Yes, phosphites probably are not that flammable, but still strong neurotoxins. It could form a positive azeotrope, which can change the distillation, so I would agree with BRSM going with the literature examples.
3. Pi acidity changes how it interacts with the impurities. It's the ability to interact with electron density of the impurities which has everything to do with the distillation. I was not referring to cone angle, just that it is a common reference comparing phosphorus L type ligands electronic properties. It has everything to do with phosphorus' ability to be effective.
Forgive my ignorance, but I still can't see the relevance of Pi acidity here. Pi acidity refers to the ability of a compound to accept electron density into empty Pi orbitals. This interaction is impossible with SOCl2
etc --- they simply don't have orbitals of the correct symmetry for this kind of interaction. Seriously, draw me an orbital diagram; if I'm wrong I'd like to know why. Have a look at a metal-phosphine two-way bond (https://en.wikipedia.org/wiki/Metal_phosphine_complex
) and explain to me how chlorine is doing that.
All that's going on here is attack of the phosphite lone pair on an electrophile of the "Cl+
" type: S2
, whatever. One way movement of electrons. Simple, first year orgo. No electron density is moving from the electrophile to phosphorus. Thus pi acidity---the ability of the phosphine to accept electron density---does not seem relevant to me. The phosphite is just sucking up "Cl+
" donating impurities in SOCl2
as a sigma nucleophile
. That's why the alternative of olefin-rich terpines like linseed oil is offered in The Purification of Laboratory Compounds. Really, any soft nucleophile will do. Pi acceptor ability isn't needed here.
Also, nobody's serious proposing the preparation of SOCl2
from sulfuryl chloride (SO2
), right? SOCl2
is dirt cheap, and actually making it from any other substance is not going to be worth your time. Firstly, I wouldn't count on phosphites to reduce SO2
in the way you mean, as SO2
is chlorine rather than an oxygen donor. Look at its reactivity --- it's a chlorinating reagent! Can anyone find me a reaction where a nucleophile attacks SO2
on oxygen? And even if you could reduce SO2
, in my opinion you'd be crazy to even bother.