- Pha 112 Bio Organic Medicinal Chemistry Experiment 4 Oxidation Of Benzyl Alcohol To Benzoic Acid Significance To Pha 1 (48.24 KiB) Viewed 93 times
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Potassium permanganate is an oxidising agent and may cause burns. Safety glasses and laboratory coats must be worn at all times METHOD 1. Place 4.2 g potassium permanganate (0.027 mole) in a 250 mL conical flask and add 60 ml water. Warm the solution to dissolve all the permanganate, then cool to about 30 °C 2. Add 2.0 mL benzyl alcohol (2.1 g. 0.02 mole) and swirl the mixture. Note that the solution becomes hotter due to the exothermic reaction and that the odour of benzaldehyde becomes apparent. Continue swirling the flask and note the highest temperature reached by the solution. After about 5 minutes, the smell of benzaldehyde should have diminished. It does not entirely disappear. 3. In a fume cupboard, add 20 ml water and 6 mL of 50% sulfuric acid (0.054 mole, about 50% excess), then add 25 mL 20% sodium sulfite solution (0.04 mole anhydrous, 50% excess) slowly while swirling the flask. The manganese dioxide (MnO2) should all dissolve, leaving a colourless solution and a white solid. 4. If the solution is not colourless, test with indicator to determine if the solution is acidic and if not, add a small quantity of acid. If the solution is acidic but not colourless, add further small amounts of sodium sulfite solution swirling all the while. 5. Filter off the benzoic acid at the vacuum pump and wash with a little cold water. Recrystallise the benzoic acid using a minimum amount of hot water as the solvent. If solid impurity is present, perform a hot filtration as follows. Put a fluted filter paper onto a clean glass funnel over a 100 mL conical flask and place the set up onto the hotplate. Pipette a small amount of hot water via the filter paper into the flask and allow this set up to be heated on the hotplate. Pour carefully the hot solution of your product containing the solid impurity through the filter paper into this fiask. When the hot solution has been filtered, remove the flask from the hotplate and allow to cool slowly. Once the crystals appear, place the
flask in an ice bath to complete crystallisation, and then collect the purified product by vacuum filtration. 6. Dry the purified solid and determine the yield. Determine the melting point of the dried benzoic acid synthesised in this exercise. Submit the product in a labelled sample bag to the demonstrator.
REAGENT Mol. QUANTITY USED Theoretical Ratio USED Weight mL d g mol Mole Ratio Used Yield: 11 g mole Theoretical Yield: g ..... mole % Yield:
Observed Value Literature Value Reference Physical Property Melting Point