Alcohols

What are the methods for the production of alcohols [2]? And the conditions required [3 & 4]?

→ Hydration of alkenes:

Conditions: 300°C (steam), 60-70atm, phosphoric acid catalyst.

→ Fermentation:

Conditions: 30-40°C, yeast, anaerobic conditions, aqueous glucose.

Why does FERMENTATION of glucose require specific conditions?

• 30-40°C → the optimum temp for yeast.

• Anaerobic conditions → to ensure that only the desired products are made.

• Aqueous glucose → enzymes work in aqueous conditions.

What are the products of the anaerobic and aerobic FERMENTATION? And what can the product be used for?

• Anaerobic conditions: C6H12O6 -> 2C2H5OH + 2CO2

• Aerobic conditions: C6H12O6 + 6O2 -> 6CO2 + 6H2O

Ethanol produced by fermentation is then seperated by fractional distillation and can be used as a biofuel.

What is the proof for ETHANOL produced by FERMENTATION being theoretically carbon-neutral [4]?

• 6CO2 + 6H2O -> C6H12O6 + 6O2 (photosynthesis)

• C6H12O6 -> 2C2H5OH + 2CO2 (fermentation)

• 2C2H5OH + 6O2 -> 4CO2 + 6H2O (combustion)

• The CO2 taken in during photosynthesis is equal to the CO2 released during combustion.

Why is the ETHANOL produced by FERMENTATION also not considered as a carbon-neutral fuel [4]?

As the energy required for the farming, transport, fermentation and distillation of maize all come from fossil fuels.

What are the ethical [3] & environmental [4] problems with using the ETHANOL produced by FERMENTATION?

• Ethical → maize could feed the hungry, the land could be used to grow food for the hungry or homes for the homeless.

• Environmental → deforestation, destruction of habitats, the loss of biodiversity, fertilisers and pesticides run-off and cause water pollution.

How are alcohols oxidised [2]? And what are the products of the oxidation of primary [2], secondary [1] & tertiary alcohols?

Alcohols are oxidised by acidified potassium dichromate, producing a colour change of: orange solution to a green solution.

• Primary alcohol + [O] → Aldehyde

• Primary alcohol + 2[O] → Carboxylic acid

• Secondary alcohol + [O] → Ketone

• Tertiary alcohol + [O] → X

How do you favour a product in the oxidation of PRIMARY ALCOHOLS?

• Aldehyde → use distillation. (has a lower boiling point)

• Carboxylic acid → use reflux. (due to aldehydes lower boiling point once they evaporate they'll condense back into the flask)

How do you differentiate between the different alcohols [4]?

• Primary & secondary alcohols both go from a orange solution to a green solution, when reacted with acidified potassium dichromate solution. Whereas tertiary alcohols have no effect (solution remains orange).

• For the products of a primary & secondary alcohol, fractional distillation is used to collect the products.

• Then test both the products with Fehlings solution or Tollens.

• ONLY the products of a primary alcohol should show a positive result (due to the aldehyde).