Ugi_Synthesis_Collaborative_Project.pdf

The combinations we are investigating are:

The combinations with the gallic acid (3,4,5-trihydroxybenzoic acid) precipitated very quickly. I was a little alarmed about that so I instructed the Wednesday group to weigh out all their compounds first and then add them together sequentially as soon as the previous mixture was homogeneous. I noticed that in the Monday group sometimes students would take 10 minutes or more to locate the next reagent and weigh it out. As far as I can tell, that did not make much difference, but it is something to consider. We did not have any problems with solubility, other than a rather rapid onset of precipitation.

We doubled the amounts (1 mmole to 2 mmole) from what is typically done by the UsefulChem group. In my experience, it is always a good idea to give undergraduate students as much product as possible to play around with. With a group of students, anomalies always crop up. Some may be due simply to inattention (“human error” as my students report in their write-ups), others are more subtle and insidious. It is always a good idea to characterize all the reagents – they tend to pop up in student “products.” Its not hard to spot in the anomalous vials in our photos.

The second set of reagents corresponds to UsefulChem experiment 171H (Spreadsheet number: 171HV2B8) which have crystals for within 8-10 days.

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Week Two:

Crystallization:

This week we harvested crystals from those reactions that gave a precipitate and attempted to obtain a solid from those reactions that had not spontaneously formed a precipitate. The two reaction mixtures with 3,4,5-trihydroxybenzoic acid tended to form precipitates the most readily, but not all of them did. The two reaction mixtures with 2,4,6-trihydroxybenzoic acid precipitated very slowly with mostly brown solid. A couple of them had what looked like transparent crystals covered in brown syrup . Several of the vials were dried down with forced air to encourage crystallization. In some a solid was formed, in others a brown syrup resulted. We tried to find a solvent that would dissolve the brown impurities and not the Ugi product or dissolve the Ugi product and not the impurities. This game plan did not work so well. The best idea seemed to be to carefully clean the crystals with methanol in a vacuum filtration funnel . I suppose the best thing to do would be to those that didn’t form a precipitate another week, but that didn’t seem possible, since it’s the end of the semester and all. Is the Ugi reaction slow in forming products or are the products slow in precipitating from solution?

Analysis:

All of the Ugi reactants gave a GC trace. GC-FID analysis of the filtrate gave some non-reactant peaks. However, the Ugi product collected by filtration did not appear to “fly” in the GC. We did IR KBr windows with a few of the Ugi products. We have and archaic system of making the salt windows with a bolt and two screws so the quality of the windows and subsequent IRs is not too good. We do see carbonyl peak and a phenolic hydroxyl peak. The UV spectra of the products are generally useful in distinguishing between different products and seem somewhat different than the reagent UV spectra..

2008 Student Comments: The Ugi Synthesis Collaborative Project

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