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Selenium dioxide is prepared by oxidation of selenium by burning in air or by reaction with nitric acid or hydrogen peroxide, but perhaps the most convenient preparation is by the dehydration of selenous acid. 2 H 2 O 2 + Se → SeO 2 + 2 H 2 O 3 Se + 4 HNO 3 + H 2 O → 3 H 2 SeO 3 + 4 NO H 2 SeO 3 ⇌ SeO 2 + H 2 O
The Riley oxidation is a selenium dioxide-mediated oxidation of methylene groups adjacent to carbonyls. It was first reported by Harry Lister Riley and co-workers in 1932. [ 1 ] In the decade that ensued, selenium -mediated oxidation rapidly expanded in use, and in 1939, Andre Guillemonat and co-workers disclosed the selenium dioxide-mediated ...
A number of other reagents bring about this reaction. Scheme 1. Selenium dioxide oxidation. In terms of reaction mechanism, SeO 2 and the allylic substrate react via pericyclic process beginning with an ene reaction that activates the C−H bond. The second step is a [2,3] sigmatropic reaction.
Selenium forms two oxides: selenium dioxide (SeO 2) and selenium trioxide (SeO 3). Selenium dioxide is formed by the reaction of elemental selenium with oxygen: [5] + It is a polymeric solid that forms monomeric SeO 2 molecules in the gas phase. It dissolves in water to form selenous acid, H 2 SeO 3.
Selenium trioxide may be synthesized by dehydrating selenic acid, H 2 SeO 4, which is itself produced by the oxidation of selenium dioxide with hydrogen peroxide: [26] SeO 2 + H 2 O 2 → H 2 SeO 4 Hot, concentrated selenic acid reacts with gold to form gold(III) selenate.
Selenium in these reactions is almost always stereogenic, and the effect of epimerization at selenium (which is acid-catalyzed and occurs readily) on the elimination reaction is nearly unknown. In one example, separation and warming of selenoxides 1 and 2 revealed that 2 decomposes at 0 °C, while 1 , which presumably has more difficulty ...
It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide: SeO 2 + H 2 O 2 → H 2 SeO 4. Unlike the production sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method. [4]
Reaction scheme for the mechanism of a selenoxide oxidation. Date: November 2006: ... selenium dioxide. propylene. reaction mechanism.