A sulfite ester is a functional group

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 with the structure (RO)(R'O)SO. When substituents R and R' differ, the compound is chiral owing to the stereogenic sulfur centre. They are commonly prepared by the reaction of thionyl chloride

Thionyl chloride

Thionyl chloride is an inorganic compound with the formula SOCl2. It is a reactive chemical reagent used in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure that decomposes above 140 °C. Thionyl chloride is sometimes confused with sulfuryl...

 with alcohols in the presence of a base such as pyridine

Pyridine

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

:

2 ROH + SOCl₂ + 2 C₅H₅N → (RO₂SO + 2 C₅H₅NH⁺Cl^-

The pesticide endosulfan

Endosulfan

Endosulfan is an off-patent organochlorine insecticide and acaricide that is being phased out globally. Endosulfan became a highly controversial agrichemical due to its acute toxicity, potential for bioaccumulation, and role as an endocrine disruptor...

 is a sulfite ester. Some simple members include ethylene sulfite, dimethyl sulfite

Dimethyl sulfite

Dimethyl sulfite is a sulfite ester with the chemical formula 2SO.Dimethyl sulfite is used as an additive in some polymers to prevent oxidation. It is also a potentially useful high energy battery electrolyte solvent.-Structure and conformation:...

, and diphenylsulfite. Many examples have been prepared from diols, such as sugars.