Dr. Beaker
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sodium malonaldhydate - easily sublimes
Hi all,
I prepared yesterday in my lab sodium malonaldhydate by acidic hydrolysis of 1,1,3,3 tetramethoxy propane followed by reaction of the free 1,3
dialdehyde with NaOH. it crystalyzes as the monohydrate, and I needed the anhydrous compound so I tried to remove the water of crystalization by
heating to about 50 deg. C under vaccum of about 10^-3 bar. to my surprized the salt just sublimated and much of it just resolidify as fine powder on
the glassware leadind to the trap...
correct me if I'm wrong but I don't know of Na salt that sublimes under such mild conditions.
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unionised
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I can see how that stuff would hydrolyse to the di-aldehyde.
Why would it form a sodium salt? I know that a lot of malonic acid derivaties are acidic , but are you sure you don't just have the free aldehyde
(would that be a solid) or a polymer?
There doesn't seem to be a lot of data in my books about malonaldehyde- nobody seems to sell it. Is it stable?
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Dr. Beaker
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the methylene group that is alpha to 2 carbonyles is quit acidic, and OH- is basic enough to take a proton from it, leaving the anion C3H3O2- which is
resonance stabilized (an enolate). the free aldehyde is unstable and react by different pathways such as dimerization and cleavage. I know that I got
Na C3H3O2 * H2O since I have the proton NMR. I once thought that maybe under vacuum+ heating I get NaOH and the free aldehyde, the powder being a
polymer of that aldehyde. however when I kept the sublim. condition almost all of the stuff sublimed! (the residue was too litle to be the NaOH,
though basic. this is, offcourse, an excellant way to clean this compond.
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unionised
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Well, I'm good at asking stupid questions; does the sublimation change the NMR spectrum?
Subliming Na salts seems pretty weird but I guess if it happens then it happens.
BTW, how good is the NMR?
In my day they would have struggled to distinguish the Na salt of the dialdehyde (2 peaks in a 2:1 ratio) from the dimerisation/ dehydration product
ie. 3 aldehyde Hs and 3 CH protons in a mixture of isomers. (They would really have struggled if I were doing the interpretation.)
[Edited on 17-7-2006 by unionised]
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Dr. Beaker
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| Quote: | Originally posted by unionised
Well, I'm good at asking stupid questions
[Edited on 17-7-2006 by unionised] |
not at all. I havent got the chance yet to make NMR spectum of the sublimate. the NMR of the hydrate is very clean and in accoordance to data in the
lit. so I'm quit sure that's the sole product. I guess this particular salt has quit a weak latice bonding. (maybe due to the relatively large and
charge disperssed anion?)
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Marvin
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Have you tried a test on the sublimate to see if it contains the sodium ion?
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YT2095
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a simple ablative spectrogragh should show a nice peak at about 590nm if it does contain it, a lot easier than booking NMR time 
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Marvin
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I was thinking more along the lines of a qual test for sodium. I think there is an organouranium reagent that produces a ppt with sodium. Maybe
Vogel has something simpler.
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YT2095
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well yes, you could always do an Ash test as used in some assays, that would work too
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Dr. Beaker
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identifying the presence of Na is a nice support. thank for the ideas. I was thinking to use AA equipment in our student lab to accomplish this.
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