Why Did the Aspirin Melting Point Decrease in This Experiment?

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SUMMARY

The experiment revealed that the melting point of the synthesized acetylsalicylic acid (aspirin) was 122-125 degrees Celsius, lower than the expected 134 degrees Celsius. The use of a water bath at 90 degrees Celsius instead of 50 degrees Celsius likely introduced impurities, which could have resulted from incomplete reaction or side products. The negative ferric chloride test indicated the absence of phenolic compounds, suggesting that the product was not pure. Impurities, possibly from unreacted starting materials or solvent, are responsible for the decreased melting point.

PREREQUISITES
  • Understanding of organic chemistry reactions, specifically esterification.
  • Knowledge of melting point determination techniques.
  • Familiarity with the ferric chloride test for phenols.
  • Experience with recrystallization methods for purifying organic compounds.
NEXT STEPS
  • Research the principles of esterification reactions in organic chemistry.
  • Learn about the significance of melting point as an indicator of purity in organic compounds.
  • Study the ferric chloride test and its application in identifying phenolic compounds.
  • Explore recrystallization techniques to improve the purity of synthesized compounds.
USEFUL FOR

Chemistry students, organic chemists, and laboratory technicians involved in synthesis and purification of organic compounds, particularly those studying aspirin synthesis and its properties.

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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!
 
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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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