Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Babcock_Hall on June 24, 2020, 05:18:17 PM
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I attempted to convert methyl 4,4-dimethoxybutanoate into its aldehyde using acid hydrolysis for subsequent chemical synthesis. I followed the protocol in Drinan, Martin A. and Lash, Timothy D. Journal of Heterocyclic Chemistry, 31(1), 255-7; 1994. https://doi.org/10.1002/jhet.5570310144. This protocol was quite detailed in the volumes of solvents used in the extraction, and I tried to follow it very closely. Nevertheless my recovery was lower than the published value (which I seem to recall was 87%). I think that one reason my recovery was low (roughly 30%) is that the product is more volatile than I thought it was. I lost some mass during 30 minutes of (semi)high vacuum. I even noticed a slow loss of mass when I subsequently used a stream of nitrogen (I thought that I was removing DCM from the extraction after the hydrolysis, but now I think that most or all of the DCM was already gone).
Should I try a different protocol for hydrolysis of the acetal, or would it be better to try an entirely different approach? One possibility is to start with the 4-hydroxy ester and oxidize it under mild conditions to the aldehyde. I have found some oxidations leading to the same product via SciFinder, but I have not attempted to evaluate them.
One thing that I would do differently is to take an NMR right after the rotary evaporation. Then I would use nitrogen and follow the loss of any remaining DCM by NMR. Tedious perhaps, but better than losing product.
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I would repeat as you suggest, run nmr before applying vacuum or N2-stream.
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For the 87% recovery reported in the literature, what procedure did they use? You have some difficulty following that?
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Drinan and Lash reported an 87% yield. Others also reported high yields (the document which I used to summarize these protocols resides on a different computer, but I will check it when I have the opportunity). I chose Drinan and Lash because they provided more information on the volumes used in the extraction than the other authors did. I took care to saturate with NaCl as the protocol directed and cannot say that I had any difficulty in following it. The yield was, however, disappointing.
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That is not uncommon in chemistry to be honest. Usually, it takes few attempts to get to teh reported yields but you probably know that. I just think your product is volatile and you lost it during the drying.