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Topic: Degassing glacial acetic acid & reaction control  (Read 2363 times)

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Offline yesway

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Degassing glacial acetic acid & reaction control
« on: January 23, 2016, 09:30:45 AM »

I'm in the need of strictly anhydrous and degassed acetic acid as solvent for a reaction involving a very oxidisable reagent and product. The first part seems to be no problem... refluxing for 6 h under N2 with KMnO4 and acetic anhydride, as per the "purification of lab. chemicals" book. Now I wonder if the acetic acid is oxygen-free enough to conduct my reaction after distillation under n2 from the drying pot, or should I further look to degas the solvent? I'm envisioning directly distilling the dried AcOH into the reaction vessel. The last time I tried the freeze-pump-thaw degassing with such polar solvents led to a bad surprise (glass cracked on thawing). And also, I don't trust the nitrogen purging method. Is there any consensus that after reflux under n2, distillation under N2 will lead to effectively degassed solvents?

Second question, one reagent of said reaction boils way below the temperature the reaction is intended to run. Will this mean I need to use a pressure tube? Have you had any experience of blowing "off" a volatile reagent at elevated temps under Schlenk conditions?

All the best & thank you in advance!

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