Alcohols, Phenols and Ethers — Part 2: Reactions, uses and ethers: visual lesson, CBSE Class 12 Chemistry

Lesson

Reactions of alcohols, phenols and ethers

Part 2 — acidity, reactions of the O–H and C–O bonds, the activated ring of phenol, and ethers.

In this lesson you will

Compare the acidity of alcohols, water and phenols and explain substituent effects
Write reactions of alcohols: with metals, esterification, HX, dehydration and oxidation
Write reactions of phenol: bromination, nitration, Kolbe and Reimer–Tiemann reactions
State uses of methanol and ethanol, and write Williamson synthesis and reactions of ethers

Concept

Acidity of alcohols and phenols

Alcohols react with active metals to give alkoxides and hydrogen, but are weaker acids than water. Phenol is much more acidic: it dissolves in NaOH, because the phenoxide ion is stabilised by resonance. Neither reacts with $\ce{NaHCO3}$ .

\ce{2C2H5OH + 2Na -> 2C2H5ONa + H2}

\ce{C6H5OH + NaOH -> C6H5ONa + H2O}

Table of pKa values of ethanol, water, phenol and substituted phenols
Compound	$\text{p}K_\text{a}$
Ethanol	15.9
Water	15.7
Phenol	10.0
4-Methylphenol	10.2
3-Nitrophenol	8.3
4-Nitrophenol	7.1
2,4,6-Trinitrophenol	0.5

Diagram

Why phenol is more acidic

In phenoxide the negative charge is delocalised over oxygen and the ortho and para carbons; in ethoxide it stays on oxygen, and the alkyl group even pushes electrons towards it (+I). Electron-withdrawing groups at ortho/para (–NO₂) spread the charge further and increase acidity.

Cookies