No abstract

No abstract

Hexafluorobenzene reacts with sodium methoxide to give pentafluoroanisole which when heated with aluminium chloride yields pentafluorophenol. This strongly acidic phenol has been fully characterised and shown to resist nucleophilic attack. Its hydrazinium salt is formed when pentafluoroanisole reacts with hydrazine hydrate.

Pentafluorothiophenol and 2,3 , 5,6-tetrafluorothiophenol have been prepared by reaction of sodium hydrogen sulphide in pyridine with hexaand penta-fluorobenzene, respectively. Characterisation was effected by desulphurisation with Raney nickel. The products formed disulphides and methyl ethers. The ultraviolet and infrared absorption spectra of the compounds prepared are reported and the effects of the strongly electron-withdrawing groups briefly considered.THE susceptibility of hexa-and penta-fluorobenzene to attack by nucleophilic reagents has now been well e~tablished,l-~ for ethers, amines, and hydrazines have been prepared. Pyridine has been used3 as a solvent in which to prepare pentafluorophenol from hexafluorobenzene and potassium hydroxide; it had been employed earlier in syntheses of derivatives such as pentachlorothiophenol from hexachlorobenzene. We now report its use in the preparation of fluorothiophenols. Both hexa-and penta-fluorobenzene reacted vigorously with sodium hydrogen sulphide in pyridine-ethylene glycol to give good yields of penta-and tetra-fluorothiophenol, respectively.It has been suggested that pyridine acts in a catalytic capacity in reactions of hexachlorobenzene with nucleophiles. A similar effect on the reaction rate was noticed with substituted pyridines such as the picolines and lutidines. A notable exception, however, was 2,6-lutidine which, although a good solvent for the system, did not effect the same increase in reaction rate; this was attributed to the blocking of the hetero-nitrogen atom by the two o-methyl groups. Presumably the action of the pyridine is to increase the electron density around the halogen atom that is to be eliminated, and thus to assist it to escape as an ion from the aromatic nucleus.The possibility that a penta-or tetra-fluorophenylpyridinium fluoride might be formed as an intermediate was considered. A solution of hexafluorobenzene in pyridine rapidly darkened and, after 10-15 hr. a t 15", removal of all volatile material left a dark solid which appeared from a preliminary examination to be polymeric (cf. the reaction of pyridine with octafluorocyclobutene '). However, under the time and temperature conditions of the reaction producing pentafluorothiophenol a good recovery of the components of the mixture (hexafluorobenzene and pyridine) was made by gas-chromatographic techniques.Both fluoro-thiols were obtained as pungent liquids with strongly acidic properties, the potassium salts being easily recrystallized from water. It was of interest that crystalline potassium pentafluorothiophenoxide monohydrate became blue on storage ; this is perhaps a consequence of the presence of thiocarbonyl groups arising from electron migrations in the crystal lattice. The absence of such a blue colour in crystals of potassium 2,3,5,6-tetrafluorothiophenoxide is significant, the necessary migrations being less easy with hydrogen in the +ara-position.Cleavage of the carbon-sulphur linkages of each of the thiols was easily effected with Raney nickel, the corresponding...

The production of esters from alcohols and phenols by treatment with carboxylic acids in the presence of trifluoroacetic anhydride is described. The method can be used to esterify carboxylic acids in both the aliphatic and the aromatic series. In many cases the reaction proceeds spontaneously and is essentially complete within a few minutes. The general conditions of the reaction are relatively mild and enable, for example, acyl derivatives to be prepared in good yield from acid-labile glycosides. The method is particularly convenient for the acetylation and benzoylation of polysaccharides and also for the production of poly-esters.DURING the course of a study of the preparation and properties of trifluoroacetates of carbohydrates, details of which will be given in subsequent communications, an attempt was made to prepare trifluoroacetyl derivatives of cellulose. Whereas there was no apparent reaction between untreated cellulose and trifluoroacetic anhydride, a sample of cellulose which had been swollen in glacial acetic acid dissolved slowly in trifluoroacetic anhydride. However, the product, which was readily soluble in chloroform, contained no fluorine and consisted of cellulose acetate. This observation prompted a comprehensive examination of the action of trifluoroacetic anhydride in the presence of carboxylic acids on various hydroxy-compounds, and some preliminary results are herein reported.We have shown that trifluoroacetic anhydride promotes the esterification of a wide range of alcohols and phenols by carboxylic acids in both the aromatic and aliphatic series. This new method seems to be generally applicable and convenient for the preparation of esters, which can be isolated rapidly and in good yield.Briefly, the technique consists in treating the alcohol or phenol with a slight excess of the requisite carboxylic acid in the presence of trifluoroacetic anhydride, following which the reaction mixture is poured into aqueous sodium hydrogen carbonate and the ester is isolated by one of the usual methods. Esterification frequently proceeds spontaneously and exothermally when the reagents are mixed and, in certain cases, is virtually complete by the time the temperature has returned to normal. This is true for the acetylation of @-naphthol and mannitol and for the propionylation of a-methylglucoside. Benzoylation does not usually occur spontaneously and the best results are obtained when the reaction mixture is warmed. As a general method it is probably better to warm the carboxylic acid with trifluoroacetic anhydride for a short time before adding the hydroxy-compound.An important advantage of the new esterification process is that it can be applied, without modification, to cases in which the alcohol (or phenol) and carboxylic acid are both solids. Thus we have employed it successfully for the preparation of such esters as P-naphthyl palwitate,