Selenium oxydichloride is the inorganic compound with the formula SeOCl2. It is a colorless liquid. With a high dielectric constant (55) and high specific conductance, it is an attractive solvent. Structurally, it is a close chemical relative of thionyl chloride SOCl2, being a pyramidal molecule.
Selenium oxydichloride can be prepared by several methods, and a common one involves the conversion of selenium dioxide to dichloroselenious acid followed by dehydration:[1]
SeO2 + 2 HCl → Se(OH)2Cl2
Se(OH)2Cl2 → SeOCl2 + H2OThe original synthesis involved the redistribution reaction of selenium dioxide and selenium tetrachloride.
Pure selenium oxydichloride autoionizes to a dimer:
SeOCl2 ↔ (SeO)2Cl + Cl-The SeOCl2 is generally a labile Lewis acid and solutions of sulfur trioxide in SeOCl2 likely form [SeOCl]+[SO<sub>3</sub>Cl]- the same way.
The compound hydrolyzes readily to form hydrogen chloride and selenium dioxide, and very few organic compounds dissolve in it without reaction. At elevated temperatures, it is a strong oxidizer, yielding a chloride, selenium dioxide, and diselenium dichloride.[2]