Sciencemadness Discussion Board

Trialkyl Phosphites from Alkoxide and PBr3?

Sauron - 23-9-2007 at 10:58

I would like to prepare some trialkyl phosphites for various projects. I can't buy these, damn it, nor can I buy PCl3 which they are usually prepared from. You can see the general procedure in Org.Syn. under Triethyl Phosphite.

In that prep, the alcohol in pet.ether along with a tertiary amine (diethylaniline recommended) is reacted with phosphorus trichloride in same solvent, with initial cooling. Vigorous stirring prevents any local accumulation of HCl which otherwise might cleave the final P-OR bond and give rise to diethyl hydrogen phosphite and ethyl chloride.

The tertiary marine is scavenger for the HCl.

Now, the problem with substituting PBr3 is that HBr is far more efficient at cleaving the ester bond. In fact without heroic efforts such as low temperatures (-10 to - 20 C) only dialkyl hydrogen phosphite forms with PBr3.

A Russian investigator made triethyl phosphite from PCl3 in absence of tertiary amine by employing magnesium ethoxide. With alkoxide rather than alcohol no hydrogen halide forms, instead you get a salt as byproduct.

So I am thinking, sodium ethoxide in anhydrous ethanol reacting with PBr3.

If this works my need for PCl3 and red P to make it from will dwindle significantly.

It is my opinion that the alkoxide ought to react with PBr3 at a significantly faster rate than the alcohol

I'd appreciate comments and criticism.

Eclectic - 23-9-2007 at 11:43

It's just this line of inquiry that points out why chemists NEED to be familiar with toxins and explosives. It's necessary so that you don't ACCIDENTALLY kill yourself and your neighbors. :o

How will you separate your product from the NaBr dissolved in EtOH? That may be the point of using MgEt in footnote 8 of the OrgSyn procedure. Maybe solubility and workup issues?

[Edited on 9-23-2007 by Eclectic]

Ozone - 23-9-2007 at 12:01

Modified Wittig;), simple alkylation or fun with a-diketones (which I think could harnessed to make all sorts of interesting things from sugar)?

This is not a trivial problem!

We were recently informed (the "official" notification) of the new DHA strictures on chemicals and the amounts that we can have...

This pretty much axes phosphorus chemistry as the classic "pickles" are now off-limits without truly heinous bureaucracy.

It looks like academics will be needing to make this stuff too! Seriously!

Nevermind that DHA is not regulating departments...it is regulating sites. This means that we are not just counting the Chemistry Dept. We are counting chemistry, biology, etc. Nightmare.

Anyway, now that the absolute need for this has been addressed, maybe we need to address, wlong with the direct preparation of alkyl phosphites, the preparation of the pickles themselves...without, obviously, the use of oxalyl or thionyl chloride (which, thank God, is not regulated as severely)? Nevermind all of the diethylaniline.

I am not one to try chlorinating phosphorus (this would be difficult to explain).

How about some sort of metathesis, maybe with SbCl5 (which has eaten gloves off of my hands)?

I am looking into this.

Cheers,

O3

Sauron - 23-9-2007 at 12:02

I have nothing truly toxic in mind. The lower trialkyl phosphites are for the final coupling step in the BEDT-TTF prep in Org.Syn. Have a look. In that process part of the phosphite gets oxidized to phosphate but that can be seperated out and the rest reused.

The product is a charge transfer compound based on the tetrathiafulaene system, and is the basis for some experimental organic superconductors. I have been steadily acquiring the wherewithal to get started (chloroacetyl chloride, ethanedithiol, N-chlorosuccinimide, Potassium ethyl xanthate) but if I am denied the reagent for the final step, what's the point?

There are a few things I might like to try in the future which call for PCl3, and may or may not work with PBr3 with modified procedures. One such is mexamethylphosphorous triamide - not the familiar solvent HMPA, but same molecule except that the P is trivalent rather than quintavalent. No P=O. It can be oxidized to HMPA easily, P wants to be quitavalent about as much as the One Ring wants to get back to its maker.

But this is not a priority as HMPTA isn't very synthetically versatile (it's like a one trick pony, see Org.Syn.)

Eclectic - 23-9-2007 at 12:13

I didn't mean you, Sauron. I mean someone who just starts messing about with synthetic chemistry WITHOUT understanding toxins or explosives.

With all the regulation impairing research and learning, it looks like we may be in for out own "Cultural Revolution".

Ozone - 23-9-2007 at 12:25

Thanks!

I was trying to explain that, perhaps, even academic chemistry will be pushed underground--And that the last bastion may well be folks like us.

Anyway, sorry. I don't wish to derail this thread any further. I'm doing a some research, but, unfortunately, this does not happen instantly.

Back to the fux0red (i kind of like that one) lawn, heat and predatory insects.

O3

Sauron - 23-9-2007 at 12:40

I would truly hope that the clueless beginner would have the commonsense to stay away from OP, certain areas of organosulfur chemistry, essentially all arsenicals, Se and Te, Be, most of the heavy metals...at least till he or she grows up and acquires wisdom, discretion, and caution tinged with fear.

But look at all the kewls who pop up and post about TATP, thermite etc. The former will take you right out. One of my classmates in high school was luckier with thermite, the heat singed off his eyebrows. Lesson. Use a LONG Mg ribbon. O3, you'd probably recognize his name, his family owned the biggest musical instrument store on Canal Street for many many years. Werlein's.

So there is a certain amount of evolution in action.

Ozone - 23-9-2007 at 13:38

NO kidding?

Small, small world. If you needed a piano, it was the place. I was with Foster's for guitars, though.

It is too bad that DHS and the nannies are against "evolution in action" to the point where I have community college students complaining b/c theyare not allowedto work with the chemicals...in a Chemistry lab.

O/P's are heinous. One mistake can absolutely be the last, and unlike energetics, can persist to do in those who show up to see what happened to you. These are to be handled only by those who have distinct skill in the art and the facilities suitable for practice.

Pickles and sulfites are not too crazy, but many of the things you can accidentally prepare may well be.

If any-one of us wishes to sacrifice themselves upon the altar to the god of Chemistry then so be it. Accidental inclusion of the unwitting is not reconcilable.

I want to know what happens if a *tiny* bit of P is added to SbCl5. I have not been able to find any literature to this effect. Probably for good reason.

I have found fewthings that do *nothing* with SbCl5, however.

Cheers friends, may we be together for a long time,

O3

Eclectic - 23-9-2007 at 14:35

And those community college students who were never allowed to actually work with chemicals are probably far more qualified to do so than most of the people who usually end up as LEO or hazmat "lab busters". :o

Fleaker - 23-9-2007 at 17:27

Quote:
Originally posted by Ozone
I want to know what happens if a *tiny* bit of P is added to SbCl5. I have not been able to find any literature to this effect. Probably for good reason.

I have found fewthings that do *nothing* with SbCl5, however.

Cheers friends, may we be together for a long time,

O3



Now I'm curious! I think I shall try it! SbCl5 from direct chlorination right? (I'll go visit Brauer shortly). If it gives something useful, it might be a viable option for Sauron (assuming he can get red/white P?).

I agree that OPs are best left to those with the facilities, the talent, and the balls to work with them. Interesting as the chemistry is, I would never attempt it.

Edit: page 600 in Brauer, SbCl5 is made from SbCl3 and chlorine, then redistilled.

[Edited on 23-9-2007 by Fleaker]

Eclectic - 23-9-2007 at 17:35

I suspect you will get PCl3 or PCl5 in the mix, with SbCl5 giving up Cl2 to go to SbCl3. Not sure how energetic this would be. The real question is would SbCl3 and P react and what would they make?

Or SbCl3 and PBr3? Could you distill off PCl3?

[Edited on 9-23-2007 by Eclectic]

Sauron - 24-9-2007 at 05:28

The situation in USA is going to approach what things were like during WWI when reagent manufacturing was effectively a German monopoly and American chemists were cut off from that supply.

Two things came out of that: Eastman's chemical division and Org.Syn.

Org.Syn was originally conceived of by Roger Adams et al toprovide reliable checked preperative procedures for badly needed reagents to allow American chemists to made their own building blocks, and get on with their work.

Well, today we won't have to wait for publishers. We have this great cyber-samizdat so we can communicate directly with each other. Because we are chemists, we make what we need.

Fleaker - 24-9-2007 at 08:37

PCl3 is more volatile than SbCl3 (the assumed other product). It would be nice though, if you merely add SbCl5 to red P and distill off the PCl3. Then just rechlorinate the SbCl3 with chlorine and add more phosphorus! Almost a continuous process in my opinion. If that works (and at the moment I'm just talking), then I think it might be a viable option for you Sauron. Shall we give it a try?

Sauron - 24-9-2007 at 08:52

Saunders et al used SbF3 to fluorinate PCl3 and POCl3 to PCl2F abd POCl2F, but yields were lousy (,30%).

So I suspect that SbCl5 or even SbCl3 might be expected to chlorinate red P, P2O5, H3PO3, or H3PO4. I haven't tripped over any lit. on this though.

It's anyone guess as to the efficiency of this. IIRC SbCl3 is a liquid like AsCl3, called butter of antimony. My guess would be that the pentachloride would be solid, like PCl5, and look at the difference in MW.

I'd say, hunt for some lit before cutting and trying. Besides, I have no red P.

Eclectic - 24-9-2007 at 09:21

I'd be worried about thermal runaway trying to chlorinate P with SbCl3 or SbCl5. Direct chlorination seems safer if you already have red or white P, as the reactant density is lower. It's a lot easier to throttle a stream of chlorine than it is to remove a liquid or solid reactant from a mix. :o

Sauron - 24-9-2007 at 09:40

I would not willingly work with WP. Did it once long ago and survived to tell the tale.

A series of articles in J.Chem.Soc. by Gerrard and coworkers studies the interaction of phosphorus trihalides and oxyhalides with a number of optically active secondary alcohols in an effort to elucidate the mechanism(s) involved.

It was demonstrated that a mol PBr3 in ether at --10 C added to 3 mols of the alcohol in ether along with 3 mols of any of several tertiary bases in ether, reacted quickly to precipitate the base hydrobromide, and from the filtrate the principal product recovered was in every case the trialkyl or tribenzyl ester. No bromide was formed and little diester hydrogen phosphite was formed.

In some cases similar results could be achieved by flushing the reaction with dry CO2 to remove HBr rather than scavenging it with the base.

So it appears that PBr3 can indeed substitute for PCl3 in the preparation of trialkyl phosphites.

I have assembled the Gerrard et al articles into a single pdf and placed it on 4shared for those interested.

http://www.4shared.com/dir/2245331/5a78115f/sharing.html

[Edited on 25-9-2007 by Sauron]

Ozone - 24-9-2007 at 15:24

SbCl5 is a liquid, all right. A smoking vile liquor capable of eating the top right off of an Aldrich sureseal, crosslinking the septum, eating thought the metal can and damaging the surrounding packaging (powdered vermiculite...). This was a 1M solution in DCM.

I have used the straight stuff to perchlorinate biphenyl (an EPA method for total PCB as decachlorobiphenyl). Kicks ass. Will perchlorinate frick-near anything.

It's rather like working with Bromine, though (will eat the gloves off of your hands and is difficult to store and is a fuming liquid...), so i'ts do-able (and nothing new here).

I am pretty damn sure that you will get PCl3 (maybe some V). The continual process sounds like what I was thinking, Fleaker! I just need SbCl3 some chlorine and the mythical ingredient, TIME:D.

With good ventilation and attention to detail (which involves a thorough awknowledgment of the properties of chlorine, SbCl3 and pickles) it can be done.

Try as I might, I can find no real literature on this. Maybe if we pull it off we should write a paper:cool:.

Cheers,

O3