With Replacement of one Fluorine Atom

Heating a bis[fluoroalkoxy] tellurium difluoride with an equimolar amount of fluoroalkoxy trimethylsilane in benzene at 80° produced tris[fluoroalkoxy] tellurium fluorides.  

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The trtfluoromethyl group activates the fluorine in position 4 ofperfluorotolu ene toward reaction with carbon nucleophiles Examples on the use of perfluoro-toluene as an ary lation agent abound, and in all cases, the 4-fluonne atom is replaced predominantly or exclusively [86,87,88,89,90] (equation 48) Inperfluoromesity-lene, the aromatic fluorine atoms are activated toward SN Ar reaction, and a reaction with one equivalent of methylkthium causes smooth replacement of one fluorine atom [91] (equation 49)... 

Polychlorotrifluoroethylene (PCTFE). Polychlorotrifluoroethylene (PCTFE) is made by the polymerization of chlorotrilluoroethylene, which is prepared by the dechlorination of trichlorotrilluoroethane. The polymerization is initiated with redox initiators. The replacement of one fluorine atom with a chlorine atom, as shown in Fig. 2.5, breaks up the symmetry of the PTFE molecule, resulting in a lower melting point and allowing PCTFE to be processed more easily than PTFE. The crystalline melting point of PCTFE at 218°C is lower than PTFE. Clear sheets of PCTFE with no crystallinity may also be prepared. 

Trifluoro-l,3,5-triazine 55 reacts with 2,3-dihydro-l,3-isopropyl-4,5-dimethylimidazol-2-ylidene tetrafluoroborate 136 resulting in replacement of one fluorine atom to yield difluoro-l,3,5-triazine 137 (Scheme 55) [8],... 

The reaction of 2,4-difluoro-6-(l-methylpyrrolyl-2)-l,3,5-triazine 138 with iodpropargyl alcohol affords the product 139 due to replacement of one fluorine atom (Scheme 56) [86],... 

Concluding this section all that one can say is that we found no relationship between anesthetic potency and either the ionization potentials or the frequency of the lowest ultraviolet absorption band. The observation that replacement of a fluorine atom by a hydrogen usually lowers the IP is probably of some value. However, as was pointed out above this could only indicate the possibility of charge transfer interaction if the electron affinities followed the same trend. Unfortunately these have not been determined and the variations in the frequencies of the broad UV bands are too irregular to draw conclusions. It seems that there exists an indirect relationship between the acidity of these molecules and their IPs and what counts is their proton donor ability connected with the acidic hydrogen as has been concluded from the infrared studies described in previous sections. 

The chemistry of fluorinated 1,3,5-triazines is not as well studied as the chemistry of their chloro derivatives. In case of fluorotriazines the reactions directed on the ring nitrogen atoms, displacement of fluorine atoms and reactions on carbon atoms on the ring with retention of the fluorine atoms appear to be the most characteristic ones. In this section the N-alkylation and N-acylation reactions, as well as replacement of fluorine atoms by a variety of nucleophiles will be considered. Metallation of fluorotriazines and synthesis on the basis of organometallic compounds, as well as the cross-coupling reactions were described. Also several examples of photochemical reactions and transformations are presented. 

Reactions of polyhydroxyl compounds such as carbohydrates with DAST lead to replacement of one or two hydroxyl groups by fluorine, more fluorine atoms are not introduced even when a large excess of the reagent is used [132, 139, 147] Although diethylaminosulfur tnfluonde (DAST) is the most popular, other dialkylaminosulfuranes, such as diisopropylamino- [95] pyrrolidino [95 109 /27], dimethylamino- [148], piperidino- [148] and particularly morpholinosulfur trifluonde [148,149, ISO], are also used as fluonnating agents to convert alcohols into fluorides... 

Perfluorobenzene undergoes Sf Ar reactions readily with dimethylarmne, aniline, N methylaniline [AS], piperidine, A/-tnmethylsilyliminotnmcthylphos-phorane [69], and bthinm aniUde [70], but the reactions are often accompanied by sigmficant amounts of di- or polysubstitubon However, with the lithium salt of A -tnmethylsilylanilme, only one fluorine atom in pcrfluorobenzeneis replaced [71] (equation 36)... 

The higher fluorides are prepared using excess fluorine (Figure A). All these compounds are stable in dry air at room temperature. However, they react with water te form compounds in which one or more of the fluorine atoms has been replaced by oxygen. Thus xenon hexafluoride reacts rapidly with water to give the trioxide... 

The six positions around an octahedron are equivalent, as Figure 9-25 demonstrates. Replacing one fluorine atom in SFg with a chlorine atom gives SF5 Cl. No matter which fluorine is replaced, the SF5 Cl molecule has four fluorine atoms in a square, with the fifth fluorine and the chlorine atom on opposite sides, at right angles to the plane of the square. 

An alkyl halide (also known as a haloalkane) is an alkane in which one or more hydrogen atoms have been replaced with halogen atoms, such as F, Cl, Br, or I. The functional group of alkyl halides is R—X, where X represents a halogen atom. Alkyl halides are similar in structure, polarity, and reactivity to alcohols. To name an alkyl halide, first name the parent hydrocarbon. Then use the prefix fluoro-, chloro-, bromo-, or iodo-, with a position number, to indicate the presence of a fluorine atom, chlorine atom, bromine atom, or iodine atom. The following Sample Problem shows how to name an alkyl halide. 

The processability of fluorine-containing polymers is improved by replacement of one or more of the fluorine atoms. Replacing one of the eight fluorine atoms with a trifluoromethyl group gives a product called FEP or Viton, actually a copolymer of tetrafluoroethylene and hexafluoropropylene (Equation 6.53). Polytrifluoromonochloroethylene (PCTFE, Kel F) (Equation 6.54), in which one fluorine atom has been replaced by a chlorine atom, has a less regular structure and is thus more easily processed. Poly(vinylidene fluoride) (PVDF, Kynar) (Equation 6.55) is also more easily processable but less resistant to solvents and corrosives. 

All the above examples refer to thiophenes containing functional groups indifferent to the presence of butyllithium. In reactions with reagents in an equimolar ratio, it is highly probable that only one of the fluorine atoms at the double bond of cyclene will be replaced. For example, the target product 26 (Scheme 8) was prepared by either a one-pot reaction in the presence of a twofold excess of lithium derivative 24 with respect to per-fluorocyclopentene or in two steps including the isolation of monofluoride 25 (99IZV10n). 

An unusual six-electron cycloaddition could be observed in the reaction of CgQpjg with tetrathiafulvalene (TTF) [70], TTF is not added to one of the free double bonds but replaces two of the fluorine atoms in a way that leaves the CgQpjg moiety, whose structure is described above (Figure 9.1). Under loss of F2 the product Cjq Fi6(TTF) is formed (Figure 9.7). 

Treatment of adamantane (2) with sulfur tetrafluoride results in the replacement of one, two or three bridgehead hydrogen atoms by fluorine the degree of fluorination depends on the reaction temperature. When the reaction is conducted in hydrogen fluoride solution, substitution of all four bridgehead hydrogens occurs at relatively low temperature.185... 

In polyfluorobenzenes having other substituents in addition to fluorine, including per-fluoroalkyl or perfluoroaryl groups, the elimination of only one fluorine atom proceeds more readily, with the para position in pentafluorobenzene derivatives being replaced first. The reaction conditions used for monosubstitution of fluorine depend markedly on the substrate and on the nucleophilic agent chosen. In most cases the reaction can be carried out in ethylene glycol/pyridine using sodium hydroxide as base (Table 3). 

The reaction of diethyl tartrate with sulfur tetrafluonde at 25 °C results in replacement of one hydroxyl group, whereas at 100 °C, both hydroxyl groups are replaced by fluonne to form a,a -difluorosuccmate [7(52] The stereochemical outcome of the fluorination of tartrate esters is retention of configuration at one of the chiral carbon atoms and inversion of configuration at the second chiral center [163,164, 165] Thus, treatment of dimethyl (+)-L-tartrate with sulfur tetrafluonde gives dimethyl meso-a,a difluorosuccinate as the final product [163, 164], whereas dimethyl meso tartrate is converted into a racemic mixture of D- and L-a,a -difluorosuccinates [765] (equation 80)... 

Replacements of one or two chlorine atoms and hydrogen by fluorine were observed in various organosilicon compounds in reactions with xenon difluoride99,135, while aryl-silicon bond cleavage was observed in the presence of potassium fluoride136,137 (Scheme 57). 

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