Chapter 16 - Organic Synthesis

Question 1

What are the 3 steps for synthesising organic liquids

Answer 1

Preparation
Extraction
Purification

Question 2

Explain preparation

Answer 2

It’s combining all the reagents under required conditions to produce the desired products.
You may need a heat source for this (water bath, heating mantle, bunsen burner)

Question 3

When to use a Bunsen Burner to prepare

Answer 3

When the reaction requires temperature more than 100 degrees.
There are no flammable reagents.

Question 4

When to use a Heating Mantle to prepare

Answer 4

When the reaction require temperatures more than 100 degrees.
There may be flammable reagents.

Question 5

When to use a Water bath to prepare

Answer 5

When the reaction requires temperatures less than 100 degrees.
It doesn’t matter if there are any flammable reagents.

Question 6

When to reflux to prepare

Answer 6

When reaction at RTP is too slow.
Advantages of Reflux?
It doesn’t boil away the reactants.
It increases the rate of the reaction, by overcoming the activation energies and the heat source depends on the substances.

Question 7

When to distil to prepare

Answer 7

When there is a liquid organic product that needs to be separated from the reaction mixture as it’s being produced. It also requires a condensor to separate the liquid organic product.

Question 8

What are the 2 ways to extract?

Answer 8

Distillation

Separating funnel

Question 9

Distil to extract?

Answer 9

1. Liquid organic product is miscible in reaction mixture.
2. Has a boiling point that is significantly different from any other substances in the reaction mixture.
3. The product has the lower b.p and it evaporates out of the mixture first.
4. Then it enters the condensor and cools down.
5. It leaves via the receiver.
6. A thermometer will be needed.
7. Once bubbling has stopped and the temperature has increased again, then you know you have collected all your product.

Question 10

Separating funnel to extract

Answer 10

Only when the liquid organic product is immiscible in the reaction mixture.
Ensure that:
- The tap is closed
- Pour in reaction mixture
- Allow time for the substances to settle
- Into 2 different layers
- Place a flask under the separating funnel.
- Open the tap (of the funnel)
- Decant the bottom layer.

Question 11

What are the 2 layers that should be formed in the separating funnel?

Answer 11

1. Organic (insoluble in water)
2. Aqueous (Water and other dissolved substances)

It’s based on densities.

Question 12

What test many need to be done in the separating funnel?

Answer 12

An aqueous test.
Because it is colourless, transparent and liquid.
TEST:
1. Close the tap
2. Add deionised water to the mixture.
3. The layer that increases in volume is the aqueous layer (as the water can dissolve only in the aqueous layer)

Question 13

What does purification do

Answer 13

Removes traces of unwanted substances:
Acid 
Water
Aqueous salts 
Organic later / extracted liquid

Question 14

What is in a usual reaction mixture whilst refluxing

Answer 14

Reactants (unreacted)
Catalyst 
Anti-bumping granules
Water 
Indicator 
Products (desired)
Products (undesired)
By products 
Catalysts (dissolved)

Question 15

What is the first thing you should do whilst purifying

Answer 15

1. Remove solids by decant.

Repeat it by adding distilled water again and again and remove all the solids.

Question 16

What is the second thing you should do whilst purifying

Answer 16

2. Remove all the (aq) impurities
   By using a separating funnel. You can use some distilled water for this.

Continue decanting. Or you can let the mixture settle and separate properly.

Question 17

What is the third thing you should do whilst purifying

Answer 17

Remove the Acid.
Add some NaCO3.
Shake the funnel and open in every now and then to allow the gases out.
Continue until all the fizzing stops.
The acid is turned into NaX salt, H20 or CO2.

Question 18

What is the fifth thing you should do whilst purifying

Answer 18

Decant again, giving you small traces of H20 and another aqueous impurity.
Transfer this solution to a beaker.

Question 19

What is the sixth thing you should do whilst purifying

Answer 19

Use a drying agent like MgSO4. It forms a colourless bubble which has the H20 and the drying agent. The organic layer should be left in the solution.
To separate from the bubble, decant by pouring into another beaker.

Question 20

What is the last thing you should do whilst purifying

Answer 20

Then, you should have a liquid with the products and another aqueous impurity. To separate them, perform fractional distillation.