Hydrogen fluoride electrolysis

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

Fluorocarbons are made commercially also by the electrolysis of hydrocarbons in anhydrous hydrogen fluoride (Simons process) (14). Nickel anodes and nickel or steel cathodes are used. Special porous anodes improve the yields. This method is limited to starting materials that are appreciably soluble in hydrogen fluoride, and is most useflil for manufacturing perfluoroalkyl carboxyflc and sulfonic acids, and tertiary amines. For volatile materials with tittle solubility in hydrofluoric acid, a complementary method that uses porous carbon anodes and HF 2KF electrolyte (Phillips process) is useflil (14). 

Silver Fluoride. Silver fluoride, AgF, is prepared by treating a basic silver salt such as silver oxide or silver carbonate, with hydrogen fluoride. Silver fluoride can exist as the anhydrous salt, a dihydrate [72214-21-2] (<42° C), and a tetrahydrate [22424-42-6] (<18° C). The anhydrous salt is colorless, but the dihydrate and tetrahydrate are yellow. Ultraviolet light or electrolysis decomposes silver fluoride to silver subfluoride [1302-01 -8] Ag2p, and fluorine. 

C19-0034. Fluorine is manufactured by the electrolysis of hydrogen fluoride dissolved in molten KF ... 

The acidic properties of methanesulphonic acid that have just been mentioned have been responsible for two other accidents. When this acid is contact with methyl and vinyl oxide, this caused the latter to polymerise violently. The electrolysis of methanesulphonic acid with an aqueous solution of hydrogen fluoride gives rise to a violent detonation that was put down to the formation of oxygen difluoride that is explosive. 

Nobel Prize for chemistry 1906). Produced by electrolysis of potassium fluoride in aqueous hydrogen fluoride (HF). 

It is a toxic colourless gas which is dangerously explosive in the gaseous, liquid and solid states [1]. It is produced dining electrolysis of nitrogenous compounds in hydrogen fluoride [2], Later work (perhaps with purer material ) did not show the explosive instability [3], The shock-sensitivity is confirmed [4],... 

Fluorine was isolated by Henri Moissan at the end of June 1886 during an electrolysis of liquefied anhydrous hydrogen fluoride, containing potassium fluoride, at -23°C. The gas, produced at the anode, was fluorine. This achievement earned Moissan the 1906 Nobel prize in chemistry. Thousands of tons of fluorine are being produced today by essentially the same, albeit slightly improved, electrolytic method. Obviously, this scale of fluorine production means that fluorine chemistry has turned into an important branch of industry. This development can be understood if we look at fluorine from a chemist s point of view. 

Electrochemical fluorination in anhydrous hydrogen fluoride (Simons process) involves electrolysis of organic compounds (ahphatic hydrocarbons, haloalkanes, acid halides, esters, ethers, amines) at nickel electrodes. It leads mostly to perfluori-nated compounds, but is accompanied to a high extent by cleavage and rearrangement reactions. The mechanism of the formation of carbocations according to Eq. (1) and Scheme 1 is assumed... 

An industrial method for manufacturing fluorine gas is the electrolysis of liquid hydrogen fluoride. 

Yttrium oxalate is then ignited to its oxide, Y2O3. The oxide is heated at 750°C in a stream of anhydrous hydrogen fluoride to yield yttrium fluoride, YF3. Alternatively, the oxide is mixed with ammonium hydrogen fluoride NH4HF2 and heated at 400°C in a stream of dry air or helium. Yttrium metal may be produced from its fluoride either by metallothermic reduction or electrolysis. The more common metallothermic reduction involves reducing the fluoride with redistilled calcium in 10% excess over the stoichiometric amounts at elevated temperatures ... 

The three principal electrochemical methods are described by which fluorine can be directly introduced into organic compounds, namely electrolysis in molten salts or fluoride ion solutions, electrolysis in molten potassium fluoride/hydrogen fluoride melts at porous anodes, and electrolysis in anhydrous hydrogen fluoride at nickel anodes. Using examples from the past decade, it is aimed to demonstrate that electrofluorination in its various forms has proved to be an increasingly versatile tool in the repertoire of the synthetic chemist. Each method is described in terms of its essential characteristics, reaction parameters, synthetic utility, advantages and disadvantages, patent protection, and potential for commercial exploitation. The different mechanisms proposed to explain each process are critically reviewed. 

Electrolysis in Anhydrous Hydrogen Fluoride at Nickel Anodes. . 213... 

Electrolysis in Molten Potassium Fluoride/Hydrogen Fluoride at a Porous Anode... 

ECF is characterised by the electrolysis of organic compounds, dissolved or dispersed in anhydrous hydrogen fluoride, at nickel anodes (no other material appears to be as effective), under voltage conditions where the evolution of gaseous fluorine does not normally occur. 

Hydrogen fluoride feeds into the bath during the course of electrolysis. A trace of water in the hydrogen fluoride can react with fluorine as shown in equation 8 in the normally operated fluorine cell. 

The electrolyte consisted of anhydrous hydrogen fluoride with 0.1 M sodium fluoride. The anode was a platinum grid (3 cm2), the cathode material was also platinum and the reference electrode was Cu/CuF2. The electrolysis of 1-bromopropane was carried out at a potential of 1.65 V. The products were 2-fluoropropane(20%), 1, l-difluoropropane(30 %), and l-bromo-2-fluoropropane (40 %), as well as lesser amounts of 1,2-dibromo-3-fluoropropane, 2-bromo-l, 1 -difluoropropanc, 1,2-dibromopropane, and 1,3-dibromopropane. 

The products of the electrolysis of trimethylacctic acid in tetraethylammonium fluoride hydrogen fluoride have been compared for platinum and nickel electrodes.44 Electrolysis on platinum leads mainly to the products of nucleophilic attack of the intermediate carbocation 6 which is formed by oxidation of the /crt-butyl radical, adsorbed on the electrode. 

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