Sulfur tetrafluoride is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula S F₄. It is a colorless corrosive gas that releases dangerous

hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...

gas upon exposure to water or moisture. Sulfur tetrafluoride is a useful

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

for the preparation of organofluorine compounds, some of which are important in the pharmaceutical and specialty chemical industries.

Structure

Sulfur in SF₄ is in the +4

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

, with one

lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...

of electrons. The atoms in SF₄ are arranged in a see-saw shape, with the sulfur atom at the center. One of the three equatorial positions is occupied by a nonbonding

of electrons. Consequently, the molecule has two distinct types of F ligands, two axial and two equatorial. The relevant bond distances are = 164.3 pm and = 154.2 pm. It is typical for the axial ligands in

hypervalent In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded Octet rule, octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. P ...

molecules to be bonded less strongly. The ¹⁹F

NMR Nuclear magnetic resonance (NMR) is a physical phenomenon in which atomic nucleus, nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near and far field, near field) and respond by producing ...

spectrum of SF₄ reveals only one signal, which indicates that the axial and equatorial F atom positions rapidly interconvert via

pseudorotation In chemistry, a pseudorotation is a set of intramolecular movements of attached groups (i.e., ligands) on a highly symmetric molecule, leading to a molecule indistinguishable from the initial one. The International Union of Pure and Applied Chem ...

Synthesis and manufacture

At the laboratory scale, sulfur tetrafluoride is prepared from elemental sulfur and

cobaltic fluoride Cobalt(III) fluoride is the inorganic compound with the formula . Hydrates are also known. The anhydrous compound is a hygroscopic brown solid. It is used to synthesize organofluorine compounds. The related cobalt(III) chloride is also known but ...

:S + 4CoF₃ → SF₄ + 4CoF₂ SF₄ is industrially produced by the reaction of SCl₂ and NaF with

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...

as a catalyst :3 SCl₂ + 4 NaF → SF₄ + S₂Cl₂ + 4 NaCl At higher temperatures (e.g. 225–450 °C), the solvent is superfluous. Moreover, sulfur dichloride may be replaced by elemental sulfur (S) and chlorine (Cl₂). A low-temperature (e.g. 20–86 °C) alternative to the chlorinative process above uses liquid bromine (Br₂) as oxidant and solvent: :S(s) + 2 Br₂(l; excess) + 4KF(s) → SF₄↑ + 4 KBr(brom)

Use in synthesis of organofluorine compounds

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

, SF₄ is used to convert COH and C=O groups into CF and CF₂ groups, respectively. The efficiency of these conversions are highly variable. In the laboratory, the use of SF₄ has been superseded by the safer and more easily handled diethylaminosulfur trifluoride, (C₂H₅)₂NSF₃, "DAST": This reagent is prepared from SF₄: :

Other reactions

Sulfur chloride pentafluoride (), a useful source of the SF₅ group, is prepared from SF₄. : Hydrolysis of SF₄ gives

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

: :SF₄ + 2 H₂O → SO₂ + 4 HF This reaction proceeds via the intermediacy of

thionyl fluoride Thionyl fluoride is the inorganic compound with the formula . This colourless gas is mainly of theoretical interest, but it is a product of the degradation of sulfur hexafluoride, an insulator in electrical equipment. The molecule adopts a distort ...

, which usually does not interfere with the use of SF₄ as a reagent. When amines are treated with SF₄ and a base, aminosulfur difluorides result. SF4Scope5

Toxicity

reacts inside the lungs with moisture, forming

and

which forms highly toxic and corrosive hydrofluoric acid

References

{{Sulfur compounds Sulfur fluorides Fluorinating agents Hypervalent molecules ja:フッ化硫黄#四フッ化硫黄