Preparation of Ethers by Intermolecular Dehydration of Alcohols

Two moles of an alcohol, heated with concentrated H2SO4, can either eliminate (dehydrate to an alkene, favoured at higher temperature) or undergo intermolecular substitution to form an ether (favoured at lower temperature): ethanol with conc. H2SO4 at 443 K gives ethene (elimination), but at the lower temperature of 413 K, substitution competes over elimination and diethyl ether is obtained instead. Mechanistically, one ethanol is first protonated to the good leaving group -OH2+; a second, neutral ethanol molecule's oxygen then attacks as a nucleophile (SN2-like), displacing water, and finally the resulting oxonium ion loses a proton to give the neutral ether. This method is USEFUL ONLY for simple ethers: mixing two …