S 3671 (OTTO) Selenium dioxide, ≥99.9% Cas 7446-08-4 - used in the manufacture of other selenium compounds. Selenium dioxide is an oxidizing agent mostly used in the allylic oxidation of alkenes to produce allylic alcohols. S 3671 (OTTO) Selenium dioxide, ≥99.9% Cas 7446-08-4 - used in creating colorless glass and toner in photographic developing.