Rich_Insane
Hazard to Others
Posts: 371
Registered: 24-4-2009
Location: Portland, Oregon
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Hydroxylamine/copper
I've been interested in a particular method for formation of amides from aldehydes for a while -- the route goes through the oxime via hydroxylamine
and aldehyde, then is rearranged to the amide.
In particular, I've been interested in copper sulfate pentahydrate as a means to perform this reaction, where CuSO4 in catalytic quantities (5-10 mol
%) is used to rearrange an oxime generated in situ by reaction of the aldehyde with hydroxylamine in the presence of a base (Na2CO3 or NaCH3COO).
The procedure itself is derived from "Tetrahedron Letters 53 (2012) 1413–1416," but there are reports of other copper-involving methods from other
authors. My question however does not really concern the viability of this method (though feedback would be appreciated), but the possible
interactions between hydroxylamine hydrochloride and copper sulfate.
I had added a small amount of copper sulfate to cold water followed by a small amount of hydroxylamine hydrochloride crystal. I immediately noticed a
greenish color not typical of copper sulfate forming, as well as a brown-colored material forming after 10-15 seconds. There was also audible fizzing,
which may or may not have been air bubbles trapped in the relatively large chunk that fell into the vessel. After some research, I found a reference
to a paper from 1909 which indicated that hydroxylamine can reduce copper sulfate. Unfortunately I could only read the first page, and further search
did not yield anything different. So what exactly is going on in the solution? Will it become a problem during the formation of an oxime, or will
condensation of the hydroxylamine with aldehyde occur too quickly for this apparent redox reaction to occur?
Furthermore, just how toxic is hydroxylamine hydrochloride? Is it one of those chemicals one should avoid?
EDIT: I had a thought, would addition of the copper sulfate pentahydrate after formation of the oxime eliminate this possibility of reaction? I know
that oximes form very nice crystals, but how do I tell between oxime and other insoluble materials? How do I tell if the reaction (oxime formation,
not the whole reaction) is complete?
[Edited on 21-9-2012 by Rich_Insane]
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