Sciencemadness Discussion Board

Protonation of oximes

Rich_Insane - 19-9-2013 at 17:02

Hey everyone. I have no formal organic chemistry education, so forgive me if this a very basic question.

Let's say I have an aldoxime that is heated beyond its melting point and is in solution. What I was wondering is whether it is possible to protonate the oxygen on the aldoxime and then have the unstable (-OH2+) and the extra hydrogen come off as H3O+, thus regenerating the acid. The result is a nitrile.

In this case, I was thinking of using p-TsOH, as it is a very strong organic acid.

Is this mechanism feasible, or will the initial protonation of the nitrogen screw up the entire process?

My reasoning behind this is that a common method of forming nitriles from oximes is heating the oxime with acetic anhydride. I am not sure if the process occurs by anhydride's dehydration of the oxime or if the oxime oxygen is acetylated and then leaves as acetic acid... If this idea of protonating the oxime oxygen is absolutely ridiculous, would it be possible to substitute acetic anhydride with a less risky acid anhydride such as phthalic anhydride?

I should also note that I plan to carry out this process in DCM or a very volatile solvent. After the reaction completes, I want to boil away the solvent and wash with water to remove phthalic acid and then use a method of oxidative hydration to form the amide.

Rich_Insane - 22-9-2013 at 13:51

I'm guessing that this is a really stupid question.

eidolonicaurum - 9-1-2014 at 08:20

I would answer the question myself, but I do not know the answer. Almost all questions, no matter how stupid, are answered.

Metacelsus - 9-1-2014 at 18:39

Many, many reagents can do this, and new ones are constantly being developed:

Phthalic anhydride and acetic anhydride are very different beasts. I am not sure your scheme would work.

Edit: This should probably be merged with Rich_Insane's previous thread on this subject:

[Edited on 10-1-2014 by Cheddite Cheese]