Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: nj_bartel on November 24, 2008, 10:45:23 PM
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A reaction I'm going to be running to determine the efficacy of a catalyst uses benzaldehyde and butyl acrylate. The butyl acrylate is polymerization inhibited with hydroquinone monomethyl ether (MEHQ). The MEHQ requires a 5-21% O2 by volume concentration to remain effective and avoid explosive polymerization. However, the benzaldehyde undergoes oxidation with O2 to yield benzoic acid. I'm unsure of the rate at which the benzaldehyde is oxidized, but the reaction duration will be 2+ days, and I have reason to believe from past experiments that there would be a significant amount of oxidation taking place in that time. The problem is not that the benzoic acid would hurt the reaction - it would most likely serve to expedite it. However, the if we're seeking to determine the efficacy of a proposed catalyst, the benzoic acid would be an x factor - we wouldn't be able to determine whether the benzoic acid was necessary for the reaction to proceed or not. The reaction would be performed small-scale (~5g total) and neat - benzaldehyde, butyl acrylate, catalyst.
Any ideas on potential ways to run this? Or any comments in general?
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You could setup an experiment to see how quickly the benzaldehyde turned to benzoic acid in air. That way you're not dealing with feelings but cold hard numbers.
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That would make data publishable, but it still doesn't solve the problem of desiring data with no benzoic acid (to speed the reaction, it would only need to be present in catalytic amounts). Do you have any idea if antioxidants like lycopene work in this type of oxidation they same way they do in radical oxidations? If lycopene would be effective, that'd be great - easily separated, unreactive. It would be barely soluble in the reactants, but a stir bar would be running for the duration.
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I think your just going to have to perform a batch of these experiments small-scale and in triplicate, step back, and analyze the results. I would also recommend adding systematic amounts of benzoic acid to your reaction to see what effect that has on the yield. It just seems like you need more data about this potential problem. Nothing wrong with collecting data.
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Had a talk with a grad student today - MSDS only says explosive, but it's actually explosive in that it releases a fair amount of gas that can build up. He said working under nitrogen would be fine, just to have it hook up to a bubbler. Benzoic acid's going to be added if the reaction doesn't proceed without, at varying temperatures.