Chemistry Unit 2- Alcohols

Classification
1. Primary
  1. Where the carbon with the OH is attatched to only 1 other carbon
2. Secondary
  1. Where the carbon with the OH is attatched to only 2 other carbons
3. Tertiary
  1. Where the carbon with the OH is attatched to only 3 other carbons
4. You can't have a quaternary alcohol because carbon can only have 4 bonds
Production
1. Hydration of ethene
  1. Method:
    1. 1. Electrophilic addition of an alkene with H2SO4 to produce an alkyl hydrogen sulphate
      1. Hydrolysis of the alkyl hydrogen sulphate to produce an alcohol
  2. Equation:
    1. C2H4 + H2SO4 + H2O----> C2H5OH + H2SO4
      1. If we remove the catalyst:
        C2H4 + H2O---> C2H5OH
        Instead of using H2SO4 as a catalyst, industrially, a more powerful catalyst is used: H3PO4/Phosphoric acid
  3. Conditions:
    1. 1. Catalyst
      1. High temperatures: 300 degrees
        High pressures: 60 atmospheres
        These will encourage a faster rate of reaction
  4. Advantages:
    1. A relatively fast process
      1. A continous process-- Requires little labour
        Produces pure ethanol of high purity and high yeild
  5. Disadvantages:
    1. Expensive: specialist vessels needed to withstand high pressures
      1. And also uses a lot of energy to intiate and maintain the pressure
        Ethene- A non renewable source as it comes from crude oil
        Dangerous- High temperatures and pressures required
2. Fermentation of glucose
  1. This method uses enzymes from yeast to ferment sugars into alcohol and CO2
    1. IIt's an anaerobic process so has to be done in the absence of air
      1. Equation:
        C6H12O6------> 2C2H5OH + 2CO2
  2. Conditions:
    1. Needs to be done in a sealed container: Anaerobic
      1. Optimum temp for the enzymes: around 35 degrees
  3. Advantages:
    1. 1. Uses a renewable source
      1. 2. A low technology process
        Cheap: not energy intensive
  4. Disadvantages: A batch process- needs to be emptied and cleaned
    1. A slow process
      1. Doesn't produce pure ethanol. Low yeild and purity
Reaction of Alcohols
1. Oxidation
  1. This doesn't simply mean 'adding oxygen' otherwise we would have a combustion reaction
    1. We need to find a reagent that provides oxygen atoms
      1. The oxidising agent is represented as [O]
  2. Primary Alcohols
    1. Primry alcohols are oxidised into aldehydes
      1. Two hydrogen atoms will have been removed from the alcohol. The structure is:
        The names of the aldehyde formed will end in '-al'. e.g. ethanal
      2. Oxidising Agent: Acidified Potassium/Sodium dichromate
        The dichromate ion (Cr2O7 2-) will be what is used to oxidise the alcohol
        It will go from a Cr2O7 (2-)-------> Cr3+ ions
        It has been oxidised as the oxidation state has gone from a +6 to a +3. Each chromium has lost 3 electrons.
        Colour change from orange to green
      3. Conditions: Excess Alcohol
        Required amount of oxidising agent
        The aldehyde is to be DISTILLED off as it forms to prevent further oxidation
      4. Further oxidation into carboxylic acids
        Functional group:
        Oxidising agent: Acidified potassium/sodium dichromate
        Conditions
        Excess oxidising agent
        Heat under reflux
        A carboxylic acid cannot be oxidised further
  3. Secondary Alcohols
    1. Secondary alcohols are oxidised into ketones
      1. They have the functional group:
        Because of this functional grouo, ketones are only found in the middle of a chain and never at the end of a chain
      2. When you oxidise a secondary alcohol, you pull off the H from the OH, and you pull off the only hydrogen that there is to pull off
      3. Their name ends in '-one' e.g. propanone
        It's not possible to have ethanone or methanone
        You can't oxidise a ketone further because that would mean breaking a C-C bond which is way too strong
      4. Conditions: Heat under reflux
        Excess oxidising agent
        Acidified potassium/sodium dichromate-- goes from orange to green
  4. Tertiary Alcohols
    1. Not possible because breaking the OH bond would form a double bond to the carbon and then the carbon would have too many bonds
      1. And breaking a C-C bond to fix this is going to be hard because they've got such similar electronegativities
        Adding oxidising agent will give you no visible change because no reaction will occur
Distinguising between:
1. Tetiary and primary andsecondary:
  1. Add acidified potassium dichromate
    1. No visible change
      1. Tertiary alcohol
    2. Orange to green
      1. Primary or secondary alcohol
        You cant add acidified potassium dichromate as they both give the same colour change. A weaker oxidising agent is required
        Fehlings Test
        A solutuon containing Cu2+ ions
        Its gains electrons as it is the oxidisng agent so it is being reduced to become Cu atoms
        This will form a brick red precipitate
        This won't happen with ketones
        Tollens reagent
        A solution containing Ag+ ions
        It will gain electrons as it further oxidises the aledhyde (primary) into a carboxylic acid
        Silver atoms will have formed (Ag) to form a silver mirror
        This won't happen with ketones
Elimination
1. This is also called dehydration, where the alcohol returns to the alkene and water
2. Conditions
  1. A catalyst is used: Phophoric acid, or aluminium oxide
    1. Requires heat
      1. The hydrogen that is lost will come from the carbon that is adjacent to the carbon attatched to the OH group
  2. Heat
    1. Phosphoric acid or aluminium oxide catalyst
      1. H always removed from carbon adjacent to the OH group
Uses:
1. Chemical Feedstock (used to make other chemicals)
2. Drinks
3. Detergents
4. Solvents
5. Fuel
  1. If the alcohol is made from fermentation, then this is good because it is renewable as it's a biofuel
    1. It's carbon neutral: So gives out as much CPO2
Uses:
1. Drinks
2. Detergents
3. Solvents
4. Fuels
5. Chemical feedstock

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Chemistry Unit 2- Alcohols

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	Created by bilkis-21 almost 11 years ago