Transcript Slide 1
Experiment 15 A: Isolation of Pure Aspirin From Aspirin Tablets B: TLC of a Dye Mixture Objectives Isolation of a pure component from a commercial tablet To become familiar with the technique of thin-layer chromatography To separate a dye mixture into its constituent components Introduction – 15A Commercial pharmaceutical tablets contain a variety of components Drug molecule Binders Flavours Colours Co-administered drug molecules Experimental Weigh one tablet of aspirin Grind and transfer to a 50 ml flask Add 20 ml of acetone and heat Filter off the insoluble binding material Evaporate to dryness Record the weight of crude aspirin Experimental Crude aspirin is recrystallized from water Dissolve in 3-4 ml of boiling water Allow to cool and crystallize Isolate the crystals Allow to dry, get weight and mp Introduction – 15B Thin Layer Chromatography Common separation technique Separation based on polarity Qualitative analysis Used to test purity, reaction completion, decomposition Introduction TLC plate – sheet of metal covered in a thin layer of silica Silica is polar – polar compounds have a greater affinity for silica Solvent allowed to travel up the plate Compounds with a higher affinity for the solvent will travel further up the plate Introduction Choice of solvent is important Affects distance travelled by spots Affects separation of spots Common solvent systems include mixtures of Ethyl Acetate/Hexane and Dichloromethane/Methanol Large scale – purification by column chromatography Rf values Rf value of a spot is the distance travelled by the spot over the distance travelled by the solvent front Rf depends on solvent system dX Rf ds Thin Layer Chromatography Rf = 0.74 Rf = 0.74 Rf = 0.53 Rf = 0.52 Rf = 0.16 Rf = 0.16 Viewing TLC plates Spots not always visible – can be colourless Can be viewed under UV light Developed using iodine to stain spots Other dyes/stains – vanillin, ninhydrin O HO O O O vanillin O ninhydrin Viewing plates Experimental Use a capillary spotter to spot the dye mixture on a TLC plate Insert slide into a jar for development Solvent level must be below the spot level – otherwise spots dissolve Allow solvent front to rise close to top, remove plate, mark the solvent front Experimental Using pencil, circle all the spots Calculate the Rf values for each colour spot in the dye mixture Develop the TLC plate in both toluene and ether – solvent affects the distance travelled and separation Keep toluene and ether in the fumehood at all times Report Record the distance travelled and Rf value for each colour component in both the solvents used Comment on the relative solubilities of the colour components in the two solvents used Brief discussion on TLC