For sulfur tetrafluoride

The 2003 ACGIH ceiling threshold limit value (TLV-C) for sulfur tetrafluoride is... 

The local ionization potential is intended to reflect the relative ease of electron removal ( ionization ) at any location around a molecule. For example, a surface of low local ionization potential for sulfur tetrafluoride demarks the areas which are most easily ionized. 

The most intense bands, as well as overtone bands at 1744 and 1281 cm"1, are used as purity probes for sulfur tetrafluoride.9 The mass spectrum of sulfur tetrafluoride shows a weak molecular peak and strong fragmentation peaks corresponding to SF/, SF2+, SF+ and F+ ions.10... 

Treatment of certain 1,3-diketones with sulfur tetrafluoride using diethyl ether as solvent leads to the formation of unsaturated /i-fluoro ketones and mixtures of E- and Z-isomers are obtained, e.g. I.8 In this case the monoenolic form of the 1,3-diketone is the substrate for sulfur tetrafluoride. When diethyl ether is not used, the expected conversion of one or two carbonyl groups into difluoromethylene groups occurs. 

It is also possible to encounter a molecule that seems to have too many valence electrons. When that happens, we expand the valence shell of the central atom. Consider the Lewis structure for sulfur tetrafluoride SF4, for example, which contains thirty-four valence electrons. 

Thus you expect lone pairs to occupy equatorial positions in the trigonal bipyramidal arrangement. For sulfur tetrafluoride, this gives a seesaw (or distorted tetrahedral) geometry (Figure 10.10). 

Preparation. In the laboratory, sulfur tetrafluoride is made by combining SCI2 and NaF suspended in acetonitrile at ca 77°C (106). For commercial production, SF is made by direct combination of sulfur with elemental fluorine (107). Commercial appHcations of SF are limited. It is available from Air Products and Chemicals. 

Toxicity. Sulfur tetrafluoride has an inhalation toxicity comparable to phosgene. The current OSHA standard maximum allowable concentration for human exposure in air is 0.4 mg/m (TWA) (54). On exposure to moisture, eg, on the surface of skin, sulfur tetrafluoride Hberates hydrofluoric acid and care must be taken to avoid bums. One case of accidental exposure of electrical workers to decomposed SF gas containing SF has been cited (108). 

The standard synthesis method features side-chain chlorination of a methylpyridine (picoline), followed by exchange-fluoriaation with hydrogen fluoride or antimony fluorides (432,433). The fluoriaation of pyridinecarboxyHc acids by sulfur tetrafluoride (434) or molybdenum hexafluoride (435) is of limited value for high volume production operations due to high cost of fluorinating agent. 

Mechanism Several possible pathways for the reaction have been proposed by Hasek et alP and by Martin and Kagan, one of which is presented here. It takes cognizance of the fact that a significant concentration of hydrogen fluoride is essential for the reaction. Since definite interaction or compound formation between covalent fluorides and sulfur tetrafluoride is known to... 

A series of reactions with gases have been selected for the rapid quantification of many of the major products from the oxidation of polyolefins. Infrared spectroscopy is used to measure absorptions after gas treatments. The gases used and the groups quantified include phosgene to convert alcohols and hydroperoxides to chloroformates, diazomethane to convert acids and peracids to their respective methyl esters, sulfur tetrafluoride to convert acids to acid fluorides and nitric oxide to convert alcohols and hydroperoxides to nitrites and nitrates respectively. 

Sulfur tetrafluoride appears as two broad singlets at room temperature, as one broad singlet at 85 °C, and (when dry) as two sharp triplets at -30 °C. SF6, with its symmetrical octahedral geometry, appears as a sharp singlet at all temperatures. The activation energy for pseudorotation of SF4, which interconverts its axial and equatorial fluorines, is 12kcalmor1.3... 

The chemistry of the sulfur diimides (65) has been investigated in some detail, because such compounds might act as S—N or N—S—N transfer agents and thus allow access to novel heterocyclic systems. They are generally prepared by the action of sulfur tetrafluoride on primary amines.90 Some of their reactions parallel those of the /V-sulfinylamines— for example, the... 

Sulfur tetrafluoride provides an inexpensive method for selectively converting a carbonyl to a difluoromethyl group. However, the reactions involving sulfur tetrafluoride, in general, require pressure equipment constructed of fluorine-resistant material such as Hastelloy-C bombs.8 Phenylsulfur trifluoride may be used to advantage for the same reaction, where small amounts are involved, since the reaction may be run at atmospheric pressure in glass, polyethylene, or metal containers. 

C—Deviations from ideal behavior depend on the size and the intermolecular forces between the molecules. The greatest deviation would be for a large polar molecule. Sulfur tetrafluoride is the largest molecule, and it is the only polar molecule listed. 

Thiadiazole oxides and reduced forms are readily prepared via [4 -h 1] cyclizations (Table 4). The reagents employed for this purpose are thionyl chloride, sulfuryl chloride, sulfur tetrafluoride, N,N -bis(p-toluenesulfonyl)sulfur diimide, cyclic diimides, pentafluoroethyliminosulfur difluoride and sulfamide. 

Molecular orbitals do not need to be directly involved in bonding to be informative. For example, the highest-occupied molecular orbital (HOMO) of sulfur tetrafluoride clearly reveals that the molecule incorporates a lone pair on sulfur pointing in the direction of the... 

The results (electrostatic-fit charges based on Hartree-Fock 6-3IG wavefunctions) are ambiguous. Relative to dimethylsulfide as a normal-valent standard , the sulfur in oxygen loses about half an electron, and the sulfur in dimethylsulfone loses 1.7 electrons. This would seem to suggest that dimethylsulfoxide is halfway to being a zwitterion, but that dimethylsulfone is most of the way. Charges on sulfur in sulfur tetrafluoride and sulfur hexafluoride (relative to sulfur difluoride) show more modest effects, in particular for the latter. Overall, it appears that hypervalent molecules possess significant ionic character. 

Sulfur tetrafluoride is obtainable in one-pound cylinders from the Organic Chemicals Department of E. I. du Pont de Nemours and Co., Wilmington, Delaware. Directions for its synthesis by the action of sodium fluoride on sulfur dichloride in acetonitrile have been published,2 and a more detailed version of these directions has been submitted to Inorganic Syntheses. 

There are two nonequivalent pairs of S-F bonds in the sulfur tetrafluoride molecule, the shorter equatorial S-F bonds (1.545 A) and the longer axial S-F bonds (1.646 A). The bond angles arc equally 101 33 and 186" 56 for equatorial and axial bonds, respectively.5 The shorter and the longer S-F bond energies are, respectively, —20.31 and — 13.74 eV. The electric charge distribution in the sulfur tetrafluoride molecule is as follows + 1.70 on the sulfur atom, — 0.35 on the equatorial fluorine atoms and —0.50 on the axial fluorine atoms.5... 

---