3.5 Alcohols Flashcards
General formula of alkanes
C₂ₙH₂ₙ₌₂
Functional group of alcohols
R-O-H
How can alcohols be classified?
Primary, secondary or tertiary (based on the number of carbon atoms attached directly to the C bonded to oxygen)
Why do alcohols have relatively high melting and boiling points?
They form hydrogen bonds
Why are alcohols with a low Mr soluble in water?
They form hydrogen bonds with the water molecules
Reagent for the hydration of alcohols
Steam
Conditions for the hydration of alcohols
- 300°C
- 60atm
- Phosphoric acid catalyst (H₃PO₄)
Uses of alcohols
- Feedstock for chemical processes
- Solvents
- Alcoholic drinks
- Fuels
Methods for industrial preparation of ethanol
Fermentation and hydration of alkenes
Process for fermentation
- Carbohydrates from crops are broken down into sugar
- Sugars converted to ethanol by anaerobic respiration
- Ethanol is separated from the mixture with fractional distillation
Reagents for fermentation
- Glucose
- Yeast (catalyst)
Conditions for fermentation
- 30-40°C
- Aqueous
- Anaerobic
Products of fermentation
Ethanol + Carbon dioxide
Why is fermentation carried out under anaerobic conditions?
This prevents oxidation of ethanol to form ethanoic acid
Why is a temperature around 35°C used for fermentation
This is a compromise between maximising rate of reaction and avoiding denaturing enzymes
When does the fermentation reaction stop?
Around 15% ethanol (higher concentrations of ethanol damage the yeast enzymes)
Quality of ethanol produced through hydration of alkenes
Pure
Quality of ethanol produced from fermentation
Inpure
Rate of reaction of hydration of alkenes
Very fast
Rate of reaction of fermentation
Very slow
What type of process is hydration of alkenes?
Continuous
What type of process is fermentation?
Batch
Raw materials for the hydration of alkenes
Crude oil
Biofuel
A fuel derived or produced from renewable biological sources
Why is the statement that bioethanol is carbon neutral not valid?
- Fossil fuels are burnt in farming equipment, transportation, and refining the bioethanol
- This fuel releases carbon dioxide when burnt
Disadvantages of using crops for the production of fuels
- Less land available for food production
- Fertilisers are used to increase crop production
- Deforestation
Reagent for the elimination reaction of an alcohol
Concentrated sulfuric acid catalyst
Conditions for elimination reaction of an alcohol
Heat
Which small molecule is produced in the elimination reaction of an alcohol
Water
(this is a dehydration reaction)
What can be used to oxidise alcohols?
Acidified potassium dichromate(VI)
Acidified potassium dichromate(VI)
K₂Cr₂O₇ + H₂SO₄
Abbreviated to: H⁺/Cr₂O₇²⁻
Symbol for a generic oxidising agent
[O]
Oxidation (organic chemistry)
An increase in carbon-oxygen bonds
How can tertiary alcohols be distinguished from other alcohols?
They are not oxidised when mixed with acidified potassium dichromate(VI), so there will be no colour change.
Possible oxidation products of primary alcohols
Aldehydes and carboxylic acids
Oxidation products for secondary alcohols
Ketones
Reagent/conditions for oxidation of an alcohol to an aldehyde
Acidified potassium dichromate
Apparatus for oxidation of an alcohol to an aldehyde
Immediate distillation
Why is immediate distillation used to produce aldehyde from alcohols?
It prevents further oxidation of the aldehyde to a carboxylic acid
Why do aldehydes have lower boiling points than carboxylic acids?
Aldehyde have permanent dipole dipole force between molecules and carboxylic acids have hydrogen bonds
Reagents/conditions for oxidation of alcohols to form carboxylic acids
- Acidified potassium dichromate
- Reflux
Apparatus for producing carboxylic acids from alcohols
Reflux
Why is reflux used to produce carboxylic acids from alcohols?
Any aldehyde produced is returned to the reaction and further oxidised to carboxylic acids
