5.4.3 Organic Synthesis

Question 1

What is the purpose of refluxing?

Answer 1

To ensure you don’t lose volatile organic substances.

Question 2

What is the purpose of anti-bumping granules?

Answer 2

To make the boiling of a substance smoother.

Question 3

Why do volatile organic compounds need to be refluxed?

Answer 3

They’ll evaporate or catch fire before they have time to react.

Question 4

How would you set up apparatus for refluxing?

Answer 4

Attach a Liebig condenser to a round bottomed flask. Ensure the water enters the condenser at the bottom.

Question 5

How does the reflux setup work?

Answer 5

It condenses the vapours, recycling them back into the round bottommed flask.

Question 6

Why does water have to enter a Liebig condenser from the bottom?

Answer 6

To ensure the Liebig condenser is full of cold water.

Question 7

Why might you want to “wash” an organic product with sodium hydrogen carbonate solution?

Answer 7

To remove any excess acid.

Question 8

How would you extract the waste product of a reaction from a mixture after washing it with sodium hydrogen carbonate solution.

Answer 8

Use a separating funnel.

Question 9

Explain the process of solvent extraction.

Answer 9

You can separate a product from a mixture by dissolving it in a solvent. Shake the mixture with fresh solvent several times to extract as much product as possible.

Question 10

Give an example of a drying agent.

Answer 10

Anhydrous calcium chloride.

Question 11

When would you “dry” the products of an organic reaction.

Answer 11

When water is produced or used.

Question 12

Explain the process of drying a mixture with anhydrous calcium chloride.

Answer 12

It removes water from the mixture by forming solid crystals which can be filtered off.

Question 13

What does recrystallisation achieve?

Answer 13

It allows you to remove a small amount of impurity in a solid.

Question 14

Outline the process of recrystallisation.

Answer 14

Add very hot solvent to the impure solid until it just dissolves. Cool the solution slowly to form crystals of the product. Remove the solution of impurities by filtration and washing with ice-cold solvent.

Question 15

What must be considered when choosing a solvent for recrystallisation?

Answer 15

The product should be very soluble in hot solvent but nearly insoluble in cold solvent.

Question 16

Why should a minimum amount of hot solvent be added during recrystallisation?

Answer 16

To avoid losing product in the solution and therefore maximise yield.

Question 17

What does melting a boiling point indicate about the purity of products?

Answer 17

If products are impure, melting point is lowered and boiling point is raised. If a product is very impure, melting a boiling will occur across a wide range of temperatures.

Question 18

How would you accurately measure boiling point of a product?

Answer 18

Measure the temperature that the liquid is collected at during distillation.

Question 19

How would you accurately measure melting point?

Answer 19

Place a small amount of the solid in a capillary tube and place it in a beaker of oil with a very sensitive thermometer. Slowly heat and stir until it dissolves and record temperature when it does.

Question 20

What does fractional distillation do?

Answer 20

Separate multiple liquids with different boiling points.

Question 21

Explain the equipment used for fractional distillation.

Answer 21

A round bottomed flask with glass beads in a fractionating column. A Liebig condenser is connected to the column next to a thermometer to measure the temperature at that point.

Question 22

How does fractional distillation work?

Answer 22

As temperature rises, different compounds reach the top of the column, deepening on their boiling point.

Question 23

Give one disadvantage of standard fractional distillation.

Answer 23

The high temperatures may cause a reduct to decompose.

Question 24

Explain the process of steam distillation.

Answer 24

Steam is passed into the mixture to lower the boiling point of the product so that it evaporates at a temperature that doesn’t cause it to decompose.

Question 25

What is Cholesteryl benzoate?

Answer 25

A chemical used in liquid crystal displays, hair colours and cosmetics. It is an ester of cholesterol (alcohol) and benzoin acid. But is prepared from benzoyl chloride.

Question 26

Outline the process of producing cholesteryl benzoate.

Answer 26

Dissolve cholesterol in pyridine (toxic). Add benzoyl chloride, heat in a steam bath for 10 minutes then cool and add methanol. Recrystallise using ethyl ethanoate as the solvent.

Question 27

Outline the process of producing Methyl 3-nitrobenzoate.

Answer 27

Dissolve methyl benzoate in conc sulfuric acid that has been cooled in an ice bath. Add a 50:50 mix of of conc sulfuric and nitric acids dropwise with constant stirring. Keep the temperature below 10ºC with ice. Stir for 15 minutes, pour it over crushed ice in a beaker. When ice has melted, filter crystals and wash with water. Recrystallise with ethanol.

Question 28

What is the functional group of an acid anhydride?

Answer 28

-COOCO-

Question 29

How do you name a compound with more than one prefix?

Answer 29

List them in alphabetical order.

Question 30

What reagents would you use when converting an alcohol into a bromoalkane?

Answer 30

NaBr and H2SO4, reflux.

Question 31

Give an example of chemistry providing an alternative synthesis to natural sources.

Answer 31

Paclitaxel is a cancer drug discovered in the bark of the pacific yew tree, a protected species inhabited by protected birds. Chemists developed a synthesis method using a different yew tree.

Question 32

Give an example of when chemists changed a natural product to improve its qualities or reduce its side effects.

Answer 32

Aspirin was originally salicylic acid, derived from the bark of willow trees, but it caused stomach and mouth irritation. It is now acetylsalicylic acid, which does;t have the side effects.

Question 33

Explain combinatorial chemistry.

Answer 33

Hundreds of similar molecules are made at once by passing various reactants over reagents held on a polymer support. This process is automated and creates a “library” of chemicals.