Alcohols, Phenols and Ethers – Comprehensive Study Notes

Overview and Unit Objectives

• After completing this unit you should be able to:

  • Name alcohols, phenols and ethers following IUPAC rules.

  • Describe synthetic routes to alcohols from alkenes, carbonyls & carboxylic acids.

  • Explain preparation of phenols from halo‐arenes, sulfonic acids, diazonium salts & cumene.

  • Outline formation of ethers from (i) alcohols (acidic dehydration) and (ii) alkyl-halide/alkoxide (Williamson).

  • Relate physical properties (b.p., solubility, acidity) to structure & H-bonding.

  • Predict / rationalize chemical reactivity on the basis of –OH or –OR functional group.

• Industrial relevance:

  • Alcohols → detergents, solvents, fuels.

  • Phenols → antiseptics (carbolic acid), resins, pharmaceuticals.

  • Ethers → fragrances, anaesthetics (e.g., diethyl ether).

Classification Schemes

• Hydroxyl Count

  • Monohydric, dihydric, trihydric, polyhydric.

• Hybridisation of C–OH Carbon

  • $\text{sp}^3$ (alkyl) → further classed as

  • Primary $1^\circ$, Secondary $2^\circ$, Tertiary $3^\circ$ (based on C–OH substituents).

  • Allylic (adjacent to C=C) & Benzylic (adjacent to aromatic ring) forms—may still be $1^\circ/2^\circ/3^\circ$.

  • $\text{sp}^2$ (vinylic or aryl) → vinylic alcohols, phenols.

• Ethers

  • Simple / symmetrical (R–O–R) vs. mixed / unsymmetrical (R–O–R′).

Nomenclature Essentials

(a) Alcohols

• IUPAC: Replace terminal -e of parent alkane with -ol; retain -e for polyols (diol, triol).

  • Number chain from end nearer to –OH.

  • Example: $HO–CH<em>2CH</em>2–OH \;\longrightarrow \; \text{ethane-1,2-diol}$.

• Common: Alkyl name + “alcohol” (e.g., methyl alcohol).

• Cyclic: prefix cyclo, C-1 carries –OH.

(b) Phenols

• Simple parent: Phenol (accepted IUPAC).

• Disubstituted positions often described by ortho/meta/para in common names.

  • E.g. $o\text{-cresol}=2\text{-methylphenol}$.

  • Dihydroxy benzenes: catechol (1,2), resorcinol (1,3), hydroquinone (1,4).

(c) Ethers

• Common: Alphabetical listing of alkyl/aryl groups + “ether” (diethyl ether, methyl phenyl ether).

• IUPAC: larger alkyl chain = parent; smaller + -oxy prefix.

  • $CH<em>3OCH</em>2CH<em>2CH</em>3 \to 1\text{-methoxypropane}$.

Structural Features

• Alcohols: C–O $\sigma$ bond by overlap of $sp^3(C)$ & $sp^3(O)$; bond angle slightly < $109.5^\circ$ due to lone-pair repulsion.

• Phenols: O attached to $sp^2$ carbon; shorter C–O (136 pm) because (i) partial $\pi$ bonding via conjugation, (ii) $sp^2$ hybrid.

• Ethers: $sp^3$ oxygen with two lone pairs; C–O–C angle slightly > $109.5^\circ$ due to R-group repulsion (≈ $110–115^\circ$); C–O 141 pm.

Preparative Methods

A. Alcohols

1. From Alkenes

   • Acid-catalysed hydration $RCH{=}CH<em>2 + H</em>2O \xrightarrow{H^+} RCH(OH)CH_3$ (Markovnikov).

   • Hydroboration–oxidation $BH<em>3$ then $H</em>2O_2/NaOH$ → anti-Markovnikov alcohol.

2. From Carbonyls

   • Catalytic hydrogenation or NaBH4 / LiAlH4.

     • Aldehyde → $1^\circ$ alcohol; Ketone → $2^\circ$ alcohol.

3. From Carboxylic Acids / Esters

   • $LiAlH_4$ gives $1^\circ$ alcohol; industrially via ester → catalytic hydrogenation.

4. Via Grignard reagents $RMgX + R'CHO \xrightarrow{H_2O} R'CH(OH)R$.

   • $CH_2O$ → $1^\circ$; other aldehydes → $2^\circ$; ketones → $3^\circ$.

B. Phenols

1. Dow process: $C<em>6H</em>5Cl \xrightarrow[320\,atm]{NaOH,\,623\,K} C<em>6H</em>5ONa \xrightarrow{H^+} C<em>6H</em>5OH$.

2. Sulphonation route: $C<em>6H</em>5SO<em>3Na + NaOH (\ell) \to C</em>6H<em>5ONa \to C</em>6H_5OH$.

3. Diazonium hydrolysis $C<em>6H</em>5N<em>2^+Cl^- + H</em>2O \to C<em>6H</em>5OH+N_2$.

4. Cumene process (industrial): Cumene $\xrightarrow[air]{\text{oxidation}}$ cumene hydroperoxide $\xrightarrow{H^+}$ phenol + acetone.

C. Ethers

1. Acidic dehydration of alcohols (only primary) $2ROH \xrightarrow[413\,K]{H<em>2SO</em>4} ROR + H_2O$.

2. Williamson synthesis $R'ONa + R–X \to R'–O–R + NaX$ (SN2).

   • Best with primary halide; $3^\circ$ halides give alkenes.

Physical Properties & Structure–Property Correlation

• Boiling points (b.p.)

  • \text{ROH} > \text{R–O–R} \sim \text{R–R} (same $M_W$) because of intermolecular H-bonding.

  • Branching ↓ b.p. (less surface area).

• Solubility in $H_2O$

  • Small $n$ alcohols & phenols miscible via \text{ROH···H–OH} H-bonds.

  • Solubility ↓ as hydrophobic chain ↑.

• Acidity order

  • ArOH > ROH ; within phenols: EWG (e.g., $–NO<em>2$) (\uparrow) acidity (especially o-/p-), EDG (e.g., $–CH</em>3$) (\downarrow).

  • Representative $pK_a$: phenol 10.0, $o$-nitrophenol 7.2, ethanol 15.9.

Chemical Reactivity

A. Alcohols

• (i) Cleavage of O–H

  • With Na, K → alkoxide + $\tfrac12 H_2$.

  • Esterification with acids/acid chlorides (acetylation → aspirin from salicylic acid).

• (ii) Cleavage of C–O

  • HX (Lucas): $ROH + HX \to RX$; reactivity 3^\circ > 2^\circ > 1^\circ.

  • $PBr<em>3, PCl</em>3, SOCl_2$ analogues.

  • Dehydration → alkenes (443 K, $H<em>2SO</em>4$). $3^\circ$ > $2^\circ$ > $1^\circ$.

• Oxidation patterns

  • $1^\circ$ → aldehyde (PCC) → acid (KMnO$_4$).

  • $2^\circ$ → ketone (CrO$_3$).

  • $3^\circ$ resistant; undergo cleavage under drastic conditions.

• Catalytic dehydrogenation (Cu, 573 K) $1^\circ$ → aldehyde; $2^\circ$ → ketone; $3^\circ$ → alkene.

B. Phenols (Ring-directed electrophilic substitution)

• Nitration

  • Dil. $HNO_3$ (298 K): $o$- & $p$-nitrophenol (steam volatility difference: $o$ volatile via intramolecular H-bond).

  • Conc. $HNO<em>3/H</em>2SO_4$ → picric acid (2,4,6-trinitrophenol).

• Halogenation

  • $Br<em>2/CS</em>2$ (low T) → mono-bromo (o,p-).

  • $Br_2$ water → 2,4,6-tribromophenol (white ppt).

• Kolbe–Schmitt $C<em>6H</em>5ONa + CO_2 (4–7 atm, 400 K) → o$-salicylic acid.

• Reimer–Tiemann $\text{PhOH} + CHCl_3 + NaOH → o$-hydroxybenzaldehyde.

• Zn dust reduction → benzene.

• Oxidation (CrO$_3$) → p-benzoquinone.

C. Ethers

• Generally inert; weak dipoles.

1. Cleavage by conc. HX (HI > HBr)

   • $ROR' + HI \xrightarrow{\Delta} RI + R'OH \xrightarrow{excess\,HI} R'I$.

   • Alkyl-aryl ether → phenol + alkyl halide (C–O cleavage on alkyl side).

   • Mechanism: protonation → SN2 (primary) or SN1 (tertiary).

2. Electrophilic substitution on aromatic ethers (anisole)

   • Friedel–Crafts alkylation/acylation: ortho/para products.

   • Halogenation / nitration: activated ring.

Named & Special Reactions (Quick Reference)

• Hydroboration–Oxidation (anti-Markovnikov hydration).

• Lucas Test (ZnCl$_2$/conc HCl) — qualitative $1^\circ/2^\circ/3^\circ$ alcohol identification via turbidity.

• Kolbe–Schmitt (phenoxide + CO$_2$ → salicylic acid).

• Reimer–Tiemann (chloroform base → formylation at ortho).

• Williamson Ether Synthesis (alkoxide + primary halide).

• Dow Process (haloarene → phenol).

• Cumene Hydroperoxide Route (industrial phenol).

Commercially Important Alcohols

• Methanol (wood spirit)

  • Produced via $CO + 2H<em>2 \xrightarrow[ZnO–Cr</em>2O<em>3]{250–300\,^\circ C,\, 50–100\,atm} CH</em>3OH$.

  • Uses: formaldehyde, solvents; toxic—causes blindness/fatality; antidote: ethanol.

• Ethanol

  • Fermentation of glucose/fructose (invertase → zymase) $C<em>6H</em>{12}O<em>6 \to 2C</em>2H<em>5OH + 2CO</em>2$ (anaerobic, 14 % limit).

  • Alternative: acid-catalysed hydration of ethene.

  • Denatured alcohol: CuSO$_4$ (colour) + pyridine (odour).

Tables & Numeric Data

• Representative $pK_a$ values (lower = stronger acid):

  • $o$-nitrophenol 7.2 < $m$-nitrophenol 8.3 < phenol 10.0 < ethanol 15.9.

• Boiling points (K): $n$-pentane 309, ethoxyethane 308, butan-1-ol 390.

Conceptual Connections & Ethical Notes

• Hydrogen bonding explains anomalies in boiling/s solubility → biology (water miscibility), materials (antifreeze $HOCH<em>2CH</em>2OH$).

• Oxidative metabolism of methanol to formic acid → medical emergency; illustrates biochemical oxidation parallels with lab CrO$_3$.

• Electrophilic activation by –OH/–OR groups parallels resonance donation in electrophilic aromatic substitution; contrast with –NO$_2$ withdrawal.

• Industrial cumene route couples phenol & acetone demand—economics of process design.

Exam Tips & Pitfalls

• Williamson: use primary halide; tertiary halide gives alkene (elimination).

• Acidic dehydration: temperature controls ether (≈413 K) vs. alkene (≥443 K).

• Grignard: moisture destroys reagent; remember formaldehyde gives $1^\circ$ alcohol.

• Phenol acidity: invoke resonance stabilisation of phenoxide & inductive effects.

• HI cleavage of ethers: identify weaker C–O bond; for anisole, CH$_3$I + phenol.

• Steam volatility: intramolecular H-bond lowers b.p. (o-nitrophenol).

Quick Problem-Solving Heuristics

• Identify type of alcohol (1°,2°,3°) → predicts reaction pathway (SN1 vs SN2, oxidation level, dehydration).

• For electrophilic substitution on phenol/anisole: always draw resonance forms to justify ortho/para orientation.

• When stuck on naming ethers: locate longer carbon chain → parent; prefix shorter + “oxy”.

• Use \text{BDE}{C–Cl} > \text{BDE}{C–O} in aryl ether to justify cleavage side.

Summary Map (One-glance)

ALKENES  →(H⁺/H₂O)                 ALKYL HALIDE + NaOR → ROR'  (Williamson)
          →(BH₃·THF/H₂O₂–OH⁻)                     ↑
CARBONYLS →(H₂/Pt  OR  LiAlH₄)  → ROH            | acid 413 K, primary ROH → ROR
 CARBOXYLIC ACID + LiAlH₄ → ROH                  | acid 443 K → alkene
ROH + Na → RO⁻;  ROH + HX → RX;  ROH + CrO₃ → aldehyde/ketone/acid
Phenol + CO₂/NaOH → salicylic acid   Phenol + CHCl₃/NaOH → salicylaldehyde
ROR + HI (Δ) → RI + R'OH/(RI)       R–O–Ar + HI → ArOH + RI

These bullet-point notes integrate every concept, reaction, mechanism, example and data value mentioned in the transcript, enriched with contextual connections, cautionary biomedical notes, and exam-oriented advice to serve as a comprehensive single-source PDF study guide on Alcohols, Phenols & Ethers.