Author Topic: Sulfuric Acid as Peracid Catalyst  (Read 1613 times)

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bio

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Sulfuric Acid as Peracid Catalyst
« on: September 27, 2004, 03:57:00 PM »
The following table (from the Percarbonate/Perborate review on Rhodiums site) is the percentage of Available Oxygen present as "peracid type" as determined by titration after NaPerborate/carboxylic acid (1:10 molar)mixing at 40deg.

   ACID                    .5hr    1hr     2hr     3hr

   Formic                  >90%    >90     >90     >90
   Acetic                   20      46      66      73
   Propionic                 2       9      19      31
   Acetic + 1% H2SO4        56      72      78      80

 
Since the perborate is mostly consumed in about an hour at 70deg (in my experience) it can be easily seen that the peracid formation should be essentially  complete within about 2 hours for maximum yield in the Baeyer/Villiger oxidation of unsaturated ketones. In fact in the reaction I am referring to the bulk of the O2 is released in only about 30-45min although it continues slowly for another 2 or 3 hours depending on the temperature.

My question is; does the 1% Sulfuric Acid amount (no examples are given) mean 1 mole percent, which would be 100mm or about 9.8 grams, or 1% of the weight of acid (about 6g for acetic)????

Rhodium

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1% H2SO4
« Reply #1 on: September 27, 2004, 04:10:00 PM »
I believe they are referring to the proportions given in

https://www.thevespiary.org/rhodium/Rhodium/pdf/peracid.pdf




bio

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Peracid Catalysts
« Reply #2 on: September 28, 2004, 03:59:00 PM »
Yes, thank you Rhodium.

I recall reading this before when you had posted it in twodogs thread. Very interesting that there is such a huge difference in the time  to maximum concentration 80hrs using 30% H2O2 (journal article) versus about 3hours, review article not definite on time to max concemtration. This  can't be explained by temperature alone (22 versus 40 deg) and would seem to confirm the reviews statement that something more than just peracid formation is happening (boron species?)

I am preparing to  treat the NaPerborate 4H20 with 35% H2O2 per the patent (US2491789) found recently in another thread. These explain that drying the perborate after additional H2O2 treatment has a much greater effect on activity that simple adding more H2O2 to the reaction, which must be the water effect.

If any of you other bees out there with experience in peracid reactions especially catalysed ones would be willing to share your data I would also reciprocate and perhaps not reinvent the wheel again.

What is found in the Journals is not always optimum from the standpoint of simplicity combined with best yields. Apparently Mn Sulfate is a good peracid catalyst ( best of 20 or so tested). Has anyone tried this?

Also I would like to get a discussion going on the "recycling" of the oxidation mixture which according to some patents can bring yields approaching quant if done "appropriatly".