4.3.2 - Organic Synthesis Flashcards
When do you use reflux?
For organic conditions which might catch fire or evaporate before they have time to react.
What is the name of the condenser and what does it do?
Liebig condenser and it continuously boils, evaporates and condenses the vapour and recycles them back into the flask, giving them time to react.
What is the heating in reflux and why is it used?
Electric, e.g electrically controlled water baths, as this avoids naked flames that might ignite the compound.
What and why is also added to reflux?
Anti-bumping granules that make boiling smoother.
How do the substances evaporate in distillation?
In order of increasing boiling point.
What is the purpose of the thermometer?
Shows the boiling point of the substance that is evaporating at any given time. Can also be used if you know the boiling point of the pure product, as you can tell when it is evaporating and therefore when it is condensing.
How can distillation be used be used if the product of the reaction has a lower boiling point than the starting materials?
Then the reaction mixture can be heated so that the product evaporates from the reaction mixture as it forms.
What happens when you oxidise a primary alcohol?
It is first oxidised to an aldehyde and then to a carboxylic acid.
If you oxidise a primary alcohol how can you get the aldehyde?
Do the reaction in the distillation equipment as the aldehyde has a lower boiling point than the alcohol starting material. Therefore we can distil out the reaction mixture as soon as it forms.
If a product and its impurities have different boiling points how can we separate them?
Redistillation
How does redistillation work?
Use the same distillation apparatus but this time you’re heating an impure product. When the liquid you want boils you place a flask at the open end of the condenser to collect the product.
When can you use separation?
If the product is insoluble in water you can use separation to remove any impurities that do dissolve in water, such as salts or water soluble organic compounds.
How does separation work?
Once the reaction is complete, the mixture is poured into a separating funnel and water is added. The funnel is then shaken and allowed to settle. The organic layer is less dense than the aqueous so will float on top.
How do you remove the aqueous layer from the organic layer in separation?
Open the stopper on the separating funnel and run off the aqueous layer.
What happens if you use separation to purify a product?
The organic layer will end up containing trace amounts of water which need to be dried.
