Sulfone

In organic chemistry, a sulfone is a organosulfur compound containing a sulfonyl (R−S(=O)₂−R') functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms^{[dubious – discuss]} and has a single bond to each of two carbon atoms, usually in two separate hydrocarbon substituents.^[1]

The structure of a sulfone

Dimethyl sulfone, an example of a sulfone

Synthesis and reactions

By oxidation of thioethers and sulfoxides

Sulfones are typically prepared by organic oxidation of thioethers, often referred to as sulfides. Sulfoxides are intermediates in this route.^[2] For example, dimethyl sulfide oxidizes to dimethyl sulfoxide and then to dimethyl sulfone.^[1]

From SO₂

Synthesis of sulfolane by hydrogenation of sulfolene.

Sulfur dioxide is a convenient and widely used source of the sulfonyl functional group. Specifically, Sulfur dioxide participates in cycloaddition reactions with dienes.^[3] The industrially useful solvent sulfolane is prepared by addition of sulfur dioxide to buta-1,3-diene followed by hydrogenation of the resulting sulfolene.^[4]

From sulfonyl and sulfuryl halides

Sulfones are prepared under conditions used for Friedel–Crafts reactions using sources of RSO⁺
₂ derived from sulfonyl halides and sulfonic acid anhydrides. Lewis acid catalysts such as AlCl₃ and FeCl₃ are required.^[5][6][7]

Sulfones have been prepared through nucleophilic displacement of halides by sulfinates:^[8] $${\displaystyle {\ce {ArSO2Na + Ar'Cl -> Ar(Ar')SO2 + NaCl}}}$$ In general, relatively nonpolar ("soft") alkylating agents react with sulfinic acids to give sulfones, whereas polarized ("hard") alkylating agents form esters.^[9] Allyl, propargyl,^[10] and benzyl^[11] sulfinates can thermally rearrange to the sulfone. Esters without an activated bond generally do not so rearrange.^[12]

Reactions

A relatively inert functional group, sulfones are typically less oxidizing and only 4 bel more acidic than sulfoxides.^[13] They eventually eliminate to an alkene in base,^[14] but leave about 9 bel more slowly than chloride.^[15]: 109 In the Ramberg–Bäcklund reaction and the Julia olefination, sulfones eliminate sulfur dioxide to form an alkene.^[13]

Sulfones are strongly electron-withdrawing,^[16] and vinyl sulfones are electrophilic Michael acceptors.^[17]

The behavior of the α carbon depends on context. Non-nucleophilic bases deprotonate to an enolate-like carbanion.^[15]: 107 Contrariwise, Lewis acids on the sulfone oxygens give a Pummerer-like electrophile that undergoes nucleophilic substitution.^[15]: 117

Sulfones can also undergo reductive desulfonylation.^[15]: 108

Applications

Sulfolane is used to extract valuable aromatic compounds from petroleum.^[4]

Polymers

Some polymers containing sulfone groups are useful engineering plastics. They exhibit high strength and resistance to oxidation, corrosion, high temperatures, and creep under stress. For example, some are valuable as replacements for copper in domestic hot water plumbing.^[18] Precursors to such polymers are the sulfones bisphenol S and 4,4′-dichlorodiphenyl sulfone.^[19]

Pharmacology

Dapsone, an antibiotic used for the treatment of leprosy.^[20]

Examples of sulfones in pharmacology include dapsone, a drug formerly used as an antibiotic to treat leprosy, dermatitis herpetiformis, tuberculosis, or pneumocystis pneumonia (PCP). Several of its derivatives, such as promin, have similarly been studied or actually been applied in medicine, but in general sulfones are of far less prominence in pharmacology than for example the sulfonamides.^[21][22]

See also

• Organosulfur chemistry
• Sulfonanilide
• Sulfoxide
• Sulfonic acid (–OH substituent)