Picric-A
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Oxalyl Chloride
The synthesis of Oxalyl chloride is described here;
http://translate.googleusercontent.com/translate_c?hl=en&...
"This colourless, sharp-smelling liquid, the diacid chloride of oxalic acid, is a useful reagent in organic synthesis. It can be prepared by treating
oxalic acid with phosphorus pentachloride"
Today i tryed the synthesis of oxalyl chloride exactly as descirbed on the German forum and got a yield very similar to his(?), 1.4ml, around 32% of
theory.
I made the PCl5 myself from phosphours + chlorine and the oxalic acid was dryed in an oven (with much loss due to sublimation). As a result of me
making the starting reagents such low yields are not accceptable and i now want to look at ways of making larger quantities (~10ml) so i can make
appreciable amounts of TCPO.
Does anybody know of better ways to perform this reaction or other methods to improve the yield?
Why does thionyl chloride not work in chlorinating oxalic acid? I have plenty of thionyl chloride to use but there is next to no literature on the
topic.
Erowid uses the same PCl5 method to make the chloride;
http://www.erowid.org/archive/rhodium/chemistry/oxalylchlori...
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Picric-A
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I recieved a couple of U2U's form people asking me how i made the phosohorous pentachloride starting material so instead of replying to you seperatly
i'll add it here for completeness.
2P4 + 40Cl2 --> 16PCl5
Chlorine was generated using the TCCA/HCl method and the chlorine was dryed by bubbling it through a conc. sulphuric acid bubbler. 200g of TCCA was
used, it was ground up into small granules so as not to release chlorine to fast but not too slow either. 300ml of hardware store conc. hydrochloric
acid was added slowly via a pressure equalising addition funnel.
The phosphous was bought from Acros Organics and so no furthur purification was needed.
Chloroform was reagent grade from acros but was dryed before use.
The red phosphorous, 20g, was suspended in 200ml of dry chlroform (dryed by shaking with a quarter of its volume of conc sulphuric acid followed by
distillation over phsophorous pentoxide) Chlorine was slowly intoduced into the well stirred phsophorous suspension. No cooling was used but the
reflux condenser made sure no solvent was lost.
After 1 hour it was evident the reaction was complete. The red colour of phosphorous had been replaced by a clear green solution of chlorine in
chloroform and a pale yellow precipitate of PCl5.
The apparatus was then changed to a distillation the the chloroform was evaporated under vaccum. This gave a cake of PCl5 in the flask which was
easily broken up with a spatchula. This was done through a baloon septum as to avoid atmospheric moisture intake.
The yield was 49g of pale yellow, dry PCl5. This gives a approximate 97% yield. My guess is product was lost in hanfdling and manipulation and so if
this reaction is scaled up (which i guess is completly feasable), the yield would increase furthur.
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mario840
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Why yield was so low !? On german forum guy made from 10 g P 65 g PCl5 ! Did you tried one more time this reaction to compare the yields ?
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chemx01
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I think that if you haven't used white phosphorous the equation should be 2P+5Cl2-->2PCl5 so from 20g of red phosphorous you should obtain 134g of
PCl5 so your yield was really really low.
Anyway I think that this method of making oxallyl chlorid is not very good yields are in the reange of 35-50% but i havent seen experiment where 50%
yield is obtained in home setup.
And I also think that buying oxallyl chloride is much better than making it, I recall that you have very efficent fume hood because oxallyl chloride
is much like phosgene in terms of inhlation hazard and it's really irritating (but the smell reminds me of fresh fruit, i know i'm mad :-) )
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Picric-A
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Sorry, that was a mistake, the yield was actually 130g, 97% yield. My lab notes had ethanol spilt on them so i can barely make out my own writing :s I
may have used more HCl as well, couldnt quite make that out. This is irrelevant however.
That is not very pleasing news about the fact there are no more efficient synthetic routes. Does anybody know how it is made industrially? It is not
too expencive at £25 for 100g, but i would like to crack down on this reaction before i go ahead and buy some.
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plastics
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The only other homebrew method of synthesising oxalyl chloride I know of is by reacting cyanuric chloride (TCT) with anhydrous oxalic acid:
https://www.sciencemadness.org/whisper/viewthread.php?tid=88...
According to some of Sauron's posts TCT can be prepared by chlorination of methyl thiocyanate if you can't buy it. Methyl thiocyanate can be prepared
from methyl iodide and KSCN in ethanol. This seems a rather long winded way to go about things
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mario840
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Try to read again this paper and tell me one more thing : how long you gassed the CHCl3/P mixture , 1 hour and done ???? not 3 ???
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chemx01
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Regarding the TCT method, one must think about the solvents which are used.
In the method that Sauron mentioned they used acetone (b.p. 57°C) as a solvent and TEA (b.p. 89°C) as a base.
That brings us big probllem because oxalyl chloride has b.p. of 64°C which will make removal of acetone nearly impossible so a different solvent must
be used.
Also one can't use oxallyl chloride in acetone since TCPO and DNPO are quite soluble in it.
And the minor thing is that MeSCN is quite like tear gas and the by product prom chlorination are quite nasty and smelly, but that's just a detail :-)
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plastics
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At least with PCl5 you don't need a solvent. Just mix the two powders and wait or gently heat. Does this not work with TCT?
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