Alcohols, Phenols and Ethers — Formula Sheet

Markovnikov addition: OH goes to the carbon with fewer H atoms. Mechanism: protonation gives the more stable carbocation, water attacks, H⁺ is lost.

Net anti-Markovnikov addition of water — a terminal alkene gives a 1° alcohol. Boron adds to the less substituted carbon; H₂O₂ in aqueous NaOH then replaces B by OH.

Aldehydes → 1° alcohols, ketones → 2° alcohols. Use H₂ with Pt, Pd or Ni, or NaBH₄ / LiAlH₄. Carboxylic acids need LiAlH₄ (NaBH₄ does not reduce –COOH).

Methanal (HCHO) gives a 1° alcohol, any other aldehyde a 2° alcohol, and a ketone a 3° alcohol. The R′ group forms a new C–C bond to the carbonyl carbon.

Cumene (isopropylbenzene) is air-oxidised to cumene hydroperoxide, which dilute acid splits into phenol and acetone. This is the industrial route; acetone is a valuable by-product.

The diazonium salt is made ice-cold, then hydrolysed by warming with water or dilute acid.

Shows the acidic O–H. Acid strength of alcohols: 1° > 2° > 3° (alkyl groups push electron density onto O and destabilise the alkoxide). Alcohols are weaker acids than water.

Phenoxide is resonance-stabilised (charge spread into the ring); ethoxide is not. –NO₂ (electron-withdrawing) raises acidity, most at o/p (pKa o 7.2, m 8.3, p 7.1); –CH₃ (electron-releasing) lowers it. Phenol reacts with aqueous NaOH; ethanol does not.

Lucas reagent = conc. HCl + anhydrous ZnCl₂. The insoluble alkyl chloride makes the mixture turbid: 3° — immediately; 2° — after a few minutes; 1° — no turbidity at room temperature. Order follows carbocation stability.

Ease of dehydration: 3° > 2° > 1°. Milder conditions work for 2° (85% H₃PO₄, 440 K) and 3° alcohols (20% H₃PO₄, 358 K).

1° alcohol → aldehyde with PCC (pyridinium chlorochromate) or anhydrous CrO₃; acidified KMnO₄ takes it all the way to the carboxylic acid. 2° → ketone. 3° alcohols resist oxidation; strong oxidants at high temperature break C–C bonds.

Alcohol vapour over Cu at 573 K: 1° → aldehyde, 2° → ketone, but a 3° alcohol is dehydrated to an alkene. Another way to tell the three classes apart.

–OH strongly activates the ring, so bromine water gives a white precipitate of 2,4,6-tribromophenol. For monobromination use Br₂ in CS₂ or CHCl₃ at low temperature → o- and p-bromophenol (p major).

Separate by steam distillation: o-nitrophenol is steam-volatile (intramolecular H-bond); p-nitrophenol is not (intermolecular H-bonds associate the molecules). Conc. HNO₃ gives 2,4,6-trinitrophenol (picric acid).

Phenoxide (phenol + NaOH) is even more reactive than phenol, so the weak electrophile CO₂ substitutes, mainly at the ortho position. Product: 2-hydroxybenzoic acid.

Introduces –CHO at the ortho position. The intermediate (a substituted benzal chloride, –CHCl₂) is hydrolysed by the alkali. Do not confuse with Kolbe, which gives –COOH.

Alcohols and phenols react with acids, acid anhydrides or acid chlorides. Water is removed (or pyridine added with acid chlorides) to push the reaction forward. Acetylation of salicylic acid with acetic anhydride gives aspirin.

SN2 attack of an alkoxide on an alkyl halide. Use a PRIMARY (or methyl) halide. The alkoxide is also a strong base, so with 2° halides elimination competes, and a 3° halide gives only the alkene. Sodium phenoxide + R–X gives alkyl aryl ethers.

Same reagent as ethene formation but a lower temperature (413 K ether, 443 K alkene). Suitable only for unhindered 1° alcohols giving symmetrical ethers; 2° and 3° alcohols give alkenes.

Reactivity HI > HBr > HCl. With 1°/2° groups the smaller alkyl becomes the iodide (SN2); with a 3° group the 3° iodide forms (SN1). Alkyl aryl ethers always give phenol + alkyl halide, since the O–aryl bond is stronger.