Aromatic difluorides

The new fluorescent poly(aryl ethers) derived from nonfluorescent monomers have gained significant attention from polymer scientists [20]. These polymers are prepared by the polymerization of phenolphthalein and its derivatives with activated aromatic difluorides. 

Smith et al. prepared poly(arylene ether ben-zoxazole)s as shown in Figure 5.30 by the aromatic nucleophilic displacement reaction of two bis(hydroxyphenyl benzoxazole)s with activated aromatic difluorides [59]. The polymers had TgS ranging from 204 to 275 °C (Table 5.4). 

Miyatake and Hay [46] reported the first phosphonic acid containing polymers and copolymers from three phosphine-containing aromatic difluorides, prepared in accordance with the following Scheme 1 ... 

Polycarbonates can be formed by nucleophilic aromatic substitution involving aromatic difluorides and carbonate ion. Give a structure for the polymer produced from the monomers shown in the following, and propose a mechanism for its formation ... 

Some high-valency fluorides applied at moderate temperatures are capable of replacing individual hydrogens in aromatic rings Thus benzene affords fluoro benzene on treatment with silver difluoride [/] and with chlorine pentafluoride [2] (equations 1 and 2)... 

The results given in both Table 1 and in the reviews [4, 5 7, 8, I0 show that xenon difluoride reacts with a wide variety of aromatic substrates to produce regioselecuvely monofluorinated aromatics An example is the preparation of 6-fluoro-L DOPA [83] (equation 48)... 

Xenon difluoride may be used as the pure reagent or as a graphi te intercalate for the effective fluonnation of polynuclear aromatics [86 87] (equations 49 and 50)... 

Carboxylic acids react with xenon difluoride to produce unstable xenon esters The esters decarboxylate to produce free radical intermediates, which undergo fluonnation or reaction with the solvent system Thus aliphatic acids decarboxylate to produce mainly fluoroalkanes or products from abstraction of hydrogen from the solvent Perfluoro acids decarboxylate in the presence of aromatic substrates to give perfluoroalkyl aromatics Aromatic and vinylic acids do not decarboxylate [91] (equation 51)... 

Recently, the pyrazole group containing bisphenols have been synthesized from activated aromatic dihalides and 3,5-bis (4-hydroxy phenyl)-4-phenyl pyrazole or 3,5-bis(4-hydroxy phenyl)-1,4-diphenyl pyrazole. A novel synthesis of imido aryl containing bisphenols has been reported [32]. N-substituted l,4-bis(4-hydroxy phenyl)-2,3-naphthalimides were prepared from phenolphthalein and copolymerized with aromatic sulfone or ketone difluorides to obtain the poly(imidoaryl ether) sulfones/ ketones. 

The nucleophilic aromatic substitution reaction for the synthesis of poly(arylene ether ketone)s is similar to that of polysulfone, involving aromatic dihalides and aromatic diphenolates. Since carbonyl is a weaker electron-withdrawing group titan sulfonyl, in most cases, difluorides need to be used to afford high-molecular-weight polymers. Typically potassium carbonate is used as a base to avoid the... 

Furthermore, in the particular type of phosphate molecule under discussion (VI) we showed that when X is fluorine, compounds of high toxicity result whereas myotic effect is absent and toxicity of a low order if X = H, Et, OH, OEt, OCH2CH2C3, OCH2CH2F, Cl, NH2, NHMe, NHPh, CH2CH2F, CN, SON, etc.1 In Chapters rv and vi, however, we consider in more detail cases where X is not fluorine, but nevertheless toxicity results. Toxicity is also of a low order in the aromatic series for example, diphenyl phosphorofluoridate is relatively non-toxic and devoid of myotic properties. We also showed that ethyl phosphoro-difluoridate, (C2H50)P0F2, had neither myotic nor toxic action.1... 

Safety precautions applicable to direct liquid phase fluorination of aromatic compounds are discussed [1]. Attention is drawn to the hazards attached to the use of many newer fluorinating agents [2], In a study of fluorination reactions of hafnium and zirconium oxides by the fluoroxidisers xenon difluoride, chlorine trifluoride and bromine trifluoride, reactivity decreased in the order given [3],... 

Pyridine is converted into perfluoropiperidine (82) in low yield by reaction with fluorine in the presence of cobalt trifluoride (50JCS1966) quinoline affords (83) under similar conditions (56JCS783). Perfluoropiperidine can be obtained electrochemically. This is useful, as it may be readily aromatized to perfluoropyridine by passing it over iron or nickel at ca. 600 °C (74HC(14-S2)407). Recently, pyridine has been treated with xenon difluoride to yield 2-fluoropyridine (35%), 3-fluoropyridine (20%) and 2,6-difluoropyridine (11%), but it is not likely that this is simply an electrophilic substitution reaction (76MI20500). 

Fluorodcsulfurizations of thiols,311 phenyl thioglycosides,290 1,2-dithiolans.312 aromatic dithiocarboxylic acids,399 or orthothioesters313 in hydrogen fluoride systems with N-chloro-or N-bromosuccinimide as a coagcnt are facile methods for the generation of monofluorides, gem-difluorides, and trifluoromethyl derivatives, e.g. formation of 11,311 12,312 13,313 and... 

Extensive work on the interaction of aromatic compounds with xenon difluoride has been carried out in order to investigate the reaction mechanism and the scope of the fluorination depending on the substituents electronic nature.26-59 62 It has been found that benzene and substituted aromatics react with xenon difluoride at room temperature in the presence of hydrogen fluoride to form the typical products of electrophilic fluorination contaminated with low quantities of difluoro-substituted molecules. 

Perfluoroalkanccarboxylic acids react with xenon difluoride to form corresponding unstable fluoroxenon esters, which decompose to give perfluoroalkyl radicals successfully trapped by various substrates. Treatment of benzene in dichloromethane with a modest excess of tri-fluoroacetic acid and xenon difluoride at room temperature gives trifluoromethylbenzene in 33-42% yield. The better yields are achieved with aromatics bearing electron-withdrawing substituents.8x86... 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

Aromatic amines do not give iminosulfur difluorides in their reactions with sulfur tetrafluoride, but, instead, independent of the nature of the aromatic ring substituents, give the corresponding bis(phenylimino)sulfur 12 exclusively.170,201... 

Difluorotri(phenyl)-/.5-stibane, the most readily accessible among the aromatic anti-mony(V) fluorides, can be synthesized by several alternate methods in addition to those described above, i.e. by substitution of fluorine for chlorine in dichlorotri(phenyl)-/i5-stibane with potassium fluoride109 or hydrogen fluoride,110 and by oxidative fluorination of triphenylstibane with fluorine (in chloroform),111 perfluoro-l-fluoropiperidine,112 (difluoroiodo)ben-zene,107 or xenon difluoride.10 1... 

Tetrabutylphosphonium hydrogen difluoride [Bu4PF (HF)] and dihydrogen trifluoride [Bu4PF (HF)2] have been shown to be expedient reagents for nucleophilic fluorination of aromatic substrates containing a chlorine or bromine atom or a nitro group under mild conditions in non polar solvents. Thus, for example l-chloro-4-nitrobenzene (28) is converted to l-fluoro-4-nitrobenzene (29) in 90% yield.219... 

Fhiorination of aromatics. The reagent reacts with toluene to form benzyl fluoride as the major product ( 65% yield). It is also useful for fluorination of phenols- and of alkyl ethers of phenols the or/Ao-isomcr is formed as the major product. Reactions with this reagent thus differ from those with xenon difluoride, which generally favors formation of paro-isomers. 

An interesting class of compounds of the formula ArH(SiF2) , where n = 2 to 8, has recently been prepared by the reaction of silicon difluoride with aromatic compounds at low temperatures (186). The compounds... 

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