Originally posted by Kinetic
A quick search for toluene to benzaldehyde gave me - unsurprisingly - a lot of hits. The extract from the article below is a solvent-free oxidation
with potassium permanganate supported on montmorillonite, but does not suffer from the particularly large amounts of oxidant often required for such
transformations. Still, it isn't a procedure you'd use on a large scale. The following is exemplified for indane -> indanone, with the same
procedure giving benzaldehyde in 60% yield in 18h when applied to toluene. Taken from Tetrahedron Letters, 43, 5165-5167
(2002):
2.1. Oxidation of indan under classical conditions
Potassium permanganate (3.16 g, 20 mmol) and montmorillonite K10 (6 g) were ground together in a mortar until a fine homogeneous powder was obtained.
Indan (0.24 g, 2 mmol) was added to this KMnO4/K10 mixture (4.5 g, 9.9 mmol) in a 25 mL round bottomed flask and mixed magnetically at room
temperature until TLC (eluent: hexane–ethyl acetate) analysis indicated a completed reaction (20 h). The residue was then washed with CH2Cl2 (2×20
mL). After filtration and removal of the solvent, the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give
purified product (0.22 g, 1.7 mmol, 85%)
Using microwave irradiation, as below, gave benzaldehyde in 54% yield in 12 minutes:
2.3. Oxidation of tetralin under microwave irradiation
In a 25 mL Teflon beaker, tetralin (0.26 g, 2 mmol) was added to KMnO4/K10 (4.5 g, 9.9 mmol). After 3 min of mechanical stirring, the mixture was
irradiated at medium power for 25 min. At the end of exposure to microwave irradiation, the mixture was cooled to room temperature and eluted with
CH2Cl2 (2×20 mL). After filtration and solvent removal the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give
purified product (0.24 g, 1.7 mmol, 82%).
Some other references for the oxidation of toluene to benzaldehyde are:
Synthetic Communications, 29(7), 1177-1182 (1999), using sodium bromate and cerium dioxide;
Tetrahedron Letters, 28(10), 1067-1068 (1987), using ceric methanesulfonate (91% yield);
DE168291, in which 'air and water' is used;
DE127388, using nickel oxide (edit: duh, of course this is the same as posted by S. C. Wack above);
DE101221 (which appears to be the one cited by Orgy as DE102221), DE107722 and Journal of the Chemical Society, 91, 263 (1907), using manganese dioxide and sulfuric acid;
DE158609, using cerium dioxide and sulfuric acid;
and DE175295, using 'manganese dioxide sulfate'.
That's pretty much it for the easy to get reagents. I haven't read any of the papers (partly as I don't speak German) so I'll keep my fingers crossed
that they are of use.
[Edited on 17-1-2005 by Kinetic] |
) chloroform/water and salt
- which proceeds in ~90% conversion and almost total selectivity. The beauty of this procedure is that there is no need for hydrochloric acid (or
exotic chlorinating agents) the Chlorine is generated in situ from the electrolysis of the upper aqueous layer, and apparently passes through the
interface between the layers quite well.
- I will try with stainless steel and carbon/graphite).
The MnO2/30%H2SO4 method for the oxidation of bezylic alcohol has worked out
selectively over aromatic methyl oxidation into corresponding aldehyde in 50% yields.