Alcohols, Phenols and Ethers
Alcohols, phenols and ethers tests preparation, acidity, reaction mechanisms and simple distinguishing tests.
Alcohols
Alcohols are prepared by hydration of alkenes, reduction of carbonyls, and Grignard addition. They undergo dehydration with H2SO4, oxidation (1° → aldehyde → acid; 2° → ketone; 3° resistant), and esterification. Lucas reagent distinguishes 3° (immediate turbidity), 2° (within minutes) and 1° (no reaction at room temperature).
Phenols
Phenol is acidic because the phenoxide ion is resonance-stabilised; it is more acidic than water but less than carboxylic acids. Phenol gives a violet colour with neutral FeCl3, undergoes electrophilic substitution readily, and forms tribromophenol with bromine water. It does not undergo the alcohol-type Lucas test.
Ethers
Ethers are prepared by Williamson synthesis: alkoxide + 1° alkyl halide. They are cleaved by HI, giving alcohol and iodoalkane; with excess HI, phenol and iodoalkane can form from aryl ethers. Ethers are relatively inert, which makes them useful solvents.
Worked example
To distinguish ethanol, phenol and ethoxyethane: add neutral FeCl3; phenol gives violet. To the remaining two, add a small piece of sodium; ethanol gives brisk effervescence, ethoxyethane does not. Reason from functional-group reactivity, not smell.
Mark-losing traps
Using a 3° halide in Williamson synthesis, which gives elimination instead of ether; writing phenol as more acidic than acetic acid; forgetting that phenol reacts with bromine water without a catalyst; and confusing Lucas turbidity with the iodoform test are common errors.