The dehydration of alcohols affords ethers:
: 2 R–OH → R–O–R + HO at high temperature
This direct nucleophilic substitution reaction requires elevated temperatures (about 125 °C). The reaction is catalyzed by acids, usually sulfuric acid. The method is effective for generating symmetrical ethers, but not unsymmetrical ethers, since either OH can be protonated, which would give a mixture of products. Diethyl ether is produced from ethanol by this method. Cyclic ethers are readily generated by this approach. Elimination reactions compete with dehydration of the alcohol:
: R–CH–CH(OH) → R–CH=CH + HO
The dehydration route often requires conditions incompatible with delicate molecules. Several milder methods exist to produce ethers.