[Fishman43]

I am curious about a "truth" that is often said in my other life as a beekeeper where oxalic acid is used to treat for the bee pest varroa mite.  The oxalic acid is sublimated/vaporized with the use of heat into the beehive.  The sublimation temperature of oxalic acid is 157-189c (315-372f).  The "truth" that is often said is that if heated over the sublimation temp. the oxalic acid will break down into formic acid and carbon dioxide, BUT that can't happen in an open heating situation (I.e. the hot open top pan). So here is my question:

Can Oxalic acid break down/degrade into formic acid and CO2 in an open heating pan or will it just vaporize/sublimate in the oxalic form?

[Borek]

Can Oxalic acid break down/degrade into formic acid and CO2

That definitely looks to me like a plausible decomposition path, but not necessarily the only one - CO₂, CO and H₂O look as reasonable products as well.

I don't see how an open pan (ie access of the fresh air) can change the outcome - other than allowing produced formic acid or carbon monoxide to oxidize to CO₂ and H₂O. Unless what they really mean is that open pan is more difficult to overheat.

[Fishman43]

I think the idea of the open pan is that even if the pan is overheated as the oxalic acid heats up it will sublimate as it heats up, before it can degrade.

[mjc123]

You may find this of interest (though of course you may be aware of it already): http://scientificbeekeeping.com/oxalic-acid-heat-vaporization-and-other-methods-part-2-of-2-parts/
The "truth" you refer to is there attributed to the CRC handbook, which I don't have at hand to check, but should be pretty reliable.
According to the Sigma-Aldrich catalogue the dihydrate melts at 104-106°C, while the anhydrous acid melts at 189.5°C with decomposition (it doesn't say into what; the MSDS mentions carbon oxides, but not formic acid). This abstract (I can't access the full paper) indicates that it does form formic acid: http://pubs.acs.org/doi/abs/10.1021/jp9638191

[Fishman43]

Thank you mjc123, I am aware of Randy Oliver's linked document and that is in part the reason I am asking folks more into chemistry to find out if oxalic sublimates or degrades in an open system. I admitadly do not understand much of chemistry reaction, or eve what the CRC handbook is. 

[mjc123]

I can only agree with Borek; I can't see an open pan making much difference. The key thing, according to the linked article, seems to be the temperature - below the degradation temperature it sublimes unchanged; above that temperature it decomposes. In an open pan - it says so explicitly. So your temperature control seems crucial.

[Fishman43]

I agree based on the linked article it womd seem that an open system would not change anything and degradation would occur. However the linked article does not reference anything to support that particular claim. Others on the wonderfully acurate internet claim that a closed setting is required to achieve heating the o alic above the vaporization temperature. Again, I am not good with chemistry and also dubious of Internet claims so figured I would ask on a chemistry forum