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Equilibria between aluminium(III), pyrocatechol (1,2-dihydroxybenzene, H2L) and OH− were studied in 0.6 M Na(Cl) medium at 25°C. The measurements were performed as emf titrations (glass electrode) within the limits 1.5 ≤ − log[H+] ≤ 9; 0.0005 ≤ B ≤ 0.015 M; 0.006 ≤ C ≤ 0.03 M and 2 ≤ C/B ≤ 30 (B and C stand for the total concentrations of aluminium(III) and pyrocatechol respectively). All data can be explained with a main series of complexes: A1L+, log β−2,1,1 = − 6.337 ± 0.005; A1L2−, log β−4,1,2 = −15.44 ± 0.017 and A1L33−, log β−6,1,3 = − 28.62 ± 0.024 together with two minor species: Al(OH)L22−, log β−5,1,2 = − 23.45 ± 0.079 and Al3(OH)3L3, log β−9,3,3 = − 29.91 ± 0.066. Of the two, the latter probably is a type of average composition complex principally occurring at low C/B quotients. The first acidity constant for pyrocatechol as determined in separate experiments is log β−1,0,1 = − 9.198 ± 0.001. The standard deviations given are 3σ(log β p,q,r). Data were analyzed with the least squares computer program LETAGROPVRID. In a model calculation using kaolinite as solid phase, we compared the complexation ability of this system with that of the system Al3+-OH−-salicylic acid, reported earlier in this series. 相似文献
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