7. Alcohols & Ethers
Alcohols are the Swiss-army knives of organic chemistry: they can be oxidized, dehydrated, or converted into good leaving groups — and their oxygen can build ethers.
Oxidation
- PCC (mild): primary alcohol → aldehyde; secondary alcohol → ketone.
- Jones reagent (CrO3/H2SO4, strong): primary alcohol → carboxylic acid; secondary → ketone; tertiary alcohols do not oxidize (no H on the carbinol carbon).
Example: 1-Butanol + PCC → butanal; 1-butanol + Jones → butanoic acid; 2-butanol + either → 2-butanone.
Dehydration and Substitution
With concentrated H2SO4 and heat, alcohols dehydrate (E1) to alkenes — Zaitsev's rule picks the major product. With HX, the –OH is protonated to a good leaving group (H2O) and substitution follows SN1/SN2 as usual.
Williamson Ether Synthesis
An alkoxide plus an alkyl halide gives an ether by SN2 — so the halide should be primary or methyl for a good yield.
Example: $$\text{CH}_3\text{CH}_2\text{O}^-\text{Na}^+ + \text{CH}_3\text{I} \rightarrow \text{CH}_3\text{CH}_2\text{OCH}_3 \quad \text{(ethyl methyl ether)}$$
Practice Problems
- What does PCC oxidation of cyclohexanol give?
- What happens when tert-butanol is treated with Jones reagent?
- Give the product of phenol + CH3I with NaOH (Williamson).
- What is the major dehydration product of 2-methyl-2-propanol?
Answers: 1. Cyclohexanone 2. No reaction — tertiary alcohols resist oxidation 3. Anisole (methoxybenzene) 4. 2-methylpropene