5.5.1

Production of Alcohols

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Types of Alcohols

Alcohols can be either primary, secondary, or tertiary.

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Primary alcohols

  • A primary alcohol is one which has one carbon bonded to the carbon bonded to the functional group.
    • E.g. ethanol.
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Secondary alcohols

  • A secondary alcohol is one which has two carbons bonded to the carbon bonded to the functional group.
    • E.g. propan-2-ol.
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Tertiary alcohols

  • A tertiary alcohol is one which has three carbons bonded to the carbon bonded to the functional group.
    • E.g. 2-methyl-propan-2-ol.

Alcohol Production

There are a variety of methods for synthesising alcohols. Different methods are used for industrial purposes and for drinking purposes.

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Industrial alcohol production

  • Alcohols are produced industrially by hydration (adding water) of alkenes in the presence of an acid catalyst.
  • The most common catalyst is phosphoric (V) acid. It’s done at 300oC and 60 atm pressure.
  • The mechanism is via an electrophilic addition.
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Hydration of ethene

  • The mechanism above shows how:
    • The acid catalyst acts first to add to the alkene.
    • The lone pair on the oxygen then attacks the carbocation intermediate.
    • Finally, a proton is lost to give an alcohol and to reform the acid catalyst.
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Fermentation

  • For some purposes, ethanol is produced by fermentation. This makes alcohol that is drinkable, but it can also be used for making biofuels.
  • Fermentation uses yeast to turn glucose into ethanol.
  • The reaction for it is:
    • C6H12O640oCYeast2C2H6O+2CO2C_6H_{12}O_6 \xrightarrow[{40^oC}]{\text{Yeast}}2C_2H_6O + 2CO_2
  • Ethanol is separated by distillation.
  • The process is cheap, but distillation adds extra cost.

Biofuels

Biofuels are fuels composed of grown organic matter.

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Biofuel

  • Ethanol is produced by fermentation and then separated by fractional distillation.
    • This can then be used as a biofuel.
  • Biofuels are greener than petrol.
    • This is because they are renewable - we can grow more plants so they won't run out.
      • They are more sustainable.
    • They are carbon neutral (kind of). They release CO2 when they burn, but they absorb it when they grow.
      • These cancel each other out.
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Problems

  • Switching to biofuels is problematic:
    • Car engines aren’t built to run on ethanol.
    • Land that's growing biofuel isn't producing food.
      • This could lead to food shortages.
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Carbon neutrality

  • Earlier, we said that biofuels are kind of carbon neutral.
    • It’s true that what they release in CO2, they absorb when they grow.
  • But this is not the full story:
    • You need fossil fuels to make crop fertilisers, to harvest crops, and to transport the biofuel.
    • All these processes make CO2, so it's not completely carbon neutral.

Jump to other topics

1Physical Chemistry

2Physical Chemistry 2 (A2 Only)

3Inorganic Chemistry

4Inorganic Chemistry 2 (A2 Only)

5Organic Chemistry 1

6Organic Chemistry 2 (A2 Only)

6.1Optical Isomerism (A2 Only)

6.2Aldehydes & Ketones (A2 Only)

6.3Carboxylic Acids & Esters (A2 Only)

6.4Aromatic Chemistry (A2 Only)

6.5Amines (A2 Only)

6.6Polymers (A2 Only)

6.7Biological Organic (A2 Only)

6.8Organic Synthesis (A2 Only)

6.9NMR Spectroscopy (A2 Only)

6.10Chromatography (A2 Only)

6.11A-A* (AO3/4) - Organic 2

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