Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: johnj7 on February 12, 2008, 01:17:43 AM
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Hello, i'm struggling with another extraction problem
The problem states:
"Data for solubility for 1 g of aspirin or salicylic acid:
Aspirin - 300 mL of H20, 17 mL of chloroform, 12 mL of ethyl ether
Salicylic acid - 460 mL of H20, 42 mL of chloroform, 3 mL of ethyl ether.
If you had a mixture of equal weights of aspirin and salicyclic acid, which solvent pair (ether-water) or (chloroform-water) would give the most efficient extraction. Why?"
I orginally thought that the answer was ether-water. I first calculated the partition coefficients for each solvent pair. Then I saw that the ether-water partition coefficients were larger, and so thought that ether-water would give the most efficient extraction.
However, the answer states: "Chloroform-water. Neither will be very good because both aspirin and salicylic acid will largely extract into the organic phases in all cases. However, the chloroform-water system elaves mroe in the aqueous phase and thus allows a better separation. A different means of purifying the compounds is needed."
Could someone help me out/help understand what's going on?
Thanks
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Or you could just convert the salicylic acid into aspirin with acetic anhydride and potassium carbonate. Then could recrystallize pure aspirin. :P
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Dear Johnj7;
Let’s give you the results first:
In this particular case, your decision from your stomach is: Right!
In this particular case, the other argumentation is completely: Wrong!
In this particular case, your own argumentation is also: Wrong!
How would you define “Efficiency” for such an Extraction?
Hint: Which Phase would you collect?
Recipe for visualisation:
With your new definition in mind, put 10.0 g ASA and 10.0 g SA together, and extract/calculate the Extraction following: "Solubility Problem (Extraction!) (http://www.chemicalforums.com/index.php?topic=23713.msg90149#msg90149)”, – and be surprised!
Good Luck!
ARGOS++
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Or you could just convert the salicylic acid into aspirin with acetic anhydride and potassium carbonate. Then could recrystallize pure aspirin. :P
How is this a separation?
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Dear Agrobert;
How true!, – Maybe a young “Colt”.
Good Luck!
ARGOS++
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Or you could just convert the salicylic acid into aspirin with acetic anhydride and potassium carbonate. Then could recrystallize pure aspirin. :P
How is this a separation?
It's not, he was just making a joke, on the assumption you're separating in order to obtain the ASA.
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Dear Minimal;
I never interpreted it different, or as something else.
Good Luck!
ARGOS++