Potassium fluoride, reaction

The residue left from conversion of the chloro to the fluoro compound exploded during distillation at 1.3 mbar [1], Reheating the residue from distillation caused violent decomposition [2], Traces of an aci-nitroquinonoid species (structure str02, p. S1-S7) may have been formed in the chlorodinitrobenzene-potassium fluoride reaction system [3],... 

A niamber of reactions have been examined using these phase transfer catalytic species. These include displacement reactions of solid potassium phenoxide, solid sodium azide and aqueous sodium azide on racemic ethyl-2-bromopropionate in toluene (similar to reaction 5), sodium borohydride (solid) reductions of acetophenone and octan-2-one, chalcone epoxidations using aqueous H2O2/OH" (reaction 4) and Michael additions of nitromethane to chalcone in the presence of anhydrous potassium fluoride (reaction 3). Details of these results will be published in due course and at the moment it is possible to record only a few representative examples of the displacements and reductions. 

Torgov introduced an important variation of the Michael addition allylic alcohols are used as vinylogous a -synthons and 1,3-dioxo compounds as d -reagents (S.N. Ananchenko, 1962, 1963 H. Smith, 1964 C. Rufer) 1967). Mild reaction conditions have been successful in the addition of ],3-dioxo compounds to vinyl ketones. Potassium fluoride can act as weakly basic, non-nudeophilic catalyst in such Michael additions under essentially non-acidic and non-basic conditions (Y. Kitabara, 1964). 

Chloroacetate esters are usually made by removing water from a mixture of chloroacetic acid and the corresponding alcohol. Reaction of alcohol with chloroacetyl chloride is an anhydrous process which Hberates HCl. Chloroacetic acid will react with olefins in the presence of a catalyst to yield chloroacetate esters. Dichloroacetic and trichloroacetic acid esters are also known. These esters are usehil in synthesis. They are more reactive than the parent acids. Ethyl chloroacetate can be converted to sodium fluoroacetate by reaction with potassium fluoride (see Fluorine compounds, organic). Both methyl and ethyl chloroacetate are used as agricultural and pharmaceutical intermediates, specialty solvents, flavors, and fragrances. Methyl chloroacetate and P ionone undergo a Dar2ens reaction to form an intermediate in the synthesis of Vitamin A. Reaction of methyl chloroacetate with ammonia produces chloroacetamide [79-07-2] C2H ClNO (53). 

The preparation of fluoroaromatics by the reaction of KF with perhaloaromatics, primarily hexachloroben2ene, has received considerable attention. Two methods were developed and include either the use of an aprotic, polar solvent, such as /V-methy1pyrro1idinone (8), or no solvent (9). These methods plus findings that various fluoroaryl derivatives are effective fungicides (10) prompted development of a commercial process for the production of polyfluoroben2enes (11). The process uses a mixture of sodium and potassium fluorides or potassium fluoride alone in aprotic, polar solvents such as dimethyl sulfoxide or sulfolane. 

Lead Fluoride. Lead difluoiide, Pbp2, is a white oithorhombic salt to about 220°C where it is transformed into the cubic form some physical properties ate given in Table 1. Lead fluoride is soluble in nitric acid and insoluble in acetone and ammonia. It is formed by the action of hydrofluoric acid on lead hydroxide or carbonate, or by the reaction between potassium fluoride and lead nitrate. 

Use of excess sodium drives the reaction, usually done under an argon or helium blanket, to completion. After cooling, the excess sodium is leached with alcohol and the sodium and potassium fluorides are extracted with water, leaving a mass of metal powder. The metal powder is leached with hydrochloric acid to remove iron contamination from the cmcible. 

Alkyl fluorides have been prepared by reaction between elementary fluorine and the paraffins, by the addition of hydrogen fluoride to olefins, by the reaction of alkyl halides with mercurous fluoride, with mercuric fluoride, with silver fluoride, or with potassium fluoride under pressure. The procedure used is based on that of Hoffmann involving interaction at atmospheric pressure of anhydrous potassium fluoride with an alkyl halide in the presence of ethylene glycol as a solvent for the inorganic fluoride a small amount of olefin accompanies the alkyl fluoride produced and is readily removed by treatment with bromine-potassium bromide solution. Methods for the preparation of alkyl monofluorides have been reviewed. ... 

Stenc effects are presumably also responsible for the surprising formation of a chlorinated product from reaction of a hindered fluorinated olefin with potassium fluoride and iodine chloride [U6] (equation 18). 

Polymer-supported tetraphenylphosphonium bromide is a recyclable catalyst for halogen-exchange reactions. The reaction of 1 equivalent of chloro-2,4-dinitrobenzene with 1 5 equivalents of spray-dned potassium fluoride and 0.1 equivalent of this catalyst in acetonitnle at 80 C for 12 h gives 2,4-dinitro-fluorobenzene m 98% yield An 11% yield is obtained without the catalyst [3 /]. 

Another approach is to omit the solvent andrun the reaction under supercritical conditions where potassium fluoride dissolves in the superheated reactant This approach is illustrated by the conversion of 2-chloromethoxy-l,l,l,3,3,3-hexa tluoropropane to 2-fluoromethoxy-l,l,l,3,3,3 hexafluoropropane with either potassium fluoride or sodium fluoride as the fluorine source (equation 31)... 

Difluoromethoxy-2-chloro-l,l,l-trifluoroethane and potassium fluoride produce 2-difluoromethoxy-1,1,1,2-tetrafluoroethane [50] The yield of the latter reaction is improved by adding a phase transfer catalyst or crown ether, tetra-methylammonium chlonde, tetrabutylammonium chloride, or 18-crown-6 with a solvent like sulfolane can be used for this purpose [5/] (equation 32)... 

The conversion of octachloronaphthalene to octafluoronaphthalene with potassium fluoride and either 18-crown-6, dibenzo-18-crown-6, cis,j>m,cis-dicyclohexano-18-crown-6, cis,anti,cis-dicyclohexano-l 8-crown-6, or irons,syn,trails-dicyclohexano-18-crown-6 demonstrates that 18-crown-6 or dibenzo-18-crown-5 increases the yield and selecuvity and decreases the reaction time [55] Treatment of 3,4-dichloro-],2,5-thiadiazole with potassium fluonde in sulfolane with and without 18-crown-6 present shows that less severe conditions can be used with either 18-crown-6 or dibenzo-18-crown-6 to form 3,4-difluoro-l,2,5-thiadiazole (equation 34)... 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

Table 7. Reactions of Primary Alkyl Halides with Potassium Fluoride and Hexadecyltributylphosphom um Bromide [6S]...

The reaction ot tormamides with sulfur tetrafluoride in the presence of potassium fluoride leads to replacement of both carbonyl oxygen and hydrogen with fluorine. The formyl group is directly converted into the trifluoromethyl group A-(trifluoromethyl)amines are formed in near quantitative yields [233] (equation 121)... 

Fluorodenitration of nitroaliphatics has been primarily restricted to polyni tromethanes (Table 9) Side reactions involving potassium nitnte by-product reduce yields of fluoromtromethane The novel use of the adduct of potassium fluoride with hexafluoroacetone in diglyme as a source of fluoride ion for the fluorodenitration of tetranitromethane significantly increases the yield of fluorotn nitromethane [102] (equation 29)... 

Aromatic fluorodenitration was first discovered in the reaction of polychloro-nitrobenzenes with potassium fluoride, when 2,3,5,6-tetrachlorofluorobenzene was prepared in 37% yield from 2,3,5,6-tetrachloronitrobenzene 105] The technique has been adapted to prepare aryl fluorides from other activated nitro aromatics for applications in pharmaceutical and polymer chemistry (equation 31) Fluorodenitration also has been applied to prepare radiolabeled ( F) fluo-roaromatics [74, 106]... 

The reaction of 2H-nonatluoro-2-methylpropane with iodine monochloride in sulfolane in the presence of potassium fluoride produces 2-chlorononafluoro-2-methylpropane in 92% yield at 50% conversion [2d]. 

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