Alcohols

• Production of ethanol

  • Steam hydration of ethene to produce ethanol
  • Fermentation
• Steam hydration of ethene

  1. Ethene reacts with acid catalyst and water

  2. Mechanism shows phosphoric acid acting as catalyst as there is no absorption of phosphorus in the product

  3. 300 degrees celsius, 60 atm

  4. Produces ethanol
• Hydration of alkenes with concentrated sulfuric acid


  1. Alkene reacts with acid in electrophilic addition

  2. Hydrogensulfate compound reacts with steam/water in nucleophilic substitution
• Fermentation

  1. C6H12O6(aq) -> 2CH3CH2OH(aq) + 2CO2(g)
  2. Enzymes (collectively known as zymase) from yeast
  3. 25 ≤ t°C ≤ 42
  4. neutral pH
  5. Anaerobic conditions (else produces vinegar)
  6. Must have 4. and 5. else the enzymes will denature (NOT dies)
• Ethanol produced by fermentation is separated by fractional distillation and can be used as a biofuel
• Synthesis of biofuel ethanol

  • Sugar produced via photosynthesis

  6CO2 + 6H2O -> C6H12O6 + 6O2

  • Fermentation

  C6H12O6 -> 2CH3CH2OH + 2CO2

  • Combustion

  2CH3CH2OH + 6O2 -> 4CO2 + 3H2O

  
  

  6 moles of CO2 in = 6 moles of CO2 out which suggests it is carbon neutral

  
• Why can the synthesis of biofuel ehtanol not truly be considered carbon neutral?

  
  

  • Energy required for other steps
  • Harvesting and plantation of sugars
  • Deforestation, overcultivation, loss of biodiversity, desertification (huge environmental impacts)
  • Transport of sugar to distillery
  • Fractional distillation of fermented product
  • Transport of alcohol from distillery to our location
• Carbon neutral


  No net/overall carbon dioxide emission to the atmosphere
• Selective oxidation of alcohols

  • Choice of reaction conditions to favour different products (maximise yield, not only reaction)
  • ie whether a primary alcohols oxidises into an aldehyde or a carboxylic acid
  • Ketone is the only product from oxidation of secondary alcohols
• Different organic product formed when acidified potassium dichromate(VI) is not in excess
• Reason for two layers

  Organic product separates from aqueous layer
• Impurities in organic layer

  Unreacted hydrochloric acid
• Advantages of steam hydration

  • High atom economy compared to fermentation
  • No energy output for post production processing (ie doesn't produce greenhouse gases to produce energy for processing)
• Hydration of alkenes

  • 1st step: Electrophilic Addition (with sulfuric acid)
  • 2nd step: Nucleophilic Subsititution (steam/water reacts with products to form the corresponding alcohol)
• Oxidising Agents

  • 3rd type of 'ingredient'
  • Used to oxidise alcohols
  • Common - K2Cr2O7 (acidified potassium dichromate (VI))
• Cr2O72-

  • Dichromate ion
  • Contains Cr in a +6 oxidation state, where it is bright orange
  • When acidified potassium dichromate is used as an oxidising agent it turns from orange to green (as it forms green Cr3+ ions)
  • In equations, [O] is used to represent the oxidising agent
• Classification of alcohols

  • Primary, secondary or tertiary
  • Primary alcohols > aldehydes > carboxylic acids
  • Secondary alcohols > ketones
  • Tertiary alcohols cannot usually be oxidised
• Synthesising aldehydes

  • Oxidation of 1°  alcohols
  • Reagents: 1°  alcohol, acidified potassium dichromate
  • Conditions to maximise yield:

  1. distillation at a t°C above the b.p that of the aldehyde but below the b.p. of the alcohol
  2. Collect immediately (to avoid further oxidation) in an iced flash
• Distillation setup

  • As simple as possible
  • Thermometer in the neck
  • Completely open (unobstructed) passage from the start to the end
  • Liebig condenser (water in at the bottom, out at the top)
  • Pigtail (danger of pressure build up as gases produced; would lead to thermometer turning into a projectile, dangerous)
  • Roundbottom flask (for reaction)
  • Collection vessel (smaller roundbottom flask)
• Synthesisng carboxylic acids

  • Further oxidation of 1°  alcohols
  • Reagents: 1° alcohol, acidified potassium dichromate
  • Condition: Reflux (to ensure all the aldehyde is further oxidised into a carboxylic acid)
• Reflux setup

  • Water in at the bottom, out at the top - creates a steam jacket, prevents waterfall effect on only one side of the flask
  • No thermometer - prevents it exploding
  • Heat via a heating mantle (different sizes for different flasks) - constant, gentle, heating
• Synthesising ketones

  • Oxidation of 2° alcohols
  • Reagents: 2° alcohol, acidified potassium dichromate
  • Conditions: reflux to ensure all the secondary alcohol is oxidised to the ketones
• Fehling's Solution (just aqueous CuSO4)

  • Distinguishes between aldehydes and ketones
  • Compound to be tested is added to Fehling's solution and heated in a water bath
  • Alkaline solution of blue copper (II) ions is refuced to red copper (I) ions by aldehydes
  • Ketones (which cannot be oxidised) do not react
  • Positive result: blue solution forming a brick red precipitate of copper (I) oxide [Cu2O]
  • Aldehyde and α-hydroxy ketones give a positive result (brick red ppt.)
  • Ketones give no change (stays blue)
  • Ionic equation: RCHO + 2Cu2+ + 5OH--> RCOO- + Cu2O + 3H2O
• Tollen's Reagent


  • Used to distinguish between aldehydes and ketones
  • Compound to be tested is added to Tollen's Reagent and heated in a water bath
  • Result for aldehydes: formation of a silver mirror from the reduction of Ag+ (aq) ions to metallic Ag(s) as the aldehyde is oxidised to a carboxylic acid
  • Result for ketones: nothing
  • RCHO + 2Ag+ + 3OH- -> RCOO- +2Ag +2H2O
• Elimination


  • Alkenes can be formed from alcohols by acid catalysed elimination reactions - this is also known as a dehydration reaction
  • Reagents: conc. H2SO4/H3PO4
  • Conditions: 150-200°C
  • Step 1: Protonation of the hydroxyl group
  • Step 2: Elimination of a joined water molecule by forming a double bond (there must be atleast one H bonded to an adjacent carbon atom). If the only adjacent carbon atoms are tertiary, elimination can NOT occur
  • Reaction shows regeneration of H+ ion, demonstrating that the acid is acting like a catalyst
• Elimination - pros and cons

  • Advantage: Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil
  • Disadvantage: Mixture of products MAY be formed in the second step
• Antibumping Granules 


  • Used in distillation and reflux
  • Prevent bumping (violent boiling) by providing a large surface area for bubbles to form, even heat distribution, preventing large bubbles