One oxidation reaction in organic compounds occurs when there is a oxygen inlet (or hydrogen output) in the organic molecule.
| One mild oxidation only occurs in hydrocarbons with unsaturation, that is, with double (alkenes) or triple (alkyne) bonds. |
For saturated hydrocarbons to oxidize, more energetic oxidation is needed.
Mild oxidation uses the Baeyer reactive, which corresponds to an aqueous solution of potassium permanganate (KMnO4) in a neutral or slightly alkaline (basic – OH1-), cold medium. This reactive is so called because German chemist Adolf Von Baeyer proposed a test, called the Baeyer's test, to identify alkenes and their cyclan isomers.
This test works as follows: as we will see later, an alkene reacts with the permanganate of potassium, thus its color, initially violet, becomes colorless and there is the appearance of a precipitate brown (MnO2). However, cyclans do not react with potassium permanganate. So if the solution remains violet, it's a cyclan.
The figure below shows that the test was positive for alkenes only in the test tube on the left, as the brown precipitate appeared.
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The oxidation reaction of alkenes starts with the decomposition of the permanganate, producing oxygen:
Mild oxidation of alkenes:
This produced oxygen will react with the double bond of the alkene forming a epoxide which, later, through hydrolysis, becomes a alcohol or vicinal diol (glycol), that is, two OH groups on neighboring carbons.
In the example below we see the mild oxidation of propene:
Mild oxidation of alkynes:
In the case of alkynes, the product formed will be diketones. With the exception of the ethyne (HC≡CH), where there are two hydrogens bonded on each carbon participating in the triple bond, a aldehyde.
Note the mild oxidation of propyne, with formation of a diketone:
By Jennifer Fogaça
Graduated in Chemistry
Brazil School Team
Would you like to reference this text in a school or academic work? Look:
FOGAÇA, Jennifer Rocha Vargas. "Soft oxidation"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/oxidacao-branda.htm. Accessed on June 28, 2021.
