Selenium monochloride

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Selenium monochloride
IUPAC name
Selenium monochloride
Other names
Dichlorodiselenide, Diselenium dichloride, Selenium chloride, 1,2-dichlorodiselane
3D model (JSmol)
ECHA InfoCard 100.030.022
Molar mass 228.83 g/mol
Appearance Reddish-brown oily liquid
Density 2.7741 g/cm3
Melting point −85 °C (−121 °F; 188 K)
Boiling point 127 °C (261 °F; 400 K) at 0.997 atm
Solubility in other solvents Soluble in chloroform, carbon disulfide, and acetonitrile
−94.8·10−6 cm3/mol
R-phrases (outdated) R23/24/25-R34
S-phrases (outdated) S22-S26-S36/37/39-S45
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.[1] Selenium monochloride is mainly used as a reagent for the synthesis of Se-containing compounds.

Structure and properties[edit]

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.[2]

In acetonitrile solutions, it exists in equilibrium with SeCl2 and SeCl4.[3]


Selenium monochloride was originally produced by the chlorination of selenium.[4] An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:[5]

3 Se + SeO2 + 4 HCl → 2 Se2Cl2 + H2O

A 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:[5]

2 Se + 2 SO3 + 3 HCl → Se2Cl2 + H2SO3 + SO2(OH)Cl

The crude selenium monochloride product is collected via distillation.


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.[6] 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.[6] Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.[6]


  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  2. ^ Prascher, Brian P.; Wilson, Angela K. A Computational Study of Dihalogen-μ-Dichalcogenides: XAAX (X = F, Cl, Br; A = S, Se). Journal of Molecular Structure. 2007, 814, 1-10.doi:10.1016/j.theochem.2007.02.040
  3. ^ Marc Lamoureux and John Milne "Selenium chloride and bromide equilibria in aprotic solvents; a 77Se NMR study" Polyhedron 1990, Volume 9, pp. 589-595. doi:10.1016/S0277-5387(00)86238-5
  4. ^ J. J. Berzelius, Annales de chimie et de physique 1818, vol. 9, 225. See also Kao, C. H.; Lenher, V. The Preparation of Selenium Monochloride and Monobromide, J. Am. Chem. Soc., 1925, 48, 772-774. doi:10.1021/ja01680a025
  5. ^ a b Fehér, F. "Diselenium Dichloride". In Handbook of Preparative Inorganic Chemistry; Brauer, G., Ed.; Academic Press: New York, 1963; Vol. 1; p 422-433.
  6. ^ a b c Back, Thomas G.; Moussa, Ziad "Diselenium Dichloride" Encyclopedia of Reagents for Organic Synthesis 2003 doi:10.1002/047084289X.rn00201