Regarding the interesting patent that Axt attached above:
What is perhaps interesting that these lead salts aren't obvious acid base products, but adducts of some sort, and that they involve the nitrogroups
themselves.
They are formed by dissolving the polynitroaromatic acid in excess of PbO, or by dissolving the lead salt (as formed by precipitating with PbAc2) in
excess PbO.
Using *less* than i.e. 4 moles of PbO with lead picrate, however, does not yield the desired (precipitated) product, so it does need this 4x excess.
It is however possible to add 1 mol of Pb to each nitro group if a PbO (6 molar excess rather than 4) is stirred into *hot* solution of lead pictrate.
The reaction takes some time and its completion is indicated in all cases by precipitation of the adduct.
They tested this for (where the starting compound was the ordinary lead salt in all cases)
- Lead picrate, forming an adduct containing C12H4O18N6Pb5 (4 mole PbO to 1 Pb picrate) - dark yellow and insoluble
- Lead trinitroresorcinate (red powder, deflagration at 255 deg C), containing C6HO11N3Pb4 (3mole PbO to 1 PbTNR)
- Lead trinitrobenzoic acid (red powder), C14H4O20N6Pb5 (4 mole PbO to 1 PbTNBA)
- Lead nitranilate (red powder) (2 mole PbO to 1 PbNA) C6O10N2Pb3
I wonder what the structures of these things are, for instance the adduct of the PbTNBA...
All these adducts are different to the normal lead salts because of
- higher insolubility than normal lead salt
- higher sensitivity, i.e. the Pb picrate adduct explodes when exposed to flame while normal Pb picrate doesn't. |