4.2.3 Organic Synthesis Practical Skills

Quickfit apparatus connection

Grease the joints using some petroleum jelly on the inside of the joints before connecting the pieces together.

Continuous water flow in distillation

So that the water remains cool in order for the mixture to be distilled.

Method to separate immiscible liquids

Pour the mixture into a separating funnel and some distilled water, add the stopper and invert the flask to mix the mixture, equalise the pressure by opening the stopper as required, continue shaking until there is no 'whistle' sound, to collect the water in the lower layer, open the stopper and place a beaker under the spout, use another beaker to collect the desired organic layer, shake the liquid with some drying agent.

Drying agents

Magnesium sulphate, Calcium chloride.

How to use drying agents

Add a selected drying agent to the organic product, if the drying agent forms clumps add some more until they are moving freely, use gravity filtration to collect the dry product. Filtrate is the product.

Re-distillation

When a liquid is purified by using multiple distillations.

Testing unsaturated hydrocarbons

Use bromine water, add few drops of bromine water to the sample and mix well. Positive test - bromine water turns colourless.

Reagents to test haloalkanes

Reagents - silver nitrate, ethanol and water. Observations - chloro- : white precipitate, Bromo- : cream precipitate, iodo- : yellow precipitate.

Reagents to test carbonyls

Acidified potassium dichromate, Fehling's solution, Tollens' reagent.

Observations with acidified potassium dichromate

Ketones - no change, Aldehyde - turns from orange to green colour.

Observations with Fehling's solution

Ketones - no change, Aldehyde - dark red precipitate.

Observations with Tollens' reagent

Ketones - no silver mirror, Aldehydes - silver mirror.

Reagents to test carboxylic acid

Universal indicator - pH of weak acid, Reactive metal - hydrogen effervescence, Metal carbonate - carbon dioxide effervescence.