Preparation of aspirin

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Andre Van stone
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#1
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Why is it important to use warm, not hot nor cold, ethanol-water mixture in the recrystallization of aspirin?
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iElvendork
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Too cold - byproduct of acetic acid will solidify and affect the purity
Too hot - bad for the ethanol
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Andre Van stone
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(Original post by iElvendork)
Too cold - byproduct of acetic acid will solidify and affect the purity
Too hot - bad for the ethanol
Thank you so much for replying, but can you please explain more? I am sorry but I am not so good with chemistry as I am an engineering student and that is for a uni course I have to take.
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iElvendork
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(Original post by Andre Van stone)
Thank you so much for replying, but can you please explain more? I am sorry but I am not so good with chemistry as I am an engineering student and that is for a uni course I have to take.
So the point of recrystallisation is to isolate the one product and get nice crystals, and you do that by choosing a solvent system, so in this case ethanol and water. Ethanol dissolves the impurities, and the product 'crashes out' in the water - filter off and get the nice product
However, if the ethanol/water is too cold, one of the byproducts - acetic acid - who's melting point is about 10*C could solidify in the solution, get filtered off with the product and ruin purity. On the other hand, if the ethanol/water is too hot, you'll start to boil off the ethanol and the impurities won't be fully dissolved and could affect the purity of the product, also if you don't have a fumehood to do this in, boiling off ethanol isn't a nice process
So you comprise with a warm solution - get good dissolving of impurities, product crashes out and nobody has to inhale ethanol
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Andre Van stone
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(Original post by iElvendork)
So the point of recrystallisation is to isolate the one product and get nice crystals, and you do that by choosing a solvent system, so in this case ethanol and water. Ethanol dissolves the impurities, and the product 'crashes out' in the water - filter off and get the nice product
However, if the ethanol/water is too cold, one of the byproducts - acetic acid - who's melting point is about 10*C could solidify in the solution, get filtered off with the product and ruin purity. On the other hand, if the ethanol/water is too hot, you'll start to boil off the ethanol and the impurities won't be fully dissolved and could affect the purity of the product, also if you don't have a fumehood to do this in, boiling off ethanol isn't a nice process
So you comprise with a warm solution - get good dissolving of impurities, product crashes out and nobody has to inhale ethanol
thank you a million times again and sorry for my confusion
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iElvendork
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(Original post by Andre Van stone)
thank you a million times again and sorry for my confusion
You're welcome, I always forget people aren't as well versed in recrystallisation as I am
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