Klute
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Trimethylphosphate from P2O5
I've often read in forums that trimethylphosphate can be easily made with MeOH and P2O5.
When searching for details on this, I realized most of the patents and procedures use POCl3 and drive off the formed HCl under slight vacuum before
vacuum distilling the product.
I considered the reaction of MeOH with phosphorus pentoxide (or P4O10) to be
P2O5 + 3MeOH --> Me3PO4 + H3PO4
But on reading US 2410118, about making trialkylphosphates by pyrolysis of mono- and di-alkylphosphates, I came to think that adding 3 moles of MeOH
to one of P2O5 would rather yield of mix of mono- and di-alkylphosphates, as they claim:
P2O5 + 3MeOH --> Me2HPO4 + MeH2PO4.
They claim that on adding a sufficient amount of NaOH after reaction with P2O5, a 56% yield of TMP can be obtained, by heating to >200°C.
I would like to know if anyone here has first hand information, or further references, on obtaining TMP from P2O5. I would have though that simply
heating at a solid reflux and then a vacuum distillation with slight P2O5 excess would be enough to fully esterify the phosphates, but apparently,
this isn't the case. Any comments welcome.
Attachment: R2HPO4_pyrolysis.pdf (402kB)
This file has been downloaded 877 times
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unionised
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I can't remember the details but I think you can get trialkyl phosphates from P2O5 and an ether.
I'd be a bit concerned (with any method using P2O5) that you might get the pyrophosphate ester because I know the ethyl ester's nasty and I don't know
about the other esters.
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Sauron
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It is by no means that easy to make tetraalkyl pyrophosphates so I would not be worried about this as side reaction.
Generally, alcoholysis of P4O10 does not proceed to the tri-ester You will indeed get a mix of the mono ester and diester.
Trust the literature, but do not put a lot of faith in patents.
Sic gorgeamus a los subjectatus nunc.
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Klute
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Making and handling dimethylether wouldn't be very practical for me. I will try the patents procedure on a small scale, they do have an interesting
procedure were they use some TMP with P2O5 to form metaphosphoric esters that apparently give higher yields on trialkyphosphates on pyrolysis, after
MeOH addition. Of course, they recycle formed TMP.
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