J. C. Tatlow

Fluorinations with high valency metal fluorides and by the electrochemical method : Are they oxidation processes?

Abstract It is suggested that fluorination with high valency metal fluorides (e.g. AgF2, CoF3, MnF3, CeF3) involves the initial oxidation of the substrate by the metal ion either to a radical-cation or, less commonly, by the abstraction of a hydrogen atom. This is essentially the same as many aqueous oxidations, the difference coming in the next step where the first-formed intermediate is quenched by fluorine (as an ion or atom) instead of some hydroxylic species. It is possible to rationalize many features of the fluorinations of benzene and some of its derivatives, thiophen and tetrahydrofuran in this way. The fluorinations of olefins, hydrocarbons and hetero-atom compounds are also discussed as oxidation processes. The fluorinating powers of the reagents vary with the oxidation potentials of the metal ions in accord with the oxidation hypothesis, i.e., AgF2 > CoF3 > MnF3. More tentatively, it is also suggested that electrochemical fluorination is an anodic oxidation process. Fluorination with xenon difluoride is also discussed in terms of radical-cation intermediates.

Aromatic polyfluoro compounds—XXVIII : Further reactions of the pentafluorophenyl anion

The pentatluorophenyl anion from pentailuorophenyllithihium has been used as a nucleophile and as a source of tetrafiuorobenzyne. As a nucleophile it was used to make poly-lluorobiand -terphenyl derivative-s from perfluorotoluene, perfluoro-o-xylene, pcntiuoronitrobenzene and bromopentafluorobenzene, and polyfluoropolyaryls from pcrfluorobiphenyl. It also attacked decafluorocyclohexene and chlorotrifluoroethylene presumably, by an additionelimination sequence. Reactions using the tetrafluorobenzyne intcrmcdiati were carried out in the presence of excess bromopentatluorob, pentafluorobenzene and various lithium halides, in some cases with variation of the solvent. A mechanism for some of these reactions is postulated. PENTAFLUOROPHENYL-LITHIUM, previously prepared by two methods is a useful precursor in the synthesis of pentafluorophenyl derivatives.* Also, at temperatures above 0” it decomposes to give a tetratluorobenzyne intermediate. Further reactions of the pentafluorophenyl anion used both as a nucleophile and as a source of tetrafluorobenzyne are now described. In three recent communicationss-s similar reactions have been reported. The chemistry of 2-bromo-nonafluorobiphenyl, observed’ during attempts to prepare pentafluorophenyl derivatives of metals using pentafluorophenyl-lithium in etherhexane mixtures, was investigated and its structure indicated by Pe NMR. A tentative mechansim for the reactions involved was based on the formation of tetrafluorobenzyne. In our work the reaction of pentafluorophenyl-lithium with excess of bromopentafluorobenzene was lirst carried out at -40” in ether. A pale yellow ether insoluble fraction, which was mainly organic and contained Br and F, and probably a mixture of poly-phenyls, C!,,Fs(C,F~,Br was obtained together with an ether soluble fraction shown by gas chromatography to contain three components. Separation using preparative gas chromatography gave 1,2-dibromotetrafluorobenzene, 2bromononafluorobiphenyl and 4bromononatluorobiphenyl in the ratio of 1: 1: 8. The structures of these three compounds were proved unambiguously. The dibromotetrafluorobenzene was identical to that prepared by bromination of 1,2,3,4-tetrafluorobenzenea and the bromononafluorobiphenyls were synthesized independently. 1 Part XXVII, J. Chem. See. 6329 (1965). a P. L. Coe, R. Stephens and J. C. Tatlow, J. Chem. Sot. 3727 (1962). a D. E. Fenton, A. J. Park, A. G. Massey and D. Shaw, Tetrahedron letters 16,449 (1964). ’ D. E. Fenton, A. J. Park, A. G. Massey and D. Shaw, J. Organometallic Chem. 2,437 (1964). 6 N. N. Vorozhtsov Jr., V. A. Barkharsh. N. G. Iranova and A K. Petrov. Tetrahedron fetters 47, 3575 (1964). E M. Hellman, A. J. Bilbo and W. H. Pummer. J. Amer. Chem. Sot. 77,365O (1955).

Aromatic polyfluorocompounds—XLIII: Reactions of tetrafluorobenzyne with aromatic and heteroaromatic compounds

Abstract Tetrafluorobenzyne reacts with benzene, toluene, the isomeric xylenes, durene, thiophen, 1-methylpyrrole, cyclopentadiene and styrene to give Diels-Alder type adducts. In the cases where mixtures of isomers formed these have been separated and their ratios determined. The further chemistry of some of the adducts is described.

Polyfluorobicyclo(2.2.1)heptanes—I : 1H-undecafluoro- and 1H,4H-decafluorobicyclo(2.2.1)heptane and a novel elimination process

Abstract The vapour-phase fluorination of bicyclo(2.2.1)heptadiene with cobaltic fluoride gave a complex mixture containing substantial amounts of perfluoro-, 1H-undecafluoro- and 1H,4H-decafluorobicyclo(2.2.1)heptane. The formation of perfluorocarbanions from the latter two compounds has been demonstrated by isotopic exchange in aqueous potassium hydroxide. The undecafluorobicyclo(2.2.1)heptyl anion has been formed also using methyl-lithium in ether at −55°, and trapped by reaction with acetaldehyde, bromine, methyl bromide and deuterium oxide. Near room temperature lithium undecafluorobicyclo(2.2.1)heptyl decomposed in a novel elimination process, thought to involve a transient bridgehead olefin, to give lithium fluoride and either 1-iodo-, or 1-bromo-, nonafluorobicyclo(2.2.1)hept-2-ene, depending on whether the methyl-lithium used to generate the anion was prepared from methyl iodide or methyl bromide, respectively. A similar decomposition in the presence of furan produced a furan adduct.

Polycyclic fluoroaromatic compounds—III : Octafluoroacenaphthylene, and decafluoro-indane, -acenaphthene, -anthracene, and -pyrene

Abstract Perfluoroperhydro-indane, -fluorene, -acenaphthylene, -phenanthrene, -anthracene and -pyrene have been prepared, by fluorination of the aromatic hydrocarbons with cobaltic fluoride. When defluorinated in the vapour phase over heated metal gauze perfluoro-indane, -acenaphthylene, -acenaphthene, -anthracene and -pyrene were obtained.

Polyfluorobicyclo(2,2,1)heptanes Part II. Further derivatives made from 1H-undecafluorobicyclo(2,2,1)heptane

Abstract 1 H -Undecafluorobicyclo(2,2,1)heptane has been lithiated with methyllithium in ether, and thence converted into a range of derivatives including 1-iodo-, 1-hydroxymethyl-, 1-carboxy- and 1-aceto-undecafluorobicyclo(2,2,1)-heptane. The latter reacts further to give α-(undecafluorobicyclo(2,2,1)heptan-1-yl)vinyl acetate. The iodide gave a Grignard reagent, the decomposition of which was studied, and a bis-mercurial. Bridgehead derivatives in this series are easily synthesised. The pyrolytic decarboxylation of anhydrous sodium undecafluorobicyclo(2,2,1)heptane-1-carboxylate and the decomposition of 1-lithio-undecafluorobicyclo(2,2,1)heptane have been studied, and the decomposition products correlated with transient bridgehead olefins.

Studies on a vapour-phase process for the manufacture of chlorofluoroethanes

Abstract Fluorination of hexachloroethane or of tetrachloroethylene + chlorine by hydrogen fluoride at ca. 400°C in the presence of an aluminium fluoride catalyst gives the unsymmetrical isomers of dichlorotetrafluoroethane and of trichlorotrifluoroethane as the major products. Under similar conditions but using a catalyst of aluminium fluoride containing small amounts of iron, chromium and nickel, symmetrical trichlorotrifluoroethane is the major product. Analogous fluorinations of various intermediates over these catalyst systems have been studied and detailed information about the reaction pathways obtained. Under suitable conditions, s-trichlorotrifluoroethane or s-dichlorotetrafluoroethane can be prepared in a high state of purity.

Polyfluoro diethyl and ethyl methyl ethers: their preparation using cobalt (III) fluoride and potassium tetrafluorocobaltate (III) and their dehydrofluorination

Abstract Diethyl ether has been fluorinated with CoF3 to yield a mixture from which dl -threo and -erythro 1,2-difluoroethyl 1,2,2-trifluoroethyl ether, dl and meso bis(1,2,2-trifluoroethyl) ether and dl-1,1,2,2-tetrafluoroethyl 1,2,2-trifluoroethyl ether were isolated. Fluorination with KCoF4 at ca 200° afforded ethyl 1,2,2-trifluoroethyl ether as the sole isolable product; at higher temperatures some of the above ethers were formed. Similar fluorination with CoF3 of methyl ether afforded 1,2,2-trifluoroethyl methyl ether, 1,2,2-trifluoromethyl ether, 1,2,2-trifluoroethyl difluoromethyl ether and 1,1,2,2-tetrafluoroethyl methyl ether; with KCoF4 1,2,2-trifluoroethyl methyl ether was the sole product. Dehydrofluorination, using fused potassium hydroxide, of either isomer of bis(1,2,2-trifluuoroethyl) ether gave a mixture of (E,Z,) and (Z,Z) bis(1,2-difluorovinyl) ethers and (E) and (Z) 1,2,2-trifluorethyl 1,2-difluorovinyl ethers. Similarly, 1,1,2,2-tetrafluoroethyl 1,2,2-trifluoroethyl ether yielded (E) and (Z) 1,1,2,2,-tetrafluoroethyl 1,2-difluorovinyl ether in the ratio 1:4. Dehydrofluorination of 1,2,2-trifluoroethyl fluoromethyl ether yielded (E) and (Z) fluoromethyl 1,2-difluorovinyl ethers with a trace of fluoromethyl 2,2-difluorovinyl ether.

Polyfluorobicyclo(2,2,1)heptanes Part III. Derivatives from 1H,4H-decafluorobicyclo(2,2,1)heptane

Abstract The title compound was converted via its mono-lithio derivative into the 1,4-disubstituted decafluorobicyclo(2,2,1)heptanes: (1) X -C 7 F 10 - Y (4), where X = H and Y = D, -CH(OH)CH 3 , -Br, -I, -CO 2 H, -CH 3 , -CH(OH)C 6 H 5 , -C(OCOCH 3 ) = CH 2 ; X = Y = D; X = Y = Br; X = Y = I; X = Y = CH 3 ; X = CH 3 , Y = CO 2 H. The lithio derivative decomposed in refluxing ether via a transient bridgehead diradical to give 1,4-disubstituted perfluorobicyclo(2,2,1)hept-2-enes, but related Grignard reagents did not.

Reactions of tetrafluoroethylene oligomers. Part 1. Some pyrolytic reactions of the pentamer and hexaher and of the fluorine adducts of the tetramer and pentamer

Abstract Pyrolyses of these highly branched fluorocarbons over glass beads caused the preferential thermolyses of CC bonds where there is maximum carbon substitution. Fluorinations of perfluoro-3,4-dimethylhex-3-ene (tetramer) (I) and perfluoro-4-ethyl-3,4-dimethylhex- 2-ehe (pentamer) (II) over cobalt (III) fluoride at 230° and 145° respectively afforded the corresponding saturated fluorocarbons (III) and (IV), though II gave principally the saturated tetramer (III) at 250°. Pyrolysis of III alone at 500—520° gave perfluoro-2-methylbutane (V), whilst pyrolysis of III in the presence of bromine or toluene afforded 2-bromononafluorobutane (VI) and 2H-nonafluorobutane (VII) respectively. Pyrolysis of perfluoro-3-ethyl-3, 4-dimethylhexane (IV) alone gave a mixture of perfluoro-2-methylbutane (V), perfluoro-2-methylbut-1-ene (VIII), perfluoro-3-methylpentane (IX), perfluoro-3,3-dimethylpentane (X), and perfluoro-3,4- dimethylhexane (III). Pyrolysis of IV in the presence of bromine gave (VI) and 3-bromo-3-trifluoromethyl-decafluoropentane (XI): with toluene, pyrolysis gare VlI and 3H-3-trifluoromethyldecafluoropentane (XII). Pyrolysis of II at 500° over glass gave perfluoro-1,2,3-trimethylcyclobutene (XIII) and perfluoro-2,3-dimethylpenta-1,3(E)- and (Z)-diene (XIV) and (XV) respectively. The diene mixture (XIV and XV) was fluorinated with CoF 3 to give perfluoro-2,3-dimethylpentane (XVI) and was cyclised thermally to give the cyclobutene (XIII). Pyrolysis of perfluoro-2- (1′-ethyl-1′-methylpropyl)-3-methylpent-1-ene (XVII) (TFE hexamer major isomer) at 500° gave perfluoro-1-methyl-2-(1′-methylpropyl)cyclobut-1-ene (XVIII) and perfluoro-2-methyl-2-(1′-methylpropyl)buta-1,3-diene (XIX). Fluorination of XVIII over CoF 3 gave perfluoro-1-methyl-2- (1′-methylpropyl)cyclobutane (XX), which on co-pyrolysis with bromine gave VI. XIX on heating gave XVIII. Reaction of XVIII with ammonia in ether gave a mixture of E and Z 1′-trifluoromethyl-2-(1′-trifluoromethyl- pentafluoropropyliden-1′-yl)tetrafluorocyclobutylamine (XXI) which on diazotisation and hydrolysis afforded 2-(2′trifluoromethyl- tetrafluorocyclobut-1-en-1′-yl)-octafluorobutan-2-ol (XXII).