clearly_not_atara
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Disproportionation of phenylphosphinic acid: OTC triphenylphosphine?
| Quote: | | According to the literature reference cited, this reaction must be carried out under the mildest possible conditions--i.e. at room temperature or at a
temperature only slightly above it--because the phosphonous acids formed in the reaction are said to disproportionate at elevated temperatures into
the corresponding phosphonic acids and the (foul-smelling and poisonous and hence exceptionally undesirable) primary phosphanes; the
disproportionation is based on the following equation: ##STR3## |
https://www.google.com/patents/US4485052
Phenylphosphonous acid, also known as phenylphosphinic acid, written PhP(H)(=O)OH, disproportionates to phenylphosphine, PhPH2, and phenylphosphonic
acid. I assume you could separate them by forming salts of the phosphonic acid. While phenylphosphine is an unpleasant-smelling, poisonous,
pyrophoric-when-concentrated liquid, it's still far less dangerous than its parent compound phosphine -- LC50 of PhPH2 is 4x that of phosphine on a
molar basis, or about 10x on a weight basis; it's 38 ppm in rats for four hours. I wouldn't think of it as safe, but not the worst thing ever.
I cannot find a reference, but everything I know about chemistry tells me that PhPH2 will react with Br2 or Cl2 to PhPBr2 or PhPCl2. I'm guessing the
reaction with chlorine will be very exothermic and prone to side-reactions. The synthesis of Ph3P from these reagents by nucleophilic arylation is a
classic and requires no discussion.
The production of phenylphosphinic acid might start from a salt or ester of pyrophosphite, H2P2O5(2-), which is produced when monobasic phosphite
salts are heated. Since this is an acid anhydride, you should be able to arylate phosphorus by breaking one of the bonds in the P-O-P linkage with
e.g. phenylmagnesium bromide. Alternatively, Friedel-Crafts conditions might work with an ester.
Or something else. I can't get past here. Nobody mucks around making phosphines if they can buy phosphorus. Any ideas?
Edit: Acyl H-phosphonates are phosphinylating agents. These possibly from acyl halides and H-phosphonic acid. The only reactivity mentioned is with
alcohols (no carbanions :/):
https://books.google.com/books?id=GkybXPPOFOwC&pg=PA399&...
Edit 2: Here pentafluorophenyl carbonate is used instead of pivaloyl chloride to activate phosphonic acid. Looks like they're not fucking around.
Guessing benzoyl chloride doesn't work.
http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC31056...
The good news is that phosphitylating reagents derived from phosphonic acid do exist... the bad news is there are no reports using them to
phosphitylate anything but alcohols.
[Edited on 2-3-2016 by clearly_not_atara]
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AvBaeyer
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Unless you are an addict to self-flagellation, you will be extremely frustrated trying to make any headway in the area. I spent several years working
with phosphonic and phosphinic acids in the enzyme inhibitor arena. If you want a challenge, that's the area to be in. Normal rules of organic
chemistry do not apply. I am being a bit facetious here but truthfully, you need to develop a good background in organophosphorous chemstry before
moving into it. Some of the most basic and interesting work is in the Russian literature as well as the British chemical literature of the late 1940's
and into the 1950's.
Have fun.
AvB
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DFliyerz
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I'm a little confused: how is phenylphosphinic acid OTC?
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clearly_not_atara
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It has to do with the possibility of making dipivaloyl H-pyrophosphonate from sodium H-pyrophosphonate (also called sodium pyrophosphite, from the
dehydration of sodium biphosphite) and adding this to a phenyl anion synthon. This works when the nucleophile is an alkoxide, guving phosphonic
esters, but I haven't found any phosphinylations of carbanions with acylphosphonates. Often the phosphinylating agent is an O-pivaloyl-O'-ethyl mixed
phosphonic anhydride-ester. It's not clear if phenylmagnesium or phenyllithium or phenylcopper will be superior, or maybe the strategy requires a
different arylation entirely. Perhaps the acyl group should be replaced with a (less electrophilic) sulfonyl group.
But the starting point is just sodium phosphite, or really sodium hydrogen H-phosphonate; phosphites do not reduce iodine and are sold as weedkillers.
I gave up more or less because of a lack of published information, although I could try searching in Russian. The theoretical yield is low (33%) but
the starting materials are easy to obtain and the product is reusable in most of its reactions.
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CuReUS
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found four high yielding procedures,but most likely not OTC
http://pubs.acs.org/doi/abs/10.1021/cs4002767 (yield-99%)
http://www.google.com/patents/US4212831?cl=en (99 %)
http://pubs.acs.org/doi/abs/10.1021/ja301764m (85%)
couldn't find this one-"Timokhin, B. V.; Dmitriev, V. K.; Dmitriev, V. I. J. Gen. Chem. USSR (Engl. Transl.), 1982 , vol. 52, # 3 p. 543 - 547,476 -
480 "
[Edited on 31-5-2016 by CuReUS]
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clearly_not_atara
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Actually, the third one is potentially useful, except that the methods are not very nice. Diphenylphosphine is potentially very useful, as it is the
precursor to not only triphenylphosphine but all sorts of multifunctional ligands, particularly 1,2-bis(diphenylphosphino)ethane. So if you can
produce phenylphosphinic acid, you might be able to convert to diphenylphosphinic acid and reduce that, which eliminates any wasting reagents.
However, it says it only reduces phosphine oxides and not diphenylphosphinic acid, although it might be possible to work around this somehow.
https://www.google.com/patents/US4990674 describes the reduction of mixed alkyl-aryl phosphinic acids with trichlorosilane and triethylamine in
toluene, although this is not the primary object of the patent, and significant preparatory difficulties are noted:
| Quote: | One process is to react the mixed phosphinic acid with triethylamine and trichlorosilane in toluene to produce the mixed phosphine followed by
oxidation to produce the mixed phosphine oxide (see E. P. Horwitz et al., Sol. Ext. and Ion Exch., 4, 449-494, 1986.): ##STR3## However, during the
addition of trichlorosilane a voluminous, thick white precipitate is obtained and it is not possible to stir the reaction mixture unless large amounts
of solvent are used. Difficulties are also encountered with stirring during the hydrolysis. As a result, yields are erratic and poor. Further work
showed that the triethylamine can be eliminated, which reduced the stirring problems. However, if the toluene solution of the acid was below 20° C.
during the addition of trichlorosilane, the reaction mixture would freeze into a sticky solid which made stirring extremely difficult. Yet the
reaction could not be heated above 30° C. during trichlorosilane addition because unreacted trichlorosilane boils at about 31° to 32° C.
It is also possible to produce the mixed phosphine oxide from the mixed phosphinic acid by means of a Grignard reaction. However, the use of a
Grignard reagent requires handling ether, which is highly flammable. Special equipment and facilities are required which are not economical for making
small amounts of materials or for making materials that do not justify the expense. |
It is possible that the difficulty may be reduced by using a different base (diisopropylethylamine), a different solvent or mixture of solvents
(toluene-ethylbenzene eutectic?), etc, or by first performing the Grignard reaction, or that the Grignard reagent might also reduce the phosphine
oxide all the way to the phosphine (??? never heard of this before). However, trichlorosilane is not an impossible goal, nor is it significantly more
dangerous than many other volatile things people here have tried to produce.
That leaves the question of how to get diphenylphosphinic acid, apparently. Phenylphosphinic acid might be part of the answer, but it's not clear how
to make that either. Grignards apparently reduce phosphines, so that's probably out as far as attaching a phosphinyl to an arene. Organolithiums are
more reducing than Grignards, so I wouldn't bet on that either.
One possibility is to make p-dimethylaminophenylphosphinic acid and then use MeCl + hv/[H] to remove the dimethylamino groups. Phosphorus might not be
a good electrophile, but we can use a better nucleophile to compensate; phosphinylating agents might work in this case.
[Edited on 1-6-2016 by clearly_not_atara]
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CuReUS
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see if you can find this papers
"Synthesis, , # 3 p. 198 - 208 J. Gen. Chem. USSR (Engl. Transl.), , vol. 55, # 1 p. 11 - 26,8 - 22" - diphenylphosphinic acid from diphenylphosphine
oxide (98 %)
"Russian Journal of General Chemistry, , vol. 67, # 10 p. 1553 - 1555" - from diphenylphosphine
| Quote: | | Phenylphosphinic acid might be part of the answer, but it's not clear how to make that either. |
see this
http://www.sciencedirect.com/science/article/pii/S0022328X04...
http://www.sciencedirect.com/science/article/pii/S0040402009... - this one talks about making both phenyl and diphenylphosphonic acid
from the above references it can be clearly seen that making TPP is not a joke.Since its not a watched chemical,I feel the best way is to buy a small
quantity and use it catalytically.
Wiki gives two references to catalytic reactions
| Quote: | | The phosphorus reagent can be used in catalytic quantities.[5][6] |
https://en.wikipedia.org/wiki/Appel_reaction
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clearly_not_atara
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Interesting. Just to point out: the Xantphos ligand used in the second prep can itself be made from diphenylphosphine (by mild chlorination and
reaction with dilithio-xanthene) although it's not easy, involving a directed lithiation. But the major interest (as of yesterday) is that you can
synthesize all sorts of phosphine ligands from diphenylphosphine, and doing this (sorta-kinda) OTC is cool.
Unfortunately, the snake eats its tail. You can make Xantphos, but you need Xantphos to make Xantphos. Worse, hypophosphite is required, and ordering
that will send agents to your house faster than you can say "pseudoephedrine deoxygenation". However, it might still prove possible to make
diphenylphosphinic acid from monophenylphosphinic acid, so this is something, if monophenylphosphinic acid can be made some other way, that is.
I didn't think this was realistic (still don't), but it's gotten somewhere. This book might be useful:
http://link.springer.com/chapter/10.1007/128_2014_558
Interestingly it appears that the Friedel-Crafts reaction of PCl3 with ethylbenzene gives a diarylchlorophosphine. This is a much easier route to
these compounds, although the goal was to avoid P (and thus avoid PH3).
You might also be able to perform some higher-octane reaction that isn't as useful for modern chemistry, like the direct reduction of phenylphosphonic
acid with trichlorosilane. I doubt you can find references on something like that (and it might be a huge mess).
[Edited on 1-6-2016 by clearly_not_atara]
[Edited on 1-6-2016 by clearly_not_atara]
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CuReUS
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I found two alternatives to TPP. One is the non-ingenious tributylphosphine but the other one is little different,triethyldicholorophosphite,which is
made by reacting triethylphosphite with CCl4.It is formed in-situ and can then be used to do the appel reaction similar to TPP.
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