Sulfoxide: structure, properties, synthesis and uses

Structure and stereochemistry

At the core of a sulfoxide is a sulfur center double-bonded to oxygen and singly bonded to two carbon substituents. The sulfur also carries a non-bonding electron pair, which gives the center a pyramidal geometry rather than a flat trigonal shape; related descriptions may be found under sulfur and oxygen. Because the sulfur is bonded to two different carbon groups, R and R', and has an available lone pair, many sulfoxides are stereogenic and can exist as enantiomers: see chiral centre.

Preparation and typical reactions

Sulfoxides commonly arise from the controlled oxidation of thioethers (also called sulfides). Mild oxidizing agents convert a thioether to the sulfoxide without carrying the oxidation all the way to the sulfone; for related terms see thioethers and sulfone. The S=O bond is often depicted as a double bond (double bond) though its bonding has significant dative and polar character. Sulfoxides undergo a variety of reactions: further oxidation to sulfones, reduction back to thioethers, and transformations at adjacent carbon atoms in organic synthesis.

Properties and coordination chemistry

Physically, sulfoxides are polar, often have relatively high boiling points for their size, and many have distinctive odors typical of organosulfur compounds. The lone pair on sulfur and the polar S=O group make sulfoxides competent ligands for metal centers; they may coordinate through oxygen or, less commonly, through sulfur depending on metal and conditions. For general ligand behavior see ligands and transition metals.

Applications and notable examples

One of the best-known sulfoxides is dimethyl sulfoxide (DMSO, (CH3)2S=O). DMSO is widely used as a polar aprotic solvent in organic and biochemical laboratories, prized for dissolving both polar and nonpolar compounds; see solvent and biochemistry. Sulfoxides also appear as reagents in named oxidations and as building blocks or chiral auxiliaries in asymmetric synthesis. Their coordination chemistry enables their use in catalysis and in stabilizing metal complexes.

Practical considerations and safety

Handling of sulfoxides depends on the compound. DMSO, for example, is miscible with water and readily penetrates skin, carrying dissolved substances with it, so gloves and care with contaminants are advised. Some sulfoxides have strong odors; storage and ventilation are practical concerns. Environmental and toxicological profiles vary by compound, so consult material safety data for specific guidance.

Summary

• Sulfoxides are R–S(=O)–R' compounds formed by partial oxidation of thioethers (thioethers).
• The sulfur center is stereogenic in many cases and bears a lone pair (lone pair).
• They serve as solvents, reagents, and ligands and include important examples such as DMSO.
• Careful handling is recommended because of skin penetration and odor properties (carbons).

Further reading and specialized entries can be found through introductory resources (molecule) and chemical databases (sulfur, transition metals).