16 - Organic Synthesis Flashcards
When do we use distillation
there are times that a reaction does not go to completion or there are other chemicals produced as well as the desired product
Which compound will distill first
lowest boiling point will distil first
When do we use distillation - example
produce an aldehyde from a primary alcohol
Distillation process - producing an aldehyde
- primary alcohol + acidified potassium dichromate solution is placed into a pear-shaped or round bottomed flask
- Anti-bumping granules are added
- Quickfit apparatus is then set up, including a still head and condenser connected to the side
- thermometer can be used, with the thermometer bulb sitting where the vapours will pass into the condenser
- A steady and constant stream of water passes through the condenser in = enters at the bottom of the condenser and the drainage pipe removes the water from the top of the condenser
- The reaction mixture is heated until it boils using a heating mantle
- The distillate which forms in the condenser drips directly into a receiving vessel
Why do we use anti bumping granules
to promote smooth boiling
Why are the joints of the apparatus often have thin layer of silicon grease on
to give a better seal as well as to make it easier to disassemble the equipment afterwards
Why do we use electrical heating mantles
temperature can be controlled, and because you are using chemicals which are flammable
Advantages of heating under reflux
• allows the mixture to react as fully as possible without the loss of any reactants, products or solvent
Reflux process
• reaction mixture is placed into a pear-shaped or round bottomed flask
• Anti-bumping granules are added
• The flask is placed in a heating mantle or it can be immersed in a water bath for heating
• Quickfit apparatus is then set up with the condenser clamped vertically in place
• A steady and constant stream of water passes through the condenser
• The water is heated and the reaction mixture allowed to boil
• The heated is stopped and the mixture allowed to cool back to room temperature
Why do we heat reactions?
To overcome activation energy/increase rate of reaction
What is the advantage of heating under reflux?
Enables liquid to be continuously heated, prevents volatile components evaporating and the flask boiling dry.
Advantages of ant bumping granules
Ensures contents boil smoothly
• Prevents large bubbles forming and thus prevents the glass from bumping violently
3 steps to purify organic solvents
• Separating funnel
• Drying agents
• Redistill
If a substance needs to be neutralised before purified what should we do
adding sodium carbonate solution to the reaction vessel or separating funnel
How to tell which layers which in the separating funnel
adding water and seeing which layer increases in volume
Method for separating funnel
- Ensure that the tap is closed
- Pour mixture into the funnel, place a stopper in top, invert + mix contents.
- Allow the layer to settle
- Add some water – the layer that increases is the aqueous layer.
- Place a conical flask under the separating funnel, remove the stopper, open the tap until the whole of the lower layer has left the funnel.
- Collect the second layer into a different conical flask
Method for removing acid impurities
• Add aqueous sodium carbonate and shake in funnel
• Hold upside down
• Any acid will react with sodium carbonate, releasing carbon dioxide
- Slowly open tap to release gas
Purpose of drying agents
• May be water left in the product
• Removed by adding a drying agent
What are drying agents
• Anhydrous inorganic salt
Examples of drying agents
• Anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous magnesium sulfate.
Process of using drying agent
spatula of drying agent is added into the organic product and swirled
Why would we add a lid when using drying agents
• If the organic product has a low boiling point, a lid / stopped can be added to reduce the potential evaporation of any product
What happens if the drying agent clumps together r
then there is still water in the organic liquid
When do we stop adding drying agent
until some remains dispersed in the organic liquid as a fine powder
