An advantage of phase-transfer catalysis is the ability to perform controlled oxidations. Two of the earliest PTC oxidation patents (Lee, G.; Freedman, H.; (Dow Chemical) US Patent 3,996,259, 1976 and 4,079,075, 1978) described the conversion of methoxybenzyl alcohol to anisaldehyde while avoiding over-oxidation to the corresponding benzoic acid. PTC was used with sodium hypochlorite as the oxidant in those old patents.
In the new patent shown in the figure, PTC and molybdate or tungstate co-catalysts were used with hydrogen peroxide as the oxidant to oxidize several alcohols to aldehydes in high yield including piperonal, anisaldehyde and benzaldehyde.
The inventors examined several phase-transfer catalysts, hydrogen peroxide concentrations and other process parameters. They found that the pH was crucial. Too acidic or too basic resulted in low yields. A buffer was used with of sodium dihydrogen phosphate and disodium hydrogen phosphate. Near quantitative yield was achieved with only 1.1 equiv of peroxide. That’s impressive.
When the oxidation was performed WITHOUT SOLVENT using 0.5 mole% each of TBAHSO4 and molybdate, but using the higher excess of H2O2 at 1.3 equiv, a yield of 96% was achieved.
This patent is consistent with other PTC hydrogen peroxide patents in that:
- tungstate or molybdate co-catalysts work well
- the presence phosphorous seems to be important (e.g., in-situ phosphotungstate) and
- the hydrogen sulfate form of the quat seems to be better than other forms
This is a nice patent worth reading.
If you or your company can benefit from achieving higher process performance in a shorter development time for this PTC reaction or any other reaction, by having access to the best PTC expertise available, NOW CONTACT Marc Halpern to inquire about using phase-transfer catalysis to achieve low-cost high-performance green chemistry. Remember, PTC excels in thousands of reactions in more than 30 reaction categories including strong base reactions, nucleophilic substitutions, oxidations and reductions.
If you’re not sure if PTC can help your reaction, now fill out the PTC Project Evaluation Form and E-mail a scanned copy to Marc Halpern or send it by fax to Dr. Halpern at +1 856-222-1124. If your company does not have a secrecy agreement with PTC Organics Inc. already in place, please use “R-groups” instead of the exact chemical structures.
