Sl. Simpson et al., ALUMINUM(III)-PYROCATECHOL VIOLET EQUILIBRIA - A POTENTIOMETRIC STUDY, Journal of the Chemical Society. Dalton transactions, (11), 1995, pp. 1799-1804
The equilibrium reactions between aluminium(III) and the dye pyrocatec
hol violet yclohexa-2,5-dien-1-ylidene)methyl]benzenesulfonic acid, H(
4)L} have been studied by potentiometric titration in aqueous solution
, / = 0.10 mol dm(-3) K(Cl), 25.0 degrees C. Equilibrium constants log
beta(pqr) for the reactions pH(+) + qAl(3+) + rH(3)L(-) reversible ar
row Hp+Alq3+(H(3)L(-))(r)(p+3q-r) were determined, as were the dye dep
rotonation constants, log beta(-n,0,1) (n = 1-3). The dye displayed bo
th quinonoid and 1,2-dihydroxyaryl binding. The data were interpreted
in terms of a series of complexes [Al(H(2)L)(n)]((3-2n)+) (quinonoid b
inding) forming at -log h < 4.5, where, h is the free hydrogen-ion con
centration, whereas at high -log h values the 1,2-dihydroxyaryl comple
xes [Al(HL)(n)L(3-n)]((n-9)+) (n = 1-3) form. Mixed-site binding occur
red at intermediate -log h values. Calculations confirmed that -log h
= 5.6-6.5 is optimum for spectrophotometric measurements, with a 1:2 c
omplex dominating in this range. Modelling calculations indicated that
the presence of gibbsite colloids in natural waters could lead to a s
ignificant error in the determination of Al3+.