Selenium oxydichloride

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.

Preparation and reactions
Selenium oxydichloride can be prepared by several methods, and a common one involves the conversion of selenium dioxide to dichloroselenious acid followed by dehydration:
 * SeO2 +  2 HCl   →  Se(OH)2Cl2
 * Se(OH)2Cl2  →  SeOCl2  +  H2O

The original synthesis involved the redistribution reaction of selenium dioxide and selenium tetrachloride.

Pure selenium oxydichloride autoionizes to a dimer:
 * SeOCl2 ↔ (SeO)2Cl$+ 3$ + Cl&minus;

The SeOCl2 is generally a labile Lewis acid and solutions of sulfur trioxide in SeOCl2 likely form [SeOCl]+[SO3Cl]&minus; 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.