a001... 

All the homopolymers or copolymers that have been obtained show very interesting properties in terms of thermal stabiUty. They generally present rather low TgS and good stability at high temperature and may thus be used over a wide range of temperature. Fmthermore, in the search for new materials for new applications, the obtention of polymers with specific properties is required, and depending on the nature of their main chain (alkyl, fluoroalkyl, aryl, fluoroaryl, aUcyl ether, etc.) and on the nature of their side chains, these hybrid silicones may be directed to exhibit specific properties. 

Scheme 2.52 Structure of sulfonated poly(arylene ether sulfone) ionomers with three different types of acidic groups (fluoroalkyl sulfonic, aryl sulfonic, and alkyl sulfonic acids). Taken from Ref. [185].

Later on, a more efficient and mild way to prepare this compound in a two-step process (Scheme 14.2) was revealed by Babb et al. in 1993 [4], Starting from phenolic precursors, the first step is fluoroalkylation with 1,2-dibromotetrafluoroethane (BrCF2CF2Br) to give 2-bromotetrafluoroethyl aryl ethers. In this reaction, BrCF2CF2Br (widely used as nontoxic fire extinguishing agent) served as a fluoroalkylation agent and as a trifluorovinyl precursor. 

In contrast to the well-known alkylation paths, namely, S l and Sn2, the fluoroalkylation reaction was rationalized by an unusual ionic chain mechanism [26]. As shown in Scheme 14.3, the reaction was initiated with the direct attack of electron-positive bromine (5+) on the BrCF2CF2Br by phenoxide. Tetrafluoroethy-lene (CF2=CF2) was generated in situ after loss of bromide anions. The phenoxides added to the CF2=CF2 to give the reactive fluorocarbanions, which were quickly terminated by bromide to form 2-bromo-tetrafluoroethyl aryl ethers. In the elimination step, zinc inserted into the C—Br bond of 2-bromo-tetrafluorethyl aryl ethers in a similar way to the preparation of Grignard reagents. Finally, the aryl trifluorovinyl ethers were obtained by the elimination of ZnBrF salt at elevated temperature. 

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