selenium dioxide

noun

Definition of selenium dioxide 

: a poisonous white crystalline compound SeO2 that sublimes to a yellow-green vapor, that is made by oxidation of selenium with nitric acid or air or by dehydration of selenious acid, and that is used chiefly as a catalyst and an oxidizing agent in organic chemistry (as for oxidizing a methylene group next to a carbonyl group to a second carbonyl group)

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