Experiment: Separating the components of a Counterfeit Pharmaceutical Question:

Question

Experiment: Separating the components of a Counterfeit Pharmaceutical

Question:

Describe and explain the possible effect(s) on your result for the following possible experimental errors. In each case, specify the component(s) whose percentage(s) would be too high or too low and briefly explain why.

a) After adding DCM to the counterfeit pharmaceutical at the beginning, you didn't stir or shake the mixture before finishing

b) During the NaHCO3 extraction, you failed to mix the organic and aqueous layers thoroughly.

c) You mistakenly extracted the DCM solution with 5% HCl rather than 5% NaHCO3

d) You neutralised the NaHCo3 solution to pH7 rather than pH2

Explanation / Answer

Hi,

here i am posting whatever i know from your questions.

C)when the NaHCO3 reacts with aspirin, it forms sodium acetylsalicylate that dissolves into an aqueous layer so that aspirin separates from acetanilide,

D)but at ph7 the HCO3 wouldnt be able to act as a bass and extract a proton from the aspirin because at ph7 it would be protonated itself, so it wouldnt be able to react with the aspirin.

B)The acid will be soluble in the ether and the aqueous solution. The reason you're adding aqueous NaHCo3 and not just water is to neutralize the acid. When you neutralize the acid you're placing a charge on the molecule and increasing the solubility in the aqueous layer. If the NaHco3 was not thoroughly mixed the acid would remain somewhat soluble in the ether and the extraction would be less efficient.

The benzophenone, although it is capable of hydrogen bonding, is pretty large and is much more soluble in ether than in water, so it will remain in the organic layer. If the NaHco3 is not thoroughly mixed this will have several effects. Obviously the yield of the isolated acid, as you predicted will be lower than you would expect because some acid will remain in the organic layer. The yield of the benzophenone, however will be greater than you would expect because it contains impurities (the acid).

Ether is easily evaporated due to its low bp, and when this happens the resulting solid will be a mixture of benzophenone and the acid. Because it contains impurities the mp of the benzophenone solid will be lower than the reported mp. Although the acid was low in yield, it would be expected to be pure, and thus the mp should not change.

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Thanks in advance

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