Lower Sulfur Fluorides

Nonmeta.ls, Sulfur reacts with fluorine to yield the remarkably stable sulfur hexafluoride, SF. Operating conditions must be controlled because a mixture of the lower fluorides such as disulfur difluoride [13709-35-8] 2 2 disulfur decafluoride [5714-22-7] 2 10 sulfur tetrafluoride [7783-60-0] SF4, may also be formed. When this reaction is carried out between 310 and 340°C, SF is primarily obtained and essentially no SF and only trace amounts of lower fluorides. Below 300°C, and preferably at ca 275°C, SF is the primary product. At 450—500°C, a mixture comprising ca 50% SF and the lower sulfur fluorides is formed (see Fluorine compounds, inorganic-sulfur). 

Sulfur tetrafluoride is very stable when compared to the lower sulfur fluorides. It can be stored at room temperature for an indeflnite period of time. It is very reactive and is valued as a selective fluorinating agent for both organic and inorganic compounds. Its remarkable fluorinating ability has been the subject of recent reviews. ... 

The reaction is strongly exothermic. Lower sulfur fluorides are formed as byproducts together with the extremely poisonous disulfur decafluoride. Most of the lower sulfur fluorides are easily hydrolyzable, but sulfur decafluoride can only be decomposed by pyrolysis ... 

Steele, F. "Lower Sulfur Fluorides" in Advan. Inorg. Chem. Radiochem. 1974, 16, 297. 

However, high temperatures are not essential to produce unstable, reactive species in the gas phase under matrix conditions. This is exemplified by investigations of the lower sulfur and selenium fluorides. These can be prepared near room temperature and at low pressure by fast reactions between a solid and a precursor (type a) or between a gas and a precursor (type b) ... 

Fig. II. Koopmans theoretical XPS chemical shifts (in %) versus Hirshfeld DFT total charges (in fractional number of electrons remaining on the central atom) for fluorides of the first elements. Contmry to Table 3, chemical shifts here were calculated with reference to the free atoms in their lowest-multiplicity state. (Il-a) upper left Is shifts for the central atom in fluorides LiF, BeF2, BF3, CF4, NF3, OF2 and F2 lower left Is shifts for the central atom in fluorides NaF MgF2, AIF3. SiF4, PF3, SF2 and CIF lower and upper right 2s and 2p shifts in the same compounds (r is the correlation coefficient of the 4th-order fit displayed). (11-b) middle left, lower right and upper right, respectively Is, 2s and 2p shifts in the various silicon, phosphorus and sulfur fluorides.

Sulfur hexafluoride is made commercially by the direct fluorination of molten sulfur. Some higher and lower toxic fluorides formed in the process are removed, and the commercial product is more than 99.5 mole percent pure. A high-purity etchant grade is also available for the electronics industry. Common impurities include small amounts of carbon tetrafluoride, nitrogen, and water vapor. 

Sulfonation of aromatic hydrocarbons with sulfuric acid is cataly2ed by hydrogen fluoride or, at lower temperatures, by boron trifluoride (144). The products obtained are more uniform and considerably less sulfuric acid is needed, probably because BF forms complexes with the water formed ia the reaction, and thus prevents dilution of the sulfuric acid. 

Zirconium is completely resistant to sulfuric acid up to Foiling temperatures, at concentrations up to 70 wt %, except that the heat-affected zones at welds have lower resistance in >55 wt % concentration acid (Fig. 1). Fluoride ions must be excluded from the sulfuric acid. Cupric, ferric, or nitrate ions significantly increase the corrosion rate of zirconium in 65—75 wt % sulfuric acid. 

Sulfur tetrafluoride, SF4, though extremely reactive (and valuable) as a selective fluorinating agent, is much more stable than the lower fluorides. It is formed, together with SFg, when a cooled film of sulfur is reacted with F2, but is best prepared by fluorinating SCI2 with NaF in warm acetonitrile solution ... 

Reduction of cnviromncntal pollution requires lower energy use and new technology to decrease emission of gases such as sulfur dioxide and carbon dioxide, and to prevent toxic fluoride, heavy metal, and radioactive wastes from discharging into the environment. 

Many aldehydes and ketones have been converted to g m-difluoro compounds with sulfur tetrafluoride (SF4), " including quinones, which give 1,1,4,4-tetra-fluorocyclohexadiene derivatives. With ketones, yields can be raised and the reaction temperature lowered, by the addition of anhydrous HF. Carboxylic acids, acyl chlorides, and amides react with SF4 to give 1,1,1-trifluorides. In these cases the first product is the acyl fluoride, which then undergoes the ge i-difluorination reaction ... 

Double asymmetric induction operates when the azomethine compound is derived from a chiral a-amino aldehyde and a chiral amine, e.g., the sulfin-imine 144 [70]. In this case, the R configuration at the sulfur of the chiral auxihary, N-tert-butanesulfinamide, matched with the S configuration of the starting a-amino aldehyde, allowing complete stereocontrol to be achieved in the preparation of the diamine derivatives 145 by the addition of trifluo-romethyl anion, which was formed from trifluoromethyltrimethylsilane in the presence of tetramethylammonium fluoride (Scheme 23). The substituents at both nitrogen atoms were easily removed by routine procedures see, for example, the preparation of the free diamine 146. On the other hand, a lower diastereoselectivity (dr 80 20) was observed in one reaction carried out on the imine derived from (it)-aldehyde and (it)-sulfinamide. 

Trichloro-l,3.5-triazine (cyanuric chloride, 5) can be converted using a sixfold excess of sulfur tetrafluoride at 250 C into 2,4,6-trifluoro-l,3,5-triazine (cyanuric fluoride, 6) with lower proportions of sulfur tetrafluoride, cyanuric chlorofluorides are formed.191... 

Carbon disulfide gives an essentially quantitative yield of carbon tetrafluoride (4) and sulfur on reaction with sulfur tetrafluoride at 450 C in the presence of arsenic(III) fluoride as catalyst. At lower temperatures and with boron trifluoride as catalyst, bis(trifluoromethyl) polysulfides 5 and 6 are formed.205... 

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