thunderfvck
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Unknown derivative of maleic anhydride
Okay. This has been plaguing me for quite some time now. I did this lab like last week, we had to identify an unknown compound. I'm usually quite
good at this kind of thing but this one just baffles me.
Maleic anhydride was added to distilled water which also contained some zinc flakings. To this solution concentrated HCl was added so that the zinc
would produce hydrogen gas. This hydrogen gas reduces maleic anhydride to some mysterious compound. The product is a white crystalline substance,
melting point 180-184C (I am told this is quite the accurate melting point). Titration proved that this compound has a molar mass of about 67 g/mol (I
might be off on this one). Slightly soluble, weak acid (as expected, why else would we do a titration?...DUH..).
IR absorabnce peaks 2500-330 cm^-1, broad, looks to be hydrogen bonding. A double headed peak at 1700.
NMR has one peak (looks to be a singlet) at about 2.3ppm. Another very small bumb at about 12.
I have a feeling it's a carboxylic acid but I really can't find anythign that even comes CLOSE to any of this information. And it has one
peak (aside from that at 12) in the NMR, so WTF? Normally things like that just give the structure away but I'm lost here. Maybe you guys could
help out.
Another thing, the guy who originally did this sought to obtain tetrahydrofuran but instead got this mystery compound.
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unionised
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My first thought was succinic acid, the Mpt (187-109C) isn't far off and the equivalent weight (59) is in the right ballpark, particulaly if the
stuff is damp.
Anyone care to comment on the IR. It's got the right number of peaks in the NMR but that's about as much as I can say- it's been a
while since I did any NMR.
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thunderfvck
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That looks pretty good actually. I thought it could have been something that looked like this, only it had a double bond in the center. But since
it's being reduced!....I'm fairly certain this is it now...The molar mass I obtained was by using the assumption that the compound was
monoprotic, but this is diprotic so I'm guessing my value for the molar mass is now effectively doubled? Which fits in nicely with succinic
acid's molar mass.
And the NMR seems to correspond to this, the adjacent carbons (to the carbonyl group) are both identical, ie. they're both split by the same
things, since it's symmetric.
Thanks a lot, I think the problem is now solved. And I kick myself in the ass for not thinking of this. I was close with that other compound (whose
name has been lifted from my memory) but never thought it could be that...I guess the extra oxygen comes from water then, huh?
Thanks again!
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Hydrolysis to maleic acid and hydrogenation to succinic acid (Or the other way round).
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thunderfvck
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Yeah. I read that maleic anhydride decomposes in hot solvent. So the solvent being water in this case, is it simply being hydrolysed at the high
temperature?
About it now being diprotic, will the molar mass (67) double? I'm fairly certain of this but I was an expert's opinion.
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Yes, the titration result will make it look like a monobasic acid with half the molecular weight.
I see it is now nearly 1 in the morning so I'm giving up for the night.
(How come there isn't a smiley for "knackered"?)
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