[Rycus]

Hi. I've been scratching my head trying to solve a problem and was hoping someone more experienced could help.

I recently performed an experiment to create the protected phosphine of chloro-bis-diethylaminophosphine [(Et2N)2PCl]. The reaction involved adding PCl3 and diethylamine in a solution of hexanes within N2 flowing through the vessel, filtering out the precipitate, which I believe to be [Et2NH2]Cl and then removing the solvent by rotovap. I had a good looking solution going into the rotovap, but afterwards there was no solution left, only a yellow solid lining the edge of the flask.

The solid seemed damp so I removed what I could using a pipette pressed against the bottom of the flask but after the vacuum distillation, no product was attained, even after going well beyond the 120C that was needed.

Now I'm certain no product was lost in the rotovap because the temperature/pressure were such that it could not have boiled off as well as the receiver flask did not turn yellow like it would have. The solution going into the rotovap also looked good. The experiment used stochiometry to make it di-substituted.

I'm wondering, what happened and what was the solid lining the flask?

My TA couldn't figure it out. They went to perform NMR on the PCl3 but that turned out to be pure. Was it the exposure to air? Any ideas?


Thank you,

Rycus

[discodermolide]

These compounds are very air and moisture sensitive. Also they can decompose thermally to give you phosphines. So be very careful here.
Keep everything under argon and don't heat it too hard. This is a known compound, look up its boiling point.

[Rycus]

So if I understand, you think that H3PO4 was created as the by-product? When the temperature of the recovered solution reached high temperatures ~170, most of the solution had evaporated but wasn't condensing. This is higher than its boiling point (158), so that might be the case although the liquid was yellow and not colourless. The heated flask was a sort of burnt brownish-yellow colour, do you know if this is consistent with what should be expected of heated phosphoric acid (phosphates?)?

Thank you for your insight.

[discodermolide]

As I said these compounds decompose at higher temperatures to give phosphines. The fact that nothing distilled is worrying. Ultimately they will burn to give phosphates, but the yellow solids are indicative of some phosphorus polymer.
T once tried to distill methyl dichlorophosphine, it just would not boil, like you I went up with the temperature and eventually something came over, but not much. When I opened the system I got a nice flame and a schocking smell, as well as a yellowish solid formed.
Another one of my compounds formed a yellow orange solid on standing, I filtered it off and started a fire.
If you must filter the hydrochloride do it under argon in a closed system.
Note that you can buy some of these chloro phosphoramidates from Strem chemicals I think.
Might be easier to get them that way.