Preparing alcohols and phenols

Making alcohols.

From alkenes, with acid and water (acid-catalysed hydration). Split water into H and OH and add them across the double bond. Markovnikov's rule decides where they go: the OH goes to the double-bond carbon with fewer hydrogens, and the H to the one with more. So but-1-ene, CH₃CH₂CH=CH₂, gives butan-2-ol.

From alkenes, by hydroboration-oxidation. Add diborane (B₂H₆), then hydrogen peroxide in alkali (H₂O₂/OH⁻). This time the result is the opposite of Markovnikov: the OH goes to the carbon with more hydrogens, the end carbon. But-1-ene now gives butan-1-ol. This gives a primary alcohol in good yield.

By reduction of aldehydes and ketones. Add hydrogen across C=O: one H to the oxygen and one to the carbon. Aldehydes give primary alcohols; ketones give secondary alcohols. The reagents: H₂ with Pd, Pt or Ni, sodium borohydride (NaBH₄) or lithium aluminium hydride (LiAlH₄). LiAlH₄ is the strongest and can even reduce carboxylic acids and esters to primary alcohols; NaBH₄ is milder and leaves esters alone.

With Grignard reagents (RMgX). The R group behaves as R⁻ and adds to the carbon of C=O. A simple way to get the product: write the carbonyl compound, put an H on the oxygen, and attach the R group to the carbon. Then hydrolyse. The type of alcohol depends on the starting carbonyl:

• Methanal (HCHO) gives a primary alcohol.
• Any other aldehyde gives a secondary alcohol.
• A ketone gives a tertiary alcohol.

For example, CH₃MgBr with methanal, then water, gives ethanol, CH₃CH₂OH.

Making phenol. The book gives four routes:

• From chlorobenzene: heat with NaOH at 623 K and 300 atm, then acidify. (This is Dow's process.)
• From benzenesulphonic acid: sulphonate benzene with oleum, fuse the sulphonic acid with NaOH, then acidify.
• From a diazonium salt: treat aniline with NaNO₂ and HCl at 273-278 K to make benzenediazonium chloride, then warm with water.
• From cumene (isopropylbenzene): oxidise it with air to cumene hydroperoxide, then treat with dilute acid. This gives phenol and acetone together, and is how most phenol is made in industry.