Reactions of Sulphur Fluorides

The major aim of the research was the preparation of compounds which could be used as heat-transfer agents. Chemical inertness and high thermal stability were important properties of the materials. Sulphur hexa-fluoride and many of its derivatives are stable and, initially, research was directed towards the synthesis of substituted S(VI) fluorides. Substitution into S(Vl) fluorides is not a convenient route for the preparation of the desired compounds and in most cases reaction takes place with complete breakdown and formation of unidentified solid products. The chlorofluorination of sulphur tetrafluoride with mixtures of chlorine and caesium fluoride has previously proved successful for the preparation of sulphur chloride penta-fluoride and, in the present work, this method is extended to include substituted S(II) and S(IV) fluorides. When chlorinated in the presence of caesium fluoride dimethylaminosulphur trifluoride produces sulphur chloride pentafluoride, while the straightforward chlorination gives sulphur tetrafluoride. Trifluoromethylsulphur chloride tetrafluoride results from the chlorofluorination of trifluoromethylsulphur trifluoride. This reaction is highly stereospecific, in that only the TRANS isomer is isolated. In contrast to the behaviour of dimethyl-aminosulphur trifluoride, methyliminosulphur difluoride reacts with chlorine with substitution of chlorine into the methyl group. Both mono and dichloro derivatives, chloromethyliminosulphur difluoride and dichloromethyl-iminosulphur difluoride, are isolated. Depending on the reaction conditions and the proportion of reactants used, trifluoromothyliminosulphur dichloride is also formed. A mechanism involving isomerisation of C-Cl to C-F bonds is postulated to explain the formation of the trifluoromethyl compound. Various reactions between sulphur tetrafluoride and sulphur-oxygen compounds were investigated. With dialkylsulphites and sulphates, sulphur tetrafluoride gives alkylfluorosulphites and fluorosulphates respective No stable alkoxysulphur fluorides could be prepared from sulphur tetrafluoride and alkoxysilanes and only products resulting from the decomposition of the (RO)x SF4-x (x = 1, 2 or 3) derivatives were observed. There was much greater stability with phenoxy derivatives and the complete series of phenoxysulphur fluorides, (PhO)xSF4-x (x = 1, 2, 3 or 4), were prepared. N. M. R. results are consistent with a trigonal bipyramid geometry for these compounds with the phenoxy groups in the equatorial plane. Sulphur tetrafluoride reacts in a complex manner with dimethylsulphoxide to produce bis(fluoro-methyl)ether as the major product. Sulphur tetrafluoride behaves as an oxidative fluorinating agent towards trivalent phosphorus compounds of the type L3P (L = Me2N, MeO and MeS) to produce fluorophosphoranes, L3PF2. With pentavalent phosphorus derivatives, L3PO or L2L'PO (L' = Me), there was no evidence for fluorination of the phosphoryl group and the products are best regarded as being formed by a series of competitive exchange reactions. Reactions between sulphur fluorides and amines were studied, Methyliminosulphur difluoride reacts with dimethylamine to yield bis (dime thylainino ) sulphur , tetra-methylene diamine and bis(dimethylimino)sulphur. The latter compound is also formed by the action of dimethyl-aminosulphur trifluoride with monomethylamine. Dimethyl-aminosulphur trifluoride is the only known dialkylamino derivative of sulphur tetrafluoride. Evidence is presented which suggests the possibility of a series of dialkylaminosulphur fluorides, (Me2N)xSF4-x