S 1335 (OTTO) Selenium dioxide, 99% 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 1335 (OTTO) Selenium dioxide, 99% Cas 7446-08-4 - used in creating colorless glass and toner in photographic developing.