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Author: Subject: Is hydrazidation rxn of carboxylic ester requires anhydrous condition
Elmoush3
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[*] posted on 9-3-2018 at 23:03
Is hydrazidation rxn of carboxylic ester requires anhydrous condition


While im trying to convert ester to hydrazide using hydrazine 80% in ethanol I got v small yield, amate said it requirs 99% hydrazine ,which is not logical for me, as reaction dosnt seem to be that reversable, and even 99 his hydrazine hydrate.
Also I tried to het hyddrazide directly from carboxylic acid using boric acid and hydrazine hydrate 80% which also failed
Aby suggestion or correction and I,ll b thankful
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Crowfjord
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[*] posted on 10-3-2018 at 07:48


Did you use inert atmosphere and degassed solvents? Hydrazine reacts with oxygen. Did you use a large excess of hydrazine? If not, bis-hydrazides may have formed. Also, what was the ester substrate? This matters too. Stearics and presence of other functional groups can have effects on the outcome of a reaction. For example, hydrazine can reduce double bonds in the presence of oxygen. See the attached paper.



[Edited on 10-3-2018 by Crowfjord]

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Elmoush3
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[*] posted on 10-3-2018 at 10:01


thanks crowfjord for yourb aluble information
I didnot use inert condition , and my ester has no reducable group, hydrazine was 5 molar ratio to ester.
I wana ask concerning anhydrous condition is it must,and if I wana use boric acid for direct carboxylic acid hydrazine hydraization will it b possible?

[Edited on 10-3-2018 by Elmoush3]
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[*] posted on 10-3-2018 at 10:33


From the couple of papers I have read, anhydrous conditions do not seem to be necessary. Hydrazine hydrate and 95% ethanol seemed to work fine. You might have better luck with oxygen-free conditions and a 20:1 ratio of hydrazine to ester like in the above paper.
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Elmoush3
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[*] posted on 10-3-2018 at 11:02


Thanks

[Edited on 10-3-2018 by Elmoush3]
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S.C. Wack
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[*] posted on 10-3-2018 at 11:30


Why not stay at 5:1 and drop the ethanol, or have you tried refluxing the ester in 50-85% hydrazine hydrate for several hours.



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Elmoush3
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[*] posted on 11-3-2018 at 02:01


Actually the rxn time was 24 hr
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[*] posted on 11-3-2018 at 02:32


I'm familiar with the synthesis of hydroxamic acids via this approach (albeit with hydroxylamine solution rather than hydrazine) and the yields were always shitty until it was found that some NaOH helps alot. I can't rememeber the exact quantities but I think it was something like 5 eq NH2OH and 2 eq NaOH (as 20% aqueous solution) with EtOH (I think) as solvent.
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S.C. Wack
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[*] posted on 11-3-2018 at 08:15


The reaction has been treated as trivial in what I've read on benzhydrazides. Google gives confirmation in the form of a JACS submission from Squibb, who appear to be in the know. Their general procedure is 6 hr reflux of 0.5 M ester with just 50% excess hydrazine. "The acid hydrazides were prepared by refluxing the methyl or ethyl ester with an excess of 85% hydrazine hydrate, either with or without the use of ethanol as additional solvent. In general, the reactions were spontaneous and exothermic and with some methyl esters proceeded to completion without external heating. Since no outstanding antituberculous activity was found among the aliphatic, alicyclic and aromatic carboxylic acid hydrazides, the emphasis in this program has been on hydrazides of heterocyclic carboxylic acids."

The recommendation in The Systematic Identification Of Organic Compounds is to reflux the methyl or ethyl ester with 85% hydrazine hydrate before adding enough ethanol to mix nicely and reflux more.

Any suggestions to use stronger hydrazine for this remain unseen.

[Edited on 11-3-2018 by S.C. Wack]




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11-3-2018 at 13:36
Elmoush3
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[*] posted on 16-3-2018 at 20:55


I did try with and without ethanol... the best yield was when I used with ethanol 10%.
Now im thinking about using hydrazine hydroquinone complex , as hydrazine donar ,but well it be good idea as my ester is aliphatic liquid,
And will it be able to convert carboxylic acid directly to hydrazide by reacting with hydrazine hydroquinone complex
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