Also, I have received a few questions about what to focus on in the Conclusion in the Aspirin Synthesis report. As you might have realized, this experiment is only composed of a few steps between the actual synthesis and the recrystallization to purify the compound, and the product is only analyzed by melting point determination. Therefore, there is a relatively limited amount of information to discuss in the conclusion. You should therefore focus your conclusion on analyzing the following:
What would cause a low (i.e., < 100%) yield? There are a few main sources that could lead to decreased yield. One involves a step following recrystallization that might prohibit you from collecting as much solid as possible from your dissolved recrystallization solution à what procedural step could cause this? Leftover reagents will also decrease the yield, so you should explain why unreacted material would lead to lower overall yield (hint: some of the unreacted material would be lost during filtration and would therefore not be collected with your final product). Additionally, there is a unique case for this reaction where heat from the recrystallization process can actually reverse the formation of product à what is this mechanism called? Moreover, what could be done to help prevent this reverse reaction if the experiment were to be performed again? What would cause a broadened and/or lowered melting point range? As with all previous labs, be sure to account for anything present alongside your product that would result in its melting point being either broadened, decreased, or both. Hint: You probably noticed that your product looked like a damp paste after the final filtration (and possibly even after folding it in half in the filter paper). What does this imply about your product, and how would that alter the melting point? Finally, I’ve attached the mechanism that I drew on the board in class as a PDF file. I realized that I actually made a small error regarding the second protonation of the acetic anhydride portion of the intermediate species in class, so this version shows the correct mechanism for the whole reaction. As always, please use a reaction scheme and not a full reaction mechanism in your reports. Be sure to include both reagent structures and both product structures in your scheme. Any solvents or catalysts can be written out short-hand above or below the equilibrium arrows. If you have any questions, please let me know.