Fluoride transfer

Boron trihalides are strong Lewis acids that react with a wide collection of Lewis bases. Many adducts form with donor atoms from Group 15 (N, P, As) or Group 16 (O, S). Metal fluorides transfer F ion to BF3 to give tetrafluoroborate salts LiF + BF3 LiBF4 Tetrafluoroborate anion is an important derivative of BF3 because it is nonreactive. With four <7 bonds, [BF4 ] anion has no tendency to coordinate further ligands. Tetrafluoroborate salts are used in synthesis when a bulky inert anion is necessary. 

It was found that treatment of a mixture of 120 and 121 with tris(diethylamino-sulfonium) trimethyldifluorosilicate [TASF(Et)] resulted in smooth addition-elimination to the naphthoquinone to form the y-alkylation product 125 (85 %). TASF(Et) is a convenient source of soluble, anhydrous fluoride ion [47]. It is believed that exposure of 121 to TASF(Et) results in fluoride transfer to generate a hypervalent silicate anion, as depicted in structure 124. The transfer of fluoride between TASF(Et) and 121 may be driven by stabilization of the anionic species 124 by delocalization of the carbon-silicon bond into the LUMO of the unsaturated ketone. 1,4-Addition-elimination of this species to the naphthoquinone 120 would then form the observed product. 

The committee notes that the electrode damage may become more severe when feeds containing fluorine and chlorine are processed. In the fluoride transfer test discussed earlier, the titanium electrodes were severely corroded and the Pt coating was pitted or peeling off. This more severe damage would be unacceptable during full-scale plant operation. 

Preparation. Assemble an apparatus as shown in Fig. 109. Mix 2 g of dry quartz sand with 2 g of calcium fluoride. Transfer the mixture into a Wurtz flask and add 15 ml of a 96% sulphuric acid solution. Close the flask with a stopper. The funnel must touch the surface of the water in the beaker. Heat the flask. What do you... 

Not only the reaction conditions, but also the structure of the starting material has a strong influence if fluorohydrins are formed or rearrangement occurs. Tricyclic epoxides 6a, b react with boron trifluoride-diethyl ether complex to give fluorohydrins 7 via fluoride transfer, whereas 6c undergoes isomerization.32... 

An interesting case of simultaneous exchange of two fluorides has been reported recently22. In compounds 2g and 2h there is one tetra- and one pentacoordinate silicon. Fluoride transfer from the pentacoordinate silicate to the silane was found to be inter-molecular, with a large negative entropy of activation. It was concluded that exchange takes place simultaneously between two complexes, through a cyclophane-like transition... 

In contrast to 179, the reaction of 180 with CgFsLi affords not only the expected compound 190, but also the fluoride transfer product 191 and the tetrafluorobenzene insertion product 192 in 1 2 1 ratio (equation 180)312. 

ICR mass spectrometry has been employed to study the kinetics and equilibria of the generation of silylenium ions by hydride transfer from silanes to carbenium ions (43,47). The kinetics of the formation of silylenium ions from fluoromethylsilanes [(CH3) SiF4 , n = 1-3] have also been investigated by this technique (48). Fluoride transfer was the dominant reaction in this system. 

The appearance of SnF+ ions is also observed in the mass spectra of p- or m-CF3C6FLt)4Sn and it becomes the major ion in the spectra of the perfluorinated (C6F5)4Sn species. This fluorine migration has been rationalized in terms of hard/soft acid base theory (HSAB) by considering Sn + as a hard acid that favors fluoride transfer . 

Fluoroalkanes can be obtained by fluoride transfer from complex fluoride anions to carbocat-ions in the nitrosative decomposition of certain aliphatic azides. Several complex nitrosonium salts, such as NO " BF4, NO PF(, , and NO ShF ". " have been used for this purpose. This reaction is similar to the decomposition of arenediazonium tetrafluoroborate salts to form aryl fluorides (the Balz-Schiemann reaction, discussed in Sections 1.1.8.5. and Vol. F 10a, p686ff). in which fluoride is transferred from a very weak nucleophile, such as the complex tetrafluoroborate anion, to an electron-deficient center. 

The addition ofsmall amounts of water (1-2 mol equiv) to the nitrosonium salt, before reaction with the azido nitrile, minimizes telrazolc formation and enhances the amount of fluoro nitrile products obtained (see Table 1, entries 5-7). Water probably results in aquation of the Lewis acids formed during the fluoride transfer, thus minimizing tctrazole production. ... 

Pentahalides form adducts with nearly all types of neutral or anionic donors. " The high Lewis acidity of MF5 is illustrated by facile fluoride transfer and formation of anionic adducts. Species such as MF ", n = 1-4) and M2Fn have been detected in HF solutions of the metals using a selective fluoride ion electrode or by F NMR. These complexes... 

CF from CF4 are generally too high, and even photoelectron-photoion coincidence experiments provide only upper limits (Brehm et al., 1974 Powis, 1980). We therefore performed a series of experiments designed to determine this heat of formation (Fisher and Armentrout, 1990d). In contrast to a literature report (Babcock and Streit, 1981), we demonstrated that there can be no fluoride transfer equilibrixrm between CFj and SF at thermal energies by examining both the forward and reverse reactions (21) ... 

Ion trap instruments also provide the possibility to study ion-ion reactions, e g., reactions of multiple-charge peptide or protein ions with ions of opposite polarity. Mostly, proton-transfer reaction are performed, but electron transfer, fluoride transfer reactions, and even attachment reactions may occur as well [81]. Ion traps, either three-dimensional or linear ones, with multiple ion sources are appUed in such experiments [82]. 

The perfluorethyl and -isopropyl derivatives readily deconq)ose. Possible deconq)osition mechanisms are fi-fluoride transfer from carbon to sulfur under formation of perfluoroalkenes and SF5" or heterolytic cleavage of the C-S bond to give Rp" and SF4 as the primary products (26). 

Moens and co-workers used the fluoride transfer reaction frommethyl fluoride to Sr+ (resulting in the formation of SrF+) to separate the strontium isotope pattern from a rubidium-containing background matrix, with the aim of making Rb-interference free isotope ratio measurements of strontium. However, it has been proposed that mass discrimination effects due to the ion-molecule reaction can alter the experimentally determined isotope pattern, thereby degrading the accuracy of isotope ratio measurements made using this approach. Consider the reaction... 

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