Alcohols

• General formula alcohols


  CnH2n+1OH
• Naming Alcohols


  1. Have the ending -ol

  2. If necessary the position number for the OH group is added between the name stem and the –ol

  3. If the compound has an –OH group in addition to other functional groups that need a suffix ending then the OH can be named with the prefix hydroxy-
• Alcohols with multiple OH groups

  • ethane-1,2-diol
  • propane-1,2,3-triol
• Types of alcohols


  • Primary (1 carbon attached to the carbon adjoining the oxygen)
  • Secondary (2 carbons attached to the carbon adjoining the oxygen)
  • Tertiary (3 carbons attached to the carbon adjoining the oxygen)
• Bond angles in Alcohols

  • H-C-H bonds and C-C-O are 109.5o (tetrahedral shape)
  • H-O-C bond is 104.5o (bent line shape)
• Hydrogen bonding in alcohols

  Alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bonds between alcohol molecules
• Solubility of alcohols in water

  Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules
• Partial Oxidation of Primary Alcohols

  1. Reaction: primary alcohol → aldehyde

  2. Reagent: potassium dichromate (VI) solution and dilute sulfuric acid

  3. Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it forms
• Aldehyde


  • An aldehyde's name ends in –al
  • It always has the C=O bond on the first carbon of the chain so it does not need a number in its name
• Full Oxidation of Primary Alcohols


  1. Reaction: primary alcohol → carboxylic acid

  2. Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

  3. Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)
• Carboxylic acid


  Carboxylic acids have the formula RCOOH
• Oxidation of Secondary Alcohols

  1. Reaction: secondary alcohol → ketone

  2. Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

  3. Conditions: heat under reflux
• Ketone


  • Ketones end in -one
  • When ketones have 5C's or more in a chain then it needs a number to show the position of the double bond
• Tertiary alcohols cannot be oxidised at all by potassium dichromate
• Distinguishing between Aldehydes and Ketones

  1. Aldehydes can be further oxidised to carboxylic acids whereas ketones cannot be further oxidised

  2. This is the chemical basis for two tests that are commonly used to distinguish between aldehydes and ketones
• Tollens' Reagent test


  1. Reagent: Tollens' reagent formed by mixing aqueous ammonia and silver nitrate

  2. Conditions: heat gently

  3. Reaction: aldehydes only are oxidised by Tollens' reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms

  4. Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no visible change
• Fehling's Solution test


  1. Reagent: Fehling's solution containing blue copper(II) ions

  2. Conditions: heat gently

  3. Reaction: aldehydes are oxidised, reducing the blue copper(II) ions to red/orange copper(I) oxide

  4. Observation: with aldehydes, a red/orange precipitate forms. Ketones result in no visible change
• This is because there is no hydrogen atom bonded to the carbon with the -OH group
• Aldehydes


  Can be further oxidised to carboxylic acids
• Ketones


  Cannot be further oxidised
• Tollens' Reagent


  1. Reagent: Tollens' reagent formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+

  2. Conditions: heat gently

  3. Reaction: aldehydes only are oxidised by Tollens' reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms

  4. Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no visible change
• Fehling's solution


  1. Reagent: Fehling's solution containing blue Cu2+ ions

  2. Conditions: heat gently

  3. Reaction: aldehydes only are oxidised by Fehling's solution into a carboxylic acid. The copper (II) ions are reduced to copper(I) oxide

  4. Observation: Aldehydes: Blue Cu2+ ions in solution change to a red precipitate of Cu2O. Ketones do not react
• The presence of a carboxylic acid can be tested by addition of sodium carbonate. It will fizz and produce carbon dioxide.
• Reaction of Alcohols with Dehydrating Agents


  1. Dehydration Reaction: removal of a water molecule from a molecule

  2. Reaction: Alcohol → Alkene

  3. Reagents: Concentrated sulfuric or phosphoric acids

  4. Conditions: warm (under reflux)

  5. Role of reagent: dehydrating agent/catalyst

  6. Type of reaction: acid catalysed elimination
• Some 2o and 3o alcohols can give more than one product, when the double bond forms between different carbon atoms


  • Butan-2-ol can form both but-1-ene and but-2-ene, although more but-2-ene would be formed
• Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil.
• Acid catalysed elimination mechanism

  The H+ comes from the conc H2SO4 or conc H3PO4
• Fermentation


  • Glucose → ethanol + carbon dioxide
  • Conditions needed: Yeast, no air, temperatures 30-40°C
  • Optimum temperature around 38°C
• Fermentation


  • Batch process which is slow and gives high production costs
  • Ethanol made is not pure and needs purifying by fractional distillation
  • Depletes land used for growing food crops
• Industrial formation of ethanol from ethene

  • Faster reaction
  • Purer product
  • Continuous process (which means cheaper manpower)
  • High technology equipment needed (expensive initial costs)
  • Ethene is non-renewable resource (will become more expensive when raw materials run out)
  • High energy costs for pumping to produce high pressures
• Hydration of ethene


  1. Essential Conditions: high temperature 300°C, high pressure 70 atm, strong acidic catalyst of conc H3PO4

  2. Reagent: ETHENE - from cracking of fractions from distilled crude oil

  3. Type of reaction: Hydration/addition
• Hydration


  The addition of water to a molecule
• Acid catalysed addition mechanism for hydration of ethene

  The H+ comes from the conc H3PO4
• Biofuel


  A fuel produced from plants
• Ethanol produced from fermentation is a biofuel.
• Ethanol produced from fermentation can be argued to be carbon-neutral because any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphere.
• This does not take into account any energy needed to irrigate plants, fractionally distil the ethanol from the reaction mixture or process the fuel. If the energy for these processes comes from fossil fuels then the ethanol produced is not carbon neutral.
• Removal of CO2 by photosynthesis

  6 CO2 + 6 H2O → C6H12O6 + 6 O2
• Production of CO2 by fermentation and combustion

  C6H12O6 → 2 CH3CH2OH + 2 CO2

  2 CH3CH2OH + 6O2 → 4 CO2 + 6 H2O
• Overall for every 6 molecules of CO2 absorbed, 6 molecules of CO2 are emitted. There is no net contribution of CO2 to the atmosphere.