Trifluoromethyl groups fluorides

Reactions Involving the Trifluoromethyl Group. Aluminum chloride effects chlorinolysis of ben2otrifluoride to give ben2otrichloride (307). High yields of volatile acid fluorides are formed from ben2otrifluoride and perfluorocarboxyUc acids (308). 

Fluorination and iodination reactions are used relatively littie in dye synthesis. Fluorinated species include the trifluoromethyl group, which can be obtained from the trichi oromethyl group by the action of hydrogen fluoride or antimony pentafluoride, and various fluorotria2iQyl and pyrimidyl reactive systems for reactive dyes, eg, Cibacron F dyes. 

Triethylbenzylammonium chloride and potassium fluoride containing 1% water can provide chlorine-fluorine exchange of activated halides in the absence of a solvent. This mixture also can displace the chlorine of a chlorodifluoromethyl group to form a trifluoromethyl group [62] (equation 36). 

Carboxylic acids react both with fluoroaminosulfiiranes such as DAST and with sulfur tetrafluonde. Whereas DAST converts the acids to acyl fluorides only, sulfur tetrafluonde further fluorinates the primarily formed acyl fluorides and ultimately converts the carboxyl group to a trifluoromethyl group. 

Treatment of 2,5 and 2,4-furandicarboxylic acids with sulfur tetrafluonde in an excess of hydrogen fluoride leads simultaneously to conversion of the carboxylic groups into trifluoromethyl groups and addition of two fluorine atoms to the furan ring to give highly fluorinated diastereoisomersof2,5-dihydrofuran [225,226,227] (equations 117 and 118)... 

The reaction ot tormamides with sulfur tetrafluoride in the presence of potassium fluoride leads to replacement of both carbonyl oxygen and hydrogen with fluorine. The formyl group is directly converted into the trifluoromethyl group A-(trifluoromethyl)amines are formed in near quantitative yields [233] (equation 121)... 

Alkyl fluorides are more reactive than other alkyl halides under Friedel-Crafts conditions, whereas trifluoromethyl groups are less reactive than other trihalomethyl groups Thus, a bromoindane is prepared from 1-bromo-l-fluoro-2,2,3,3-tetramethylcyclopropane and benzene [5] (equation 8) whereas 3-tnfluo romethylphenyldiphenylchloromethane is obtained from 3-trifluoromethyl-benzotrichloride and benzene [9] (equation 9)... 

Hydrolysis of the trifluoromethyl group of 2 tnfluoiomethylimidazoles is promoted by the formation of the anion, which readily eliminates fluoride. The resultant ditluorodiazafulvene then easily adds water The remaining steps in the hydrolysis ate predictable When aqueous ammonia is used, 2-cyanoimidazoles result [40] (equation 4])... 

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. 

Though not available commercially, trifluoronitroethane shows some interesting chemistry consistent with the powerful electron-withdrawing effect exerted by the nitro group. Fluoride-mediated nitroaldol reactions were reported [144] with aldehydes affording a valuable entry to trifluoromethyl amino alcohols... 

Trifluoromethyl)benzene (benzotrifluoride, 15) was the first organic fluoride to incorporate a trifluoromethyl group. By a standard nitration process, it formed l-nitro-3-(trifluoromethyl)-benzene (16) which was reduced to the 1-amino derivative, 17. This we a-directive influence on electrophilic aromatic substitution contrasted with that for fluorobenzene, which gave 4-and 2-nitro products. 

It was recognized in the 1930s that Swarts work on (trifluoromethyl)benzene opened the way to the synthesis of many side-chain-fluorinated arenes. Aryl trichloromethyl groups were found to be readily converted to trifluoromethyl groups by anhydrous hydrogen fluoride, and systematic work in the area was initiated. This included commercial investigations, and patents were filed on potential uses of both side chain and nuclear fluorinated arenes. 

The fluorination of allylic231 232 and benzylic positions by halogen replacement using hydrogen fluoride has found very wide interest, since trifluoromethyl groups are highly desired substituents in many applications. Some representative examples are given by the formation of 10,232 II,233- 235 and 12.236... 

Formation of a six-membered ring by cyclization of a,y-carboxylic acid groups is also observed in the reaction of sulfur tetrafluoride with (1 / , S)-( + )-camphoric acid besides 1,2,2-trimethyl-3-(trifluoromethyl)cyclopentanecarbonyl fluoride (20) and camphoroyl difluoride (21). the bicyclic tetrafluoro ether, 2,2,4,4-tetrafluoro-l,8,8-trimethyl-3-oxabicyclo[3.2.1]octane (22). is formed. The ratio of products strongly depends on the reaction conditions.250... 

Unlike sulfur tetrafluoride, there has only been one reported case of the conversion of a carboxylic acid to a trifluoromethyl group with DAST. Treatment of benzoic acid with DAST in th presence of sodium fluoride at 80°C yields (trifluoromethyl)benzene (5).58... 

Decarboxylation of (bromodifluoromethyl)malonates (9) reminiscent of Krapcho s deal-koxycarbonylation process, is observed on treatment with potassium fluoride in dimethyl sulfoxide at 170 °C to give 2-(trifluoromethyl)-substituted esters 10.43 The precursors are prepared by reacting diethyl malonates 8 with dibromodifluoromethane in the presence of sodium hydride. The exchange of bromine for fluorine in 9 followed by decarboxylation is an excellent method of introducing a trifluoromethyl group a- to an ester group. 

The conversion of the bromodifluoromethyl group to a trifluoromethyl group is only possible after cleavage of one ester group. The direct SN2 displacement of bromide ion by fluoride ion is prevented by electronic and steric factors. 

The methyl group in aromatics could be converted similarly to the trifluoromethyl group using the chlorine, hydrogen fluoride and aluminum trifluoride system as a catalyst.21 22... 

Reactions of pcrfluoroalkadienes with antimony(V) fluoride are similar to those of per-fluoroalkenes. Terminal dienes 1 rearrange with antimony(V) fluoride at 0-20 C selectively to internal dienes 2, in which the terminal trifluoromethyl groups are predominantly in the configuration.3,37,38 Higher temperatures and a threefold excess of catalyst lead to cyclo-pentenes (see Section 5.3.3.1.). 

Perfluoro ketones and perfluoro a-diketones, with a trifluoromethyl group in the -position to the carbonyl, cyclize in the presence of antimony(V) fluoride to give furan derivatives, as reviewed by Krcspan and Petrov.4 Perfluoro(4-methylpentan-2-one) (1) rearranges to per-fluoro(2,4-dimethyltetrahydrofuran) (2) in 84% yield, when heated in the presence of anti-mony(V) fluoride.5... 

Perfluoro a-diketones 5, containing a -trifluoromethyl group, arc transformed in good yield to perfluoro(2-methyl-3-oxotetrahydrofurans) 6 when heated in the presence of antimony(V) fluoride.5... 

In perfluoro a-diketone 7, which lacks a trifluoromethyl group /i to the carbonyl in the 2-position. it is the carbonyl in the 3-position that participates in the cyclization to form per-fluoro(2-acctyltetrahydrofuran) (8), when 7 is heated at 150 C in the presence of antimony(V) fluoride.5 Perfluoro(2-methyltetrahydropyran-3-one) also rearranges to furan derivative 8 in high yield when heated at 100 C in the presence of antimony(V) fluoride for 20 hours.5... 

The mechanism for the cyclization of these perfluoro ketones, proposed by German and coworkers5 and discussed in the review by Krcspan and Petrov.4 involves initial activation of the carbonyl with antimony V) fluoride and a 1.4-fluorine shift from the /1-trifluoromethyl group. The resultant difluoromethylene carbocation then cyclizes with the carbonyl oxygen to give the tetrahydrofuran. 

A consequence of the high C —F bond strength is that fluorine is an especially poor leaving group. Alkyl fluorides are 102-106 less reactive toward nucleophilic displacement than other alkyl halides.8 9 gera-Difluorides and trifluoromethyl groups are essentially unreactive toward nucleophilic displacement of fluorine. 

Likewise open-chain, cyclic five- and six-memhered a,a,a, a tetrafluoro-ethers are opened by anhydrous hydrogen fluoride at elevated temperatures to give acyl fluorides terminated with a trifluoromethyl group A six-inembered ether such... 

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