Selenium Dioxide (SeO2) in Organic Chemistry || Super-Tricks || Jee Mains, Advance | NEET | AIIMS

Описание: Hello Guys, In this Lecture we are going to discuss a very important reagent in Organic chemistry for Jee Mains, Advance, NEET and AIIMS.
Selenium Dioxide:
Selenium dioxide (SeO2) is a colorless crystalline solid. It is soluble in solvents like dioxane, ethanol, acetic acid and acetic anhydride. It is extremely poisonous and should be carefully handled while working with it. However, it is very selective oxidant.

Allylic Oxidation:
Allylic oxidation is an important organic transformation because it provides a direct access to the allylic alcohols from the readily available alkenes. SeO2 is found to be an effective reagent for this transformation. The stoichiometric as well as catalytic amount of SeO2 can be used but the later requires an oxidant such as t-BuOOH to reoxidize the reduced selenium(II) to SeO2. The reactivity order in ethanol solvent is as follows CH2 greater than CH3 greater than CH but the order may change depending on the reaction conditions.

Mechanism:
The reaction proceeds via ene reaction of allylic compounds with SeO2 to afford allylic seleninic acid that undergoes [2,3]-sigmatropic rearrangement to give selenium ester, which on hydrolysis gives the desired alcohol.

Oxidation of Carbonyl Compounds (Riley Oxidation):
SeO2 oxidizes active methylene or methyl group present adjacent to the carbonyl group to give 1,2-dicarbonyl compounds . This reaction is called Riley oxidation. It has been widely used for the synthesis of natural products and biologically active compounds.

Mechanism:
The proposed mechanism is similar to that of allylic oxidation i.e. ene reaction followed by [2,3]-sigmatropic rearrangement and then elimination gives the desired 1,2-dicarbonyl compounds.

Oxidation of Alkynes:
In the presence of acid, SeO2 oxidizes alkynes to give 1,2-dicarbonyl compounds. Internal alkynes can be converted into 1,2-diketones, where as terminal alkynes are transformed into glyoxylic acid.

Benzylic Oxidation:
SeO2 is also capable of oxidising benzylic C-H bond to give aldehydes or ketones. When the methylene group is flanked by two aromatic rings, the methylene is readily converted into ketone.


Preparation of α,β-Unsaturated Carbonyl Compounds:
The reaction involves α selenylation of carbonyl compounds followed by oxidation of selenium with peroxides or peracids and subsequent elimination provides the desired α,β-unsaturated carbonyl compounds.

Many other roles of SeO2 like dehydrogenation and as a Catalyst has been deal in details.

Our Other Very important Lectures:-

Sodium Borohydride in Organic Chemistry
   • Sodium Borohydride in Organic Chemistry | ...  

LiAlH4 in One Shot | Concept Booster
   • LiAlH4 in One Shot | Concept Booster | Exp...  

DIBAL-H in Organic Chemistry
   • DIBAL-H in Organic Chemistry || Explained ...  

Anhyd. AlCl3 in Organic Chemistry
   • Anhyd. AlCl3 in Organic Chemistry | Friede...  

Nomenclature of Heterocyclic Compounds
   • Nomenclature of Heterocyclic Compounds | S...  

N-BromoSuccinimide in organic Chemistry
   • N-BromoSuccinimide (NBS) in Organic Chemis...  

Thanks for Watching.
Keep Sharing, Keep Supporting!!!
Team IITian Explains