Author Topic: Benzaldehydes from halobenzenes  (Read 576 times)

0 Members and 1 Guest are viewing this topic.

bottleneck

  • Guest
Benzaldehydes from halobenzenes
« on: March 24, 2003, 06:14:00 AM »

Patent US6462242



----------------

"Example 1

4-Trifluoromethylbenzaldehyde

3.38 g of 4-trifluoromethylbromobenzene, 0.32 g of bis(triphenylphosphine)palladium dichloride and 1.53 g of sodium formate were placed in a flask fitted with a reflux condenser and a gas inlet tube, 15 ml of DMF were added and the mixture was stirred and heated at 110°C while passing in CO. After the conversion was complete (GC monitoring), the reaction mixture was allowed to cool to 21°C and the catalyst was separated off by filtration through silica gel.
This gave a crude product containing 91% of 4-trifluoromethyl-benzaldehyde and 8% of trifluoromethylbenzyl alcohol (percentages are based on the areas in the GC)."

pHarmacist

  • Guest
nice
« Reply #1 on: March 24, 2003, 06:18:00 AM »
nice


bottleneck

  • Guest
Thanks. Yes, it seems okay, doesn't it?
« Reply #2 on: March 24, 2003, 06:39:00 AM »
Thanks.

Yes, it seems okay, doesn't it? Except for the need for carbon monoxide.

I would think it might work with chlorobenzenes as well, and I guess one might possibly find some references to that in one of the citations in the beginning of the patent.

A patent I just mentioned in another thread,

Patent US4988416

seems similar, except electrolysis is used in place of the palladium-catalysis (dehydrogenation?), and here it also works with fluorobenzenes, chlorobenzenes and iodobenzenes in addition to the bromobenzene.

They use sacrificial anodes of your choice, either aluminum, zinc or magnesium. I don't know anything about sacrificial anodes other than that they dissolve with time. Whether less, equal to, or more than one molar equivalent of the metal is required, I don't know. It would be a bit expensive to have to use a mole of aluminum for every mole of benzaldehyde. Okay, maybe not "expensive", but polluting then.

It would be great if this worked with "inert" anodes, but tbey don't make that clear in the discussion in the beginning of the patent. They just say that other authors have gotten poor yields when using divided cells AND inert anodes (graphite), but there is no mention of the yields of using inert anodes and a non-divided cell (i.e., no porous barrier to protect against the cathode).