Sidmadra - 31-7-2018 at 16:18
I've been looking over literature a bit and I notice that while oxidations with excess MnO2 tend to be efficient, in certain cases a lot of substrate
can tend to get adsorbed to the MnO2 and lost. Some compounds like high molecular weight ones being more prone to this than others. I saw one paper
state that upon filtration and evaporation of solvent, only 50% of the material was recovered out of something like 5g of starting material. This was
even after washing the MnO2 multiple times with solvent.
Is there any reasonable way to release substrates from the MnO2 surface that don't involve excessive heating when solvent washes don't work? Losing
such high amounts of yields to adsorption seems unreasonable.
Maybe a light acid wash? Or perhaps refluxing the MnO2 in solvent?
unionised - 31-7-2018 at 22:24
If you add something like sodium bisulphite it will dissolve the MnO2 - that will free up any remaining product (as long as the product won't react
with the bisulphite)
Sidmadra - 31-7-2018 at 23:21
My product is a carbonyl so adduct formation is likely, which I presume would not dissolve in the solution, whereas the MnO2 would.
I'm not familiar with the reaction of bisulfite with MnO2. Do you have a procedure for doing this? Like would I need to heat/reflux to dissolve the
MnO2, or just stir at RT?
[Edited on 1-8-2018 by Sidmadra]
UC235 - 1-8-2018 at 03:59
Active MnO2 dissolves fairly rapidly in bisulfite solutions. Stirring at RT is probably sufficient. An excess can however, cause precipitation
Mn(SO3)2*3H2O which is poorly soluble.
Sidmadra - 1-8-2018 at 06:22
So it would be wise to use just under a molar equivalent? I don't need to dissolve all of the MnO2, just the bulk of it if it frees up trapped
reagent.