Wildareal's ChemistRy Questions

[wildareal]

A solvent in which aspirin is insoluble, but acetic anhydride, salicylic acid and sulfuric acid are soluble in.

Any ideas?

Thanks.

[wildareal]

 In the isolation of aspirin why was vacuum filtration used instead of gravity filtration?

Thanks.

[Mao]

A solvent in which aspirin is insoluble, but acetic anhydride, salicylic acid and sulfuric acid are soluble in.

Any ideas?

Thanks.

That's quite a tough one. I'm not sure what the answer should be. It is possible to simply have salicylic acid as the limiting reagent and thus use water as a solvent (aspirin is not soluble in water). It is also possible to use acid-base extraction technique (not in VCE), but that requires a modification to the simple technique that involves having an organic (DMSO) and polar layer (water), then adding an organic base then an organic acid with an intermediate strength (such as citric acid, stronger than aspirin but weaker than salicylic acid). This will force out the the salicylic acid into water, and rendering the organic base soluble (citric acid is already water soluble, which can be extracted by evaporating the organic solvent then rinsing with water). But again this method is not reliable for separating acids of similar strengths.

Most aspirin synthesis methods simply react acetic anhydride (pure liquid), salicylic acid (solid) and sulfuric acid (conc aq) with acetic anhydride as the excess reactant. This is done at a high temperature, the result is all of the salicylic acid would react in this 'slurry'. This solution is later rinsed with water to remove sulfuric acid (soluble in water) and acetic anhydride (hydrolyse in water to acetic acid, which is soluble in water). We then filter it, redissolve it (in hot water), then recrystallize (in ice bath) and filter to obtain the pure product.

[Mao]

In the isolation of aspirin why was vacuum filtration used instead of gravity filtration?

Thanks.

vacuum filtration is much faster.