Alcohols, Phenols and Ethers
Alcohols, Phenols and Ethers covers classification, acidity, characteristic tests and preparation. Distinguishing alcohols from phenols is a recurring exam task.
Alcohols and phenols
Alcohols react with sodium to give alkoxide and hydrogen. Dehydration with concentrated H2SO4 gives alkenes. The Lucas test uses concentrated HCl and ZnCl2: tertiary alcohols react immediately, secondary in about five minutes, primary only on heating. Phenol is acidic because the phenoxide ion is resonance-stabilised; it reacts with NaOH but not with NaHCO3. Phenol undergoes bromination to 2,4,6-tribromophenol and gives Kolbe and Reimer-Tiemann reactions.
Ethers
Williamson synthesis is R-O-Na+ + R'-X -> R-O-R' + NaX; primary halides work best. Ethers are cleaved by HI, giving an alcohol and an alkyl iodide. They can form explosive peroxides on storage.
Worked example
Phenol + NaHCO3 gives no carbon dioxide, while acetic acid gives CO2. Phenol has pKa about 10, whereas carbonic acid has pKa1 about 6.35, so phenol cannot protonate HCO3- to carbonic acid. The reasoning is thermodynamic: the weaker acid cannot displace the stronger acid from its salt.
Traps
Calling phenol a strong acid, using NaHCO3 to distinguish phenol from carboxylic acids, and ignoring the ether cleavage stoichiometry are common errors.