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...

An m. p. of 106-107" has been given 2O for the acid.

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Coe, Stephens, and Tatlow. 3227 622. Aromatic PolyJluoro-compounds. Part XI.* PentaJluorophenyl-lithium and Derived Compounds.

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B15 2 T l ) Suintnary New evidence from exchanges in neutral D,0-CU3COCD3, involving (CF,),CH and bridgehead compounds together, reopens a n old controversy.

Pentafluorobenzaldehyde has been converted into a range of derivatives by reactions involving the carbonyl group, viz., a pentafluorostilbene, a pentafluorocinnamic acid, an azine, an oxime, and a range of acetals. Other derivatives were made by reactions involving replacement of fluorine using dimethylamine, sodium hydrogen sulphide, sodium thiophenoxide, and sodium methoxide.