M6 Organic Synthesis Q&A
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An organic liquid was prepared using a given reaction (e.g. a haloalkane from an alcohol). Describe the method you would use to obtain a pure sample of the organic liquid from the reaction mixture.
• (If there are acidic impurities, add neutralising agent e.g. sodium carbonate Na2CO3) • Use a separating funnel to separate the organic (usually top) layer from the aqueous (usually bottom) layer (refer to density data if given in the Q) • Dry with an anhydrous salt (e.g. MgSO4) to the organic liquid to act as a drying agent and remove any remaining water. Add until the salt swirls freely and filter to remove solid salt. • (Re)Distil the remaining liquid and (refer to boiling point data if given in the Q) collect the fraction at this temperature (state the temperature) to obtain the pure, dry liquid.
An organic solid was prepared using a given reaction (e.g. aspirin). Describe the method you would use to obtain a pure sample of the organic solid from the reaction mixture.
• Filter off the impure solid (under reduced pressure) • Recrystallise the solid by dissolving in the minimum volume of hot solvent • Allow to cool in an ice bath (the pure solid crystals recrystallise from the solution) and then filter off the pure solid (under reduced pressure) • Wash the crystals with cold solvent and allow to dry. • The purity of the solid may be tested using melting point determination and / or thin layer chromatography.