11.18 KMnO4 oxidation of alkynes
The same reaction can happen with the two pi-bonds of an alkyne. Since there are two pi-bonds, the dihydroxylation can happen twice, resulting in a species with four hydroxyl groups on it. This is unstable. Two water molecules are eliminated resulting in an α-diketone (alpha-diketone). Under neutral KMnO4 conditions, the α-diketone is the product.
The double dihydroxylation of the alkyne makes sense. Look closely how the two molecules of water are lost leaving only two oxygen atoms behind on neighboring carbon atoms.
