Alcohols

• Alcohols have the functional group O which is called the hydroxy
• Types of alcohols


  • Primary alcohols
  • Secondary alcohols
  • Tertiary alcohols
• Primary alcohols


  Have one alkyl group attached to a carbon which is attached to the O
• Secondary alcohols


  Have two alkyl groups attached to the carbon with the O
• Tertiary alcohols


  Have three alkyl groups attached to a carbon with the O
• Dehydration of alcohols to make alkenes

  1. Eliminate water

  2. Form alkene
• Alkenes made from alcohols via fermentation are more sustainable than using crude oil
• Mechanism for dehydration of alcohols

  1. Alcohol reacts with H+ from acid catalyst

  2. Forms oxygen intermediate

  3. Carbocation intermediate forms

  4. Electrons from C-H bond break to stabilise carbocation

  5. Water is eliminated

  6. Alkene is formed
• Non-primary alcohols can form two different alkenes during dehydration
• Distillation to purify alkenes from dehydration

  1. Heat impure product

  2. Separate components by boiling point

  3. Use separating funnel to further purify
• Specific reaction: Making cyclohexene from cyclohexanol

  1. Distill cyclohexanol with acid catalyst

  2. Separate cyclohexene layer

  3. Dry cyclohexene with desiccant
• Hydration of alkenes to form alcohols

  1. Alkene reacts with H+ and water

  2. Forms carbocation intermediate

  3. Water bonds to carbocation

  4. Hydrogen is lost, forming alcohol
• Fermentation can be used to produce alcohols sustainably from plant material
• Stabilize positive charge


  1. Electrons from bond jump into oxygen

  2. Oxygen neutralized/stabilized

  3. Hydrogen lost
• Product


  CH3CH2 (alcohol, ethanol)
• Proof it's a catalyst: H+ at start and H+ reformed at end
• Fermentation is a sustainable way to produce alcohol or alkenes
• Fermentation


  1. Uses yeast in anaerobic conditions

  2. Glucose converted to ethanol and carbon dioxide
• Enzymes


  • Prefer to work at 30-40°C
  • Denatured at high temperatures
• Temperature increases


  Rate of reaction increases
• Fractional distillation


  Used to obtain pure alcohol product
• Fermentation


  • Requires little equipment
  • Cheap process
  • Slow with low yield
• Biofuels


  Made from dead biological matter
• Biofuel


  • Ethanol used as fuel, e.g. in Brazil
• Advantages of biofuels


  • Renewable
  • More sustainable than crude oil
  • Carbon neutral
• Disadvantages of biofuels


  • Expensive
  • Converts land from food to fuel production
• Biofuels not completely carbon neutral due to fossil fuels used in production
• Oxidation of alcohols


  1. Primary alcohols oxidized to aldehydes then carboxylic acids

  2. Secondary alcohols oxidized to ketones

  3. Tertiary alcohols cannot be oxidized
• Potassium dichromate


  Mild oxidizing agent, changes colour from orange to green
• Oxidation of primary alcohols

  1. Distillation used to collect aldehydes before further oxidation to carboxylic acids

  2. Reflux used to fully oxidize to carboxylic acids
• Oxidation of secondary alcohols


  Reflux used to oxidize to ketones
• Fehling's and Tollens' reagents

  Used to test for and distinguish aldehydes and ketones
• Aldehydes give positive tests with Fehling's and Tollens' reagents, ketones do not