Fluorination replacement

FIuorosihca.tes, Compared to the simple sUicates, these crystals have more complex chain and sheet stmctures. Examples from nature iaclude hydrous micas and amphiboles, including hornblende and nephrite jade. In glass-ceramics, fluorine replaces the hydroxyl ion fluorine is much easier to iacorporate ia glass and also makes the crystals more refractory. Eour commercial fluorosUicate glass-ceramic compositions and thek properties are Usted ia Table 2. 

Fluorine replacement by alkoxyl may also be achieved with free alcohol in the presence of a rhodium(in) catalyst (equations 4 and 5) [6, 7] or a chromium(VI) complex [, 0] (equation 5). 

Chromium complexes of fluoroaromatics undergo fluorine replacement more readily and in high yield [24] (equation 14). 

Fluorine replacement m perfluorobenzene can be achieved in good yields and high selectivity when heavy metal thiolates are used as nucleophiles [29, 30, 31, 32] (equations 19-21). 

Fluorine Replaces a Hydrogen Involved in the Catalytic Cycle... 

Rubidium fluoride offers no advantage over cesium fluoride in fluorine replacement reactions. For example, in the reaction of / -(nitrophenyl)dimethylsulfonium methyl sulfonate (21) with cesium and rubidium fluoride, rubidium fluoride afforded the fluoro derivative 22 in 51 % yield as well as the side product 23. In contrast cesium fluoride gives 66% yield of 22 and only 20% of the side product 23.180... 

A nitro group in the 2- or 4-position relative to fluorine enhances the possibility of fluorine replacement by a hydroxy group.43,44 Hydrolysis of pentafluoronitrobenzene (11) gives three substituted phenols.45... 

The SNAr reaction between thiolates and monofluorobenzene and its derivatives requires high temperatures and polar aprotic solvents [19, 20, 21]. Polyfluoroaro-matics show very little selectivity for fluorine replacement [22, 23] (equation 13 J. 

Tropical upwelling is the main process through which halocarbons are carried up into the stratosphere. Once there, they are distributed polewards along sloped isentiopic surfaces, and subject to photolysis by UV radiation. As Chou [13] have pointed out, UV absorption cross-sections of halocarbons depend strongly on the number of chlorine atoms attached to a particular carbon atom. Hence, stability and thus atmospheric life times increase with increasing number of fluorine replacing chlorine atoms (see 4. and table 1). 

If in other groups of compounds one is also only concerned with the replacement of one halogen by another, then, since the dipole moment undergoes little change thereby, one can in the first instance likewise calculate with a fixed change of boiling points fluorine replaced by chlorine 50°, chlorine by bromine 28.5°, and bromine by iodine 40°. 

While this method has been used for a variety of compounds, replacement of F by N is very rare, although unusual compounds like the nitrenes OsF5(NC1) [83] or ReFs(NF) [84] have been isolated from such reactions. Even less favorable is fluorine replacement by Cl. Therefore this type of reaction is limited to very special but interesting cases [85,86] ... 

Fluorine replacement in aromatic compounds occurs quite smoothly when the rings contain electron-withdrawing groups. For example, ammonia and the amide ion react with arene 1 to yield the 2-substitutcd and 4-substituted derivatives, 2 and 3, resptectively. ... 

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