[knight820]

1)What is the effect on acidity of solution when V2O5 is added to molten AlCl3?
It seems no common ion effect on it, but I have no idea on what reaction will occur on it.

2)What is the order of lewis acid strength of these compounds towards N(CH3)
BF3,B(C2H5)3,B(OC2H5)3,BBr3

Thank you!

[magician4]

ref. 1): "acidity" is not well defined in non-aqueous "solutions" ( i.e. V₂O₅ in molten Al₂Cl₆ as "solvent")
.. so I don't see how something not defined might be influenced here
(furthermore, it is quite difficult to have a melt of Al₂Cl₆, as it usually sublimes before it melts)

ref. what happens, two potential reactions come to mind:

- V₂O₅ being a strong oxidizer, it might well produce some chlorine initially at elevated temperatures, for example:
V^(+V) + 2 Cl^-  V^(+III) + Cl₂
V₂O₅ + 4 Cl^-  2 VO₂^- + 2 Cl₂ + O^2-
(amongst other redox-processes)
the oxygen-dianions stepwise will transform Al₂Cl₆ to Al₂O₃ + 6 Cl^-

- this chlorine, however, might transform V₂O₅ to VOCl₃ , which is voilatile under these conditions (b.p. 127 °C )
6 Cl₂ + 2 V₂O₅  4 VOCl₃  + 3 O₂

the oxygens produced thereby in turn might re-oxidize the V(+III), so my total process expectation would be
2 Al₂Cl₆ + 2 V₂O₅  4 VOCl₃ + 2 Al₂O₃

... but I wouldn't bet the ranch on that


ref order of lewis acid strength:
take a look at what kind of inductive effects the different substituents are known to have
the less electron density remains at the boron, the more strong a  lewis-acid it will become

regards

Ingo

[knight820]

For the second question, don't the steric effect taken place?
I know BBr3 is stronger acid than BF3 due to pi-interaction,
but how about BBr3 and B(C2H5)3?

Thanks!