Alcohols Flashcards
Functional group in alcohol
OH
hydroxyl
Alcohols are either
Primary
Secondary or tertiary
Explain primary secondary and tertiary alcohols
Primary - this is when the carbon with OH group attached is attached to 1 carbon
Secondary - this is when the carbon with OH group attached is attached to 2 other carbons
Tertiary - this is when carbon with the OH group attached is attached to 3 other carbons
How to make alcohols to alkenes
Dehydration reaction
Elimination of water
General equation for dehydration
CnH2n+1OH —> CnH2n + H2O
How are alcohols produced?
Hydration of alkenes
Conditions for hydration
High temp (300•c)
High pressure (70atm)
Have to say concentrated Phosphoric acid catalyst or sulphuric acid
How can ethanol be produced
Fermentation of glucose
Hydration of ethene with steam
Advantages of hydration of ethanol with ethene
Faster production
Continuous process
Virtually pure product
Disadvantages of hydration of ethene
Ethene is non renewable - comes from crude oil fractions
Crude oil will run out and ethene will be expensive
And expensive initial costs
Is fermentation endo or Exothermic
Exothermic
Conditions of fermentation
Addition of yeast
Anaerobic conditions
Temp of 35 degrees
Equation for fermentation
C6H12O6 (aq) —-> 2C2H5OH (aq) + 2CO2 (g)
Why is yeast added during fermentation
Yeast produces an enzyme which converts sugars such as glucose into ethanol and carbon dioxide
Why is temp of fermentation done in 35 degrees (30-40)
The enzyme works at this optimum temp
If too cold the reaction is slow
If too hot enzyme denatured damaged
In fermentation what happens when ethanol is formed
It’s separated from the rest of the mixture by fractional distillation
Advantages of fermentation
It’s low tech
Uses cheap equipment
Uses renewable resources (sugar)
Disadvantages of fermentation
- The last fractional distillation step that’s needed to purify ethanol takes extra time and money
- Batch process
What kind of fuel is ethanol
Biofuel
What is a biofuel
A fuel that’s been made from biological material (plants) that’s recently died
Advantages of biofuel
Renewable energy resource - won’t run out so more sustainable
They’re carbon neutral (they produce co2 when burnt however plants take in same amount of co2 during photosynthesis)
Disadvantages of biofuels
When switching from fossil fuel to biofuel in cars - they’re car engines would have to be modified to use fuels with high concentrations of ethanol
Land used to grow crops for fuel cannot be used to grow food
If countries use land to grow biofuel crops instead of food they may be unable to feed everyone in a country
Explain why bioethanol (biofuel) is carbon neutral using equations
So burning biofuel produces CO2, the same amount of CO2 is taken in by plants when growing so bio ethanol carbon neutral
Plants take in carbon dioxide to produce glucose by photosynthesis…..
6CO2 + 6H2O —> C6H12O6 + 6O2 ….. 6 mol of co2 taken in from atomosphere to produce one mol of glucose
In fermentation process, glucose converted to ethanol …
C6H12O6 —> 2C2H5OH + 2CO2 … 2 mol of co2 rel into atmosphere when 1 mol of glucose converted to 2 mol of ethanol
When Ethanol is burned CO2 and water are produced…
2C2H5OH + 6O2 —> 4CO2 + 6H2O … 4 mol of CO2 released when 2 mol of ethanol are burned completely
So therefore If you combine all 3 equations exactly 6 mol of co2 are taken in and exactly 6 mol of co2 are given out
Why isn’t fermentation method to produce bioethanol completely carbon neutral
Fossil fuels will need to be burnt to power the machinery used to make fertilisers for crops, harvest the crops and refine and transport the bioethanol, this produces co2. So using bioethanol made by fermentation isn’t completely carbon neutral.
Describe the mechanism for formation of an alcohol by the reaction of an alkene with steam in presence of an acid catalyst
Starting with Ethene … curly arrow from double bond to H+
Leaves carbocation intermediate … curly arrow from lone pair on oxygen on H20 to carbocation
O has + Beneath it Arrow from middle of the O - H bond to the O with a + beneath it
Then alcohol is formed + H+ ion
Hydration of Ethene equation
C2H4 + H2O —> CH3CH2OH
<—
Equation for combustion of ethanol
2C2H5OH + 6O2 —> 4CO2 + 6H2O
Why is ethanol as a biofuel carbon neutral
6 mol of co2 in during photo synthesis
2 mol of co2 out during fermentation plus 4 mol of co2 out during combustion
= 6 mol of co2 out
So no net release of co2
Types of alcohols
Primary
Secondary
Tertiary
What is a primary alcohol
The carbon attached to OH group is attached to one other carbon
What is a secondary alcohol
The carbon attached to OH is attached to 2 other carbons
What is a tertiary alcohol
The carbon attached to the OH group is attached to 3 other carbons
What are products during oxidation of primary, secondary and tertiary alcohols
Primary - alcohols and carboxylic acids
Secondary - ketones
Tertiary - cannot be oxidised
Oxidising agent for alcohols
Acidified potassium dichromate
K2Cr2O7
Colour change for oxidation of alcohol
Orange to green when oxidation has occurred
Oxidising agent represented as
[O]
What is byproduct in oxidation of alcohol
H20
When oxidising an alcohol eg ethanol into ethanal how do you stop it turning into carboxylic acid
To prevent into ethanooic acid you heat and distill
Condenser is diagonal
When oxidising an 1 alcohol into ethanooic acid what apparatus do you use
Heat under reflux
Condenser is vertical
Test for aldehydes
Tollens reagent (ammoniacal silver nitrate)
Aldehyde - silver mirror
Ketone - no change
Fehlings solution
aldehydes - orange precipitate
Ketones - no change
Dehydration cannot occur in alcohol if …
Carbon adjacent to carbon bonded to OH isn’t bonded to Any Hydrogens as H2O mol cannot be eliminated
Eg if carbon bonded to 3 methyl groups
Define molecular ion
Molecule with one electron lost
