Alcohols UNIT 2 Flashcards
Products of incomplete combustion
Carbon dioxide
Water
Carbon
Carbon monoxide
When an alcohol undergoes complete combustion, what products are formed
Carbon dioxide and water
What are methylated spirits
Ethanol with a small percentage of poisonous methanol added to make it unfit to drink. Can be sold without the tax which is levied on alcoholic drinks. A purple dye is also added to show that it shouldn’t be drunk
Ways alcohols can be oxidised
Combustion or heating gently in stages
Primary alcohols are oxidised to….
Aldehydes, these can be further oxidised to carboxylic acids.
Secondary alcoholics are oxidised to…
Ketones (not oxidised any further)
Do aldehydes and ketones have pleasant or unpleasant smells
Pleasant
Process of oxidising ethanol to ethanal (an aldehyde)
Dilute acids and less potassium dichromate than is needed for complete oxidation to carboxylic acid. Mixture heated gently in reflux apparatus, receiver cooled in ice to reduce evaporation of product. Ethanal vaporises as soon as it’s produced and distils off. This stops it from being oxidised further to ethanoic acid. Unrea red ethanol remains in the flask
What does reflux mean
Vapour condenses and drips back into the reaction flask
Process of oxidising ethanol to ethanoic acid (carboxylic acid)
Conc. sulphuric acid and excess potassium dichromate. Mixture refluxed. Whilst this is happening, any ethanol or ethanal vapour condense and drip back into flask until all oxidised to acid. Distil of ethanoic acid
Process of oxidising a secondary alcohol to a ketone
Acidified dichromate added
3 types of alcohols
Primary
Secondary
Tertiary
Which one it is depends on which carbon atom the hydroxyl group is bonded to
What is the alcohols general formula
CnH2n+1OH
Ethanol can be produced industrially by…..
Fermentation
At the moment,most ethanol is being produced through what process? What is wrong with this method?
By steam hydration of ethene with phosphoric acid catalyst. The ethene comes from cracking heavy fractions of crude oil.
But in the future when crude oil supplies start running out, petrochemicals like ethene will be expensive
Explain the industrial production of ethanol by fermentation
Fermentation is an exothermic process, carried out by yeast in anaerobic conditions
Yeast produces an enzyme which converts sugars, such as glucose into ethanol and carbon dioxide
The enzyme works at an optimum temp of 30 to 40c, if too cold reaction is slow, if too warm the enzymes are denatured.
When the solution reaches about 15% ethanol, the yeast dies. Fractional distillation is used to increase the conc of ethanol
Fermentation is low tech, it uses cheap equipment and renewable resources. The ethanol produced by this method has to be purified though
What is a biofuel
A fuel that’s made from biological material that’s recently died
Ethanol is what type of fuel
Almost carbon neutral
Because all the CO2 released when the fuel is burned was removed by the crop as it grew. BUT there are still carbon emissions if you consider the whole process eg making the fertilisers and powering agricultural machinery will probably involve burning fossil fuels
Ethanol is being used increasingly as a….
Fuel, particularly in countries with few oil reserves.
Eg Brazil uses sugars from sugar cane which is fermented to produce alcohol which is added to petrol. Ethanol made in this way is a biofuel
Alcohols can be dehydrated to form …..
Alkenes
You can make ethene by eliminating …….. from …… in a ……….. Reaction
Water
Ethanol
Dehydration
What are the conditions needed for dehydrating alcohols to form alkenes
Reflux
Conc sulphuric acid or phosphoric acid catalyst
What does the dehydration reaction of alcohols to alkenes allow
Allows you to produce alkenes from renewable sources
This is important because it means that you can produce polymers without needing oil
How much an alcohol can be oxidised depends on its…..
Structure
What is the simple way to oxidise alcohols
Burn them, but don’t get best products from doing this. Instead you can use an oxidising agent such as acidified potassium dichromate to mildly oxidise alcohols
Tertiary alcohols aren’t…..
Oxidised
Aldehydes and ketones are what type of compounds
Carbonyl
What is the functional group of aldehydes and ketones
C=O, as they are carbonyl compounds
General formula for aldehydes and ketones
CnH2nO
What are aldehydes
Have a hydrogen and one alkyl group attached to the carbonyl carbon atom
Their suffix is -al
What are ketones
Have 2 alkyl groups attached to the carbonyl carbon atom. Their suffix is -one.
What are carboxylic acids
They have a different functional group , COOH at the end of their carbon chain
Their suffix is -oic
You can control how far the alcohol is oxidised by controlling the…..
Reaction conditions.
Process of oxidising primary alcohols
Gently heat ethanol with potassium dichromate solution and sulphuric acid in test tube. Should produce ‘Apple’ smelling ethanal, an aldehyde. However, it’s very tricky to control amount of heat and the aldehyde is usually oxidised to form a ‘vinegar’ smelling ethanoic acid
To get just the aldehyde, need to get it out of the oxidising solution as soon as it’s formed. Can do this by gently heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus, so aldehyde (which boils at a lower temp than alcohol) is distilled off immediately.
To produce a carboxylic acid the alcohol has to be vigorously oxidised. The alcohol is mixed with excess oxidising agent and heated under reflux. Heating under reflux means you can increase the temp of an organic reaction to boiling without losing volatile solvents, reactants or products. Any vaporised compounds are cooled, condense and drip back into the reaction mixture
How are secondary alcohols oxidised into ketones
Alcohol is refluxed with warm acidified dichromate, forms ketones
Ketones not easily oxidised so even prolonged refluxing won’t produce anything more
What happens to the dichromate ion when it is reduced
Goes from orange to green
Aldehydes and ketones can be distinguished using …..
Oxidising agents
What happens with Fehlings solution and Benedicts solution
They are used as oxidising agents. They are both a deep blue Cu2+ complexes, which recuse to brick red Cu2O when warmed with an aldehyde, remain blue with ketone (as ketones aren’t easily oxidised)
What happens with Tollens reagent
Ammonical silver nitrate, (Ag(NH3)2)+ reduced to silver when warmed with an aldehyde, but not with ketone. Goes from colourless to metallic silver, which will cost the inside of the apparatus to form a silver mirror
Why can’t ketones be oxidised further
The electro positive carbon has no hydrogens attached to the ketone
