Electrochemical Fluorination for Preparing Aryl Fluorides
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Electrochemical Fluorination for Preparation of Alkyl Fluorides Toshio Fuchigami and Shinsuke Inagi Department of Electrochemistry, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan
Introduction Electrochemical fluorinations of organic compounds are classified into three processes: Simons’ process, Philips’ process, and partial (selective) fluorination process. The Simons’ process is the oldest technique, which is a highly useful route to many perfluorinated organic compounds [1, 2]. A solution or dispersion of organic substrate is electrolyzed at a Ni anode in anhydrous hydrogen fluoride (AHF). The products are mostly perfluorinated, and they are commercially significant materials like perfluoroalkanes, perfluoroacyl fluorides, perfluoroalkanesulfonyl fluorides, perfluorotrialkylamines, and perfluoroalkyl esters. The mechanism of the Simons’ process seems to involve the generation of cationic intermediates and highvalence nickel fluorides. The Phillips’ process utilizes a porous carbon anode in a molten KF-2HF electrolyte [2]. The substrate, typically a gas or volatile liquid particularly insoluble in the electrolyte, is
introduced through the porous anode and undergoes statistical replacement of hydrogen with fluorine. The products range from monofluoro to perfluoro compounds and include alkane, chloroalkane, carbonyl fluoride, and ester derivatives. The mechanism is believed to involve the generation of elementary fluorine followed by in situ reaction with the organic substrate via a free radical. Thus, this process can be classified as an indirect anodic substitution reaction. Partial electrochemical fluorination is a rather new method and it is generally carried out in an aprotic solvent containing an organic substrate and a fluoride salt as a supporting electrolyte and a fluorine source [3–5]. The products are mono- and/or difluorinated compounds, which are formed through the generation of a cationic intermediate followed by reaction with fluoride ions. Therefore, the mechanism is quite similar to other anodic substitution processes.
Electrochemical Perfluorination Electrochemical perfluorination is a process in which all the hydrogen atoms in a starting organic molecule are substituted with fluorine atoms without elementary fluorine generation during electrolysis.
© Springer Nature Singapore Pte Ltd. 2020 J. Hu, T. Umemoto (eds.), Fluorination, Synthetic Organofluorine Chemistry 1, https://doi.org/10.1007/978-981-10-3896-9
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Electrochemical Fluorination for Preparation of Alkyl Fluorides
The Simons’ Process J. H. Simons developed the electrochemical perfluorination of organic compounds in anhydrous liquid HF using nickel electrodes to provide perfluorinated products in the late 1930s, and first published the details in 1949 [6]. He is a pioneer of electrochemical perfluorination and this method is called Simons’ process. The process uses an undivided cell at low temperature to keep HF as a liquid (the boiling point of HF is 19.5 C). Although highly pure AHF has no electric conductivity, organic compounds containing oxygen
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