Hisahiko Einaga

Hydrolytic precipitation reaction of titanium(IV) from (Na, H)Cl aqueous solution

Abstract The hydrolytic precipitation of titanium(IV) in 2.0 mol dm −3 (Na, H)Cl aqueous solution at 25.0°C has been studied by measuring the free hydrogen ion concentration by a potentiometric method and the aqueous concentration of titanium(IV) by a spectrophotometric method. Under conditions where the solution is saturated with regard to precipitated titanyl(IV) hydroxide, monomeric and polycationic species, such as, TiO 2+ , TiO(OH) 2 , and [(TiO) 8 (OH) 12 ] 4+ , were deduced as being present in the solution. A scheme for the hydrolytic precipitation equilibria has been deduced.

COORDINATION OF 8-QUINOLINOL-5-SULFONIC ACID TO ALUMINIUM(III) COMPLEXES OF 8-HYDROXY-7- [(6 ' -SULFO-2 ' -NAPHTHYL)AZO]-QUINOLINE-5-SULFONATE. EVIDENCE FOR MIXED LIGAND COMPLEX FORMATION

Abstract Studies have been made on the coordination behaviour of the aluminium(III) 8-quinolinol-5-sulfonate (hqs)1 and aluminium(III) nqs1 complexes2 with hqs in 0.1 mol dm−2 aqueous sodium chloride solution at 25°. Mixed-ligand complex formation was evidenced by electronic absorption spectral and other spectrophotometric equilibrium studies. Stopped-flow kinetic studies revealed that mixed-ligand complex formation with a mono-nqs complex proceeds via its reaction with Hhqs− and hqs2- whereas formation of the tris-hqs complex proceeds via the reaction of [Al(H2O)6]3+ with Hhqs− and hqs2- and also of [Al(OH)(H2O)5]2+ with H2 hqs and Hhqs−. Coordination mechanisms and structures for the mixed-ligand and the tris-hqs complexes are also discussed.

The hydrolytic precipitation reaction of Mg(II) from aqueous NaNO3 solution

Abstract An equilibrium study has been made of the hydrolytic precipitation reaction of Mg(II) in 1.0 mol dm−3 aqueous NaNO3 solution at 25.0°C by measurements of the free hydrogen ion concentration by a potentiometric method and of the dissolved Mg(II) by a complexometric method. Under the condition that the solution is saturated with precipitated Mg(II) hydroxide, such species as Mg2+, Mg2(OH)22+, Mg3(OH)42+ and Mg(OH)2 may be present; their stability constants and solubility products were determined. A scheme for the hydrolytic precipitation equilibria of Mg(II) is presented.

Spectrophotometric determination of beryllium with calcichrome

A method is established for the spectrophotometric determination of small amounts of beryllium as a 1:1 complex with Calcichrome in slightly acidic solution. Beers law is obeyed over the range 0.05-0.6 ppm Be in the final solution and the apparent molar absorptivity is 9.7 x 10(3) l.mole(-1). cm(-1) at 625 nm. Up to about 15 mug of beryllium in the final solution can be sensitively and selectively determined with a relative error of less than 2% in the presence of EDTA as masking agent.

Spectrophotometric study of the reaction of zirconium with Chrome Azurol S and fluoride

A relatively simple and convenient procedure for the determination of small amounts of fluoride has been established. It is based on the decrease in absorbance when fluoride is added to a solution of the zirconium-Chrome Azurol S complex. Microgram amounts of fluoride can be determined with an error of better than about 2%. Some practical applications are presented.

Complex formation and precipitation reaction of titanium(IV) from (Na, H)Cl aqueous solution containing phosphate

Abstract An equilibrium study has been made of complex formation and precipitation of titanium (IV) in 2.0 mol dm −3 (Na, H)Cl aqueous solution at 25°C, in the presence of 1.3–5.4 times (in molar ratio) as much phosphate, using measurements of the free hydrogen ion, saturated titanium (IV), and phosphate concentrations. Under these condition, titanium (IV) mono-orthophosphate complex TiO(HPO 4 ) alone was found in the solution; its stability constant and solubility product were determined. A scheme of complex formation and precipitation equilibria is presented.

Ligand substitution reaction of (carbonato) bis(ethylenediamine) cobalt (III) complex with ethylenediamine

Abstract Substitution reaction of coordinated carbonate ligand in [Co(CO3)(en)2]+ in alkaline aqueous solution of 1.0 mol dm−3 chloride at 55 °C under the pesudo-first-order kinetic condition with respect to ethylenediamine has been studied, by employing the electronic absorption and circular dichroism spectral methods for the racemate and the optically active isomers. The reaction proceeded stepwise with two rate-determining steps. Δ-(−)589-[Co(CO3)(en)2]+ changed via two parallel pathways principally with racemization to [Co(OCO2)(OH)(en)2], which subsequently changed to [Co(en)3]3+ through [Co(OCO2)(en-N)(en)2]+; were OCO22− and en-N denote unidentate carbonate and ethylenediamine, respectively. Some stereoselectivity was noticed in the first base-catalyzed hydrolysis step. A substitution reaction mechanism was discussed.

Ligand substitution reactions of (bidentato-O,O and −O,N) bis(ethylenediamine)cobalt(III) complexes with ethylenediamine catalyzed by photoexcited tris(2,2′-bipyridine)ruthenium(II) complex: The role of circularly polarized light in photoirradiation

Abstract The substitution reactions with ethylenediamine of the bidentato-O,O ligand of (bidentato-O,O)bis(ethylenediamine)cobalt(III) complex have been studied in a weakly alkaline aqueous solution in the presence of tris(2,2′-bipyridine)ruthenium(II) complex under photoirradiation. The reaction was catalyzed by the photoexcited ruthenium(II) complex. Enhanced generation of the photoexcited ruthenium(II) complex and acceleration of the reaction of the bidentato-O,N ligand of (bidentato-O,N)bis(ethylenediamine)cobalt(III) complex were noticed when the optically active isomer of the ruthenium(II) complex was irradiated by the corresponding circularly polarized light.

Kinetics and mechanism of substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine) glycinatocobalt(III) complex

The substitution reaction with ethylenediamine of the coordinated glycinate ligand of bis(ethylenediamine)glycinatocobalt(III) complex has been studied at 60–70°C in a weakly alkaline aqueous solution (buffered around pH 12) of 1.0 mol dm−3 chloride concentration. The reaction was studied under the pseudo-first-order kinetic conditions with respect to ethylenediamine and followed by means of electronic absorption spectra for the racemate and by circular dichroism spectra for the optically active isomers. The reaction proceeds stepwise with three rate-determining steps: the first step is dependent neither on ethylenediamine nor on hydroxide ion concentration but in accompanied by loss of optical activity, while the second one is dependent both on ethylenediamine and on hydroxide ion concentrations. Mechanisms of the ligand substitution reaction are discussed.