4.3 Alcohols and Phenols

  • Created by: holly_b
  • Created on: 08-01-17 12:28
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  • Alcohols and Phenols
    • Forming primary and secondary alcohols
      • From halogenoalkanes
        • Reaction occurs by refluxing a halogeno-alkane with aqueous alkali solution (NaOH or KOH).
          • This is nucleophilic substitution.
        • 1-bromobutane can react to form butan-1-ol
        • After the reflux you need to separate the products: they are liquids with different boiling points so fractional distillation is used
      • From carbonyl compunds
        • Aldehydes and ketones can be reduced back to the alcohol by using sodium tetrahydrido-borate.
        • The nucleophile is NaBH4.
        • Reaction
        • Reduction of carboxylic acids is also possible but it requires a stronger reducing agent - LiAlH4.
    • Reactions of primary and secondary alcohols
      • With hydrogen halides
        • Bromine
          • Treat the alcohol with a mixture of sodium or potassium bromide and concentrated sulphuric acid. This produces hydrogen bromide which reacts with the alcohol. The mixture is warmed to distil off the bromoalkane.
        • Iodine
          • The alcohol is reacted with a mixture of sodium or potassium iodide and concentrated phosphoric(V) acid, H3PO4, and the iodoalkane is distilled off. The mixture of the iodide and phosphoric(V) acid produces hydrogen iodide which reacts with the alcohol.
      • With ethanoyl chloride
        • Ethanoyl chloride reacts instantly with cold ethanol. There is a very exothermic reaction in which a steamy acidic gas is given off (HCl). Ethyl ethanoate is formed.
      • With carboxylic acids
        • Esters are produced when carboxylic acids are heated with alcohols in the presence of an acid catalyst, usually concentrated sulfuric acid.
          • The esterification reaction is both slow and reversible.
    • Acidity of phenol
      • 1. Carboxylic Acids
        • 2. Phenols
          • 3. Alcohols
            • 4. Water
    • Reactions of phenol
      • With bromine
        • When adding bromine to phenol it decolourises and a white precipitate forms.
        • When adding bromine to benzene there is no reaction.
        • When adding bromine to an alkene it decolourises but no precipitate is formed.
        • If the 2, 4 or 6 position is already filled then it fills the positions available.
      • With ethanoyl chloride
        • Alcohols and phenols can act as nucleophiles by using lone pairs of electrons on the oxygen atom.
          • However the delocalisation of the lone pair in phenol makes it difficult to behave as a nucleophile.
            • Therefore phenol cannot react with carboxylic acids to form esters but it can react with ethanoyl chloride.
        • Pyridine is used to speed up the reaction and it makes the by-product C5H5NH+Cl-
        • Because the acyl chloride is less reactive due to the benzene ring, the reaction can be done under aqueous conditions.
    • FeCl3(aq) test for phenol
      • A complex is formed between the reagents that produces a purple colour.
    • Phenol
      • Used in detergents and antiseptics.
      • Slightly soluble in water due to hydrogen bonding between the OH groups.
        • Large non-polar benzene ring decreases the solubility.
      • Reacts with NaOH like a weak acid.
      • Reacts with metals to produce a salt and hydrogen.
        • Dissociates to form H+ ions when aqueous.
      • Solid under standard conditions.


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