Alcohols, Phenols, and Ethers PDF

# Alcohols, Phenols, and Ethers ## Classification - **OH attached to sp³ carbon:** - **Normal alcohols:** - 1° : CH₃-CH₂-OH - 2° : CH₃-CH(OH)-CH₃ - 3° : CH₃-C(OH)(CH₃)₂ - **Ally...

# Alcohols, Phenols, and Ethers ## Classification - **OH attached to sp³ carbon:** - **Normal alcohols:** - 1° : CH₃-CH₂-OH - 2° : CH₃-CH(OH)-CH₃ - 3° : CH₃-C(OH)(CH₃)₂ - **Allylic alcohols:** - CH₂=CH-CH₂-OH - **Benzylic alcohol:** - Ph-CH₂-OH - **OH attached to sp² carbon:** - **Vinylic alcohols:** - CH₂=CH-OH - **Phenols:** - Ar-OH ## Common Naming - **Alcohols:** - n-propyl alcohol - isopropyl alcohol - n-butyl alcohol - sec-butyl alcohol - tert-butyl alcohol - **Phenols:** - phenol - o-cresol - m-cresol - p-cresol - **Ethers:** - ethyl methyl ether - methyl phenyl ether (Anisole) - ethyl phenyl ether (Phenetole) - catechol - resorcinol - hydroquinone - quinol ## Preparation of Alcohols - **From Alkenes** - **Markovnikov Rule with rearrangement:** - Acidic hydrolysis of alkenes: CH₃-CH=CH₂ + H₂SO₄ + H₂O → CH₃-CH(OH)-CH₃ - Mechanism: - CH₃-CH=CH₂ + H⁺ → CH₃-CH⁺-CH₃ - CH₃-CH⁺-CH₃ + H₂O → CH₃-CH(OH)-CH₃ + H⁺ - **From rearrangement**: CH₃-CH=CH₂ + H⁺/H₂O → CH₃-CH₂-CH₂-OH - **Anti-Markovnikov Rule without rearrangement:** - **Hydroboration-oxidation:** - CH₃-CH=CH₂ + B₂H₆/THF → CH₃-CH₂-CH₂-BH₂ - CH₃-CH₂-CH₂-BH₂ + H₂O₂/OH^- → CH₃-CH₂-CH₂-OH - **Mechanism (Syn addition):** - CH₃-CH=CH₂ + BH₃ → CH₃-CH₂-CH₂-BH₂ - CH₃-CH₂-CH₂-BH₂ + H₂O₂/OH^- → CH₃-CH₂-CH₂-OH + B(OH)₃ - **Oxymercuration-demercuration:** - CH₃-CH=CH₂ + Hg(OAc)₂/H₂O → CH₃-CH(OAc)-CH₃, - CH₃-CH(OAc)-CH₃ + NaBH₄/OH^- → CH₃-CH(OH)-CH₃ - **Mechanism (Anti addition):** - CH₃-CH=CH₂ + Hg(OAc)₂/H₂O → CH₃-CH(OAc)-CH₃-HgOAc - CH₃-CH(OAc)-CH₃-HgOAc + NaBH₄/OH^- → CH₃-CH(OH)-CH₃ + Hg + OAc - **From alkyl halides to alcohols** - SN₁ Reaction: - CH₃-CH₂-Cl + aq. KOH → CH₃-CH₂-OH - **From carbonyl compounds** - **Reduction of Aldehyde and Ketone:** - R-CHO + [H] → R-CH₂-OH - R-CO-R + [H] → R₂-CH-OH - Reducing agent → Pt, Pd, Ni / H₂, LiAlH₄, NaBH₄, B₂H₆ - Mechanism: - CH₃-CO-CH₃ + H^- → CH₃-CH(OH)-CH₃ - **Reduction of Carboxylic Acids and its derivatives:** - **Reduction of carboxylic acid:** - R-COOH + LiAlH₄/H⁺ → R-CH₂-OH - **Reduction of acid chloride:** - R-COCl + LiAlH₄ → R-CH₂-OH - **Reduction of ester:** - R-COOR + LiAlH₄/H⁺ → R-CH₂-OH - **Reduction of amide:** - R-CONH₂ + LiAlH₄/H⁺ → R-CH₂-NH₂ → R-CH₂-OH - **Note:** - NaBH₄ only reduces aldehydes, ketones, acid chlorides - LiAlH₄ reduces *all* carbonyl compounds ## Physical Properties - **Solubility in Water:** - Lower alcohols are soluble in water: H-bond formation - Solubility decreases with increasing chain length: more nonpolar - Solubility decreases with branching: more nonpolar - **Boiling Point:** - B.P. increases with molecular weight: stronger London dispersion forces - Branching decreases B.P.: less surface area for interaction - B.P. of alcohols is greater than that of ethers and carboxylic acids: strong H-bonding - B.P. of ethers is greater than that of alkanes: dipole-dipole interactions ## Chemical Reactions - **Acidity of Alcohols:** - Acidity α -Iα +M +H - Phenols are more acidic than water and alcohols: resonance stabilization of phenoxide ion - **Reactions with Metals:** - 2R-OH + 2Na → 2R-ONa + H₂ - **Esterification:** - R-OH + R'-OH → R-OR' + H₂O - Mechanism: - R-OH + H⁺ → R-OH₂⁺ - R-OH₂⁺ + R'-OH → R-OR' + H₃O⁺ - **Reactions with Grignard reagent:** - R-Mg-X + R'-OH → R-H + Mg-X-OR' - **Reaction with HX:** - **Lucas test:** - R-OH + HX → R-X + H₂O - **Mechanism:** - SN1 reaction: - Tertiary alcohols react fastest (30 min): more stable carbocation - Secondary alcohols react slower (5 min): less stable carbocation - Primary alcohols react slowest (1 min): unstable carbocation - **Reaction with PCl₃ and PCl₅:** - SN2 reaction: - R-OH + PCl₃ → R-Cl + H₃PO₃ - **Reaction with SOCl₂ (Darzen’s Process):** - SN2 reaction: - R-OH + SOCl₂ → R-Cl + SO₂ + HCl - **Mechanism:** - Inversion of configuration: - R-OH + SOCl₂ → R-OSO₂Cl + HCl - R-OSO₂Cl + Cl^- → R-Cl + SO₂ + Cl^- - **Dehydration of Alcohols:** - Elimination reaction: - CH₃-CH₂-OH + conc. H₂SO₄ → CH₂=CH₂ + H₂O - **Mechanism:** - CH₃-CH₂-OH + H⁺ → CH₃-CH₂-OH₂⁺ - CH₃-CH₂-OH₂⁺ → CH₂=CH₂ + H₃O⁺ - **Reactivity of alcohols** - Tertiary alcohols are more reactive than secondary alcohols, which are more reactive than primary alcohols: carbocation stability - **Oxidation of alcohols:** - **Strong oxidizing agents:** - KMnO₄/H⁺, K₂Cr₂O₇/H⁺, conc. HNO₃, CrO₃/ H₂SO₄ - Primary alcohol → aldehyde → carboxylic acid - Secondary alcohol → ketone - **Mild oxidizing agents:** - Cu/300°C or red hot Cu, PCC (Pyridinium chlorochromate), PDC (Pyridinium dichromate) - Primary alcohol → aldehyde - Secondary alcohol → ketone - **Selective oxidation:** - MnO₂: oxidizes allylic and benzylic alcohols to aldehydes and ketones. - 1° alcohols → aldehydes - 2° alcohols → ketones ## Tests for Alcohols - **Lucas Test:** - Tertiary alcohols react immediately: forms a cloudy white emulsion. - Secondary alcohols react in 5 minutes: forms a cloudy white emulsion. - Primary alcohols do not react: remains clear. - **Victor Meyer Test:** - Primary alcohols form red colored nitroalkane. - Secondary alcohols form blue colored nitroalkane. - Tertiary alcohols do not react. - **Dichromate Test:** - Primary and secondary alcohols react with dichromate reagent to give green Cr⁺³ ions. - Tertiary alcohols do not react. # Ethers ## Preparation - **Williamson Synthesis:** - SN2 reaction: - R-X + R'-ONa → R-OR' + NaX - Conditions: - Primary alkyl halides are preferred as they react by SN2 mechanism. - Tertiary alkyl halides give elimination products. - Example: - CH₃-CH₂-Cl + CH₃-ONa → CH₃-CH₂-O-CH₃ + NaCl - **Dehydration of alcohols:** - CH₃-CH₂-OH + conc. H₂SO₄ → CH₃-CH₂-O-CH₂-CH₃ + H₂O - Conditions: - Primary alcohols react by SN2 mechanism at 140° C. - Secondary and tertiary alcohols give alkenes as products. - Example: - 2(CH₃-CH₂-OH) + conc. H₂SO₄ → CH₃-CH₂-O-CH₂-CH₃ + H₂O ## Physical Properties - **Boiling Point:** - Lower than corresponding alcohols. - No H-bonding - **Solubility in Water:** - Low solubility. - No H-bonding ## Chemical Properties - **Cleavage of C-O bond in ethers:** - Ethers react with HX due to cleavage of C-O bond. - Mechanism: - Protonation of ether forms an oxonium ion. - Nucleophilic attack on the oxonium ion by halide ion give haloalkane and alcohol. - R-O-R + H-X → R-OH + R-X # Phenols ## Acidity: - Phenols are more acidic than water and alcohols due to the ability of the phenoxide ion to stabilize by resonance. - Alkyl groups decrease acidity: Electron donating effect - Electron withdrawing groups (like NO₂) increase acidity: Electron withdrawing effect ## Reactions - **Reactions with Metals:** - 2C₆H₅-OH + 2Na → 2C₆H₅-ONa + H₂ - **Esterification:** - C₆H₅-OH + R-COCl → C₆H₅-OCOR + HCl - **Halogenation:** - C₆H₅-OH + Br₂/H₂O → C₆H₄(OH)Br + HBr - Mechanism: - -OH group is an ortho and para directing group, therefore, the major product is 2,4,6-tribromophenol. - **Nitration:** - C₆H₅-OH + dil. HNO₃ → C₆H₄(OH)NO₂ + H₂O - Mechanism: - -OH group is an ortho and para directing group. - Major product: o-nitrophenol - Minor product: p-nitrophenol - **Sulphonation:** - C₆H₅-OH + conc. H₂SO₄ → C₆H₄(OH)SO₃H + H₂O - Mechanism: - Major product: p-hydroxybenzene sulphonic acid - Minor product: o-hydroxybenzene sulphonic acid - **Friedel-Crafts alkylation:** - C₆H₅-OH + CH₃Cl + AlCl₃ → C₆H₄(OH)CH₃ + HCl - Mechanism: - -OH group is an *ortho and para/director*. - Major product: p-cresol - Minor product: o-cresol - **Friedel-Crafts acylation:** - C₆H₅-OH + CH₃COCl + AlCl₃ → C₆H₄(OH)COCH₃ + HCl - Mechanism: - -OH group is an *ortho and para/director*. - Major product: p-hydroxyacetophenone - Minor product: o-hydroxyacetophenone - **Kolbe's reaction:** - C₆H₅-OH + NaOH + CO₂ → C₆H₄(OH)COOH + H₂O - **Reimer-Tiemann reaction:** - C₆H₅-OH + CHCl₃ + KOH(aq) → C₆H₄(OH)CHO + KCl + H₂O - **Oxidation of phenols:** - C₆H₅-OH + K₂Cr₂O₇/H⁺ → C₆H₄O₂ (benzoquinone) - **Coupling reaction:** - C₆H₅-OH + N₂⁺ → C₆H₅-N=N-C₆H₄-OH (p-hydroxyazobenzene) - Mechanism: - Diazonium salt couples with phenol to give an azo compound. ## Test for Phenols - **Neutral ferric chloride test:** - Phenols give a violet color with neutral FeCl₃ - Alcohols do not give this color reaction.