Sulfur fluorides properties

Table 15.13 Physical properties of some sulfur fluorides...

Some physical properties of the more stable sulfur fluorides are in Table 15.13. All are colourless gases or volatile liquids at room temperature. SFg sublimes at -63.8° (1 atm) and can only be melted under pressure (—50.8°). It is notable both for its extreme thermal and chemical stability (see below), and also for having a higher gas density than any other substance that boils below room temperature (5.107 times as dense as air). 

These are rather different from the other halides and are appropriately dealt with separately. There are seven sulfur fluorides, six of which are depicted, along with their properties, in Table 12-4. The isomeric disulfur difluorides are actually thermodynamically unstable. The compound FSSF prepared by fluorination of sulfur with AgF, readily isomerizes to SSF2, which can also be obtained in other ways. However, SSF2 itself in the presence of acid catalysts (e.g., HF or BF3) rapidly dispropor-tionates ... 

Photolytically, reduction of SF5CI with H2 gives the largest known binary sulfur fluoride, disulfur decafluoride. It is also a trace by-product of the industrial preparation of SFe, but it is not isolated and is destroyed by heating to 400 °C. Disulfur decafluoride is a liquid at room temperature that will completely decompose at 200 °C to SF4 and SFe. It is intermediate in properties when compared to SF4 and SFe. It is not hydrolyzed by water alone, but it is slowly attacked by aqueous NaOH. Disulfur decafluoride can be stored at room temperature as a liquid for years. Like SF4, it is extremely... 

Table 15.5 Selected physical properties of oxygen and sulfur fluorides.

The reactivity of fluorine compounds varies from extremely stable, eg, compounds such as sulfur hexafluoride [2551-62 ] nitrogen trifluoride [7783-54-2] and the perfluorocarbons (see Fluorine compounds, organic) to extremely reactive, eg, the halogen fluorides. Another unique property of nonionic metal fluorides is great volatiUty. Volatile compounds such as tungsten hexafluoride [7783-82-6] molybdenum hexafluoride [7783-77-9] ... 

Chemical Properties. Sulfur tetrafluoride reacts rapidly with water to give hydrofluoric acid and thionyl fluoride [7783 2-8] ... 

Thiothionyl Fluoride and Difluorodisulfane. Thiothionyl fluoride [1686-09-9] S=SF2, and difluorodisulfane [13709-35-8] FSSF, are isomeric compounds which may be prepared as a mixture by the action of various metal fluorides on sulfur vapor or S2CI2 vapor. Chemically, the two isomers are very similar and extremely reactive. However, in the absence of catalytic agents and other reactive species, FSSF is stable for days at ordinary temperatures and S=SF2 may be heated to 250°C without significant decomposition (127). Physical properties of the two isomers are given in Table 6. The microwave spectmm of S=SF2 has been reported (130). 

Fluorosulfuric acid is stable to heat up to decomposition at about 900°C (13), where vapor-phase dissociation into hydrogen fluoride and sulfur trioxide probably occurs. Reviews of the chemistry and properties of fluorosulfuric acid have been pubUshed (14—16). 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

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