Alcohols Flashcards
What are alcohols?
It’s primary, secondary or tertiary depending on carbon atom on the -OH group its bounded to.
What is the general formula for alcohols?
CnH2n+2OH
How can alcohols be dehydrated to form alkenes?
Alcohols are produced industrially by hydration of alkenes in the presence of an acid catalyst:
CnH2n+2OH —H2SO4—> C2H4 + H2O
- This reaction allows you to produce alkenes form renewable resources meaning you can produce polymers without needing oil.
How do you dehydrate ethanol to form ethene?
C2H5OH —H2SO4—> C2H4 + H2O
How are alcohols produced by hydration of alkenes?
Hydrate an alkene using steam in the presence of an acid catalyst. Ethanol can be produced by the hydration of ethene by steam at 300°C and pressure of 60 atm and it needs a solid phosphoric (V) acid catalyst.
How is alcohol produced industrially by fermentation?
Fermentation is an exothermic process carried out by heat in anaerobic conditions.
C6H12O6 (aq) —30-40°C–> 2C2H5OH (aq) + 2CO2 (g)
Yeast produces an enzyme converting sugars such as glucose into ethanol and carbon dioxide. The enzyme works at optimum temperature of 30-40°C (if too cold/warm enzymes denatured).
Ethanols separated from the rest of mixture by fractional distillation.
Fermentation is low tech and uses cheap equipment and renewable resources but fractional distillations needed to purify ethanol produced taking extra time and money.
What is a biofuel?
A biofuel is a fuel that is made from biological material thats recently died.
Advantages of biofuels?
+ They renewable energy sources and won’t run out so are more sustainable.
Why is bioethanol almost carbon neutral?
Burning ethanol produces carbon dioxide which is a greenhouse gas and it can be argued burning ethanol is carbon neutral.
- Plants taking in CO2 from atmosphere to produce glucose by photosynthesis:
6CO2 + 6H2O —-> C6H12O6+6O2
- In the fermentation process glucose is converted into ethanol: C6H12O6—> 2C2H5OH + 2CO2
- When ethanols burned carbon dioxide and waters produced: 2C2H5OH + 6O2—> 4CO2 + 6H2O
BUT fossil fuels need to be burned to make fertilizers and power machinery which produces carbon dioxide meaning it isn’t completely carbon neutral.
How can alcohols be oxidized?
Need to burn them using oxidizing agent acidified dichromate to mildly oxide alcohols and the orange dichromates reduced to green chromium.
- Primary alcohol are oxidized to aldehydes and then to carboxylic acids.
- Secondary alcohols are oxidized to ketones only.
- Tertiary alcohols aren’t oxidized.
What are aldehydes?
They have hydrogen and one alkyl groups attached to the carbonyl carbon atom and their suffix is -al which is carbon-1.
What are ketones?
They have two alkyl groups attached to the carbonyl carbon atom, and their suffix is -one.
What are carboxylic acids?
They have COOH group at the end of their chain and their suffix is -oic.
How do primary alcohols oxidize to aldehydes and carboxylic acids?
- Gently heat ethanol with potassium dichromate and sulfuric acid in test-tube produces ethanol.
- To get the aldehyde you need to get it out of oxidsing solution as soon as it forms and can do this using distillation apparatus so so aldehyde is distilled.
- To produce carboxylic acid the alcohols vigorously oxidized and alcohols mixed with excess oxidizing agent heated under reflux meaning you can increase the temperature of organic reaction without losing volatile solvents, reactants or products.
How do secondary alcohols oxidize to ketones?
Refluxing secondary alcohol with acidified dichromate(VI) will produce ketone.
