Formula Se2Cl2 Boiling point 127 °C Melting point -85 °C | Molar mass 228.83 g/mol Density 2.77 g/cm³ Appearance Reddish-brown oily liquid | |
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Selenium monochloride is an inorganic compound with the formula Se2Cl2. Although it is called selenium monochloride, a more descriptive name might be diselenium dichloride. It is a reddish-brown, oily liquid that hydrolyses slowly. It exists in chemical equilibrium with SeCl2, SeCl4, chlorine, and elemental selenium. Selenium monochloride is mainly used as a reagent for the synthesis of Se-containing compounds.
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Structure and properties
Selenium monochloride exhibits C2 molecular symmetry, similar to hydrogen peroxide. The bond length of the Se-Se bond is predicted to be 2.253 Å and the Se-Cl bonds are both 2.227 Å.
In acetonitrile solutions, it exists in equilibrium with SeCl2 and SeCl4.
Preparation
Selenium monochloride was originally produced by the chlorination of selenium. An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:
3 Se + SeO2 + 4 HCl → 2 Se2Cl2 + H2OA dense layer of selenium monochloride settles from the reaction mixture, which can be purified by dissolving it in fuming sulfuric acid and reprecipitating it with hydrochloric acid. A second method for the synthesis involves the reaction of selenium with oleum and hydrochloric acid:
2 Se + 2 SO3 + 3 HCl → Se2Cl2 + H2SO3 + SO2(OH)ClThe crude selenium monochloride product is collected via distillation.
Reactions
Selenium monochloride is an electrophilic selenizing agent, and thus it reacts with simple alkenes to give bis(β-chloroalkyl)selenide and bis(chloroalkyl)selenium dichloride. It converts hydrazones of hindered ketones into the corresponding selones, the structural analogs of ketones whereby the oxygen atom is replaced with a selenium atom. Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.