Alcohols Flashcards
What is dehydration?
By removing water from an alcohol, it produces an alkene. This is dehydration
What are the alkenes produced from dehydration used for?
Making polymers, which can be used to make plastics
What does a dehydration reaction require?
An alcohol and an acid catalyst e.g. sulfuric or phosphoric
Mechanism used:
Elimination mechanism
What occurs in the elimination mechanism?
- Lone pair on oxygen molecule in alcohol group attaches to H+ from acid catalyst
- Oxygen molecule now positively charged
- Water molecule released, carbon connected to alcohol group now positively charged (carbocation)
- Carbocation loses a H+ molecule and forms a C=C
- H+ lost is regenerated catalyst
How does hydration of non-primary alcohols differ?
The C=C bond can be formed either side of the C previously attached to the
-OH group
How is dehydration carried out?
Distillation
Making cyclohexene (step 1) - Distillation
- Add sulfuric acid, phosphoric acid, and cyclohexanol to round bottomed flask (anti-bumping granules can be added)
- Warm reactants to 83 degrees
- Chemicals with boiling point less than 83 evaporate into condenser, cool into liquid and run into beaker in ice bath
Making cyclohexene (step 2) - Separation
- Add products from distillation into separating funnel
- Add water to dissolve soluble impurities
- Leave to settle
- Top layer is impure cyclohexene, bottom layer contains soluble impurities (drain this off)
Making cyclohexene (step 3) - Purification
- Take impure cyclohexene from separation and add to round bottomed flask
- Add anhydrous CaCl2 which will remove any aqueous substances
- Invert flask and leave to sit
How are alcohols produced?
By the hydration of alkenes
What is used in hydration of alkenes?
Steam and an acid catalyst. 300 degrees and 60 atm also required
Hydration mechanism
- Double bond forms bond with H+ from catalyst
- Carbocation formed
- Lone pair of electrons from oxygen molecules bonds to carbocation
- Oxygen on water becomes positively charged
- H+ lost (catalyst regenerated)
Fermentation
- Uses yeast in anaerobic conditions
- Exothermic process
- Fractional distillation used to obtain pure ethanol
- Requires little equipment, renewable
- Fractional distillation costly and takes long
- Slow, small yield
Biofuels
- Renewable
- Carbon neutral
- Expensive to convert engines to function with biofuels
- Land used to grow food taken over
Carbon neutral
When ethanol burned, carbon dioxide produced. This carbon dioxide is used in photosynthesis of growing plants. Amount of carbon dioxide produced and used up is the same. However, to transport the fuels, fossil fuels used
What can alcohols be oxidised to?
Ketones, carboxylic acids, and aldehydes
What is used to oxidise alcohols?
Potassium dichromate. Changes orange to green if oxidation occurs
What equipment can be used to oxidise alcohols?
Distillation and reflux
What is used when a primary alcohol is being oxidised to an aldehyde?
Distillation and oxidising agent
What is used when an aldehyde is being oxidised to a carboxylic acid?
Reflux and excess oxidising agent
What is used when a secondary alcohol is oxidised to a ketone?
Reflux and oxidising agent
How can you distinguish between aldehydes and ketones?
Fehling’s and Tollens’ (both oxidising agents so oxidise aldehydes, not ketones)
Fehling’s solution
- Blue solution
- Add warm to aldehydes turns brick red
- Add warm to ketones remains blue
