Potassium bifluoride, reaction

Reaction with potassium bifluoride in the presence of hydrofluoric acid creates a stable complex fluoride, K2MnFe in which Mn is in +4 oxidation state ... 

Fluorine is produced by electrolysis of molten salts on carbon anodes including KF-21TF at about 100°C, potassium bifluoride at about 250°C, and fluoride salts at about 1000°C. The decomposition potential of molten potassium bifluoride is 1.75 V at 250°C, a value close to that estimated thermodynamically [80]. The kinetics of the anodic process is characterized by a Tafel slope of 0.56 V per decade, j), = 1 x 10 A/cm [81], and by a complex reaction mechanism involving the formation of fluorine atoms on carbon. During the electrolysis, C-F surface compounds on the carbon anode are formed via side reactions. Intercalation compounds such as (CF) contribute to the anodic effect in the electrochemical cell, which can be made less harmful by addition of LiF. 

By Bifluoride Ion. Trifluoromethyldifluorophosphine and bis-trifluoromethyl fiuorophosphine are oxidized to hexacoordinate phosphorus anions [(CF3) PF5 H] when heated with potassium bifluoride 235). The reactions occur even more readily in the presence of acetonitrile at room temperature. 

The first application of the alkyltrifluoroborate salts was the conversion into alkyldihaloboranes by silyl hahdes and subsequent reaction with alkyl azides [77]. An example of a usefid synthesis was the preparation of (S)-2-phenylpyrrolidine (141) (Scheme 8.32). (S)-DICHED (3-bromopropyl)boronate (13S) was converted into the 3-azido derivative 136 at reflux temperature under phase-transfer conditions. The usual reaction with (dichloromethyl)lithium followed by phenylmagnesium bromide to form DICHED ester 137 was followed by treatment with potassium bifluoride in aqueous methanol to provide the alkyltrifluoroborate salt 138. Neither boronic esters nor alkyltrifluoroborate salts react with alkyl azides. Reaction of 138 with trimethylsi-lyl chloride yielded (S)-2-phenylpyrrolidine (141), but reaction with silicon tetrachloride proved much faster and more efficient. At first it was thought that the intermediates 139 and 140 were probably difluoroboranes in accord with literature precedent [76], but careftil reinvestigation has revealed that reaction of alkyltrifluoroborate salts with silicon tetrachloride in coordinating solvents yields alkyldichloroboranes [78]. 

The reaction of (a-chloroalkyl)boronic esters with silicon tetrachloride does not epimerize (a-chloroalkyl)boron groups. As a test, (S)-DICHED (1-chloropentyl)-boronate (142) with potassium bifluoride was converted into potassium (1-chloro-pentyl)trifluoroborate (143), which was treated with silicon tetrachloride in THF to form (l-chloropentyl)dichloroborane (144). The dichloroborane was converted into the stable pinacol ester 145, which was transesterified to the (R)- and (5)-pinanediol esters 146 and 147, respectively (Scheme 8.33). H NMR spectra of these two di-astereomers differ sufficiently to show that each was pure and free from more than 1-2% of the other. Compound 144 was shown to react readily with diethylzinc followed by base and finally hydrogen peroxide to yield the expected (S)-3-heptanol, but this chemistry awaits further development to achieve efficient synthetic procedures. 

A very rapid oxidative disintegration of chromium-bearing minerals, rocks and alloys is obtained by fusing or sintering the finely pulverized material with potassium bifluoride (platinum spoon). Potassium chromate results and may be detected by means of the diphenylcarbazide reaction. The fluoride disintegration is particularly recommended for the detection of chromium in steels or special alloys, which are likely to contain molybdenum. The latter, in the form of molybdate ions, reacts with diphenylcarbazide to yield a red-violet color and thus impairs the test for chromium. However, the fluoride method yields no M0O4" ions, but instead complex [M0O3F2] ions, which do not react with diphenylcarbazide. 

A convenient two-step access to valuable ethyl a-fluorocyclopropanecarboxylates that involves a Michael-initiated ring closure reaction between ethyl dichloroacetate and various terminal electron-deficient alkenes has been developed. In the second reaction step, fluorination reaction with potassium bifluoride takes place through a 1,2-elimination/addition pathway. 

A far more important application of potassium bifluoride is its use as electrolyte in the production of elemental fluorine in electrolysis cells [69]. The feed of additional HF into the reaction reduces the operating temperature of the cell to about 90 °C. The relation of HF to KF should not fall below KF-2HF. 

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