Theprefixthio-, when applied to a chemical, such as anion, means that anoxygen atom in the compound has been replaced by asulfur atom. This term is often used inorganic chemistry. For example, from the wordether, referring to an oxygen-containing compound having the generalchemical structureR−O−R′, where R and R′ are organicfunctional groups and O is an oxygen atom, comes the wordthioether, which refers to an analogous compound with the general structureR−S−R′, where S is a sulfur atom covalently bonded to two organic groups.[1] A chemical reaction involving the replacement of oxygen to sulfur is calledthionation orthiation.
Thio- can be prefixed withdi- andtri- in chemical nomenclature.
The word derives from Ancient Greek θεῖον (theîon) 'sulfur' (which occurs in Greekepic poetry asθέ(ϝ)ειον,théweion and may come from the same root asLatinfumus (Indo-Europeandh-w) and may have originally meant "fumigation substance".)