The dihydroxylation of an alkene consists of adding an -OH group to each carbon to form vicinal diols. This reaction can be carried out with osmium tetroxide in hydrogen peroxide, or with potassium permanganate in water.
![oxidation with osmium tetroxide oxidación con tetraóxido de osmio](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion01.png)
The product of this reaction is a vicinal diol WITHOUT
![dihydroxylation of alkenes dihidroxilación de alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion02.png)
As the alkene is flat with two faces equally accessible to the reagent, a racemic mixture is obtained as the final product. Approaching the permanganate from the top face forms one enantiomer, while approximation from the bottom forms the other.
The reaction mechanism consists in the formation of a cycle, which is broken at a later stage, leaving the diol free.
![dihydroxylation03.png dihidroxilacion03.png](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion03.png)
Stage 1. Condensation of the alkene with the permanganate
![dihydroxylation alkenes dihidroxilacion alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion04.png)
Stage 2 . Breaking the cycle releases the diol
![dihydroxylation alkenes dihidroxilacion alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion05.png)
The osmium tetroxide mechanism follows analogous steps
![dihydroxylation alkenes dihidroxilacion alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion06.png)
Stage 1. Condensation of the alkene with osmium tetroxide
![dihydroxylation alkenes dihidroxilacion alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion07.png)
Stage 2. Oxidation stage that releases the diol
![dihydroxylation alkenes dihidroxilacion alquenos](/images/stories/organica-i/alquenos-reacciones/dihidroxilacion/dihidroxilacion08.png)