Synthesis Techniques

In reactions involving volatile liquids to ensure reactants/products do not escape.

• Add anti-bumping granules to a round bottom flask. • Do not stopper the flask. • Attach a condenser vertically to the flask and allow cold water to flow through it. • Heat reaction mixture so that it boils gently, using a heating mantle.

• Add liquid to a separating funnel. • Allow the layers to settle then run off and dispose of the aqueous layer. • IF acidic impurities are present, add sodium hydrogen carbonate and shake well. • IF the crude product is alkali, and needs neutralising, add dilute acid until the mixture is neutral. • Dry the crude product by adding anhydrous sodium sulfate and swirling the mixture. • The pure product can then be separated by distillation.

• Carry out an acid-base titration (with an indicator) to find out how much acid solution is needed to neutralise 25cm³ of the alkaline solution • Transfer 25cm³ of an alkaline solution to a clean conical flask. • Using a biuret add the correct amount of acid to neutralise the alkali (don’t add indicator). • Transfer the neutralised solution to a clean evaporating basin and heat over a bunsen flame to remove the water until crystals begin to form. • Leave the mixture to cool in the evaporating basin • Filter and wash solid with cold distilled water. • Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.

• Warm excess insoluble base in dilute acid until the solution is neutralised. Leave to cool • Filter off excess base and transfer filtrate to a clean, dry evaporating basin to heat until crystals start to appear. • Allow it to cool before filtering the mixture and washing the solid residue in cold distilled water. • Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.

• Add equal volumes of the desired salt solutions in a beaker to form a precipitate of the insoluble salt and filter. • Wash precipitate several times with cold DI water. • Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.

Simple distillation. • Put anti-bumping granules in a pear-shaped flask and set up distillation apparatus (with a thermometer). • Heat the mixture with a bunsen flame (or heating mantel) until it boils gently. • When the vapour is about two degrees lower than the boiling point place a conical flask at the end of the condenser. • Collect until the temperature rises above the boiling point • Repeat if there are more compounds in a clean conical flask.

To purify solid crude organic products with small amounts of impurities.

Recrystallisation: • Select a solvent that your products is soluble in when hot and insoluble when cold. • Dissolve the mixture in the minimum quantity of hot solvent and hot vacuum filter to remove any insoluble impurities. • Leave the filtrate to cool until crystals form and collect via vacuum filtration. • Allow the solid to dry under an inverted filter funnel.

• Connect a conical flask to a vacuum pump via the sidearm and dampen a piece of filter paper in the Buchner funnel. • Switch on the vacuum pump and then carefully pour in the mixture to be filtered. • Disconnect the pump from the flask before turning off the pump to avoid ‘suck back’.