Sciencemadness Discussion Board - Direct Esterification of Phosphoric Acid

Direct Esterification of Phosphoric Acid

DDTea - 28-2-2003 at 01:53

I read some things about this on various websites, of simply reacting a Primary Alcohol with ortho-Phosphoric Acid to obtain Alkyl Phosphates. Sulfuric Acid is used as a catalyst during the reaction. Basically, the reaction proceeds much the same way as esterification of Carboxylic Acids.

However, I have not found any practical procedures in regard to this. Usually, obtaining Phosphoric Acid esters is done using Phosphorus Trichloride as the main precursor. This is unfortunate, since Phosphorus Trichloride is so difficult to come by.

At the moment, my "lab" is in pitiful condition. I have plenty of chemicals, but just about no equipment, not even a heat source or scale. As such, I am very limited in my experiments, and I cannot test this out for myself (I imagine that slight heating may be necessary). So, I am wondering if anyone else knows a bit about the topic, especially regarding yields by this method.

[Edited on 28-2-2003 by Samosa]

DDTea - 3-3-2003 at 15:31

Well, since this topic seems to be a bit dead, maybe I should bring something else to the table

.

The reaction would proceed this way ("equation" showing just part of Phosphoric Acid molecule) :

P-OH + R-OH --Drying Agent--> P-O-R + H2O

Correct? Now, am I right to assume that the more powerful the drying agent, the more efficiently the reaction is carried out?

If this is the case, if one were to make Phosphoric Acid Esters, could concentrated, fuming Sulfuric Acid be used to catalyze the reaction? I'm sure P2O5 would be an even better choice, but that is not easily obtained by everyone.

Also, would about synthesizing Pyrophosphoric Acid? One simple way to make it is to heat Ortho-Phosphoric Acid to some 215*C (I may be wrong, but this sounds right...). However, such high temperatures are a pain. Could this reaction be done with lower heats if catalyzed with a drying agent, such as said concentrated Sulfuric Acid?

madscientist - 3-3-2003 at 15:51

It probably would be possible to yield the dialkyl ester via direct esterification, but not the trialkyl ester; the third hydrogen is not very acidic. Adding a dessicant likely would help, but also would make it more difficult to separate out the ester from the reaction mixture (depending on what you used as the dessicant). Use of H2SO4 as a catalyst certainly would be a good idea; heating would also speed the reaction up.

It shouldn't be hard to heat H3PO4 to around 215C. My heavily damaged $15 hotplate can easily top 300C when standing outside in whipping -20C winds.

I don't think that H2SO4 will be of much help in the dehydration of H3PO4. Consider the fact that H2SO4 is dehydrated to SO3 by the action of P4O10. Even if it worked, it really wouldn't be removing the water from the mixture, as H2SO4 molecules dehydrate simply by coordinating water molecules around itself. You wouldn't be able to distill out the H4P2O7, which would circumvent that issue, because it will decompose into HPO3 rather than boil.

PHILOU Zrealone - 4-3-2003 at 01:18

H3PO4 can be dehydrated by long boiling!
Naturally at 40°C pure H3PO4 turns into H4P2O7
in the amount of arround 6% at equilibrium!

2(HO)3P=O <--> H2O + (HO)2P(O)-O-P(O)(OH)2
You thus have anydride of orthophosphoric acid forming naturally!And heating a little and taking the water off will form more and more anhydride!
The idea would be to heat it under 200°C under reflux with a dehydratant in another compartiment (at the output to force dehydration without any contamination).
(HO)2P(O)-OH + HO-P(O)(OH)2 <--> H2O + (HO)2P(O)-O-P(O)(OH)2
(HO)2P(O)-O-P(O)(OH)2 + HO-P(O)(OH)2 <--> H2O + (HO)2P(O)-O-P(O)-O-P(O)(OH)2
...
YOU FINALY GET POLYPHOSPHORIC ACID (what is a polyanydride of acid) often used to make certain kind of nitramines aside with conc HNO3!
(HO)2P(O)-O(-P(O)-O-)n-P(O)(OH)2

This natural presence of anhydride in the acid must explain the fast esterification of alcools!
(HO)2P(O)-O-P(O)(OH)2 + 4R-OH -->
(RO)2P(O)-O-P(O)(OR)2 + 4 H2O
(HO)2P(O)-O-P(O)(OH)2 + H2O --> 2 H3PO4
(RO)2P(O)-O-P(O)(OR)2 + ROH --> (RO)3P=O + (RO)2(HO)P=O

Anyway the best way is not to use H2SO4 since in the mix you will not only have:
(RO-)P(OH)2=O, (RO-)2P(OH)=O and (RO-)3P=O
But also RO-S(OH)O2 and (RO-)2SO2 sulfuric esters that favourise the formation of ether R-O-R and alcene R=R if the heat exceeds 170°C!

Lab procedure uses not the PCl5 since reaction is too violent!
PCl5 + 5 HO-R --> P(OR)5 + 5HCl(g)
P(OR)5 --> (RO)3P=O + R-O-R

But Cl3P=O is favourised because more controlable and less risky!
Cl3P=O + 3 R-OH --> (RO)3P=O + 3HCl(g)

DDTea - 7-3-2003 at 12:17

According to that wonderful Phosphorus-Fluorine book that Polverone uploaded, Secondary Alcohols influence an Organophosphate molecule by making more toxic... Quite a common Secondary Alcohol is Isopropanol.

If I recall correctly, TEPP reacts with the enzyme Cholinesterase by splitting in the center of the molecule, and one half of the TEPP bonds to the Cholinesterase Molecule. Therefore, you have Diethyl Phosphate bonded to the Enzyme...

Also, if I recall correctly, Ethyl-Phosphates are degraded quickly in the body, thus making their effects somewhat short-lived. On the other hand, Isopropyl-Phosphates last rather long in the body...

Where is this all leading? I theorize that the compound Tetra-Isopropyl Pyrophosphate will be a cheap, easily manufactured compound, with toxicity comparable to DFP. When this theoretical molecule (Which I cannot find any information on; perhaps I'm not searching properly) reacts with Cholinesterase, Diisopropyl Phosphate will be what bonds do it... This is similar to when DFP reacts with Cholinesterase, and the F reacts with the OH in Cholinesterase, forming HF and Diisopropyl Phosphate bonded to Cholinesterase.

I do not expect a Phosphate molecule to be as reactive as straight Fluorine, but that is why I said the toxicity would be "comparable" to DFP

. Does my reasoning seem sound?

PHILOU Zrealone - 10-3-2003 at 04:56

To get a potent nerve gas...you need it volatilised!
Pyrophospahte ester will be rater less volatile than phosphoric ester!
The fluoro part also enhance volatility, while the ester link increase molecular attraction!

PH Z

DDTea - 10-3-2003 at 15:42

I imagine that the problem of volatility could easily be solved through suitable weaponization and dispersal, so that should not be much of a concern...

Other than that, though, the big problem with Pyrophosphate Esters is that they like to hydrolyze...but last I checked, it takes about 12 hours for TEPP to hydrolyze completely.

The big advantage I see with Pyrophosphates over Phosphate Esters is that they are significantly cheaper to manufacture, thus allowing much more experimentation. Furthermore, their precursors are not watched at all (Who is going to watch Rust Remover and Rubbing Alcohol?

).

Also, if I recall correctly, Pyrophosphate Esters are more of a hazard through skin contact... I may be wrong.

But, just assuming that everything goes well and enters the test subject's body...How do you expect "Tetra-Isopropyl Pyrophosphate" to react with Cholinesterase? Would you imagine it being as I said?

tsk tsk

Polverone - 10-3-2003 at 17:16

What is this "weaponization" you speak of? This isn't Amateur Night at Edgewood Arsenal.

DDTea - 11-3-2003 at 08:27

Hehe, sorry mate... still used to the E&W ways

DDTea - 16-3-2003 at 16:54

I was thinking... would HF react with Phosphoric Acid?

I was imagining that the Fluorine would displace the OH group, which would then react with Hydrogen to form water...sort of like a reaction between an Acid and a Base. The reason I was thinking this is because Fluorine is far more reactive than Oxygen, and as such would displace the Oxygen rather than simply displace the Hydrogen.

PHILOU Zrealone - 18-3-2003 at 06:27

To my knowledge the F is important to get a very toxic stuff; thus the normal ester (pyrophosphate of phosphate will be much less toxics except maybe via injection!).

The fact secundary alcohols enhance stability towards hydrolysis is due to steric hindrance...it should be even better with tertiary alcohols.

About the toxicity:
Methyl = isoproply > ethyl is always true for all organics...our body have developped a certain resistance towards ethyl moiety!

Maybe the toxicity is increased in this case owing to electrogiving effect of the alkylic part; but I doubt it since they are esters and the oxygen (separating R from P) stops that effect quite fast.

Samosa:
If:
F2 + H2 --> HF + hell lot of energy
It reacts explosively at -200°C!
and if
F2 + O2 is stable mix and slowly turns via HOF into stable F2O.

O2 + HF is stable and gives nothing!

HF + HO-R gives no R-F

HF + HO-NO2 gives nothing!

F2 + HO-NO2 --> HF + FO-NO2

PHILOU Zrealone - 19-3-2003 at 01:17

"F2 + O2 is stable mix and * slowly turns via HOF into stable F2O."

I forgot this:
* water

F2 + H2O --> HOF + HF
HOF + F2 --> F2O + HF

Tetra-Isopropyl Pyrophosphate to Diisopropyl Fluorophosphate?

DDTea - 14-5-2003 at 07:45

Back on the idea of Tetra-Isopropyl Pyrophosphate...

Would it be possible to convert it to Diisopropyl Fluorophosphate (DFP) through a reaction with Hydrofluoric Acid? I am theorizing it would proceed as follows...

[B](Iso)P=O(Iso)-O-(Iso)P=O(Iso) + HF --> (Iso)P=O(Iso)-F + HO-(Iso)P=O(Iso) [B]

I'm guessing it would work similarly to the Fluorination step in many Organophosphates, where HF is reacted with a Chlorophosphate to produce Hydrochloric Acid and the Fluorophosphate. However, in place of the Chlorophosphate, here we have the Diisopropyl Phosphate

. Basically, a reaction where a more reactive ion replaces a less reactive ion.

Iv4 - 6-6-2003 at 21:45

It could work but I think flourinating the phosphorous before should be better(drunk and probably wont remember any of this).

Diispropylphosphono-sulfer(real drunk)is probably worth looking into.My guess is that this could be done readely from polysulfides.