Organic fluorides, formation

Organic Fluorides. Part IX. The Formation and Resolution of a-Hydroxy-a-trifluoromethylpropi-onic Acid, R. A. Darrall, F. Smith, M. Stacey, and J. C. Tatlow, /. Chem. Soc., (1951) 2329-2332. 

Organic Fluorides. X. The Formation of Fluoro-oils and Resins by the Polymerisation of Hydrofluorocarbons with Fluorine," F. Smith, M. Stacey, J. C. Tatlow, and (in part) J. K. Dawson, and B. R. J. Thomas,/ Appl. Chem., 2 (1952) 97-105. 

The formation of organic fluorides has been a difficult undertaking. However, an investigation of the effect of the solvent, leaving group, and source of the fluoride ion has shown that using tetrabutylammonium fluoride or CsF in r-amyl alcohol is able to convert arene sulfonates into fluorides rapidly at 90 °C in excellent yields (>80%).65 Since the half-life of 18F is only 110 min, this is an important advance as it allows one to label compounds with 18F for PET studies. 

The mechanism of the formation of organic fluorides from silyl etliers and fluoro-/. -phosphanes has been studied in some detail for tetrafluoro(phcnyl)-A -phosphane. The first step, which is usually quantitative at low temperatures, is the formation of an intermediate alkoxyfluoro-A -phosphane 1 and fluorotrimethylsilanc. 

By mistake, sodimn was added to excess liquid perfluoroalkylmethanol in the absence of tire diluent which had previously moderated the reaction. Vigorous initial reaction culminated in an explosion which destroyed the flask and attached glassware and cracked tire fume cupboard window, this was attributed to ignition of evolved hydrogen [1]. Since air would rapidly be swept from the flask by the gas flow, it seems probable that a hydrogen explosion sufficient to damage the hood would be external to the reaction flask. The desired fluoroalkoxide is undoubtedly thennodynamically imstable with respect to sodium fluoride formation and a number of other metal derivatives of fluorinated organics have proved explosively metastable [2]. 

The following data ( fable 1) for niolcctilcs, including hydrocarbon s, strained ring system s. molecn les with heieroatom s, radicals, and ions conies from a review by Stewart. For most organic molecules,, YM 1 reports heals of formation accurate to within a few kilocalories per rn ol. bor soni e molecules (particularly inorgari ic compoun ds wdth several halogens, such as perch loryl fluoride, even the best sem i-em pineal method fails completely. 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

There are several examples in which metabolites that toxify the organism responsible for their synthesis are produced. The classic example is fluoroacetate (Peters 1952), which enters the TCA cycle and is thereby converted into fluorocitrate. This effectively inhibits aconitase—the enzyme involved in the next metabolic step—so that cell metabolism itself is inhibited with the resulting death of the cell. Walsh (1982) has extensively reinvestigated the problan and revealed both the complexity of the mechanism of inhibition and the stereospecihcity of the formation of fluorocitrate from fluoroacetate (p. 239). It should be noted, however, that bacteria able to degrade fluoroacetate to fluoride exist so that some organisms have developed the capability for overcoming this toxicity (Meyer et al. 1990). 

The most general method for the simultaneous analysis of oxyanions by gas chromatography is the formation of trimethylsilyl derivatives. Trimethylsilyl derivatives of silicate, carbonate, oxalate, borate, phosphite, phosphate, orthophosphate, arsenite, arsenate, sulfate and vanadate, usually as their ammonium salts, are readily prepared by reaction with BSTFA-TMCS (99 1). Fluoride can be derivatized in aqueous solution with triethylchlorosilane and the triethylfluorosilane formed extracted into an immiscible organic solvent for analysis by gas chromatography [685). 

Following the reactions in Scheme 4, the olefin 13 would have to be generated before the formation of the 7r-crotyl species 2. Because the amount of the catalyst present is usually small as compared to the amount of product formed (1000 moles of product/mole catalyst), the quantity of 13 produced will not be significant and should be readily separable from the desired product. In the special case when crotyl chloride is used as the activator, hexadiene can be produced during the very first cycle of reaction, i.e., 13 = 1,4-hexadiene. Among the organic halides, the chloride derivatives are the most effective activators. Bromides are somewhat effective, while fluorides and iodide are rather ineffective (77). 

The type of reactivity shown by the formation of Chichibabin s hydrocarbon extends to the activation of substituents other than hydrogen as well. For example, molecular silver will not usually remove fluorine from organic compounds, not even from triphenylmethyl fluoride. Yet the radical parafluorophenyldiphenylmethyl reacts with molecular silver to give silver fluoride.88... 

Thallium(I) acetate, 24 630-632 Thallium compounds, in organic reactions, 24 635 Thallium formate, 24 630 Thallium halides, 24 632 Thallium ion, 24 629 Thallium nitrate, uses for, 24 636 Thallium salts, 24 630, 632 Thallium sulfate, uses for, 24 636 Thallium (III) compounds, in organic reactions, 24 635-636 Thallium(III) fluoride, 24 632 Thallium(III) ion, 24 630 Thallium(III) salts, 24 632 Thallium(III) trifluoroacetate, 24 635 Thallium (Tl), 24 627-641... 

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