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Module 4 Chapter 16 (16.1 Practical techniques in organic chemistry…
Module 4
Chapter 16
16.1 Practical techniques in organic chemistry
Preparing
Quick fit apparatus
1) Round bottom or pear shaped flask
2) Reciever
4) Condenser
3) Screw-tap adaptor
5) Still head
Heating under reflux
Equipment
Round-bottom or pear-shaped flask
Condenser
Rubber tubing
Stand and clamp
Heat source
Water bath can be used if the reaction can be carried out under 100°C
Heating mantle can be used so no naked flame- SAFETY
Prep
1)
Add anti bumping granules (so contents boil smoothly)
2)
Apply thin layer of grease to the ground-glass joint
3)
Place condenser into the flask and gently rotate the condenser to get a good seal
Clamp condenser loosely as outer glass is fragile so can break
Don't put a stopper in- cause build up of pressure and apparatus could explode
Water enters condenser at bottom and leaves at top to ensure outer jacket is full
Reflux means a liquid can be continually boiled whilst a reaction takes place - prevents volatile components from escaping
Distillation
Used to separate a pure liquid from its impurities
Apparatus
Round-bottom or pear-shaped flask
Condenser
Rubber tubing
Heat source
Stand and clamp
Screw-cap adaptor
Reciever adaptor
Still head
Thermometer
Flask clamped by its neck and still head connected to the flask
Still head adaptor is T shaped (2 ground-glass joints)- 1 for screw-cap adaptor and 1 for condenser- grease joints so they come apart easily
Clamp the receiver adaptor at the point it's attached to the condenser
Condenser
- water in at lowest point
Flask used to collect the distillate- not completely airtight
Liquid with lowest boiling point will evaporate 1st (most volatile). When it reaches the condenser it condenses into a liquid- drips into collecting flask
Purifying
2 layers will form
To tell them apart add some water- the layer that gets bigger is the aqueous layer
Steps
1)
Ensure tap of separating funnel is closed
2)
Pour mixture in separating funnel- place stopper
3)
Allow layers to settles
4)
Add water to see which is the aqueous layer
5)
Place conical flask under separating funnel, remove stopper and run off lower layer
6)
Place a second conical flask under and collect other layer
If it contains acid impurities add Na2CO3 and shake- releases CO2, open tap and hold separating funnel upside down to release gas pressure- remove aqueous sodium carbonate laer and wash organic layer with water beore running both layers off into different conical flasks
Drying
May be water left in the organic product
Remove water by adding a drying agent
Drying agent
- anhydrous inorganic salt that readily takes up water to become hydrated
Example
- Anhydrous Calcium Chloride
(CaCl2)
- drying hydrocarbons
Anhydrous Calcium Sulfate
(CaSO4)
- General drying
Anhydrous Magnesium Sylfate
(MgSO4)
- General drying
Steps
1)
Add organic liquid to a conical flask
2)
Using a spatula add some drying agent and swirl
3)
Place stopper in flask to prevent product escaping- leave for 10mins
4)
If the solid has stuck together in a lump there is still water present- add more drying agent until some solid is dispersed in the solution as a fine powder
5)
Decant liquid into another flask to remove from solid
Redistillation
If boiling points are relatively close together then prepared sample may still contain impurities
Clean, dry and set up distillation apparatus and redistillate
Only collect product with the boiling point of the compound you're trying to make
Narrower boiling range = purer product
16.2 Synthetic routes
Chemists can make new structures that can be investigated
Identifying functional groups
By identifying functional groups of a property you can predict the properties of it based on the functional groups
Target molecules
Used to describe the compound chemists are trying to prepare by organic synthesis
Two-stage synthesis
1)
Identify functional groups in starting and target molecules
2)
Identify the intermediate that links starting and target
3)
State the reagents and conditions for each step
EXAMPLE 1
EXAMPLE 2