Alcohols Flashcards
Functional group of alcohols
OH
Alcohol to alkenes dehydration reaction
Reason, catalyst, type of mechanism and overall reaction
To make plastics with alkenes (poly(alkenes))
Sulfuric acid or phosphoric acid catalyst
Elimination
Alcohol -> alkene + water
Why can dehydration of non primary alcohols lead to 2 different alkenes?
Double bonds can be formed either side of the carbon that had the OH group
Why do you need to distill after dehydrating an alcohol? What else may be needed
An impure product is obtained containing alkene, alcohol, water and acid
Distillation separates chemicals by boiling point
Further separation and purification may be needed with a separating funnel and drying agent after
Making cyclohexene practical
- Add concentrated sulfuric, phosphoric acids and cyclohexanol into a round bottomed flask with anti bumping granules
- Heat the reactants up to 83°C gently with a micro burner for distillation as cyclohexanol is flammable
- Chemicals with bps less than or equal to 83°C will evaporate and enter the condenser and condense back to a liquid
- The product is collected in a vessel like a conical flask with impurities (untracked cyclohexanol and water)
- Add the products in the flask into a separating funnel and add water to dissolve soluble impurities to create an aqueous solution
- As the solution settles, 2 layers form: top layer - impure cyclohexene, bottom layer - aqueous layer containing water soluble impurities
- Drain the aqueous layer off after removing the stopper
- Take the impure cyclohexane from step 2 and add to a round bottomed flask
- Add anhydrous calcium chloride (dehydrating agent) and will remove any aqueous substances still remaining
- Invert the flash and leave for 20-30 minutes
Hydration of alkenes (alkene directly to alcohol) reagents, catalyst, conditions
Steam reagent
acid catalyst eg phosphoric acid
300°C and 60 atm
Fermentation (alternative to ethene and steam to make ethanol)
Reason why this route is better, conditions, catalyst, Endo/exothermic, overall reaction, extra steps after, disadvantages
Using ethene requires using crude oil which is unsustainable, but glucose is a renewable source from plants
Anaerobic conditions
Yeast catalyst (enzyme)
Exothermic
Glucose -> ethanol + CO2
Fractional distillation to obtain pure ethanol
Fractional distillation requires lots of energy and time
What is a biofuel and give an example
A fuel derived from living matter - eg ethanol in countries where there is a good supply of sugar cane (fermented sugar produces the ethanol)
2 Advantages and disadvantages of biofuels
Advantages:
Renewable so more sustainable than crude oil
Carobn neutral as CO2 is absorbed by the sugar cane as it was growing
Disadvantages:
Expensive to convert existing petrol engines to take fuels with higher ethanol concentrations
Land that could be used to grow food is used to make fuel instead, causing food shortages in countries growing sugar cane eg India and Brazil
Why are biofuels considered carbon neutral? Use equations to support this.
Plant growth:
6CO2 + 6 H2O -> C6H12O6 + 6O2
Production of ethanol in fermentation:
C6H12O6 -> 2CO2 + 2C2H5OH
Combustion of ethanol when used as biofuel:
2C2H5OH + 6O2 -> 4CO2 + 6H2O
Total number of moles of CO2 used up is the same as the number of moles produced -> carbon neutral
Why are biofuels not completely carbon neutral?
Fossil fuels are burnt to transport the biofuel across the country
Fossil fuels are used to make fertilisers to put on crops
Fossil fuels are used in machinery to harvest the crops
What needs to be added to oxidise alcohols? What’s its colour change?
Acidified potassium dichromate, a mild oxidising agent- it goes from orange to green
What are primary alcohols oxidised to?
Aldehydes then carboxylic acids
What are secondary alcohols oxidised to?
Ketones
What are tertiary alcohols oxidised to?
They can’t be oxidised… they just burn
