mnick12 - 3-2-2010 at 15:08
So a while ago I bought a liter of 98% n-propyl alcohol. I bought it in hopes that I could convert it into propionaldehyde using potassium dichromate
and sulfuric acid, or chromium trioxide ( I have both), but after some reading it looks like the yields are pretty awful less than 40%.
So my question is what do you think would be the best approach for synthesizing propionaldehyde? Also do you think chromium trioxide would work better
than dichromate and sulfuric acid?
Thanks.
DJF90 - 3-2-2010 at 15:24
The best approach would be to use a reagent that won't oxidise your alcohol further than the desired aldehyde. Pyridinium chlorochromate (PCC) and
pyridinium dichromate (PDC) are such reagents you could prepare if you have pyridine. Collins reagent would also work. Examples of alternative
reagents are AgCO3/Celite (Fetizon's reagent), any number of DMSO-Moffatt type conditions (Swern, Pfitzner-Moffatt, Corey-Kim, Parikh-Doering,
Albright-Goldman, Albright-Onodera, Omura-Sharma-Swern etc etc...) or you could go via the bromopropane in the Kornblum oxidation.
Oxidation could also be achieved using TEMPO mediated NaOCl with Br- catalyst, using triphenylbismuth carbonate, Tetrapropylammonium perrhuthenate
(TPAP), Dess-Martin reagent, IBX, or Al(iPrO)3 (Oppenauer conditions). These lists are by no means exhaustive.
Using what you've got though, you want to keep the acid/dichromate mixture at a temperature just above that of the product aldehyde, and drip the
alcohol in. The aldehyde will distill off as its formed. Poor yield is something you have to deal with if you don't have the ideal reagent(s).