Replacement of aromatic fluorine

Reductive methylation of the tetrahydropyranyl ether of 17o -acetoxy-3/3-hy-droxypregn-5-en-20-one, 56 Replacement of aromatic amino groups by fluorine, 450... 

Sodium fluoride does not effect any replacement of aromatic chlorine atoms with fluorine, unless they are activated by substitution of electron-withdrawing groups in the ring. Several examples are reported for heterocyclic compounds. 

The replacement of a substituent on an aromatic ring by a nucleophile is termed arylation. This chapter considers the replacement by nucleophilic oxygen, sulfur, nitrogen, and carbon of aromatic fluorine atoms, which are often activated by electron-withdrawing groups. 

An unactivated aryl fluorine may be activated by complexation with chro-mium(VI). Replacement of the fluorine in the complexed system occurs readily, and the uncomplexed aromatic product can be generated by treatment with iodine [84] (equation 46)... 

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)... 

Diazotization procedures. Widely used for the production of aromatic fluorine is the Balz-Schiemann reaction. The approach involves diazotization of the aniline and isolation of the insoluble tetrafluoroborate salt, followed by decomposition under heating conditions (Fig. 32). Initially introduced in 1927 [137,138], it did not achieve commercial utility until the mid-1980s. A modification of the Balz-Schie-mann reaction involves replacing the tetrafluoroborate with other counterions such as a fluorine anion [139],... 

Separation of aromatic/aliphatic mixtures by pervaporation using the PBO membranes was studied by Ribeiro et al. The PBOs were prepared by the TR of ort/jo-fimctionalized fluorinated polyimide films (Figure 5.60). They used different feed streams, such as toluene/ -heptane or benzene/ -heptane mixtures. All the PBOs were selective toward the aromatic hydrocarbon. The PBO membranes showed higher selectivity (a=6.7, at 80 °C) and 25 times higher permeability (toluene, 220 Barrer, at 80 °C) in comparison to their precursor polyimides (toluene, 8.9 Barrer and a =1.9, at 80 °C). These increases in hydrocarbon permeability for the fluorinated PBO membranes are due to their larger hydrocarbon uptake and lower packing efficiency of the polymer chains, that is, increase in FFV in comparison to their precursor polyimides [91]. In all cases for a given diamine, the replacement of the >C(CF3)2 unit in the dianhydride (i.e., with the replacement of the fluorinated dianhydride with a non-fluoiinated one) resulted in an approximate 10 times reduction in hydrocarbon permeability, and consequently a reduction in total flux, with an increase in selectivity. 

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). 

Acetyl hypofluorite is very effective m the fluorination of the aryl-metal (Hg, Ge, or Si) bond, but yields are frequently low. With aryl silicon compounds some competition exists for replacement of an aromatic hydrogen [5i, 52, 55, 54] (equations 25-27). Fluoroxytrifluoromethane fluorinates p-methoxypheny 1 mercuric acetate to givep-fluoroanisole in 86% yield [52]... 

Amino groups bound to sulfur can be replaced by fluorine via diazotization. In contrast to carboxylic acid amides, fluorodediazoniation of aromatic sulfonamides IS readily accomplished to give sulfonyl fluorides in high yields [52, 7S (equation 16) Tetrazotization-fluorination of sulfanilamide can also be effected to give a 38% yield of p-fluorobenzenesulfonyl fluoride [52],... 

Replacement of an aromatic fluorine atom by a carbon nucleophile is facihtated by the presence of electron-withdrawmg groups [82] (equation 44) Replacement of an activated aryl hydrogen can occur in preference to a nonactivated aryl fluorine [Si] (equation 45) in reactions known as vicarious subsututions. 

Because of resonance stabilization of the anion, a tet-nazolyl moiety is often employed successfully as a bioisosteric replacement for a carboxy group. An example in this subclass is provided by azosemide (27). Benzonitrile analogue is prepared by phosphorus oxychloride dehydration of the corresponding benzamide. Next, a nucleophilic aromatic displacement reaction of the fluorine atom leads to The synthesis concludes with the 1,3-dipolar addition of azide to the nitrile liinction to produce the diuretic azosemi de (27). ... 

In this work we have demonstrated that a new class of heavily fluorinated acrylic and methacrylic resins can be efficiently synthesized and then cured to solid form with radical initiator at elevated temperatures. These cured resins were found to have low dielectric constants, which are close to the minimum known values for Teflon and Teflon AF. In contrast to tetrafluoroethylene, our monomers are processable owing to the fact that they are liquids or low-melting solids, and moreover are soluble in common organic solvents. Lower dielectric constants are obtained as fluorine contents on the polymer backbone or side chain increase, when acrylate is replaced by methacrylate, when ether linkages are present in the fluorocarbon, and when aromatic structure is symmetrically meta-substituted. 

Replacement, of acetylenic hydrogen atom by bromine, 45, 86 of acyl chlorine atom by fluorine atom using hydrogen fluoride, 46, 3 of amino hydrogen atoms by thio-carbonyl group, 46, 19 of aromatic bromine atom by potassium /-butoxide, 46, 89 of a-chloro atom in ester using azide ion, 46, 47... 

Hydrogenolysis (23S) of perchloryl aromatic compounds yields ArH and not ArOH, thus confirming the presence of a —Cl bond. Another useful reaction of FCIO3 involves the replacement of the active hydrogens of methylene compounds by fluorine (145, 262, 284). A typical example is the fluorination of malonic esters ... 

---