Alcohols

• Alcohols


  The OH (hydroxyl) group is alcohol's functional group
• General formula of alcohols


  CnH2n+1OH
• Alcohols


  • All alcohol names end in '-ol' -two OH group '-diol' -three OH group 'triol'
  • Boiling point increases as number of carbons increases
  • Alcohols are able to form hydrogen bonds
  • Alcohols are very water soluble, the longer the carbon chain, the less soluble the alcohol
• Classes of alcohols


  • Primary (1 carbon directly bonded to hydroxyl carbon)
  • Secondary (2 carbons directly bonded to hydroxyl carbon)
  • Tertiary (3 carbons directly bonded to hydroxyl carbon)
• Molecular structure of alcohols

  • All the H-C-H bonds and C-C-O are 109.5(tetrahedral shape), because there are 4 bond pairs of electrons repelling to a position of minimum repulsion
  • The H-O-C bond is 104.5(bent shape), because there are 2 bond pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion
• Combustion of alcohols


  1. Alcohols combust with a pale blue flame

  2. The C-C and C-H bonds break and the alcohol is completely oxidised

  3. CH₃CH₂OH + 3O₂ ⟶ 2CO₂ + 3H₂O

  4. Complete produces carbon dioxide and water

  5. Incomplete produces any of carbon, carbon monoxide and water
• Substitution reactions of alcohols to form halogenoalkanes


  1. Reacting alcohols with PCl₅ or HCl produces chloroalkanes

  2. ROH + PCl₅ ⟶ RCl + HCl + POCl₃

  3. ROH + HCl ⟶ RCl +H₂O - fastest for tertiary alcohols / slowest from primary alcohols

  4. Alcohols will react with bromide ions(KBr) in a substitution reaction to form bromoalkanes, requires acid catalyst

  5. Alcohols will react with phosphorus triiodide(PI₃) to make iodoalkanes

  
• Oxidation reactions of alcohols

  1. Partial oxidation of primary alcohols to aldehydes

  2. Full oxidation of primary alcohols to carboxylic acids

  3. Oxidation of secondary alcohols to ketones

  4. Tertiary alcohols can't be oxidised easily

  
• Aldehydes


  Ends in -al, always has the C=O on the 1st carbon, written as CHO, one alkyl group attached to carbonyl atom

  
• Carboxylic acids


  Ends in -oic acid, written as COOH
• Ketones


  Ends in -one, number shows the position of the double bond, one alkyl group attached to carbonyl atom

  
• Distinguishing between aldehydes and ketones

  1. Aldehydes can be oxidised further to carboxylic acid, ketones can't be further oxidised

  2. Fehling's (Benedict's solution) test - aldehydes are oxidised, ketones are not

  
• Dehydration of alcohols


  Reaction of alcohols with concentrated phosphoric acid to form alkenes and water

  
• Heating under reflux


  Used when heating organic mixtures for long periods, condenser prevents organic vapours from escaping, anti-bumping granules added
• Extraction with a solvent in a separating funnel

  Removes any water soluble impurities from the product
• Distillation


  Used to separate substances with different boiling points
• Drying with an anhydrous salt


  Remove traces of water from a mixture using an anhydrous salt like magnesium sulfate or calcium chloride
• Boiling temperature determination


  Purity of liquid can be determined by measuring a boiling point, using distillation apparatus or a thiele tube
• CORE PRACTICAL 5: The oxidation of ethanol
• CORE PRACTICAL 6: Chlorination of 2-methylpropan-2-ol using concentrated hydrochloric acid