Sulfur tetrafluoride
4761306
220485650
2008-06-20T02:29:50Z
Denelson83
23958
Gotta specify the F part of the fire diamond
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{{Chembox new
| Name = Sulfur tetrafluoride
| ImageFile = Sulfur-tetrafluoride-2D-dimensions.png
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| ImageName = Sulfur tetrafluoride
| ImageFile1 = Sulfur-tetrafluoride-3D-balls.png
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| ImageName1 = Sulfur tetrafluoride
| ImageFile2 = Sulfur-tetrafluoride-3D-vdW.png
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| ImageName2 = Sulfur tetrafluoride
| IUPACName = Sulfur(IV) fluoride
| OtherNames = Sulfur tetrafluoride
| Section1 = {{Chembox Identifiers
| CASNo = 7783-60-0
| RTECS = WT4800000
}}
| Section2 = {{Chembox Properties
| Formula = SF<sub>4</sub>
| MolarMass = 108.07 g/mol
| Appearance = colorless gas
| Density = 1.95 g cm<sup>−3</sup>, −78 °C
| Solubility = decomp
| MeltingPt = −121.0 °C
| BoilingPt = −38 °C
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| [[Molecular geometry|Molecular<br />geometry]]
| [[Seesaw]]
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| Section3 = {{Chembox Structure
| Coordination = C<sub>2v</sub>
| Dipole = 0.632 [[Debye|D]]<ref>Tolles; W. M. Gwinn, W. D. “Structure and Dipole Moment for SF4” The Journal of Chemical Physics 1962, Volume 36, pp. 1119-1121. {{DOI|10.1063/1.1732702}}</ref>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = highly toxic<br />corrosive
| NFPA-H = 4
| NFPA-F = 0
| NFPA-R = 2
| NFPA-O = W
| RPhrases = 14-26-34-37
| SPhrases = 26-36/37/39-38-45
}}
| Section8 = {{Chembox Related
| OtherCpds = [[selenium tetrafluoride|SeF<sub>4</sub>]]<br />[[sulfur hexafluoride|SF<sub>6</sub>]]<br />[[sulfur dichloride|SCl<sub>2</sub>]]<br />[[disulfur dichloride|S<sub>2</sub>Cl<sub>2</sub>]]<br /> Me<sub>2</sub>NSF<sub>3</sub>
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}}
'''Sulfur tetrafluoride''' is the [[chemical compound]] with the formula SF<sub>4</sub>. This species exists as a gas at standard conditions. It is a corrosive species that releases dangerous [[Hydrofluoric acid|HF]] upon exposure to water or moisture. Despite these unwelcome characteristics, this compound is a useful [[reagent]] for the preparation of [[fluorocarbon|organofluorine compounds]],<ref>C.-L. J. Wang, "Sulfur Tetrafluoride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> some of which are important in the pharmaceutical and specialty chemical industries. Aside from SF<sub>4</sub>, two other "binary" sulfur fluorides are well known, [[Sulfur hexafluoride|SF<sub>6</sub>]] and [[Disulfur decafluoride|S<sub>2</sub>F<sub>10</sub>]].
==Structure of the SF<sub>4</sub> molecule==
Sulfur in SF<sub>4</sub> is in the formal 4+ [[oxidation state]]. Of sulfur's total of six [[valence electron]]s, two form a "lone pair." The structure of SF<sub>4</sub> can therefore be anticipated using the principles of [[VSEPR theory]]: it is a [[Seesaw (chemistry)|see-saw shape]], with S at the center. One of the three equatorial positions is occupied by a nonbonding [[lone pair]] of electrons. Ignoring this lone pair, SF<sub>4</sub> has a [[see-saw]] [[molecular geometry]]. Consequently, the molecule has two distinct types of F ligands, two [[axial]] and two [[equatorial]]. The relevant bond distances are S-F<sub>ax</sub> = 1.643 Å and S-F<sub>eq</sub> = 1.542 Å. It is typical for the axial ligands in [[hypervalent]] molecules to be bonded less strongly. In contrast to SF<sub>4</sub>, the related molecule SF<sub>6</sub> has sulfur in the 6+ state, no valence electrons remain nonbonding on sulfur, hence the molecule adopts a highly symmetrical octahedral structure. Further contrasting with SF<sub>4</sub>, SF<sub>6</sub> is extraordinarily inert chemically.
The<sup>19</sup>F [[Nuclear magnetic resonance|NMR]] spectrum of SF<sub>4</sub> reveals only one signal, which indicates that the axial and equatorial F atom positions rapidly interconvert via "pseudorotation."<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref>
[[Image:SF4dyns.png|250 px|thumb|left|Intramolecular dynamic equilibration of SF<sub>4</sub>.]]
==Synthesis and manufacture==
SF<sub>4</sub> is produced by the reaction of [[sulfur dichloride|SCl<sub>2</sub>]], [[chlorine|Cl<sub>2</sub>]], and [[sodium fluoride|NaF]]:
:: SCl<sub>2</sub> + Cl<sub>2</sub> + 4NaF → SF<sub>4</sub> + 4NaCl
Interestingly, treatment of SCl<sub>2</sub> with NaF also affords SF<sub>4</sub>, not SF<sub>2</sub>. SF<sub>2</sub> is unstable, it condenses with itself to form SF<sub>4</sub> and SSF<sub>2</sub>.
==Use of SF<sub>4</sub> for the synthesis of fluorocarbons==
In [[organic synthesis]], SF<sub>4</sub> is used to convert COH and C=O groups into CF and CF<sub>2</sub> groups, respectively.<ref>W. R. Hasek "1,1,1-Trifluoroheptane" Organic Syntheses, Coll. Vol. 5, p.1082; Vol. 41, p.104. http://www.orgsyn.org/orgsyn/pdfs/CV5P1082.pdf</ref> Certain [[alcohol]]s readily give the corresponding [[fluorocarbon]]. [[Ketones]] and [[aldehydes]] give geminal difluorides. The presence of protons alpha to the carbonyl leads to side reactions and diminished (30- 40%) yield. Also diols can give cyclic sulfite esters, (RO)<sub>2</sub>SO. Carboxylic acids convert to trifluoromethyl derivatives. For example treatment of heptanoic acid with SF<sub>4</sub> at 100-130 °C produces 1,1,1-trifluoroheptane. The coproducts from these fluorinations, including unreacted SF<sub>4</sub> together with SOF<sub>2</sub> and SO<sub>2</sub>, are toxic but can be neutralized by their treatment with aqueous KOH.
The use of SF<sub>4</sub> is being superseded in recent years by the more conveniently handled [[diethylaminosulfur trifluoride]], Et<sub>2</sub>NSF<sub>3</sub>, "DAST," where Et = CH<sub>3</sub>CH<sub>2</sub>.<ref>A. H. Fauq, "N,N-Diethylaminosulfur Trifluoride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> This reagent is prepared from SF<sub>4</sub>:<ref>W. J. Middleton, E. M. Bingham" Diethylaminosulfur Trifluoride” Organic Syntheses, Coll. Vol. 6, p.440; Vol. 57, p.50.http://www.orgsyn.org/orgsyn/pdfs/CV6P0440.pdf</ref>
:: SF<sub>4</sub> + Me<sub>3</sub>SiNEt<sub>2</sub> → Et<sub>2</sub>NSF<sub>3</sub> + Me<sub>3</sub>SiF
==References==
{{reflist}}
[[Category:Sulfur fluorides]]
[[pl:Czterofluorek siarki]]