Alcohols, Phenols and Ethers

This chapter introduces three important classes of organic compounds: alcohols, phenols, and ethers, all containing a carbon-oxygen single bond. You will learn to classify and name them, and study their structures and methods of preparation. Key preparations include the hydration of alkenes for alcohols, industrial processes for phenols, and the Williamson synthesis for ethers. The chapter also covers physical properties like boiling points and solubility, linking them to the concept of hydrogen bonding.

The main focus is on the chemical reactions of these compounds. For alcohols, this includes reactions like dehydration, oxidation, and esterification, which differ based on whether the alcohol is primary, secondary, or tertiary. For phenols, you will explore their acidic nature and high reactivity in electrophilic aromatic substitution, including named reactions like Kolbe's and the Reimer-Tiemann reaction. Ethers are less reactive, with their most significant reaction being cleavage by hydrogen halides. Students often find it challenging to compare the acidity of alcohols and phenols, a concept that requires a solid understanding of resonance. The chapter builds directly on General Organic Chemistry and Haloalkanes and Haloarenes.

Formulas for Alcohols, Phenols and Ethers

Williamson Synthesis for Ethers: $R-ONa + R'-X \rightarrow R-O-R' + NaX$ R'-X should be a primary alkyl halide to favour substitution over elimination.
Fischer Esterification: $RCOOH + R'OH \rightleftharpoons[H^+] RCOOR' + H_2O$ This is a reversible reaction catalyzed by a mineral acid.
Acidic Dehydration of Alcohols to Alkenes: $RCH_2CH(OH)R' \xrightarrow{H^+, \Delta} RCH=CHR' + H_2O$ Follows Saytzeff's rule; the major product is the more substituted alkene.
Oxidation of a Primary Alcohol to an Aldehyde: $RCH_2OH \xrightarrow{PCC} RCHO$ PCC (Pyridinium chlorochromate) is a mild oxidizing agent.
Oxidation of a Secondary Alcohol to a Ketone: $R_2CHOH \xrightarrow{CrO_3} R_2C=O$ Tertiary alcohols do not undergo oxidation under these conditions.
Lucas Test for Alcohols: $R-OH + HCl \xrightarrow{anhyd. ZnCl_2} R-Cl \downarrow + H_2O$ Rate of reaction (turbidity) distinguishes 3° > 2° > 1° alcohols.
Bromination of Phenol: $C_6H_5OH + 3Br_2(aq) \rightarrow 2,4,6-Br_3C_6H_2OH \downarrow + 3HBr$ A white precipitate is formed instantly. This reaction is a test for phenol.
Kolbe's Reaction: $C_6H_5ONa \xrightarrow{(i) CO_2, \Delta} \xrightarrow{(ii) H^+} o-HOC_6H_4COOH$ This reaction is used to synthesize salicylic acid from phenol.
Reimer-Tiemann Reaction: $C_6H_5OH \xrightarrow{(i) CHCl_3 + aq. NaOH} \xrightarrow{(ii) H^+} o-HOC_6H_4CHO$ The electrophile in this reaction is dichlorocarbene (:CCl₂).
Cleavage of Ethers by Hydrogen Halides: $R-O-R' + HX \rightarrow RX + R'OH$ For 1°/2° alkyl groups, the halide attacks the smaller group. If a 3° group is present, it forms the halide.