unit 4

• Formation of alcohols from halogenoalkanes


  1. Reflux halogenoalkane with aqueous alkali (usually NaOH)

  2. Example: CH3CH2CH2CH2Br + NaOH → CH3CH2CH2CH2OH + NaBr

  
• Formation of alcohols from carbonyl compounds

  1. Reduction using NaBH4 (sodium tetrahydridoborate(III))

  2. Aldehydes produce 1° alcohols

  3. Ketones produce 2° alcohols

  4. LiAlH4 (lithium tetrahydridoaluminate(III)) used for carboxylic acids

  
• Reduction using NaBH4


  Safer than LiAlH4 due to nature of reducing agent and solvent
• Formation of chloroalkanes


  1. Pass HCl gas through alcohol with dry ZnCl2 catalyst

  2. Use PCl5 (phosphorus pentachloride)

  3. Use SOCl2 (sulfur(VI) oxide dichloride)

  
• Formation of bromoalkenes


  Heat mixture of alcohol, KBr and 50% H2SO4

  
• Formation of iodoalkanes


  Use warm damp red phosphorus and iodine to form PI3 (phosphorus(III) iodide)

  
• Formation of esters from alcohols and ethanoyl chloride


  Alcohol reacts rapidly with ethanoyl chloride, CH3COCl, forming ester and HCl

  
• Formation of esters from alcohols and carboxylic acids


  1. Reflux reactants with concentrated H2SO4 catalyst

  2. Distill and collect ester

  3. Remove ester layer, neutralise with NaHCO3, dry with CaCl2, redistill

  
• Phenol


  Aromatic compound with -OH group bonded directly to benzene ring

  
• Phenol


  • Weakly acidic, more acidic than alcohols but less than carboxylic acids
  • Lone pair on oxygen overlaps with π electron system of ring, making C-O bond stronger and H+ lost more easily
  • Phenoxide ion, C6H5O-, is more stable due to delocalisation of negative charge
  • Not soluble in water due to large hydrocarbon part, but dissolves in NaOH

  
• Phenol vs carboxylic acid

  Phenols don't react with sodium carbonate to produce CO2

  
• Phenol vs carboxylic acid

  Phenols won't react with carboxylic acids to form esters

  
• Reaction of phenol with ethanoyl chloride

  Forms ester such as phenyl ethanoate, but slow at room temperature

  
• Reaction of phenol with bromine water

  Produces white precipitate of 2,4,6-tribromophenol, bromine water decolourised

  
• Test for phenol with iron(III) chloride


  Gives purple colour

  
• Any compound with -OH group bonded to benzene ring will give positive test with iron(III) chloride