A sulfone is an organic compound in which a sulfur atom is bonded to two carbon groups and double-bonded to two oxygen atoms. Its general formula is R–S(=O)₂–R’, where R and R’ represent alkyl or aryl groups. The defining feature of sulfones is the sulfonyl group (–SO₂–), which imparts strong polarity, high stability, and distinctive chemical behavior to these compounds ^[1–4].

Sulfones are notable for their dual presence in laboratory research and real-world applications. For instance, sulfolane, a cyclic sulfone, serves as a highly effective solvent in the petrochemical industry, particularly for separating valuable hydrocarbons. In contrast, dapsone, an aromatic sulfone, is a vital drug used as an antibiotic in the treatment of leprosy and certain skin conditions.

Preparation ^[5-7]

1. By Oxidation of Thioethers and Sulfoxides

Thioethers (sulfides) undergo stepwise oxidation, first yielding sulfoxides and then sulfones:

R–S–R’  + [O] →  R–S(=O)–R’ 

R–S(=O)–R’ + [O] →  R–S(=O)₂–R’

Example: Dimethyl sulfide oxidizes to dimethyl sulfoxide using hydrogen peroxide as the oxidizing agent, and further to dimethyl sulfone. 

CH₃–S–CH₃  + H₂O₂  →  CH₃–S(=O)–CH₃ + H₂O

CH₃–S(=O)–CH₃ + H₂O₂  → CH₃–S(=O)₂–CH₃ + H₂O

2. From Sulfur Dioxide

Sulfur dioxide undergoes a cycloaddition with 1,3-butadiene to form sulfolene, which, upon hydrogenation, produces sulfolane:

CH₂=CH–CH=CH₂ + SO₂ ⟶ Sulfolene

Sulfolene + H₂ →  (CH₂)₄SO₂

3. From Sulfonyl and Sulfuryl Halides

Aromatic sulfones can be synthesized via Friedel–Crafts sulfonylation.

Example: Benzene reacts with methanesulfonyl chloride in the presence of AlCl₃ to form methyl phenyl sulfone.

C₆H₆ + CH₃SO₂Cl  → C₆H₅–SO₂–CH₃ + HCl (in presence of AlCl₃)

4. From Sulfinates

Sulfinates react with aryl halides in catalyzed cross-coupling reactions to yield sulfones:

ArSO₂Na + Ar’Cl ⟶ ArSO₂Ar’ + NaCl

Example: Sodium benzenesulfinate reacts with chlorobenzene to produce diphenyl sulfone.

C₆H₅SO₂Na + C₆H₅Cl ⟶ C₆H₅–SO₂–C₆H₅ + NaCl

Chemical Properties and Reactions ^[8-10]

Sulfones are more chemically stable than related sulfur compounds such as sulfides and sulfoxides. Their two strong S=O bonds make the sulfonyl group resistant to both oxidation and reduction under mild conditions.

1. Elimination Reaction

A hallmark transformation is the Ramberg–Bäcklund reaction, where α-halo sulfones undergo base-induced elimination to form alkenes, releasing sulfur dioxide:

R–CH(X)–SO₂–R’ ⟶ R–CH=CH–R’ + SO₂ + HX

Where X is a halogen (bromine or chlorine) and R and R’ are alkyl or aryl groups.

Example: α-bromoethyl ethyl sulfone transforms to 2-butene in the presence of potassium hydroxide.

CH₃–CH(Br)–SO₂–CH₂CH₃ ⟶ CH₃–CH=CH–CH₂CH₃ + SO₂ + HBr (in presence of KOH)

2. Alkylation

Sulfones can be alkylated at the α-carbon using alcohols as electrophiles, facilitated by a ruthenium catalyst and a base.

R–CH₂–OH + R’–CH₂–SO₂–R” → R–CH–CH(R’)–SO₂–R” + H₂O

Example: Benzyl alcohol reacts with methyl phenyl sulfone in the presence of a Ru catalyst to form benzyl ethyl phenyl sulfone.

Ph–CH₂–OH + CH₃–SO₂–Ph → Ph–CH₂–CH₂–SO₂–Ph  + H₂O (using Ru catalyst and a base)

3. Olefination

Another key reaction is the Julia olefination, in which a phenyl sulfone reacts with a benzyl alcohol derivative in the presence of a metal catalyst and a base, producing an alkene.

Ar–CH₂–OH + R–CH₂–SO₂–R’ → Ar–CH=CHR + R’SO₃Na + H₂

Example: Benzyl alcohol reacts with methyl phenyl sulfone to yield styrene, with sodium benzenesulfinate and hydrogen as by-products:

Ph–CH₂–OH + CH₃–SO₂–Ph → Ph–CH=CH₂ + PhSO₃Na + H₂ (using metal catalyst and a base)

Sulfones combine remarkable stability with various utilities, making them essential in both industry and medicine. Their chemistry illustrates how one functional group can influence diverse fields, from solvents to pharmaceuticals.