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Author: Subject: Diketo hydroxamic acid formation

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[*] posted on 2-4-2018 at 04:15
Diketo hydroxamic acid formation


I am trying to run the conversion of a diketo ester into a diketo hydroxamic acid (never described I think). To avoid, hydrolysis product or degradation of the starting material, I chose a procedure that does not involve strong basic conditions (see scheme below). The thing is, I don't know which product is formed. In LCMS, I have one peak only with the mass 434. The starting material is entirely consumed (comparison of retention times and mass) The corresponding methyl ketone is not regenerated (not the same retention time and mass) The diketo acid is not formed When I test the product with FeCl3, the test is positive I get a red complex .The mass missing from the product I want is 15, like a CH3 but I don't have any methanol, I wanted to avoid transesterification so I used ethanol. Since I don't see hydrogens of OH et NH in NMR, I don't know which experiment I could use to understand the structure I formed !

Please help.

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[Edited on 3-4-2018 by Bert]
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[*] posted on 2-4-2018 at 12:25

You will need to be a bit more specific about the diketo ester. I did some work a while back that I intend to pick up again when back home into the condensation of mono keto esters with hydroxylamine and you tend to end up with a heterocyclic product through removal of the alcohol group resulting in an oxazolone. My substrates are 3-keto-esters such as acetoacetates and benzoylacetates but 1,3 dicarbonyls react similarly; ultimately I was looking at the reaction of 3,4-diketo-hexanedioc acid to give 3,3'-bis(oxazol-5-one). But in your case it is difficult to make sensible suggestions without knowing what your substrate is. I followed your link to chemicalforums but it is equally vague.

In my work I was looking at the carbonyl reacting to give an oxime and then this undergoes cyclotization with loss of the alcohol; this generally occurs readily. In your case you want the oxamic acid to form and then not cyclotize with one of the keto groups. In my experience oxamic acids are hard to prepare from ester under mild conditions. Could you protect one or both carbonyls by say forming cyclic ethers with a glycol and use the acid chloride which will react much more easily and quickly?
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[*] posted on 2-4-2018 at 13:02

Quote: Originally posted by davefollmer  
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[*] posted on 3-4-2018 at 08:54

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