OCR A Level Chemistry 4.2.3.1 Organic Synthesis - Practical Skills, OCR A Level Chemistry 4.2.3.2 Organic Synthesis - Synthetic Routes

Why is it common for organic reactions to be heated?

Overcome the activation energy and increase the rate of reaction

What is the purpose of heating under reflux?

•Prepare an organic liquid without boiling off the solvent, reactants and products

•Ensures that the reaction reaches completion

What is the equipment required for heating under reflux?

•Round bottom or pear-shaped flask

•Condenser

•Rubber tubing

•Stand and clamp

•Heat source (usually a bunsen burner, tripod and gauze)

•Anti-bumping granules

What is the purpose of anti-bumping granules?

Added to the liquid to ensure that the contents boil smoothly; otherwise, large bubbles form and make the glassware vibrate or jump

What position is the condenser in during reflux?

Upright position

State and explain where the rubber tubing connects to the condenser

Cold water enters the condenser through the bottom for more efficient cooling and to ensure that the outer jacket is full

Explain why a stopper should never be inserted into the top of a condenser during reflux

It forms a closed system and pressure would build up inside as the heated air expands, causing the condenser to explode

What is the purpose of distillation?

•Separate pure liquid from impurities with different boiling points

•(Prevent complete oxidation of a primary alcohol and to separate the aldehyde formed)

What is the equipment needed for distillation?

•Round bottom or pear-shaped flask

•Condenser

•Rubber tubing

•Heat source

•Stand and clamp

•Screw-cap adaptor

•Receiver adaptor

•Still head

•Thermometer

What position is the condenser in during distillation?

Horizontal position

What is used to collect the distillate?

A flask

Which liquid boils first during distillation?

The most volatile (one with the lowest boiling point)

What is the function of a separating funnel?

Separate immiscible liquids

How would you use a separating funnel?

•Add the liquid

•Place a stopper

•Allow layers to settle

•Run off each layer through the tap

How would you remove acid impurities from some impure product?

Adding aqueous sodium carbonate and shaking the mixture in the separating funnel

How would you remove small traces of water from the organic product?

Adding a drying agent

Give examples of drying agents

CaCl₂, CaSO₄, MgSO₄

How would you dry the organic product?

•Add organic liquid to conical flask

•Add some drying agent and swirl

•Keep adding until some solid is dispersed as a fine powder

•Decant into another flask

After distillation, purification and drying, what else can be done to ensure the sample is pure?

Redistillation

Why might redistillation be necessary?

Some organic liquids might have boiling points that are relatively close to each other so there may still be impurities

What is meant by the term target molecule?

The compound that you are trying to prepare by organic synthesis

What is needed for a two stage syntehsis?

•Identify the functional groups in your starting and target molecules

•Identify the intermediate that links the starting and target molecules

•State the reagents and conditions for each step

How can you predict the properties and reactions of an organic molecule?

By its different functional groups