Q.Write the mechanism of acid-catalysed dehydration of ethanol to give ethene.

Step 1. Step 1 (protonation). Ethanol's oxygen lone pair is protonated by H2SO4, converting the poor leaving group -OH into the good leaving group -OH2+ (an ethyloxonium ion).

Step 2. Step 2 (concerted E2 elimination). A base (the conjugate base HSO4-, or another ethanol molecule) removes a hydrogen from the BETA-carbon (the CH3 carbon) at the same time as the C-O bond breaks and water departs from the alpha-carbon -- a single, concerted step with no discrete carbocation intermediate, since ethanol is a primary alcohol. …

Write the two-part mechanism explicitly: protonation of -OH to a good leaving group, then a single concerted E …

• Drawing a discrete carbocation intermediate for ethanol's dehydration -- primary alcohols dehydrate by the CONCERTED E2 mechanism, not the stepwise E1 mechanism tertiary alcohols use. …