Decrease in Aspirin Melting Point

  • Thread starter Puchinita5
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Homework Statement



A student performed the reaction in this experiment using a water bath of 90 degrees C instead of 50 degrees C. The final product was tested for the presence of phenols with ferric chloride. This test was negative (no color observed); however, the melting point of the dry product was 122-125 degrees C. Explain these results as completely as possible.

Homework Equations



Salicylic Acid + Acetic Anhydride -------> Acetyl Salicylic Acid (Aspirin) + Acetic Acid
Melting point of aspirin should be 134 degrees C.

The Attempt at a Solution



Ummm. I have no idea. I would assume the greater temperature would cause the reaction to shift to the right, making more of a pure product and hence the negative ferric chloride test. But I'm not sure how this would lower this melting point?

If i'm going to take a wild, WILD guess, perhaps the greater heat is also causing another product to form, which is making the aspirin less pure but this other product doesn't show up in a phenol test? And maybe this extra product is lowering the melting point somehow???But since this "other product" isn't alluded to in the reaction, I feel like I am making it up.

Thank you for your help!
 

Answers and Replies

  • #2
TeethWhitener
Science Advisor
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It's some impurity that's causing the product to melt at a lower temperature. As for what it is, if the product wasn't recrystallized, it might be the solvent; it might be some side product. Dunno, but it's definitely an impurity.
 

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