Potassium fluoride, fluorination agent

SAFETY PROFILE Poison by subcutaneous route. Can react violently with potassium. A fluorination agent. When heated to decomposition it emits toxic fumes of F and ZnO. See also FLUORIDES and ZINC COMPOUNDS. 

Halogen exchange with KF is not successful ia acetic acid (10). Hydrogen bonding of the acid hydrogen with the fluoride ion was postulated to cause acetate substitution for the haUde however, the products of dissolved KF ia acetic acid are potassium acetate and potassium bifluoride (11). Thus KF acts as a base rather than as a fluorinating agent ia acetic acid. 

Potassium fluoride is a fluorinating agent in organic synthesis. Other applications are in making insecticide formulations, as an additive to flux for making hard solder, and to control fermentation. 

The monofluoro (94) and difluoro derivatives (95) were isolated when a solution of potassium fluoride in sulfolane reacted with 4,5-dichloro-1,2,5-thiadiazole. Careful control of the reaction conditions allowed production of mainly 95, whereas 94 became the major product when oxidizing fluorinating agents were employed (e.g., XeF2, BrF3, AgF2). Open-chain products were also found (82CB2135) (Scheme 34). 

Synthesis of the thymidine derivative relies on the older two-step insertion of fluorine. Thus, the hydroxyl group in 3 -deoxythymidine benzoate (51-1) is first converted to the mesylate (51-2). Reaction with potassium fluoride in hydrogen fluoride replaces the mesylate by fluorine (51-3). The fact that this reaction, as that above, proceeds with retention of the configuration mles out simple displacement as the mechanism for this transform. The presence of the methyl group at position 5 negates the need for the chlorination step. Saponification then affords the antiviral agent alovudine (51-4) [52]. 

Attempts to effect fluorination of tetrakis(trichlorophosphine)nickel-(0) using benzoylfluoride as a fluorinating agent were also successful, tetrakis (trifluorophosphine) nickel-(0) and partially fluorinated liquid intermediates being isolated (23). The eutectic mixture potassium fluoride-hydrogen fluoride of the composition KF.3HF, on the other hand, showed no interaction with tetrakis (trichlorophosphine) nickel-(0) up to the decomposition temperature of the latter. 

A comparison of various fluorinating agents in the preparation of fluoride 13, i.e. (2-chloro-1,1,2-trifluoroethyl)diethylamine and diethylaminosulfur trifluoride (R = H), tetrafluoro(phen-yl)-A5-phosphane (R = TMS), and potassium fluoride (R = Ts), has shown that the highest stereoselectivity is achieved with potassium fluoride and (2-chloro-l,1,2-trifluoroethyl)-diethylamine.19 The fluorination with tctrafluoro(phenyl)-7.5-phosphane proceeds, at least in part, via a carbocation and with a relatively low enantioselectivity.15... 

Spray-dried potassium fluoride which is not hygroscopic is an efficient reagent for the transformation of acid chlorides 14 to acid fluorides 15.26 The reaction can be carried out at room temperature in 3 hours. The strong contrast of spray-dried to calcine-dried potassium fluoride as a fluorinating agent is apparently ascribed to the difference in the particle size. Spray-dried potassium fluoride has been shown to have much smaller particle size, much larger surface area and crystals are much more bulky compared with calcine-dried potassium fluoride.26... 

Potassium hexafluoronickelate(IV), rhombohedral nickel(III) fluoride, and nickel(lV) fluoride are exceedingly powerful fluorinating agents, more powerful than cobalt(III) fluoride. In solution or suspension in anhydrous hydrogen fluoride at room temperature, they will convert58 the cyclohexyl compound 22 into 23 (R —NiF, or NiF4) and 24 (K2NiF6). 

Silver(II) fluoride and potassium tetrafluoroargentate(III) are too powerful as fluorinating agents for tetrahydrofuran and no oxygen-containing products are detected."... 

Complex fluorides (LiBiF6, and KBiF6) are known1 and they are weaker oxidizing agents than bismuth(V) fluoride itself. If parallels with potassium tetrafluorocobaltate(III) and co-balt(III) fluoride are valid (see Section 25.1.), then they will also be weaker fluorinating agents. 

Elemental fluorine is the most powerful oxidizing agent known it may therefore not be prepared by chemical oxidations under ordinary conditions. Commercial quantities of fluorine are prepared today by electrolysis of mixtures of potassium fluoride and hydrogen fluoride (such mixtures containing the F—H—F ion). Electrodes may be of carbon or of a metal (for example, Cu or Ni) that will form a protective fluoride coating. 

The antitumor chemotherapy agent clofarabine (104) sports halogen on the purine as well as on the sugar. The major portion of the synthesis involves preparation of the requisite fluorine-substituted furanose (101). The sequence begins with the conversion of the only free hydroxyl in allofuranose bis(acetonide) (95) to its tosylate (96). This group is then displaced by fluorine in its reaction with potassium fluoride to afford... 

A unique method for the introduction of fluorine via an ester-type linkage has been used for the preparation of fluorinated nucleosides.60 It consists of the treatment of 2,3 -anhydro nucleosides with hydrogen fluoride in the presence of aluminum trifluoride in dioxane at temperatures between 150 and 200 C.61,62 The yields are in the range of 30-40%. With potassium hydrogen fluoride in diethylene glycol as fluorinating agent, yields arc even lower.61 A more recent application of this method is the synthesis of 3.62... 

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