Alcohols Flashcards
What is the functional group for alcohols
-OH
Hydroxyl group
What is a primary alcohol
An alcohol with 1 alkyl group attached to the same carbon which the -OH is attached to
What is a secondary alcohol
An alcohol with 2 alkyl groups attached to the same carbon which the -OH is attached to
What is a tertiary alcohol
An alcohol with 3 alkyl groups attached to the same carbon which the -OH is attached to
How can we sustainably make an alkene from an alcohol
Dehydrate an alcohol which is produced via the fermentation of glucose from plants in the presence of an acid catalyst
What do we call the process of eliminating water from a molecule
Dehydration
What is the benefit of dehydrating an alcohol which is produced via the fermentation of glucose from plants to produce an alkene rather than extracting them from crude oil
Crude oil is non-renewable therefore this process is not sustainable. Plants are renewable and so that process is sustainable
How can we form an alcohol from an alkene
Hydrate the alkene in the presence of an acid catalyst
Give an equation for the dehydration of ethanol to produce an alkene
Must be done in warm conditions (under reflux) and in the presence of concentrated sulfuric acid
What is the mechanism by which the dehydration of alcohols to form an alkene occurs
Acid catalysed elimination
What can alkenes which are produced by the dehydration of alcohols be used for. What is the benefit of this over an alternative method
Used to produce addition polymers without using monomers derived from crude oil.
Outline the mechanism for the formation of ethene via the dehydration of ethanol
What can occur when we dehydrate secondary or tertiary alcohols to form an alkene
May form 2 different alkenes due to the ability for the double bond to occur on either side of the OH group
When we dehydrate an alcohol, the mixture is impure. What are the components of this impure mixture
Alkene
Alcohol
Water
Acid
How can we separate an impure mixture produced from the dehydration of an alcohol
Distillation
What is distillation
The separation of chemicals by boiling point
What can we do to further purify an impure mixture produced from the dehydration of an alcohol which has already been distilled
We can use a separation funnel to separate aqueous and organic layers
The addition of a drying agent ( to remove any H2O)
What is the desired product from the dehydration of an alcohol
A pure alkene
What are the 3 steps in producing cyclohexene from an alcohol
Distillation
Separation
Purification
What alcohol is cyclohexene produced from
cyclohexanol
What is the reagent and conditions required for the dehydration of an alcohol to form an alkene
Reagent: Concentrated sulfuric acid
Conditions: Warm (under reflux)
Outline step 1 in the production of cyclohexene from cyclohexanol
Step 1: Distillation:
- Add concentrated sulfuric acid and cyclohexanol to a round bottomed flask.
- Add several anti-bumping granules to allow for a smooth boiling process
- Use a heating mantle to warm the reactants up to 83C (B.P of cyclohexanol)
- Chemicals with B.P less than 83C will evaporate, enter the condenser ,cool down and condense back into a liquid
- Product is then collected in a conical flask, yet this product will still have small amounts of impurities such as unreacted cyclohexanol and water
What is the purpose of adding anti bumping granules during distillation
Allows for a smooth boiling process by preventing large bubbles from forming
What is the boiling point of cyclohexanol
83 degrees C
Why don’t we use a Bunsen burner when distilling cyclohexanol
Cyclohexanol is flammable
Outline step 2 in the production of cyclohexene from cyclohexanol
Step 2: Separation:
- Add the products from step 1 to a separating funnel and add water to dissolve soluble impurities (creating an an aqueous solution)
- Let the solution to settle, forming 2 layers - top layer being impure cyclohexene, bottom layer being an aqueous solution of water soluble impurities
- Drain the aqueous layer off by releasing the bottom layer from the funnel
When we heat cyclohexanol, what do we get
Impure cyclohexene
Outline step 3 in the production of cyclohexene from cyclohexanol
Step 3: Purification:
- Take the impure cyclohexene from step 2 and add back into a round bottom flask
- Add the drying agent: anhydrous CaCl2, which will remove any aqueous substances still remaining
- INVERT the flask and leave it for 20-30 mins
- Keep adding the drying agent until there is no clumping, and there are only free moving grains of CaCl2, which means all the water ahs been removed from the sample
What are the conditions required for the hydration of ethene to form ethanol
high temperature 300 °C
high pressure 70 atm
strong acidic catalyst of conc H3PO4
Outline the mechanism for the formation of ethanol via the hydration of ethene
What are the 2 ways of producing ethanol
Hydration of ethene (from crude oil)
Fermentation of glucose
What are the conditions for the fermentation of glucose
Yeast
Anaerobic conditions
Temperature of 30-40 degrees C
Write the equation for the formation of ethanol via fermentation of glucose
What is the role of yeast in the fermentation of glucose
Enzyme
Sketch a graph showing how temperature effects the rate of fermentation of glucose
After we have the obtained the products from the fermentation of glucose, what process do we use to obtain pure ethanol
Fractional distillation
Why is fermentation done in anaerobic conditions
The presence of air can cause extra reactions to occur.
O2 in air oxidises the ethanol produced to ethanoic acid
(vinegar)
What are 2 advantages of producing ethanol via the fermentation glucose
- Sugar is a renewable resource
- Cheap equipment
What are 2 disadvantages of producing ethanol via the fermentation glucose
- Ethanol made is not pure and needs purifying by
fractional distillation - Depletes land used for growing food crops
What are 2 advantages of producing ethanol via the hydration of ethene
*faster reaction
*purer product
What are 2 disadvantages of producing ethanol via the hydration of ethene
*high technology equipment needed (expensive
initial costs)
*ethene is non-renewable resource
What is a biofuel
A biofuel is a renewable energy source made from dead biological matter
Give an example of a biofuel
Ethanol
What are 2 advantages of biofuels
- They are renewable so more sustainable than crude oil
- Biofuels are almost carbon neutral
What are 2 disadvantages of biofuels
- Expensive to convert existing petrol engines to take fuels with higher concentrations of ethanol
- Land that could be used to grow food is instead used to make fuel which could cause food shortages in local communities
Give 2 reasons why biofuels not 100% carbon neutral
Fossil fuels are burnt to transport biofuels which releases CO2
Fossil fuels are used to make fertilisers to put the crops used to make biofuels, which releases CO2
Machinery is required to harvest the crop which releases CO2
Write equations displaying how ethanol produced by fermentation is a carbon neutral process
Give an example of a crop used to make biofuels
Sugar cane
What 3 things can alcohols be oxidised to form
Aldehydes
Ketones
Carboxylic acids
What can primary alcohols be oxidised to form
Aldehydes then carboxylic acids
What can secondary alcohols be oxidised to form
Ketones
What is the only way to oxidise a tertiary alcohol
Tertiary alcohols are not easily oxidised. Cant be oxidised using dichromate, only by burning them yet this doesn’t produce any useful products so no point
What is the conditions and reagent required for the oxidation of primary alcohols to produce a carboxylic acid
Reagent: potassium dichromate(VI) solution and dilute
sulfuric acid
Conditions: use an excess of dichromate, and heat
under reflux (can then distil to separate products)
What is the conditions and reagent required for the oxidation of secondary alcohols to produce a ketone
Reagent: potassium dichromate(VI) solution and dilute
sulfuric acid
Conditions: use an excess of dichromate, and heat
under reflux
How do we represent an oxidising agent when writing an equation for the oxidation of an alcohol
[O]
If we want only an aldehyde when oxidising a primary alcohol, what can we do
Do not use an excess of dichromate, or heat
under reflux
What is the observation when primary alcohols are oxidised to form a carboxylic acid
The orange dichromate ion (Cr2O72-) reduces to the green Cr 3+ ion
Orange to green
What is the observation when secondary alcohols are oxidised to form a ketone
The orange dichromate ion (Cr2O72-) reduces to the green Cr 3+ ion
Orange to green
Write the an equation for the reaction using displayed formula showing the formation of a carboxylic acid from propan-1-ol
Write the equation for the reaction using displayed formula showing the formation of a ketone from propan-2-ol
What is the conditions required for the oxidation of primary alcohols to produce an aldehyde
Reagent: potassium dichromate(VI) solution and dilute
sulfuric acid
Conditions: Do not use an excess of dichromate, or heat
under reflux
How can we extract an aldehyde produced from the oxidation of a primary alcohol
We have to separate the aldehyde from the oxidising agent. We can distil the mixture since aldehydes have a lower boiling point than alcohol
Other than aldehydes, carboxylic acids and ketones, what other product do we always form when oxidising an alcohol
Water
What is the test for carboxylic acids
Addition of sodium carbonate. It will fizz and produce
carbon dioxide if a carboxylic acid is present
What 2 things can we use to distinguish between aldehydes and ketones
Fehling’s solution
Tollens reagent
What is the role of both Fehling’s solution and Tollens reagent reagent when distinguishing between aldehydes and ketones
They are oxidising agent
They oxidise aldehydes but not ketones
What does Fehling’s solution consist of
Blue solution as it contains Cu2+
What are the steps and positive test for the use of Fehling’s solution to distinguish between aldehydes and ketones
If we add WARM Fehling’s to:
Aldehyde: Blue to brick red (Cu₂O is the red)
Ketone: Remains blue
What is the formula for tollens reagent
(Ag(NH3)2)+
What are the steps and positive test for the use of tollens reagent to distinguish between aldehydes and ketones
If we add WARM tollens to:
Aldehyde: Tollens is reduced to Ag which forms a silver mirror that coats the inside of the flask
Ketone: No silver mirror formed
What is the test for alcohols
Acidified K2Cr2O7 goes from orange to green in OH-
