Hydrogenation
- Type of Reaction: Reduction/ Addition
- Hydrogenation is NOT an electrophilic addition reaction; the mechanism is solid state catalysed (adsorption) and does not involve an electrophile.
- Alkenes do not react with NaBH4
Oxidation
- The oxidation of alkenes by KMnO4 will give slightly different products under different conditions (pH, concentration and temperature)
- K2Cr2O7 is not strong enough to oxidise alkenes
| Hot | Cold | |
| Products | Cleavage of C=C → ketones, carboxylic acids, CO2 | Addition of –OH across C=C → vincinal diol |
| Acidic | Alkaline | |
| Products | Cold → diols
Hot → ketones, carboxylic acids, CO2 |
Cold → diols
Hot → ketones, carboxylates, CO32– * |
| Observations | Purple to colourless (Mn2+) | Purple to brown ppt (MnO2) |
* Under alkaline KMnO4 conditions, students commonly forget to deprotonate the acidic groups.
