Alcohols Flashcards
What is the functional group of alcohols?
What is this called?
-OH
The hydroxyl group
What is the general formula for alcohols ?
Cn H2n+1 OH
How do you classify an alcohol?
By the number of carbons attached to the carbon carrying the OH
What is the equation for the fermentation of glucose?
(Yeast)
C6H12O6 ———-> 2ethanol +2CO2
Give the conditions of the fermentation of ethanol
Yeast provides enzymes as a catalyst 35 degrees C so enzymes don’t denature Anaerobic respiration (oxygen free atmosphere)
What is the yield of ethanol from fermentation?
15%
What process is used to separate ethanol from the reaction mixture?
Fractional distillation
What are the conditions for the direct hydration of ethene?
Steam and concentrated H2SO4 or H3PO4
Give the details of a fermentation reaction
Rate: slow
Quality of product: impure
Raw material: sugar (renewable)
Type of process: batch
Give details on the hydration of ethene
Rate: slow
Quality: pure
Raw material: ethene from oil (finite)
Process: Continuous
Compare batch vs continuous processes
Batch: cheap equipment but expensive on manpower
Continuous: cheap on manpower, expensive equipment
What is a biofuel?
A fuel produced from renewable biological resources
Define carbon neutral
An activity that has no net annual carbon emissions to the atmosphere
Why is fermentation considered carbon neutral?
Photosynthesis absorbs 6 moles of CO2
Fermentation releases 6 moles of CO2
Is fermentation actually carbon neutral?
No: CO2 is produced in other processes involved eg transport and harvest
Is ethanol a biofuel?
Yes it is used as motor fuel when mixed with petrol
Mechanism for an alcohol to an alkene
Conditions??
Elimination
Heated with concentrated H2SO4
What is the name of the reaction turning an alcohol to an alkene?
Dehydration
Water is eliminated
What are the stages of an elimination reaction?
The alcohol oxygen’s lone pair is donated to a H+ provided by acid catalyst
Oxygen gains H+ and a positive charge
A hydrogen is lost from an adjacent carbon and the e- in the C-H bond move into the positively charged oxygen
What are the stages of separation for an impure organic liquid eg cyclohexene
Place impure organic liquid into a separating funnel and add a small amount (10cm3) of sodium hydrogen carbonate solution to eliminate XS acid catalyst
Stopper separating funnel and shake
Periodically invert and open tap to release pressure
Allow funnel to stand and layers to separate
Remove stopped and run off top and bottom layers into separate beakers
Discard aqueous layer
Why must you periodically open the tap of the separating funnel?
To release a build up of pressure coming from the acid catalyst reaction with the sodium hydrogen carbonate, creating CO2
Once you have separated the organic liquid, there may be a little water left. What do you do now???
Add a spatula of drying agent (eg Calcium Chloride or MgSO4) to organic liquid
Swirl and add drying agent until the liquid changes from cloudy to clear
Filter to remove drying agent
List the equipment for distillation reaction
Round bottom flask
Thermometer
Condenser
Heat
What is the distillate?
The product that evaporated and is condensed
Describe the method for distillation
Place mixture in round bottom flask attached to side arm with condenser, with a few anti-bumbing granules and heat
As product is formed it will evaporate, travel up the neck and down the condenser, where it will cool and drip into the collection vessel
How do we prevent the evaporation of the distillate?
Cool the distillate by placing the collection vessel in an ice bath
What is used to oxidise alcohols?
How is this presented in equations?
Acidified potassium dichromate
[O]
What is observed when an alcohol is oxidised?
Colour change from orange to green
What does the oxidation of a primary alcohol produce?
What if this is further oxidised?
Aldehyde
Carboxylic acid
What does the oxidation of a secondary alcohol produce?
Ketone
What does the oxidation of a tertiary alcohol produce?
Nothing
Order alcohol, aldehyde, and carboxylic acid in order of boiling point (highest to lowest)
Explain
Carboxylic acid > alcohol > aldehyde
Carboxylic acid: has hydrogen bonds and is bigger than alcohol so there are more VdW forces
Alcohol: has hydrogen bonds
Aldehyde: it’s permanent dipole-dipole forces are weaker than hydrogen bonds
Describe distillation to form an aldehyde (or ketone)!
Primary alcohol and potassium dichromate are dripped intk a WARM solution of H2SO4 (to make acidified potassium dichromate)
Aldehyde forked is immediately distilled off to prevent further oxidation
The boiling point of aldehyde is lower than that of an alcohol or carboxylic acid.
How do you produce a carboxylic acid?
Oxidise a primary alcohol under reflux
Why use reflux?
The vapour produced condensed and drips back into the reaction flask which prevents it escaping and will oxidise to form a carboxylic acid
What do
a) secondary
b) tertiary
Alcohols oxidise to?
a) ketones
b) not easily oxidised
Explain the colour changes during oxidation reactions
When potassium dichromate (orange) reacts with primary or secondary alcohols it is reduced to green chromium ions
How can oxidation reactions be used to distinguish between primary, secondary and tertiary alcohols?
Primary and secondary will go from orange to green with potassium dichromate
Tertiary will not
Give the general formula for aldehydes
How is it different to that of ketones?
Cn H2n O
It is the same
How are aldehydes different to ketones
Ketones have the C=O bond in the middle of the C chain
Aldehydes have the C=O on the end
What suffix is used for
a) aldehydes
b) ketones?
a) -al
b) -one
When do you use number in the name of an aldehyde?
NEVER
When can ketones be oxidised?
How and why is this avoided?
When reacted with a powerful oxidising agent causing C-C bonds to break and form a mixture of carboxylic acids
A milder oxidising agent must be used, which can oxidise an aldehyde but not a ketone
What two mild oxidising agents can oxidise an aldehyde but not a ketone?
Tollen’s Reagent
Fehling’s solution
a) When added to an aldehyde, what happens to Tollen’s reagent?
b) What about for a ketone?
a) Aldehyde oxidised to carboxylic acid
Silver ions reduced to silver
This produces a silver mirror
b)No observable change
Give the ionic equation when
a) Tollen’s Reagent
b) Fehling’s Solution
is added to an aldehyde
a) Ag+ + e- —-> Ag
b) Cu2+ + e- —-> Cu+
What is the colour change for aldehyde + Fehling’s Solution?
Forms a brick red PPT
Test for alkene
Shake with Bromine water (orange to colourless)
Test for carboxylic acid
Add sodium carbonate (effervescence)
Are C=O bonds polar?
What does this mean for nucleophiles?
Yes
It is readily attacked by nucleophiles
Name the mechanism for the reduction of an aldehyde/ ketone to an alcohol
Nucleophilic addition
What is used as a reducing agent to turn an aldehyde to an alcohol?
What does this provide?
NaBH4
H- ions
Name the reaction for nucleophilic addition
Reduction
Describe the mechanism for nucleophilic addition
Lone pair on H- goes to C of C=O bond, leaving O with a single bond and negative charge
Lone pair on O- goes to H+, forming an OH group
Mechanism for ketone/ aldehyde to hydroxynitriles
Conditions
Nucleophilic addition
KCN and DILUTE HCL
How do you name hydroxynitriles?
Use a hydroxy- prefix and -nitrile suffix
The nitrile carbon is always number one in the chain
Describe the nucleophilic addition to form hydroxynitriles
Lone pair on CN- goes to C of C=O bond, leaving O as negative with a single bond
Lone pair on O- goes to H+ from HCl
Nucleophilic addition forms optical isomers. What ratio are they in and what is this called?
Equal
A racemic mixture
Why are racemic mixtures optically inactive?
Equal amounts of enantiomers rotate a plane of polarised light in opposite directions equally and cancel each other.
Therefore polarised light is not rotated
For nucleophilic addition, why is a racemic mixture formed?
The carbonyl group is planar
There is an equal chance of the nucleophile attack from either side (above or below)
What is an anime functional group?
-CH2NH2
How can a nitrile functional group be turned into an anime functional group?
What kind of reaction is this?
Catalytic hydrogenation
Reduction
What is needed for the catalytic hydrogenation of nitriles?
Hydrogen
Nickel catalyst
Are nitrile or amines more reactive?
Amines
Mechanism for alkyl hydrogen sulphate -> alcohol
Hydrolysis
Warm
H2O
Alkene to alcohol
Electrophilic addition / hydration
H2O
Conc H2SO4
What kinda of IMF do aldehydes have
Dipole dipole
