Alcohols

• General formula for alcohols?

  CnH2n+2O
• Functional group

  R-OH ( R-O-H for displayed)
• Describe a primary alcohol

  carbon which is bonded to the OH group is only bonded to one other carbon (R) e.g ethanol
• Describe a secondary alcohol

  Carbon which is bonded to OH is bonded to two other carbons ( R and R) e.g propan-2-ol
• Describe a tertiary alcohol

  carbon bonded to 3 R groups so no H atoms on the C atom e.g methylpropan-2-ol
• If there are 3 or more carbon atoms in the molecule the position of the OH group must be indicated
• What are structural isomers?


  compounds with same molecular formula but different structural formula.
• Give 2 position isomers of C4H10O

  Butan-1-ol and butan-2-ol of methylpropan-1-ol and methylpropan-2-ol
• Give 2 chain isomers of C4H20O

  Butan-1-ol and methylpropan-2-ol or butan-2-ol and methylpropan-2-ol
• What is the functional group isomer of C4H20O

  An ether = R-O-R

  eg 1-methoxypropane
• Why do alcohols have relatively high boiling and melting points?

  They form Hydrogen bonds
• Explain the difference in boiling points of propane, dimethyl ether and ethanol

  Propane has weak van Der waal’s forces between molecules which are the weakest intermolecular forces so propane has the lowest boiling point as less energy is needed to overcome them. Dimethyl ether has the next highest boiling point as it has permanent dipole-dipole forces between molecule which require more energy to overcome. Ethanol has highest boiling point due to H bonds between molecules which are the strongest IMF so require most energy to overcom.
• Alcohols with a low Mr are soluble in water due to hydrogen bonding . As Mr increases, alcohols become less soluble as VDW forces between chains cannot disrupt H bonds between H2O molecules
• How can alcohols be prepared?

  Hydration of alkenes: reagent is H2o (steam)

  Conditions: H3PO4 (catalyst), 300°C, 60atm

  Break the c=c bond and add O-H
• What does the H3PO4 serve as in the hydration mechanism?

  Proton donor H+ (catalyst)
• What are the uses of ethanol?

  • Alcoholic beverages
  • solvent
  • chemical feedstock
• What are the two ways ethanol can be prepared?

  Fermentation, hydration Of ethene
• Outline fermentation 


  • Carbohydrates from crops like sugar cane and sugar beet are broken into sugars like glucose
  • the sugars are converted into ethanol (by enzymes in yeast) in anaerobic respiration
  • ethanol is then removed from the reaction mixture by fractional distillation
• Reagents for fermentation?


  Yeast, glucose
• Conditions for fermentation?


  Aqueous, anaerobic, 30-40°C
• Equation for fermentation?


  C6H12O6—> 2CH3CH2OH + 2CO2
• Why is air kept out of reaction of fermentation?

  Needs to be anaerobic to prevent oxidation of ethanol to Ethanoic acid
• Why is the compromise temperature of 35°C Used In fermentation?

  Low enough not to denature enzymes but still gives an acceptable rate of reaction.
• When the reaction mixture contains 15% ethanol, why does fermentation stop?

  It kills off the yeast if not.
• How is ethanol separated from the reaction mixture?

  Fractional distillation
• Fractional distillation is used to separate liquids of similar boiling points. For example, ethanol has a boiling point of 78°C and water is 100°C
• What is the method for fractional distillation?

  • Heat flask so ethanol and water vaporise
  • The vapours pass up the fractionating column so water and ethanol separate
  • water will condense back into flask as it has a higher boiling point than ethanol
  • Observe thermometer and keep temperature at or below boiling point of ethanol in order to avoid water vapour entering condenser
  • Ethanol passes into condenser where water in outer jacket cools the vapours so they condense into liquid which is collected
• Compare fermentation and hydration

  Raw material: H-crude oil , F-sugar cane crops

  Quality of product: H-pure, F-impure

  Rate of reaction: H-fast, F-slow

  Energy requirements: H-high, F-low

  Type of process: H-continuous, F-batch

  Atom economy: H-100%, F-51%
• Define biofuel


  Fuel derived or produced from renewable biological sources
• Ethanol is increasingly being used as a fuel and is added to petrol. When made by fermentation, ethanol is called a biofuel and in theory carbon neutral
• What is a carbon-neutral fuel?

  Uses the same amount of carbon dioxide from the atmosphere in its production as is released into atmosphere when it is use.
• Use equations to show how ethanol is carbon-neutral

  1. photosynthesis of glucose: 6CO2 + 6H2O—>C6H12O6 + 6O2 so -6O2
  2. Fermentation of glucose:C6H12O6->2CH3CH2OH + 2CO2 so +2CO2
  3. Combustion of ethanol: 2CH3CH2OH + 6O2–> 4CO2 + 6H2O so +4CO2.

  in total: OCO2
• Why is ethanol Not carbon-neutral?

  Fossil fuels burned to power machinery used to make fertilisers for crops, harvest the crops and refine and transport the biofuel which produces CO2.
• What are the disadvantages of using crops for production of fuel?

  • Lands used to grow crops for fuel can’t be used to grow food
  • Fertilisers often added to soil ti increase biofuel production
  • Deforestation to create land for biofuel crops to grow
• What are the 3 important reactions alcohols take part in?

  • Combustion
  • Elimination
  • Oxidation
• What is combustion?


  Alcohols burnin oxygen to form carbon dioxide and water (complete combustion)
• Give an equation for the combustion of ethanol

  CH3CH2OH + 3O2 --> 2CO2 + 3H2O
• What happens in an elimination reaction?

  An alcohol reacts to form an alkene

  The reaction involves dehydration as water is eliminated

  Reagent: Concentrated H2SO4

  Conditions: reflux

  The OH group is always removed, A H+ion from an adjacent c atom is also removed and a double bond forms between the two carbon atoms
• Why is elimination important?

  At present, alkenes are produced from crude oil which is non renewable. Alkenes from crude oil are used to make addition polymers but in the future, it may be more economical to make ethene from ethanol by fermentation
• What is the present route taken to make poly(ethene)

  What could be the future route?

  Crude oil -> Ethene ->Poly(ethene)

  Sugars -> ethanol -> ethene -> poly(ethene)