Alcohols Flashcards
How can alcohols be produced industrially?
Hydration of alkenes or fermentation of glucose
What are the conditions for the hydration of alkenes?
Conc phosphoric acid, 600 K, 60 atm, excess alkene
What are the conditions for the fermentation of glucose?
Yeast, anaerobic, 35 C, neutral aqueous solution
Why does yeast need to be present for the fermentation of glucose?
It produces enzymes that convert sugars into methanol
Why are anaerobic conditions needed for the fermentation of glucose?
To prevent the ethanol oxidising to form ethanoic acid
Why is a temperature of 35 C needed for the fermentation of glucose?
The reaction is too slow below 25 and the enzymes denature at 40
Why does the ethanol produced by the fermentation of glucose need to be removed from the reaction mixture?
Concentrations of ethanol above 10% can kill the yeast
How is ethanol produced by fermentation of glucose separated?
Fractional distillation
What can the ethanol produced by fermentation of glucose be used for once extracted?
Biofuel
What is biofuel?
Fuel made from living organisms or their waste
What equations shows that the production of ethanol by fermentation is carbon neutral?
Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
Fermentation: C6H12O6 → 2C2H5OH + 2CO2
Combustion: C2H5OH + 3O2 → 2CO2 + 3H2O
Why isn’t the production of ethanol by fermentation actually carbon neutral?
The fertiliser and pesticides used, the harvesting and transporting, and the fractional distillation all required energy
What is the mechanism for the formation of an alcohol by hydrating an alkene?
Electrons from the C=C bond go to the H+ from the acid. Then the lone pair on the O of H2O goes to the positive C of the carbocation intermediate and it gains the +ve charge. Then the electrons from one of the H2Os Hs goes to the oxygen forming H+ again
What type of process is the production of ethanol by fermentation?
A batch process
What type of process is the production of ethanol by hydration?
A continuous flow process
How fast is the production of ethanol by fermentation?
Very slow
How fast is the production of ethanol by hydration?
Very fast
What quality of ethanol is produced by fermentation?
Impure ethanol that needs further processing
What quality of ethanol is produced by hydration?
Much purer ethanol than fermentation
What are the reaction conditions for producing ethanol by fermentation regarding the environment?
They are gentle temperatures and atmospheric pressure
What are the reaction conditions for producing ethanol by hydration regarding the environment?
They are high temperatures and pressures that require lots of energy
What resources does the production of ethanol by fermentation use?
Renewable resources based on plant material
What resources does the production of ethanol by hydration use?
Finite resources based on crude oil
What are the advantages and disadvantages of producing ethanol by fermentation?
It’s kinder to the environment and uses renewable resources but is slow and inefficient
What are the advantages and disadvantages of producing ethanol by hydration?
It’s faster and produces purer ethanol but uses fossil fuels and energy intensive conditions
How are alcohols classified?
As primary, secondary or tertiary depending on the position of the -OH group in the carbon chain
What can primary alcohols be oxidised to?
Aldehydes then carboxylic acids
What can secondary alcohols be oxidised to?
Ketones
What can tertiary alcohols be oxidised to?
Nothing easily
What reagent is used to oxidise alcohols?
Acidified potassium dichromate
What colour is potassium dichromate when added to the alcohol?
Orange
What colour does the potassium dichromate become as the alcohol is oxidised?
Green
What are the conditions for oxidising an alcohol to form a carboxylic acid
Potassium dichromate in excess and gentle reflux
What are the conditions for oxidising an alcohol to form an aldehyde?
Alcohol in excess and distil immediately
What are the conditions for oxidising an alcohol to form a ketone?
Potassium dichromate in excess and gentle reflux
What is the equation for the oxidation of ethanol to form ethanoic acid?
CH3CH2OH + 2[O] → CH3COOH + H2O
What is the equation for the oxidation of ethanol to form ethanal?
CH3CH2OH + [O] → CH3CHO + H2O
What is the equation for the oxidation of propan-2-ol to form propanone?
CH3CH(OH)CH3 + [O] → Ch3COCH3 + H2O
What 2 reagents can be used to differentiate between an aldehyde and a ketone?
Tollens’ reagent and Fehling’s solution
How is Tollens’ reagent used to differentiate between aldehydes and ketones?
It is warmed gently with the unknown solution and if an aldehyde is present a ‘silver mirror’ forms on the sides of the reaction vessel
How is Fehling’s solution used to differentiate between aldehydes and ketones?
It is warmed gently with the unknown solution and if an aldehyde is present it turns from blue to a brick red precipitate
What enables Tollens’ and Fehling’s to differentiate between aldehydes and ketones?
That fact that aldehydes can easily be oxidised further
What reaction can alcohols undergo to form alkenes?
Elimination/dehydration
What are the 2 sets of conditions for the elimination of alcohols?
Conc sulfuric acid catalyst and 170 C or aluminium oxide catalyst and 600 C
What is the mechanism for the elimination of an alcohol?
The lone pair on the O of the alcohol’s -OH goes to acid’s H+. Then the electrons from the C-O bond in the alcohol go to the O. Then the elctrons from a C-H bond adjacent to the +ve carbon of the carbocation go to the C-C bond between those 2 Cs
What else is produced in the elimination of alcohols?
Water
What is significant about the alkenes produced from the elimination of allchohols?
They can be used to create addition polymers that aren’t derived from crude oil
What RPA involves alcohols?
Distillation of a product from a reaction
What are the 2 common versions of the distillation of a product from a reaction RPA?
Preparing cyclohexene by the dehydration and distillation of cyclohexanol and preparing ethanal by the oxidation and distillation of ethanol
What apparatus is used for the distillation of a product from a reaction RPA?
A round bottom flask attached to a condenser via an adapter which has a thermometer in the top. At the end of the condenser is a ice cooled collecting vessel. Label the water in and out of the condenser and the heat beneath the flask
Why should a water bath be used during the distillation of a product from a reaction RPA?
Because ethanol is flammable
Why are anti-bumping granules used in the distillation of a product from a reaction RPA?
To prevent large bubbles forming and the mixture boiling over into the condenser
Why should the condenser be tilted down in the distillation of a product from a reaction RPA?
So the liquid runs down into the collection flask
Where should the bulb of the thermometer be in the distillation of a product from a reaction RPA?
At the T junction connecting the flask to the condenser
Why must water enter at the bottom of the condenser?
To ensure the entire condenser is filled
Why should the collection flask not be sealed to the condenser in the distillation of a product from a reaction RPA?
The air inside the system expands as it is heated and could crack the glass apparatus
