Q.What happens when ethylene is passed through cold dilute alkaline potassium permanganate.

Step 1. Cold, dilute, alkaline KMnO4 is Baeyer's reagent, a MILD oxidant that adds across a C=C double bond WITHOUT breaking the carbon skeleton (unlike the hot, acidified version, which cleaves the bond entirely).

Step 2. Passed through ethylene (ethene, CH2=CH2), the reagent adds an -OH group to each of the two alkene carbons, converting the double bond into a vicinal diol: CH2=CH2 + H2O + [O] --> HOCH2-CH2OH (ethane-1,2-diol, ethylene glycol).

Step 3. As the oxidation proceeds, manganese is reduced stepwise -- the initial purple colour (Mn7+, as MnO4-) passes through a dark green intermediate (Mn6+) before finally depositing a dark brown precipitate of MnO2 (Mn4+). …

Distinguish Baeyer's reagent's mild oxidation (adds -OH across the double bond, giving a diol, skeleton intact) from the harsher hot/acidified KMnO4 (cleaves the double bond entirely into two separate carbonyl/acid f …

• Describing the product as a cleaved carbonyl/acid fragment (as with hot, acidified KMnO4) instead of an intact vicinal diol -- COLD, DILUTE, ALKALINE conditions sp …