Scale up week: GRAMS ON GRAMS

Going to be a short post as I’ve been pretty busy in the lab, even sleeping there a few nights so I can wake up and get to it the next day.  I just think of it as practice for graduate school!

Scaled up the acylation reaction and recovered 21g of product which was ~62% yield.  I would have liked it to be a bit higher but I wasn’t using nitrogen and ended up seeing a portion of my acyl halide disappear into HCl fumes due to water vapor.  I really need to get a Schlenk line setup.

I also scaled up the TBS protection reaction but unfortunately was limited by the remaining imidazole catalyst.

I ran the largest flash column I’ve ever run by hand and it was an experience…definitely an art form I’d say which I’m a long way from mastering.  Collecting fractions by hand while trying to keep the solvent level topped off and making sure the column doesn’t explode is something you must balance delicately.

Sadly, a lot of the early fractions had the product I wanted in them (the lowest dot on the TLC plates) alongside the two unwanted side products (2 dots up top).  I managed to snag a bunch more “pure” fractions which I didn’t end up showing, but you can see the final pooled fraction plate on the right.  I still kept the mixed product fractions as a crude testing batch, but it also looks like the “pure” fractions which have what I want have some imidazole catalyst left over, which is causing streaking.  I’ve heard getting rid of imidazole can be a pain, so maybe next time I”ll do more water washes, or throw in some LiCl2 which I think said can remove it more effectively.

While I was waiting I recrystalized some more Meldrum’s acid from a yellowish mess into nice white crystals!

As for the large purple RBF, I’ve read and was told by some people smarter than me that DMAP (http://en.wikipedia.org/wiki/4-Dimethylaminopyridine) can be a product of pyridine catalyzed reactions, even though in some cases it’s actually added as the catalyst.  In my case, I only used pyridine, but I assume because it was in DCM, and with some HCl from acyl halide reacting with residual water…that perhaps it was somehow being formed?

NMR spectra look good, but pictures of them are kind of hard to read from a digital image so I’m not even going to bother posting until maybe the end.

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