16- Synthesis of Aspirin Flashcards
Describe the method of making Aspirin from 2-Hydroxybenzoic Acid - CP16
1- weight out 2-Hydroxybenzoic acid in pear shaped flash + add Anti-bumping granules
2- In fume cupboard + wearing gloves add ethanoic Anhydride to flask = add few drops of conc H2SO4
3- Set up reflux
4- Heat gently with water bath + sweetly until all 2-Hydroxybenzoic acid has dissolved = heat for further 10 mins then remove
5- Stand products in beaker of crushed Ice + deionise water = allow crystals to form
6- Filter product under pressure with Büchner Funnel + Filter paper = Rinse with min vol of Deionised water to maximise yield
7- Transfer to conical flask + Re-Dissolve crystals in Min Vol of Hot Ethanol/Solvent
8- Filter a 2nd time = using clean Büchner funnel
9- Pat dry with filter paper + leave to dry = record mass recorded
Why is water bath preferable when heating under reflux
Controlled heating of reaction + Bunsen burner risk due to flammable Ethanol
Why is water added at the end of the reflux in CP16 when making the aspirin
Hydrolysis any unreacted Ethanoic Anhydride
Why is the products of the reflux left to stand in a beaker of iced water when making Aspirin in CP16
Causes precipitation of desired product
Insoluble at Low temp = soluble impurities do not precipitate allowing them to be separated when filtered under suction
What is the point of the first and second filtration under pressure when trying to make the aspirin pure
1st = collects the product + insoluble impurities
2nd = Collects pure product and previous insoluble impurities are soluble in ethanol and so can be removed in filtration
Why might you grease the joints when heating under reflux
Ensure seal has been made = not excess greasing as may cause contamination
Describe how to find the melting point of the sample of Aspirin produced in previous step of CP16
1- seal the end of a Capillary tube using Bunsen burner
2- place a small amount of sample in bottom of sealed tube + tap gently to ensure it goes to bottom
3- Place capillary tube + Thermometer in Apparatus shown below
4- Heat until around 90-100•C = reduce heat + heat slowly until all crystals/Sample melts
5- Record Temp range when sample starts to Melt-Fully melted + compare to data book
What will the temp range be like if the sample of Aspirin is very pure
MP range will be small + similar to value in data book
What will Melting point be like of sample of Aspirin is Impure
MP will be lower than expected + sample will melt over a range of •C due to impurities having different melting points
Describe what actually happens when mixing the 2-Hydroxybenzoic acid + Acid Anhydide
-OH group in 2-Hydroxybenzoic acid reacts with Acid Anhydride
Forms Aspirin via ester Linkage
Diagram of apparatus used to measure melting point of Aspirin
Equation for Percentage Yield
Actual/Expected x100
1- mass of dry crystals = actual
2- calculate Mr of Benzoic acid = then Calculate moles
3- Work out Mass of Aspirin produced
4- then work out percentage yeild with calculated values
