Electrochemical fluoroalkylation

Aromatic perfluoroaLkylation can be effected by fluorinated aUphatics via different techniques. One category features copper-assisted coupling of aryl hahdes with perfluoroalkyl iodides (eg, CF I) (111,112) or difluoromethane derivatives such as CF2Br2 (Burton s reagent) (113,114), as well as electrochemical trifluoromethylation using CF Br with a sacrificial copper anode (115). Extmsion of spacer groups attached to the fluoroalkyl moiety, eg,... 

Coupling reactions and related fluoroalkylations with polytTuoioalkyl halides are induced by vanous reagents, among them metals such as copper and zinc, or by an electrochemical cell. More recently, examples of carbon-carbon bond forma tion by coupling of unsaturated fluorides have been reported Both acyclic and cyclic fluoroolefins of the type (Rp)2C=CFRp undergo reducUve dimerization on treatment with phosphines [42] (equation 33) The reaction shown in equation 33 IS also accompbshed electrocheimcally but less cleanly [43]... 

This chapter does not attempt to cover electrochemical processes which involve the insertion of a group already containing carbon-fluorine bonds into an existing molecule (the building block approach), e.g., perfluoroalkyl group insertion via the Kolbe reaction, or fluoroacyloxylations or fluoroalkoxylations via electro-oxidation, or fluoroalkylation via electro-reduction. These have been reviewed elsewhere [1,2]. 

Trimethyltrifluoromethylsilane, which is now generally referred to as Ruppert s reagent [92], has been widely investigated [93-96] as an intermediate for transferring the trifluoromethyl group as a nucleophile, thus compensating for the deficiencies of poly-fluoroalkyl Grignard or lithium derivatives. This approach also complements other methods for transfer of trifluoromethide ion. A variety of procedures have now been developed for the synthesis of this compound but the electrochemical procedure [93]... 

Electrochemical Synthesis of Fluoroalkylated Sulfenimines. 83 Anodic Oxidation of Trifluoromethylated Carboxylic... 

ZnO A simple method of electrochemical deposition was adopted to prepare conductive hydrophobic ZnO thin films [504]. These ZnO films were fabricated by overpotential electrochemical deposition at room temperature, and the surface modified by a (flu-oroalkyl)silane showed superhydrophobic properties. The prepared thin films were treated with a methanol solution of hydrolyzed (heptadecafluorode-cyl)trimethoxysilane (CH30)3Si(CH2)2 (CF2)7CF3, 1.0 wt %) for 3 h and subsequently heated at 100 °C for 1 h. Wettability studies revealed that the surface of the as-prepared thin films showed a contact angle (CA) for water of 128.3 1.7°, whereas the superhydrophobic surface with a water CA of 152.0 2.0° was obtained by (fluoroalkyl) silane modification [504]. 

Poly(3-fluoroalkylthiophene)s have been prepared electrochemically [207] and show high thermal stability, chemical inactivity, and hydrophobicity. Alkyl spacers were inserted between the thiophene ring and the fluoroalkyl groups in the monomer 12 in order to neutralize their unfavorable electronic effects. The introduction of up to 50% fluorine in the structure leads to elastomeric materials with higher electroactivity than poly(alkylthiophene)s [207]. 

Three subcategories are commonly used to classify PFASs per-fluoroalkyl sulfonic acids (PFSAs), perfluoroalkylcarboxylic acids (PFCAs), and fluorotelomer alcohols (FTOHs). Historically, PFSAs and PFCAs have been prepared by electrochemical fluorination, whereas fluorotelomer alcohols are s)mthesized by telomerization [146]. The electrochemical fluorination process results primarily in straight chain homologs, but branched chain isomers are known to be present. Branched chain isomers can also be s)mthesized through telomerization s)mthesis with the use of branched chain telogen precursors. FTOHs have an even number of carbon atoms and contain a nonfluorinated ethylene group adjacent to the polar end group. Pathways for the conversion of FTOHs fo PFCAs in the environment have been proposed [147,148]. 

Table 12.53 Overview of electrochemically produced per(poly)fluoroalkyl substances. ...

By the way, trifluoroacetaldehyde is a versatile fluoro building block. However the chemical or electrochemical oxidative transformation of trifluoro-ethanol to trifluoroacetaldehyde has been unsuccessful. Trifluoroacetaldehyde is therefore generally produced by the reduction of trifluoroacetic acid ester or acid chloride using an excess of LAH. The anodic substitution at fluoroalkyl phenyl sulfides is a useful alternative because it realizes the transformation of economical trifluoroethanol to highly valuable trifluoroacetaldehyde equivalents as shown in Scheme 6.5. 

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