Klute
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Concentration of formic acid
Found this:
"A concentrated acid (ND: regarding formic acid, not acids in general) may be obtained from the diluted acid either by neutralization with soda, the
sodium salt thus obtained being then dried and heated with the equivalent quantity of anhydrous oxalic acid (Lorin, Bull. soc. chim., 37, p. 104)"
I never heard of that before, I know you can't use conc.H2SO4 or you'll poison yourself with CO, and HCl would lead to a dilute solution too... Has
anyone tried this, or has more info?
and if trying to dry crystalin oxalic acid, would dissicating with CaCl2 for example be sufficient? As oxalic acid sublimes easily, and thus can't be
heated to dry....
And, I know, 85% formic is out there, but....
http://www.1911encyclopedia.org/Formic_acid
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not_important
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Oxalic acid is dehydrated by fairly careful heating to around 100 C, but there are loses through sublimation. There are several methods around for so
in a fashion to minimise sublimation.
For some other methodes see the following, both the prep and the notes.
http://www.orgsyn.org/orgsyn/prep.asp?prep=CV1P0421
This prep seems to be based on the interchange between the free acids and their sodium salts. The reaction is driven in favour of formic acid because
the formic acid can be distilled away. I suspect that the oxalic acid wasn't perfectly dry, a trace of water helping the reaction run.
Formic acid can also be dried by producing the fairly concentrated acid by the normal means, and then using boron oxide to remove the remaining water.
The B2O3 is best made by pulling a vacuum on boric acid, and then slowly heating it to ... 150 C, I believe. I think the method is in one of the early
Inorganic Synth. books. The other route, heating boric acid under atmospheric pressure on up to the fusion of the boric oxide, takes fairly high
temperatures, you have to be careful of what you melt it in, and then you either have to pour the molten boron oxide onto a cold surface (flakes) or
drip it into a chilled inert liquid (pells) to get it into a useful form . The vacuum dehydration gives a porous, high surface area solid that reacts
quickly with water.
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leu
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You can use sulfuric acid if the formic acid is continuously removed by entrainment in the vapour of some volatile hydrocarbon. One method of doing so
is described in the attached patent 
Attachment: DE583764C1.pdf (142kB)
This file has been downloaded 474 times
Chemistry is our Covalent Bond
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Eclectic
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3A molecular sieves should work.
[Edited on 11-11-2006 by Eclectic]
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