I understand that benzoquinone's role in this oxidation is to recycle the catalyst.
Even making it unessecary to use copper salts to act as reoxidizing agents for Pd(0), and that it has a benifical effect on yeilds by somehow stabilizing the intermediates, this is evidenced in another patent which I will submit, which states the yeild improving effects of adding hydroquinone (sometimes employed also as a free radical inhibitor) to a dry methanol O2 Wacker situation.
But the stupid question posed is, why does this method employ the addition of such copious amounts of water 50 ML I think, why is this needed?
and the patents are: US 3410807 and 3475461.
and here is an abstract of these patents:the first patent gives a detailed description (example 6) of the oxidation of styrene (the closest relative to our favorite alkene). He indicates that there are a number of side products, including the aldehyde as well as isomerization that hurts yields. He concludes that the best solvent for styrene is methanol which produces the highest conversion and least side products. In this example H20 concnetration was 0.7 percent.
In the 2nd patent he admits that the previous method (above) produced the desired product (ketone) but in poor yields due to side reactions and other products (isomerization and aldehydes, etc.). To correct this he uses an inhibitor to prevent side reactions and improve the yield. These happen to include hydroquinone and benzoquinone among others.
In an example using styrene, by simply adding hydroquinone to a typical wacker oxidation using O2, CuCl2 and ethanol the yield jumped from 59% to 74% and also decreased side reactions. In this case no water was added so the final product, an acetal, had to had to be hydrolyzed with acid to form the desired ketone.
