Preparation of Glycol

Ethylene glycol (ethane-1,2-diol) is made by hydroxylating ethene with cold, dilute alkaline potassium permanganate solution (Baeyer's reagent): CH2=CH2 + H2O + [O] (cold alkaline KMnO4) gives HO-CH2-CH2-OH. This is the same syn-dihydroxylation reaction used generally to test for, and hydroxylate, alkenes: the two -OH groups are delivered to the SAME face of the original double bond via a cyclic manganate-ester intermediate, so the addition is syn (cis) rather than anti. This decolourisation of cold, dilute, alkaline KMnO4 is also the standard qualitative …