E2 Brutus? Part II

Scale: The original lab is written for microscale using 0.22 mL of 2-bromoheptane with an overall reaction volume of 2.22 mL. The 2-bromoheptane is a pretty expensive reagent and ended up being the limiting factor in how much the reaction could be scaled up. The smaller the reaction volume, the greater skill is required of the students for certain manipulations. There are, of course, advantages and disadvantages to this. It is good it help students learn to work with small quantities but the risk of “losing it all” are greater with microscale labs. I have almost always gone for quantity. There is something satisfying about seeing what you have made and subjecting it to a variety of analyses. This time I kept the scale about the same as the original lab because of the cost of the reagents. The result was that the only analyses we did were a bromine qualitative test for alkenes and GC-FID. If we would have had more quantity we could have done IR and RI as well like we do with the dehydration of 2-methyl-1-cyclohexanol lab.

The Addition of Base: The original procedure has the students mixing commercial (25% w/w) methoxide in methanol, methanol, and 2-bromoheptane. It seemed more efficient to eliminate the extra methanol –by either using the straight commercial mix or by making the diluted solution for the students. We ended up using the commercial mix right from the bottle. In the original procedure, the tert-butoxide salt is added as a solid and mixed with tert-butyl alcohol. This was problematic, I thought. The solid is rather unstable and tert-butyl alcohol is a pain to work with because it freezes at room temperature. I thought I could make up the solution ahead of time. It turned out that sodium tert-butoxide has very limited solubility in tert-butyl alcohol. I was surprised. The potassium salt is not much better but I could make a 12.5% w/w solution that seems to be  stable.



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