M.J. Blandamer

Kinetics of the formation and hydrolysis reactions of some thiomolybdate(VI) anions in aqueous solution

The kinetics of the formation of the thiomolybdate ions MoOS32− and MoS42− were determined spectroscopically from the addition of excess sulphide to MoO2S22− in pH buffered media (6–8) at 30 °C. The reverse (hydrolysis) reactions of MoO2S22− and MoOS32− were measured under the same conditions. The reaction rates measured are shown below: Values of the rate-constants (s−1) obtained at pH 7.0 were k10 2.4 × 10−3, k21 1.5 × 10−5, k30 2.1 × 10−5, k23 6.0 × 10−4, and k34 1.9 × 10−5; where the results are comparable they are in good agreement with those obtained by earlier workers, although different conditions were used. However, in this work it was found that certain reactions had to be mathematically treated as two consecutively occurring reactions. There is also a difference in interpretation of the mechanism of the hydrolysis reactions of the tri- and tetrathio ions. In general the lability towards further S replacement of O atoms, and the reverse reaction, decreased with increased S substitution. All reaction rates increased with increasing H+ ion concentration, mostly this was a linear relationship over the limited pH range examined. The effect of the H+ ion is interpreted in terms of protonation of the oxythiomolybdate ions at an O atom leading to increased lability.

Calorimetric studies of macromolecular aqueous solutions

DoUi tilration and differential scanning microcalorimelric techniques are shown to yield important information concerning the properties of macromolecules in aqueous solution. Application of titration calorimetry is examined in the context of &aggregation of cationic miceiles (e.g. hexadecyilrimethyiaonium bromide), of guest-host interactions and of enzyme-substrale interactions (e.g. CAT,,, with cllloramphenicol). Experimenlal data oblained using DSC are reviewed with reference lo the thermal stability of enzymes (e.g. DNA-Gyrase) and lo the gel to liquid crystal transition characlerising vesicles foonned by dialkylphosphates. In Uw: latter, the dependcnce of the characteristic melting temperature T,,, on chain length, counter cation and added solute is noted.

Enthalpies of solution of lanthanum, gadolinium and ytterbium trichlorides in binary aqueous solvent mixtures

Abstract Enthalpies of solution are reported for anhydrous lanthanum trichloride in methanol-, ethanol-, t-butyl alcohol-, and dimethyl sulphoxideue5f8water mixtures, for anhydrous gadolinium trichloride in methanolue5f8water mixtures, and for ytterbium trichloride in methanol- and dimethyl sulphoxideue5f8water mixtures, at 298.2 K. The estimation of enthalpies of transfer of lanthanide(III) cations into these binary aqueous solvent mixtures is discussed.

Kinetics of oxidation of ferrocene by tris-1,10-phenanthrolinecobalt(III) in t-butyl alcoholwater and acetonewater mixtures

Rate constants and activation parameters (ΔH≠ and ΔS≠)are reported for the oxidation of ferrocene by the tris-1,10-phenanthrolinecobalt(III) cation in t-butyl alcoholue5f8water and in acetoneue5f8water solvent mixtures. Solvent effects on reactivity trends for these systems, for this same reaction in methanolue5f8water mixtures, and for cobalt(II)-catalysed racemisation of Co(phen)33+ in t-butyl alcoholue5f8water solvent mixtures are analysed into initial state and transition state contributions. The dependences of solubilities on solvent composition for ferrocene and for [Co(phen)3](ClO4)3 in methanolue5f8, t-butyl alcoholue5f8, and acetoneue5f8water mixtures are also reported; these results are needed in order to establish solvent effects on the initial states of the reactions studied.

Solubilities of caesium and thallium(I) triphenylcyanoboronates and of caesium and mercury(II) tetraphenylboronates in alcohol + water mixtures; Transfer chemical potentials of the BPh3(CN)−, BPh4−, TI+, and Hg2+ ions

Abstract Solubilities(298.2 K) are reported for caesium and thallium(I) triphenylcyanoboronates in water and in methanol-, ethanol-, and t-butyyl alcohol-water mixtures containing up to 40% (by volume) alcohol. Solubilities (298.2 K) are also reported for caesium tetraphenylboronate in t-butyl alcohol- and ethylene glycol-water mixtures and for mercury(II) tetraphenylboronate in t-butyl alcohol-water mixtures, again up to 40% (by volume) alcohol. From these data and published transfer chemical potentials (based on various extrathermodynamic assumptions) for appropriate ions, we have derived estimates for the transfer chemical potentials of BPh3(CN)− and TT+ to methanol, ethanol, and t-butyl alcohol-water mixtures, for BPh4− to t-butyl alcohol- and ethylene glycol-water mixtures, and for Hg2+ to t-butylalcohol-water mixtures.

The isomerisation of cis-bis-triethylphosphine-4-fluorophenyl-chloroplatinum(II): Solvent effects and mechanism

Abstract Rate constants are reported for isomerisation, solvolysis, and thiourea substitution of cis -[Pt(PEt 3 ) 2 (4-FC 6 H 4 )Cl] in aqueous methanol and in aqueous ethanol. From these results and ancillary solubility measurements the observed effects of solvent on reactivity are analysed into initial state and transition state contributions, for isomerisation of this complex and for its reaction with thiourea. The initial state-transition state analysis for isomerisation is consistent with a dissociative mechanism, the reactivity trends being dominated by solvation of the leaving chloride ligand.