[GinaTageldin]

what is the optimum conditions for acid hydrazide formation from acid directly using chloro ethylformate and pyridine ot tri ethyl amine to form mixed acid anhydride then treating it with hydrazine hydrate to yeild acid hydrazide? I need no of moles for each stirring time need reflux or not                                        thanks alot

[discodermolide]

Depending upon the other acid the mixed anhydride may not be selective as you will also get attack at the carbonyl of the formyl side.
I would use the acid chloride or even the ester of your acid.
Are you following a literature procedure? If so, have you a reference?

[GinaTageldin]

i tried to form the ester but it needs huge time to be formed also the acid hydrazide yeild was small so i tried to use this experiment but using oyridine insted of tri ethylamine and add equimolar of k salt of acid with ethyl chloroformate and stirring on ice using chloriform then addtion of well stirred chloroform hydrazine suspention quickly to it and left over night at 0 temp when i added the hydrazine the 2 components still not solubilized , performed tlc spot correspondinf to the pottasium salt of acid and 2 or 3 spots new ,then i add dioxane and reflux  and increase amount of cholro ethylformate and hydrazine then reflux with no more progressions   sir i couldnt understand how it other attack performed on the carbonyl of formyl group ? what did you mean could you describe it by mechanism , another question how to modifying  this method  to make it works without needinf the hrs for ester and Acud hydrazide formation ? i prepare my acid hydrazide 10 equivalent to ester with no solvent but at the end many impurities in tlc shown which are dark spots i need to wash ppt by ice water quickly to remove hydrazine and polar impurities then dry and washing by toluene the problem is acid chloride highly soluble in ethanol and dissolved in water so will washing part of it lost also i crystallized it from toluene but some of it still present in toluene what is the approriate crystslization solvent  as toluene takes most of non polar impurities but not completely??  do i need to use solvent like alchol while the reaction or this kind with no solvent excess hydrazine is right?  thanks alot

[discodermolide]

Quote "well stirred chloroform hydrazine suspention"

Are you using an aqueous solution of hydrazine hydrate?

[GinaTageldin]

no using hydtazine hydrate 99% with chloroform and stirring over ice with chloroform so give suspension

[discodermolide]

I would use dioxane throughout as a solvent.
What you need to do is check the literature.
Have a look here http://www.orgsyn.org/demo.aspx?prep=v81p0254
from the acid chloride

[orgopete]

What you need to do is check the literature.

Amen!

Or as sometimes said, if all else fails, read the instructions. And... five minutes in the lab can save five days in the library, yet, five minutes in the library can save five days in the lab. Been there, done all of the above.

It is difficult for us to do these reactions remotely without structures and in my case practical experience.

The mixed anhydride method can be a little tricky, but I don't know that is the problem here. A problem with it is often decomposition and forming the ethyl ester. That doesn't sound like the problem. When I did this reaction, I used triethylamine. I would not have substituted pyridine. In my case, the TEA-HCl salt formed and I removed it by filtration. I don't know the reaction is the same with pyridine. Once the mixed anhydride is formed, then you can use pyridine or better dimethylaminopyridine. This should only require a catalytic amount at this stage. Did you form the mixed anhydride?

I had done a similar reaction some time ago. As I recall, the method I used was from an ester and it was a slow reaction of hydroxylamine. I formed my hydroxylamine from the hydrochloride in anhydrous methanol and sodium methoxide.

Still, I'd go back to the literature and try to look at a variety of similar reactions. I'd try to think of how the reactions varied and what might be appropriate for your reaction.