Alcohols
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Boiling points of alcohols
Alcohols have a relatively low volatility and high boiling points due to their ability to form hydrogen bonds between alcohol molecules
What are primary alcohols
Alcohols where 1 carbon is attached to the carbon adjoining the oxygen And so on for secondary and tertiary
What causes alcohols to oxidise
The oxidising agent potassium dichromate K2Cr2O7
Partial oxidation of primary alcohols
Reaction: Primary alcohol -> aldehyde Reagent: potassium dichromate (VI) solution, warm gently and distil out the aldehyde as it forms Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
What is distillation used for and how to maximise yield
To separate an organic product from its reacting mixture, in order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher
Where does the water go in distillation
Into the bottom of the condenser to go against gravity -> this allows more efficient cooling and prevents back flow of water
Why are electric heaters used to heat organic chemicals
Because organic chemicals are highly flammable and could set on fire with a naked flame
What can you do to the collection flask to improve yield of distillate
Cool it in ice
Full oxidation of primary alcohols
Reaction: Primary alcohol -> carboxylic acid Reagent: potassium dichromate (VI) solution and dilute sulfuric acid Conditions: use an excess of dichromate, and heat under reflux (distil of product after the reaction has finished) Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
What is reflux used for and what does the condenser prevent
When hearing organic reaction mixtures for long periods -> the condenser prevents organic vapours from escaping by condensing them back to liquids
Why should you never seal the end of the condenser in reflux
As the build up of gas pressure could cause the apparatus to explode
Why are antibumping granules added to the flask in both distillation and reflux
To prevent vigorous, uneven boiling by making small bubbles form instead of large ones
How to draw reflux apparatus
• don’t draw lines between flask and condenser • don’t have top of condenser sealed • condenser must have outer tube for water that is sealed at top and bottom • condenser must have 2 openings for water in and out that are open
Oxidation of secondary alcohols
Reaction: Secondary alcohol -> ketone Reagent: potassium dichromate (VI) solution and dilute sulfuric acid Conditions: heat under reflux Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
Why can’t tertiary alcohols be oxidised by potassium dichromate
Because there is no hydrogen atom bonded to the carbon with the -OH group
When ketones have 5Cs or more in a chain..
Then it needs a number to show the position of the double bond
Dehydration reaction
Removal of a water molecule from a molecule
Reaction of alcohols with dehydrating agents
Reaction: alcohol -> alkene Reagents: concentrated sulfuric or phosphoric acids Conditions: warm under reflux Role of reagent: dehydrating agent/catalyst Type of reaction: acid catalysed elimination
When can secondary and tertiary alcohols give more than one product in dehydration
When the double bond forms between different carbon atoms
What are the 2 methods for producing ethanol
• Fermentation • Hydration of ethene
Fermentation equation
Glucose -> ethanol + carbon dioxide C6H12O6 -> 2C2H5OH + 2CO2
Conditions for fermentation
• Yeast • No air -> anaerobic conditions • Temp 30-40*C Optimum temp is 38*C -> any lower the reaction is too slow -> any higher the yeast dies and the enzymes denature
Why is fermentation done in the absence of air
Because the presence of air can cause extra reactions to occur -> it oxidises the ethanol produced to ethanoic acid
Advantages of fermentation
• Sugar is a renewable source of • Production uses low level technology/cheap equipment