Fluonde ion

Fluonde Ion as Nucleophile and a Leaving Group in Aromatic Nucleophilic Substitution Reactions Vlasov V M J Fluorine Chem 6i. 193-216 77... 

Selective fluonnation in polar solvents has proved commercially successful in the synthesis of 5 fluorouracil and its pyrimidine relatives, an extensive subject that will be discussed in another section Selective fluonnation of enolates [47], enols [48], and silyl enol ethers [49] resulted in preparation of a/phn-fluoro ketones, fieto-diketones, heta-ketoesters, and aldehydes The reactions of fluorine with these functionalities is most probably an addition to the ene followed by elimination of fluonde ion or hydrogen fluoride rather than a simple substitution In a similar vein, selective fluonnation of pyridmes to give 2-fluoropyridines was shown to proceed through pyridine difluondes [50]... 

The striking nucleofugacity of the trimethylammonium leaving group compared with the nitro group in the reaction with fluonde ion is illustrated by the relative reactivities of p-nitrophenyltnmethylammonium perchlorate and p dmi-trobenzene [7J] (Table 4)... 

Fluonnated ylides have also been prepared in such a way that fluonne is incorporated at the carhon P to the carbamonic carbon Vanous fluoroalkyl iodides were heated with tnphenylphosphine in the absence of solvent to form the necessary phosphonium salts Direct deprotonation with butyUithium or hthium dusopropy-lamide did not lead to yhde formation, rather, deprotonation was accomparued by loss of fluonde ion Flowever deprotonation with hydrated potassium carbonate in thoxane was successful and resulted in fluoroolefin yields of45-S0% [59] (equation 54) P-Fluorinated ylides may also be prepared by the reaction of an isopropyli-denetnphenylphosphine yhde with a perfluoroalkanoyl anhydnde The intermediate acyl phosphonium salt can undergo further reaction with methylene tnphenylphosphorane and phenyUithium to form a new yhde, which can then be used in a Wittig olefination procedure [60] (equation 55) or can react with a nucleophile [6/j such as an acetyhde to form a fluonnated enyne [62] (equation 56)... 

In a different appheauon, the selective alcoholysis of methylphosphomc difluonde is promoted by the capture of fluonde ion by sihcon [8J] (equation 74)... 

Unsaturated fluorocarbons are much more reactive toward nucleophiles than then hydrocarbon counterparts owing to fluorme s ability to both stabihze carban ions and mductively increase the electrophihcity of multiple bonds and aromatic nngs Nucleophihc attack dominates the chemistry of unsaturated fluorocarbons, and the role of fluonde ion in fluorocarbon chemistry is analogous to that of the proton in hydrocarbon chemistry [129] Like the related electrophilic reactions for hydrocarbons, there are fluonde-promoted isomenzations and dimenzations (equation 9), oligomenzations (equation 10), additions (equation 11), and amomc Fnedel-Crafts alkylations (equation 12) that all proceed via carbamomc intermediates [729 7 7]... 

There are five major methods for the determination of fluonde ions m aqueous solution (1) volumetric, (2) gravimetnc, (3) null pointpotentiometry, (4) fluonde lon-selecti ve electrode (also known as specific ion electrode), and (5) ion chromatography... 

This method involves very simple and inexpensive equipment that could be set up m any laboratory [9, 10] The equipment consists of a 250-mL beaker (used as an external half-cell), two platinum foil electrodes, a glass tube with asbestos fiber sealed m the bottom (used as an internal half-cell), a microburet, a stirrer, and a portable potentiometer The asbestos fiber may be substituted with a membrane This method has been used to determine the fluoride ion concentration in many binary and complex fluondes and has been applied to unbuffered solutions from Willard-Winter distillation, to lon-exchange eluant, and to pyrohydrolysis distil lates obtained from oxygen-flask or tube combustions The solution concentrations range from 0 1 to 5 X 10 M This method is based on complexing by fluonde ions of one of the oxidation states of the redox couple, and the potential difference measured is that between the two half-cells Initially, each cell contains the same ratio of cerium(IV) and cerium(tll) ions... 

The redox solution for 0 095 M fluonde ion solution is prepared by dissolving 12 7 g of cenum(IV) ammomum sulfate m 200 mL of disnUed water and 14 mL of 18 M sulfunc acid CenumfUI) sulfate (2 8 g) is added, and the solution is diluted to I L... 

Direct analysis with the fluoride lon-selective electrode requires addition of total ionic strength adjustor buffer solution (TISAB) to the standard and to unknown samples Some advantages of this addition are that it provides a constant background ion strength, ties up interfenng cations such as aluminum or iron, which form a complex with fluoride ions, and maintains the pH between 5 0 and 5 5 According to the manufacturer s claim, reproducibility of direct electrode measurement IS 2 0%, and the accuracy for fluonde ion measurement is 0 2% [27]... 

NMR chemical shifts reported for the fluonde ion vary considerably [759, 160, 161, 162, 163]. The electronic environment associated with a fluonde ion is much more exposed to the medium than a covalent C-F moiety. Chemical shifts... 

Desflurane can be made by fluonnation of isoflurane with potassium fluonde [/J] or with bromine tnfluonde [14] (equation 2) Although approximately six times more desflurane than isoflurane is required for anesthesia, it achieves the anesthetic state and the patient recovers from this state more rapidly This feature seems to be of interest to some anesthesiologists One negative property is that it irritates the breathmg passageway, especially in children Desflurane is flammable at higher levels of anesthetic use It is the least metabolized of all the commercial anesthetics, producing tnfluoroacetic acid and fluonde ion [75]... 

Stereoselective l.4-reduction oi the 1.3-butadiene system to olefin 57 lakes place tinder the conditions of the Birch reduction. Intramolecular protonation of the intermediate carbanion at the 18-position to give 57 occurs with high selectivity syn to the hydroxymethy-iene group Conversion into phosphoric acid derivative 58 and cleavage of the phosphoric acid amide group under (he conditions of the Bcnkeser reduction provides compound 5921 Fluonde ion causes the release of free p-amyrin (1) in a final step I Li, NH3(iyTllF (1/1.75), -78 C 93%. 

Similarly, hexafluoroprapylene undergoes fluonde ion induced homotelo-merization to give a senes of dimers and trimers These telomerizations can be induced by other nucleophiles, such as amines Indeed, the selectivity of the pi oce.s can be changed significantly by varying reagents and reaction conditions [25, 26] (equations 19 and 20)... 

Cyclopentane annulation is readily achieved via an intramolecular Sakurai reaction to simple enones with either fluonde ion or Lewis acid catalysis.l3 However, we have noted two mstances in which cyclopentane annulation occurs due to 1,4-addition of an allylsdane to a conjugated dienone.14 The first example is illustrated above, where the fluonde ion-promoted cychzation of dienone 5 generates a five-membered ring. Equation 6 presents additional examples of this annulation. 

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