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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Alcane2214 on August 16, 2019, 01:39:28 PM

Title: Oxime formation
Post by: Alcane2214 on August 16, 2019, 01:39:28 PM

Hi guys

I have a question regarding oxime formation.

I have a reaction to synthetise oxime by NH2OHxHCl/KOH and another with NH2OHxHCl/HCl conc.

I tought that the one with HCl reagent was bad because of Beckmann rearrangement in acidic media, but it seems that it work. Does anybody have an explanation of why this rearrangement don't occur if we have a strong acidic solution?

Furthermore, i found almost everywhere that the synthesis of the oxime is done with HCl, but my procedure with KOH work just fine. I don't understand why.

Could somebody enlight me with the oxime formation and in wich condition i should NOT place this fonctionnal group?

Thank you

Title: Re: Oxime formation
Post by: hollytara on August 16, 2019, 01:50:03 PM

As always, it depends....

Like a lot of carbonyl chemistry, oxime formation works both acid catalyzed or base catalyzed. 

Does the Beckmann happen easily at room temperature?  Oxime formtion usually doesn't reuire heating. 

Look up the pKa of oximes - this can impact

Title: Re: Oxime formation
Post by: Alcane2214 on August 16, 2019, 04:16:17 PM

I don't know about the Beckmann rearrangement, it seems that it need strong acidic condition, so maybe it don't happen when we do it with HCl.

My compound have 2 aromatic cycles so maybe this is why we do this synthesis with KOH at 0degree

Title: Re: Oxime formation
Post by: OrganicDan96 on August 16, 2019, 04:27:05 PM

i believe Beckman rearrangements happen at quite high temperature, I also think anhydrous conditions. the conditions i used were polyphosphoric acid at 130 °C.