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I want to hydrolyse a phosphonic acid ester with TMSBr.

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I think this reaction works only with the addition of base. Without base, the product in my specific case is prone to deterioation due to acid sensitivity. In the literature I found, that Collidin is used here, which is the reason why I used this base as well. I used ACN as solvent. During the addition of base and than TMSBr to the educt I immediately observed the precipitation of a white solid. UPLC indicated, that at that time the product was not yet formed. I am wondering if white precipitate might indicate the presence of water due to formation of the Collidin-Br salt? Or is there any other explanation? The ACN was dried before over mol sieve.

raptorlane
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  • Did UPLC show the starting material gone? – Waylander Mar 20 '24 at 07:52
  • Nope, still intact. When it is the Collidin br salt, than the Acetonitrile must have been very wet, but it has been dried over mol sieve.... – raptorlane Mar 20 '24 at 08:16
  • Waylander BTW This is the acid we were discussing already for some time. It is easier to to do it this way than attaching a benzyl group which did not work well, the product was not formed in big quantities. I did not check however the silayting approach yet, but I would prefer this route, because the diethylester is formed before the monofluorphosphonic acid. – raptorlane Mar 20 '24 at 08:35
  • Did you dry your collidine? It is known to be hygroscopic – Waylander Mar 20 '24 at 08:39
  • No, used straight from the bottle (without sept). But it is fairly new batch, just couple of months old. – raptorlane Mar 20 '24 at 08:51
  • It is worth putting some activated sieves in the collidine and adding a septum – Waylander Mar 20 '24 at 09:13
  • I tried mixing Collidin and TMSBr in ACN and chloroform - no precipitation. It has to be related to my compound. I actually saw my wished product in lcms and NMR but contaminated. This is a progress however, because now I know for what mass signals I need to look for. The problem in this methodology is, traces of acids during the workup may lead to product deterioation, I observed this yesterday when I evaporated the excess TMSBr and the addition of Water led to acidic pH unfortunately. Also, during reaction controll I see my mass, but the signal seems to be accompanied by a lot of others. – raptorlane Mar 21 '24 at 18:36

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