Janusz Chatłas

Kinetics and mechanism of base hydrolysis of Reinecke's salt revisited – specific salt effects

The kinetics of base hydrolysis of the trans-[Cr(NH3)2(NCS)4]− anion follows the rate law: -d[complex]/dt = k0 + k1[OH−] (50–70 °C, [OH−] = 0.1–1.9 M and μ = 2.0 M). The specific salt effect has been investigated for eight aqueous media: NaCl, NaBr, NaI, NaClO4, KCl, KBr, CsCl and CsBr. The alkali-independent path (k0) does not show any specific effect of inert electrolyte ions, the activation parameters: ΔH‡ = 113.5 ± 0.4 kJ mol−1 and ΔS‡ = 24.1 ± 1.3 J mol−1 K−1 are interpreted in the frame of a dissociative interchange mechanism (Id). For the alkali-dependent path (k1) the specific salt effect is observed for cations of the inert electrolyte, showing an important role for ion-pair formation between the cations and reagent complex anion in the activation process. A linear correlation between lnk1 and lnK0 (K0 – ion-pair formation constant) has been found for the cations studied. The dissociative, via conjugate base, mechanism (DCB) has been proposed for the alkali-dependent path.

Kinetics and mechanism of the acid-catalyzed hydrolysis of [carbonatoethylenediamine(L)2cobalt(III)]+ ions

The kinetics of acid-catalyzed hydrolysis of the [Co(en)(L)2(O2CO)]+ ion (L = imidazole, 1-methylimidazole, 2-methylimidazole) follows the rate law −d[complex]/dt = {k1K[H+]/(1 + K[H+])}[complex] (15–30 or 25–40 °C, [H+] = 0.1–1.0 M and I = 1.0 M (NaClO4)). The reaction course consists of a rapid pre-equilibrium protonation, followed by a rate determining chelate ring opening process and subsequent fast release of the one-end bound carbonato ligand. Kinetic parameters, k1 and K, at 25 °C are 5.5 × 10−2 s−1, 0.44 M−1 (ImH), 5.1 × 10−2 s−1, 0.54 M−1 (1-Meim) and 3.8 × 10−3 s−1, 0.74 M−1 (2-MeimH) respectively, and activation parameters for k1 are ΔH1≠ = 43.7 ± 8.9 kJ mol−1, ΔS1≠ = −123 ± 30 J mol−1 deg−1 (ImH), ΔH1≠ = 43.1 ± 0.3 kJ mol−1, ΔS1≠ = −125 ± 1 J mol−1 deg−1 (1-Meim) and ΔH1≠ = 64.2 ± 4.3 kJ mol−1, ΔS1≠ = −77 ± 14 J mol−1 deg−1 (2-MeimH). The results are compared with those for similar cobalt(III) complexes.

Anionopentaaminecobalt(III) complexes with polyamine ligands 27. Activation volumes for spontaneous and Hg2+-assisted chloride release reactions☆

Abstract Activation volumes (Δ V≠) for the spontaneous and Hg2+-assisted chloride release reactions from some [CoCl(N)5]2+ complexes have been estimated from the effect of pressure (5–150 MPa, I = 1.0 M HClO4)_on the reaction rates. Δ V≠ data for the spontaneous aquation process are all small negative (−4 to −9 cm3 mol−1) whereas for the Hg2+-assisted process, Δ V≠ are small positive (+0.5 to +3 cm[su3 mol−1). The implications are discussed in terms of an interchange substitution mechanism.

KINETICS AND MECHANISM OF THE ACID-CATALYSED HYDROLYSIS OF THE CARBONATOTETRAIMIDAZOLECOBALT(III) ION

SummaryThe kinetics of the acid-catalysed hydrolysis of the [(imidazole)4Co(CO3)]+ ion was found to follow the rate law -dln[complex]/dt = k1K[H+](1 + K[H+]) in the 25–45 °C range, [H+] 0.05–1.0 m range and I = 1.0m. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated carbonato ligand (rate-determining step) and subsequent fast release of the monodentate carbonato ligand. The rate parameter values, k1 and ITK, at 25 °C are 6.48 × 10−3s−1 and 0.31m−1, respectively, and activation parameters for k1 are ΔH1≠ = 86.1 ± 1.2kJ mol−1 and ΔS1≠ = 2.1 ± 6.3 J mol−1K−1. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes.

Kinetics and mechanism of one dipicolinato ligand substitution in the chromium(III)–bis(dipicolinato) complex: an unusual rate dependence on acid concentration

The Na[Cr(PDA)2] · 2H2O complex (PDA1 = dipicolinic acid anion) and its aquation product, [Cr(PDA)(H2O)3]+, were prepared and characterized. The electronic spectra demonstrate that the bis(dipicolinato) complex undergoes very fast partial dechelation during dissolution. In acidic media, pH controlled, rapid protolytic and ring opening processes lead to coexistence of complexes with one tridentate (PDA) and the other bi- or mono-dentate (PDA′). The kinetics of PDA ligand liberation were followed spectrophotometrically within the 0.1–2.0 M HClO4 range at I = 2.0 M. The observed first-order rate constant depends on [H+] according to the equation: kobs = A[H+]/(1 + B[H+] + C[H+]2). A reaction course via the uncharged [Cr(PDA)(HPDA′)(H2O)2]0 complex is proposed. The observed rate increase, followed by rate retardation with [H+] increase, is attributed to the unreactive [Cr(PDA)(H2PDA′)(H2O)2]+ complex. In terms of the proposed mechanism, A, B, C parameters have been defined as: A = k1Q1, B = Q1, C = Q1Q2 where k1 is the rate constant of the CrIII-carboxylato oxygen bond-breaking in the monodentate HPDA ligand, Q1 is a composite value describing protolytic and dechelation processes and Q2 is the protonation constant of the uncharged [Cr(PDA)(HPDA′)(H2O)2]0 complex.