🧪 Alcohol, Phenol & Ether

INTRODUCTION: Alcohols, Phenols and Ethers are oxygen-containing organics. Alcohols/Phenols: replace one H of water by alkyl/aryl; Ethers: replace both H. Industrial: methanol/ethanol fuel, isopropyl sanitizer, ethylene glycol antifreeze, phenol antiseptic, ether anaesthetic. Faraday (early 1800s) synthetic ethanol, phenol from coal tar, ether via ethanol + H2SO4 (15th century).

7.1 ALCOHOL

-OH on aliphatic carbon. Mono‑, di‑ (ethylene glycol), trihydric (glycerol). Monohydric R-OH / CnH2n+1OH. 1°,2°,3°.

Structure: H2O 104.5°, methanol 108.9° – sp3 oxygen.

7.1.2 Physical Properties

Up to butanol colorless liquids; higher waxy solids. BP > alkanes/ethers due to H-bonding. Table 7.1: Ethanol 78.37, Propanol 97.2, Isopropanol 82.6, n-Butanol 117.7, Isobutanol 107.89. Solubility in water decreases with alkyl size.

MEMORY TRICK: BP ranking: more branching = lower BP. Self-assess: C2H5OH, CH3CH(OH)CH3, (CH3)3COH, CH3(CH2)3OH → order: t-butyl alc < isopropanol < ethanol < n-butanol.

Acidity of Alcohol

pKa: methanol 15.5, ethanol 15.9, isopropanol 16.3, t-butanol 17. Primary > secondary > tertiary acidity. Reaction: 2C2H5OH + 2Na → 2C2H5ONa + H2↑.

7.1.3 Preparations

Hydration: H2C=CH2 + H2O –H2SO4 100°C→ C2H5OH.
Hydrolysis: C2H5Cl + NaOH → C2H5OH + NaCl.
Grignard: formaldehyde → 1°; acetaldehyde → 2°; acetone → 3°.

CH3MgBr + (CH3)2C=O → (CH3)3C-OMgBr –H2O→ (CH3)3C-OH (t-butyl alcohol)

Reduction: aldehydes → 1° alcohol, ketones → 2° (H2/Ni or LiAlH4). Grignard+ester → 3° alcohol. LiAlH4 reduces acids/esters → 1° alcohol.

7.1.5 Reactions

Lucas reagent (conc HCl+ZnCl2): 3° immediate, 2° few min, 1° no reaction. C2H5OH + HCl (ZnCl2) → C2H5Cl.
SOCl2 (pyridine) → alkyl halide. Dehydration: conc H2SO4, 170°C → ethene. 3° alc fastest.
Oxidation: 1° → aldehyde → acid, 2° → ketone, 3° resistant.
Periodic acid (HIO4) cleaves 1,2-diols: ethylene glycol → 2 HCHO.

HIO4: “Periodic pops diol into twins carbonyl”.

7.2 PHENOLS

-OH directly on benzene ring. Mono (benzenol), di (catechol, hydroquinone), tri (pyrogallol). Structure: sp3 O, C-O-H ~109°.

Physical: white crystal, red if impure; high BP (H-bond); toxic; soluble in water.

Acidity of Phenol

pKa ≈ 10, stronger than alcohol. Phenoxide resonance stabilized. C6H5OH + NaOH → C6H5ONa + H2O.

Negative charge delocalized on ring → phenoxide more stable than ethoxide.

7.2.4 Preparation (diazonium)

Benzene diazonium salt + H2O → Phenol.

7.2.6 Reactions

Nitration: dil HNO3, 25°C → o-nitrophenol (55%) + p-nitrophenol (45%). Conc HNO3 → picric acid (2,4,6-trinitrophenol).

Sulphonation: 15-20°C → o-phenol sulphonic acid; 100°C → p-phenol sulphonic acid.

Halogenation: Aq Br2 → 2,4,6-tribromophenol (white ppt). Br2/CCl4 → o‑ and p‑bromophenol.

With sodium: 2C6H5OH + 2Na → 2C6H5ONa + H2.
Oxidation: K2Cr2O7/H+ → benzoquinone (yellow).

7.2.7 Alcohol vs Phenol

Alcohol: alkyl-OH, weaker acid, no resonance. Phenol: aryl-OH, acidic, aromatic substitution.

Identification tests

Alcohol: sodium test (effervescence), ester test (fruity smell).
Phenol: FeCl3 → violet complex; bromine water → white ppt 2,4,6-tribromo.

7.3 ETHERS

R–O–R’. Symmetrical/unsymmetrical. Dimethyl ether, ethyl methyl ether, diphenyl ether, anisole.
Bond angle C-O-C 110.5° (greater repulsion).

Preparation: (i) Dehydration: 2C2H5OH –H2SO4,140°C→ C2H5–O–C2H5 + H2O. (ii) Williamson: C2H5ONa + C2H5Cl → C2H5OC2H5 + NaCl.

Physical: BP lower than alcohols (no H-bond), partially soluble in water.

Reactivity: Oxonium salt with conc acid: R–O–R + H+ → R–OH⁺–R (stable in conc acid, reverts on dilution).

“Williamson: alkoxide + 1° alkyl halide → ether SN2”.

Uses: solvent for Grignard, Wurtz, anaesthetic.

Self assessment: Ethanol → ethene: Conc H2SO4 170°C. Ethanol → acetic acid: K2Cr2O7/H+. Acetic acid → ethanol: LiAlH4. Ethylene glycol → formaldehyde: HIO4.

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