Selenium monochloride explained

Selenium monochloride or diselenium dichloride is an inorganic compound with the formula . Although a common name for the compound is selenium monochloride, reflecting its empirical formula, IUPAC does not recommend that name, instead preferring the more descriptive diselenium dichloride.

Diselenium dichloride is a reddish-brown, oily liquid that hydrolyses slowly. It exists in chemical equilibrium with , , chlorine, and elemental selenium. Diselenium dichloride is mainly used as a reagent for the synthesis of Se-containing compounds.

Structure and properties

Dielenium dichloride has the connectivity . With a nonplanar structure, it has C2 molecular symmetry, similar to hydrogen peroxide and disulfur dichloride, which is referred to as gauche. The Se-Se bond length is 223 pm, and the Se-Cl bond lengths are 220 pm. The dihedral angle between the and planes is 87°.[1]

Preparation

Early routes to diselenium dichloride involved chlorination of elemental selenium.[2] An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:[3]

A dense layer of diselenium dichloride 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:[3]

The crude diselenium dichloride is removed via separatory funnel. Diselenium dichloride cannot be distilled without decomposition, even at reduced pressure.[3]

In acetonitrile solutions, it exists in equilibrium with and .[4] Selenium dichloride degrades to diselenium dichloride after a few minutes at room temperature:[5]

Reactions

Diselenium dichloride 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 selenoketones, 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.[6]

Notes and References

  1. Kniep . Rüdiger . Körte . Lutz . Mootz . Dietrich . Kristallstrukturen von Verbindungen A2X2 (A = S, Se; X = Cl, Br) . Zeitschrift für Naturforschung B . 1 January 1983 . 38 . 1 . 1–6 . 10.1515/znb-1983-0102 . free.
  2. 10.1021/ja01680a025. The Preparation of Selenium Monochloride and Monobromide. Journal of the American Chemical Society. 47. 3. 772–774. 1925. Lenher. Victor. Kao. C. H..
  3. Book: Fehér, F. . https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n447 . Handbook of Preparative Inorganic Chemistry . Academic Press . 1963 . Brauer . G. . 2nd . 1 . New York . 422-423 . Diselenium Dichloride.
  4. Lamoureux . Marc . Milne . John . 1990 . Selenium chloride and bromide equilibria in aprotic solvents; a Se77 NMR study . Polyhedron . 9 . 4 . 589–595 . 10.1016/S0277-5387(00)86238-5.
  5. Inorganic Chemistry. 1999. 38. 18. 4093–4097. 10.1021/ic981430h. Syntheses of THF Solutions of SeX2(X = Cl, Br) and a New Route to Selenium Sulfides SenS8−n(n = 1−5): X-ray Crystal Structures of SeCl2(tht)2 and SeCl2·tmtu. Maaninen. Arto. Chivers. Tristram. Parvez. Masood. Pietikäinen. Jarkko. Laitinen. Risto S..
  6. Encyclopedia: Back, Thomas G. . Moussa, Ziad. Diselenium Dichloride. Encyclopedia of Reagents for Organic Synthesis. 2003 . 10.1002/047084289X.rn00201. 0-471-93623-5.