Alcohols Flashcards
What are the 3 different types of alcohols?
1.) Primary: 1 alkyl group is attached to C with OH group.
2.) Secondary: 2 alkyl groups are attached to C with OH group.
3.) Tertirary: 3 alkyl groups are attached to C with OH group.
How can alkenes be formed from alcohols?
-Alkenes can be formed from alcohols by acid-catalysed elimination reactions.
Why is making alkenes from alcohols GENERALLY more sustainable than deriving alkenes from crude oil? What can alkenes produced be used for?
- If alcohol was made via fermentation of glucose from plants, it is more sustainable (as crude oil = non-renewable.)
- Alkenes produced can be used to produce addition polymers.
What acid catalyst could we use to produce alkenes from alcohols?
- Phosphoric acid (H₃PO₄)
What would be word equation for formation of ethene from ethanol?
Ethanol –> ethene + and H+ ion + water
Outline the mechanism for the elimination of water from alcohols, what products are formed?
Digram of this in pink hand folder - need to know!
- Lone pair on O on OH will move to H+ ion (provided by the acid catalyst.)
- Intermediate formed has + on O,pair of electrons moves from C-O bond to O+ - breaking the bond between C and O, leaving unstable carbocation intermediate.
- Pair of electrons move from C-H bond next to the C+ to form C=C bond.
- Products: alkene + water + H+ ion.
In the first stage of the mechanism of elimination of water from alcohols, lone pair moves from O to H+, where does this H+ come from? How do we know the acid definetely acts as catalyst in this reaction?
- H+ = provided by acid catalyst.
- H+ re-generated, proves that acid acts as a catalyst.
What will dehydration/ elimination of non-primary alcohols produce and why?
- Can lead to production of 2 different alkenes.
- Why: the C=C double bond can be formed either side of the C+ (from any C-H bonds next to it.)
Butan-2-ol is dehydrated in an elimination reaction, what two different alkenes could be formed?
- but-1-ene
- but-2-ene.
What is the first step of making cyclohexene from cyclohexanol?
- Add phosphoric acid + aqueous cyclohexanol in round-bottomed flask.
- Use heating mantle to warm reactants to bp of cyclohexanol (bunsen burner isn’t used because CH-ol = flammable.)
- Chemicals with boiling point less than that of CH-ol will evaporate/ condense back into liquid.
- Product = collected in vessel. But this product may have few impurities ie. unreacted cyclohexanol and water.
What is the 2nd stage in making cyclohexene from cyclohexanol?
- Add products (after distillation) into separating funnel. Add water to dissolve soluble impurities/ create aqueous solution.
- After allowing solution to settle, two layers will form. Top layer = impure cyclohexene. Bottom layer = aqeous layer (containing water-soluble impurities.)
- Drain the aqeous layer off (remember to remove stopper to ensure that there is enough pressure acting on top of solution to push layer down.)
Diagram of this on allery chem vid: 14.02
What is the 3rd stage of making cyclohexene from cyclohexanol?
- Take impure cyclohexene from step 2 and add to round-bottomed flask.
- Add anhydrous CaCl2 - this acts as dehydrating agent –> removing any aqeous substances remaining.
- Invert flask and leave for 20-30 minutes.
Although distilation will separate alkenes from their impurities, give 2 methods of further separation and purification that may be needed? State which is separation/ which is purification.
- Separation: separation funnel.
- Purification: drying agent.
How will the drying agent work to purify alkene formed from alcohol? How will we know when the alkene has been completely purified?
- Will absorb any aqeous impurities.
- Keep adding drying agent until it no longer clumps up (ie. getting bigger due to all solutes being absorbed), start to have freely-moving grains of CaCl2.
How are alcohols produced industrially?
- Alcohols are produced industrially by hydration of alkenes in presence of an acid catalyst.
What are the conditions for the formation of an alcohol from an alkene?
- Steam
- Phosphoric acid catalyst.
- High temperature/ pressure.
From the hydration of an alkene, what ion will be produced as well as the alcohol that is formed?
- H+ ion will be produced.
Outline mechanism for hydration of alkenes to form alcohol (describe where the curly arrows go.)
What are the products?
Diagram for this mechanism in alcohols notes in pink folder
- Electrons move from double bond to H+, forming a bond with the H+. Carbocation intermediate formed.
- Lone pair on water (from the steam) will move to C+ on carbocation.
- 2nd intermediate: O has 3 bonds, pair of electrons moves from O- H bond to O+.
- Alcohol + H+ ion.
As well as ethanol being produced industrially by reaction between ethene and steam (with phosphoric acid catalyst), how else is ethanol produced industrially? Why is this process somewhat better?
- Ethanol is produced industrially by fermentation of glucose.
- Doesn’t require crude oil (like ethene + steam does) so, is more sustainable and renewable as source of glucose is from plants.
What are the conditions for the fermentation of glucose to form ethanol?
- Using yeast
- anaerobic conditions (little/ no oxygen.)
- Yeast = enzyme so only works at optimum temperature (between 20 and 40 degrees celcius.)
- Aqeous glucose
Why does fermentation of glucose to form ethanol have to be at temp between 25 and 40 degrees celcius?
- Because yeast = enzyme
- Reaction will be too slow at low temperatures.
- 25-40 degrees is the optimum temp for the enzyme to work at.
- Enzyme denatures at high temperatures.
How can pure ethanol be obtained from the ethanol produced by fermentation of glucose/ yeast? What can pure ethanol obtained be used for?
- Ethanol from fermentation =separated by fractional distilation, to obtain pure ethanol.
- Pure ethanol can then be used as biofuel.
Symbol equation for formation of ethanol from glucose via fermentation of yeast.
C6H12O6 –> 2C2H5OH + 2CO2
Advantages of using fermentation to produce ethanol rather than reaction between ethene and steam. What is the main disadvantage?
- Requires little equipment/ renewable source –> cheap process.
- Disadvantage: biggest cost is fractional distilation; requires time and heat energy.
What is a “biofuel?”
- Fuels made from dead biological matter ie. ethanol.
What is ethanol produced from when it is used as a biofuel?
- Produced from sugar cane- which will be fermented to produce ethanol.
What are the advantages of use of biofuels?
- Renewable, more sustainable than crude oil.
- Biofuels produce CO2 when they are burnt but, they are classed as carbon neutral as CO2 absorbed by sugar cane whilst it is growing.
What are the envionmental/ ethical/ economical issues that need to be considered when making the decision on whether biofuels should be used or not?
- Ethical: land that should be used to grow food is being used to grow biofuel- may lead to food shortages.
- Not completely carbon-neutral process: fossil fuels burnt to transport biofuel across country/ used to make fertiliser for the sugar cane/ machinery used to harvest crops. All releasing CO2.
- Expensive to convert petrol engines to take fuels with higher concentration of ethanol.
Write the equations that support the statement: “ethanol produced by fermentation is a carbon-neutral fuel.”
pst… pst, this statement isn’t correct –> refer to other flashcard in this deck!!
- Photosynthesis equation: 6CO₂ + 6H₂O –> C₆H₁₂O₆ + 6O₂ (plants take in 6 moles of CO2.)
- Fermentation: C₆H₁₂O₆ –> 2CO₂ + 2C₂H₅OH (2 moles of CO2 produced.)
- Combustion of ethanol: 2C₂H₅OH + 6O₂ –> 4CO₂+ 6H₂O (4 moles of CO2 produced- reason why we use 2 in front of ethanol and THEN balance from there is because we take the no of moles produced in the previous equation - which is 2.)
- Total no of moles taken in –> 6 moles = no of moles produced, carbon neutral.
Why is this statement: “ ethanol produced by fermentation is a carbon-neutral fuel” not valid?
- Not completely carbon-neutral.
- Fossil fuels burnt to transport biofuel/ to make fertilisers for sugar cane/ machinery to harvest the crop.
What are the conditions to form an alkene from an alcohol (ie. dehydration?)
- High temp (180 degrees.)
- Phosphoric acid catalyst.
