[ArchStanton]

Hi

Over the last few weeks i have attempted several oxidations on  primary and secondary alcohols (very simple substrates all with a terminal olefins). I am following lit preps for these compounds using either PCC / PDC or an oxallyl chloride swern. In all cases the reactions don't go to completion and i isolate between 40-70% yield (lit > 90). Now i am beginnig to wonder if there is a trick i am missing to these reactions.

Also i dont isolate products from the addition of acid to the double bonds.

Does anyone have any tips or similar experiences?

[macman104]

I have done PCC on a primary alcohol (3-propanol attached a benzene ring).  I never got yields above 60% and that was on a good run.  More frequently it was on the lower range (30-40).

I can post the method I used later for comparison.
 

[ArchStanton]

Hmmm you seem to have the same issue as I do. I ran my systems with PDC/PCC in the presence of celite (dried) in DCM. I seem to get resonable conversion by crude NMR ~ 9:1 (filtered all the Cr rubbish through a silica plug) but poor yields.

I reckon it might be the DCM, we filter ours through an alumina column (sps system).

I am glad you have the same issues, makes me feel like less of an idiot

[reflux]

When running a Swern you should pay close attention to the temperature.  I would not go above -5 deg. C.  I have observed some elimination byproducts when I let the reaction warm past that temp.  Also, if you TFAA as your activator you have to be even more careful to avoid Pummerer rearrangements.

I would try Dess-Martin Periodinane (DMP).

[ArchStanton]

Thanks reflux, DMP chews my substrate, not sure why, but in 10 mins in dcm pretty much nothing survies a silica plug. Although i am not to carful with the temperature control on my swerns, so the non cowboy approach might work! I have been told the quality of the oxallyl chloride is very important, i have distilled it and noticed a small increase in yeld. Have you tried an NCS swern, are they any better?

[reflux]

That's funny.  DMP is usually very functional group compatable.  Something to note though is the quality of the DMP.  It's very easy to make the monoacetate depending on the DMP prep you follow this would effect the quality of the oxidation (it's happened in our lab a few times).  There are so many "tricks" that go along with using/making DMP that we could start a whole other topic I'm sure!

Anyway the quality of the oxalyl chloride does have a significant effect on my Swerns.  I've gone from low yields ca. 40-50% to 80-90% just by buying using new oxalyl chloride on the same batch of material.  I have not tried the NCS Swern.  I usually like the cowboy approach myself, but running a Swern always keeps me glued to my fume hood for several hours.