29 Jun 2015

Synthesis of Aspirin- A Lewis Acid Approach

Lab Experiment

Submitted by Kathleen Field, WPI
Categories
Description: 

This is the procedure for a Fe(III) catalyzed synthesis of aspirin, an alternative to the traditionally sulfuric acid catalyzed synthesis of aspirin.  The prep compares and contrasts the Bronsted acid catalyzed esterification reaction with a Lewis acid iron (III) catalyzed pathway.  This can be used in different courses at different levels, but is it written for a general/intro level chemistry course.    

Learning Goals: 

Intro Chemistry

  • Students will be able to compare and contrast Lewis Acids/Bases with Bronsted Acids/Bases
  • Students will be able to calculate the moles of each reactant, the aspirin product, and the percent yield of product.  
  • Students will be able to determine the limiting reagent and calculate amount of excess material

Organic Chemistry

  • Students will characterize aspirin using melting point determination, IR and NMR spectroscopy and be able to distinguish the different structural elements between the starting material (salicylic acid) and the product (aspirin)
  • Students will be able to differentiate between the Fe(III) catalyzed mechanism and the sulfuric acid catalyzed esterification mechanism

Inorganic Chemistry/upper level

  • Students should be able to relate experimental observations (color) to the d-orbital splitting of Fe(III) complexes
  • Students will be able to draw plausible intermediates and propose a mechanism for the iron catalyzed reaction in relation to the observed reaction colors
Equipment needs: 

Erlenmeyer Flasks, Hot Plate, Balance, Vacuum Filtration, NMR and IR spectroscopy

Chemicals: Acetic Anhydride, FeCl3, Salicylic Acid, Water

Implementation Notes: 

Some notes have been included in the uploaded instructor notes.  

We are interested to submit this to the Journal of Chemical Education, so we (the authors) would be very interested in examining any student data that anyone receives if using the procedure as written in addition to any modifications to the procedure for both general/intro level classes and upper level classes/labs.  

Time Required: 
1-3hr class for intro class, 4 hour class for organic, or longer for upper level classes.
Evaluation
Evaluation Methods: 

Data sheet for intro level courses along with supplemental questions.  

Lab Reports and supplemental questions for uppper classes.  

 

 

Creative Commons License: 
Creative Commons Licence

Comments

We ran this lab in our general chemistry 2 course this spring. Overall it seemed to go reasonably well. Students generally got some product but the purity was quite variable. I have included a picture of the collected samples from the 20 groups that did the synthesis. As you can see, some of the groups got quite a lot of a nice, mostly white product. Others, well, it wasn’t pretty. We characterized by IR and melting point. Melting points were close, but one group did have their sample melt in the vac. oven. I am currently running HPLC on the samples to see how they look. Let me know what specific data you would like. 

 

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