Replacement of Fluorine Atoms

The stepwise replacement of fluorine atoms in fluorocyclophosphazenes, (NPF2) n = 3—5), by methyl groups has been followed.and n.m.r. spectroscopy showed that methyl-lithium in diethyl ether generally effects a geminal replacement pattern. With N3P3F6, only mono- and di-methyl derivatives were obtained, but with N4P4F8 the dimethyl (52), trimethyl (53), and octamethyl derivatives were noted. The formation of... 

Perfluoroquinazoline (21) undergoes replacement of fluorine atoms by methoxy groups in positions 2, 4, 5, and 7.5 5... 

Multiple replacement of fluorine atoms in polyfluorobenzenes by phenylsulfanyl groups is accomplished most successfully by using heavy metal salts of benzenethiol, especially by the nickel(II) salt,54 using the same reaction conditions as described above for the synthesis of l,2,4,5-tetrafluoro-3-(phcnylsulfanyl)benzene derivatives from pentafluorobenzenes and the lead(II) salt of benzenethiol, but with an increased amount of thiolate (Table 5). 

In general, the replacement of fluorine atoms with oxygen atoms tends to stabilize higher oxidation states. This stabilization is exempli-... 

The data on NMR C spectroscopy of 6-substituted fluorinated 1,3,5-triazines have been analyzed [3, 5, 7, 8]. Replacement of fluorine atom by CF(CF3)2 group leads to upfield shift of signals of triazine carbons in NMR spectra. 

It is worth to note that the replacement of fluorine atoms in 3,5,6-trifluoro-l,2,4-triazine 18 by action of bis(trifluoromethyl)amino anion (the latter can be obtained from perfluoro-2-azapropene and cesium fluoride) provides a mixture of mono-, di-and tiisubstituted perfluorodimethylamino-l,2,4-triazines 96-98 (Scheme 41) [12],... 

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. 

Nucleophilic replacement of fluorine atoms in azaaromatic compounds can be performed under rather mild reaction conditions, and this method is certainly one of the most effective approaches to their functionalization. Incorporation of perfluoroisopropyl groups into 2,4,6-trifluoro-l,3,5-triazine 55 proceeds smoothly... 

Replacement of fluorine atoms in triazines 55,115 and 115a take place also by action of pyrrole, N-methylpyrrole and N-methylindole resulting in the formation of the corresponding 1,3,5-triazines 125-130 (Scheme 51) [8],... 

Scheme 51 Replacement of fluorine atoms in triazines 55,115 and 115a...

Replacement of fluorine atoms in 2,4-difluoro-6-heptafluoro-fi(9-propyl- and 2-fluoro-4,6-bis(heptafluoro-MO-propyl)-l,3,5-triazines 115 and 116 takes place quantitatively on reflux of 115 or 116 with methanol, isopropanol or phenols in acetonitrile (Scheme 58) [83],... 

It is known [88] that replacement of fluorine atoms in cyanuric fluoride 55 with tetra-O-benzyl- or tetra-O-acetylglucose takes place consequently with the formation of di- and trisubstituted l,3,5-triazines 143 and 144 (Scheme 60). 

Schone 60 Replacement of fluorine atoms in 55 with tetra-O-benzyl- or tetra-O-acetylglucose... 

The chemical process of replacement of fluorine atoms has found its practical apphcation for fixing of yellow and dark blue fluorotriazine dyes 153 on cellulose (Schane 64) [92-94]. 

Vinyl and phenyl mfluoromethyl groups are reactive in the presence of aluminum chloride [10] Replacement of fluorine by chlorine often occurs Polyfluori-nated trifluoromethylbenzenes form reactive a,a-difluorobenzyl cations in antimony pentafluoride [11] 1 Phenylperfluoropropene cyclizes in aluminum chloride to afford 1,1,3-trichloro 2 fluoroindene [10] (equation 10) The reaction IS hypothesized to proceed via an allylic carbocation, whose fluoride atoms undergo halogen exchange... 

Alkylthio groups replace the fluorine atoms of pentafluorobenzene derivatives tvith relative ease, but selectivity is difficult to eontrol [27] (equation 17). 

The weakly nucleophilic nng nitrogen of unsubstituted 2-aminothiazole replaces the fluorine atom of 2,4-dinitrofluorobenzene, whereas in 5-methyl 2 ami-nothiazole, the 2-ammo function acts as the nucleophile [62] (equation 31)... 

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. 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

The rate constants of kn and kx obtained using Eq. (24) reveal that (i) the activity of Fem-TAMLs in bleaching Safranine O (k ) increases more than 10-fold when the tail ethyl groups of la are replaced by fluorine atoms in lk. The rate constant kn for lk equals l(rM 1s 1 at 25°C, a value that corresponds to those found for the reactivity of horseradish peroxidase Compound II... 

Replacement of fluorine by a halogen atom of a higher period will result into greater a—it stabilization of the gauche relative to the cis conformer. 

In aromatic series, when hydrogen atoms are replaced by fluorine atoms or by fluoroalkyl groups, an enhancement of the log P occurs (Table 3) [13]. The CF3, CF3O and CF3S groups are the most hydrophobic substituents known. They are widely used in crop science [41]. 

This chapter deals with modifications of the physical and chemical properties of an organic molecule, which are induced by the replacement of hydrogen atoms by fluorines. These changes in the physicochemical properties play an important role in the behavior of the molecule when it is put into a biological environment. 

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