Topic 18.3 - Organic Synthesis Flashcards
Describe the set up for heating under reflux
- Vertical condenser, water in through the bottom and water out through the top
- Pear shaped flask joined - need to show this apparatus separate from the condenser
- Anti-bumping granules in the flask
What is heating under reflux?
The continuous heating of chemicals due to chemicals evaporating and then condensing and dripping back down into the reaction mixture
When is heating under reflux required?
If your reactant is volatile as otherwise it would evaporate before taking part in the reaction
What is the purpose of anti-bumping granules in heating under reflux
Provide a nucleation point for small bubbles to form on preventing the formation of large bubbles and encouraging smooth boiling
Describe the set up of simple distillation
- Condenser vertical and angled down, water in at further point from heat and water out at closer point
- Pear shaped flask attached to the condenser on the RHS ensuring that it is open
- Need to show the still head connections in this apparatus showing that each piece of equipment is separate
- LHS is your flask with anti-bumping granules in it, above is a tube that connects the flask to the condenser
- Thermometer placed at the height that the gas will be condensed into the condenser
Why must the reflux set up and distilling set up not be fully sealed?
To avoid pressure build up due to gas that does not condense -> glass could shatter
Why must water enter from the bottom and exit from the top in condensers?
- To prevent air pockets forming in the condenser
- This allows for the water to completely fill the condenser which will maximise the efficiency of cooling your product -> maximise your yield
Why do you need the thermometer to be placed at the specific height in simple distillation?
So that it is measuring the temperature at which your distillate is being collected (if it was too low the temperature that the distillate was being collected would appear to be higher that it was)
Why do you need to use petroleum between the still heads in your simple distillation apparatus?
To ensure that no gaseous product escapes
When is simple distillation used?
When mixtures contain only one volatile component
When is fractional distillation used?
When you have mixtures of more than one volatile liquid
Definition of miscible?
Capable of being mixed - capable of forming a homogeneous mixture that neither separates nor is altered by chemical interaction
Definition of immiscible?
Not capable of being mixed
When is steam distillation used?
When you have a liquid with a high boiling point that is immiscible with water
What is an advantage of steam distillation?
Steam distillation allows you to distill an organic compound at a temperature well below its boiling point, as the mixture of the immiscible liquid and water has a boiling point below 100 degrees ALWAYS. This reduces the chance of the organic compound decomposing on heating.
Describe briefly the set up of steam distillation and how its works
Steam distillation works by passing steam through your organic liquid. When the hot steam passes through the mixture (mixture of organic compound and water/other inorganic compounds) it condenses releasing heat energy which provides enough to boil the organic liquid.
- The water is boiled in a separate flask and the steam produced is passed through tubing to the flask with the organic liquid in it
- The flask with the organic liquid in it is connected to a condenser that is in the normal set up and collects your organic distillate and also some water
Describe the set up for suction filtration?
- Buchner flask which has a side arm (draw an arrow coming out saying to pump)
- A buchner funnel rests on top of the buchner flask
- Inside the buchner funnel you draw filter paper which is a line across and then dashed lines below
- A bung is used as a stopper on the openeing of the buchner flask
Why do we use suction filtration?
- Much quicker method of obtaining a dry product
- You end up with a drier solid in the end
What is suction filtration also known as?
Filtering under reduced pressure
Why would 2 compounds be immiscible?
If the bonds formed between the molecules of one compound are stronger than the bonds that would form between the two compounds
Describe the set up for separating 2 immiscible liquids
- Separating funnel (balloon shaped) with a tap at the bottom
- The more dense liquid is below the less dense liquid
Why is recrystallisation used?
IN order to purify our organic product - this process removes impurities from our organic product
What is one example of when recrystallisation is used?
2,4 - DNPH testing for different C=O groups in aldehydes and ketones
State the 5 stages of the recrystallisation process
- The impure solid is dissolved int he minimum volume of hot solvent - the solvent is chosen so that the impure solid dissolves well at a high temperature but has low solubility at a low temperature.
- Filter the mixture rapidly through fluted paper - HOT FILTRATION
- Cool the filtrate in an ice bath so that the solid(pure) crystallises out of solution - COLD FILTRATION
- Wash the crystals with the minimum amount of cold water
- Filter under reduced pressure, then allow the solid to dry
In recrystallisation why do you dissolve the impure solid in the minimum volume of hot solvent?
As this will result in you getting the maximum yield of your pure product in the end
In recrystallisation why is the hot filtration step performed?
Removes the insoluble impurities + anti-bumping granules from your solution
In recrystallisation why is the cold filtration step performed?
Separates soluble impurities from your pure product as the impurities remain in solution - solubility of your pure solid decreases as it is cooled hence why it crystallises out of solution
When purifying your solid why are crystals rinsed with ice cold water/ethanol?
Rinsing - removes any soluble impurities or reactant that were in excess
Ice cold water/ethanol - minimises the crystals formed from redissolving
