Selenium Compound, Organic

any of the substances containing a carbon-selenium bond in the molecule. The principal types of organic selenium compounds (R and Ar designate organic radicals) include selenides (R₂Se), diselenides (RSe—SeR), selenols (RSeH), selenoxides (R₂SeO), selenones (R_xSeO₂), seleninic acids (RSeO₂H), selenonic acids (RSeO₃H), selenonium salts (R₂Se⁺X^–, where X^– is an anion, such as Cl^–), alkyl (aryl) selenium halides (R₂SeX₂ and RSeX₃, where X is a halogen atom), and such selenium heterocyclic compounds as selenophene.

Organic selenium compounds can be obtained by the reaction of alkyl halides with Na₂Se, as shown in equation (1), or by the reaction of aryl diazonium halides with Na₂Se, illustrated in equation (2):

(1) 2RX + Na₂Se → R₂Se + 2NaX

(2) ArN₂X + Na₂Se → Ar₂Se + 2NaX + N₂

A second method involves the reaction of organometallic compounds with either Se or SeO₂:

A third method for obtaining organic selenium compounds is based on the selenization of aromatic compounds:

Selenophene (I) is obtained by the reaction of butadiene with SeO₂ or Se. An example of this reaction is

The chemical properties of organic selenium compounds are analogous to those of organosulfur compounds. Owing to the stronger metallic properties of selenium as compared to those of sulfur, the C—Se bond is more easily broken by halogens and oxidizing agents than is the C—S bond. Selononic acids are strong oxidizing agents. Selenophene derivatives, with the structural formula

are important. Selenoilacetone (R is CH₃) and selenoiltri-fluoroacetone (R is CF₃) form chelate compounds with metal ions (Cu, Th, Zr, Hf). These compounds are used in the extractive separation and isolation of elements.