Genichiro Kura

Liquid chromatographic study of the hydrolysis reactions of cyclic and linear polyphosphates in aqueous solution

Abstract Hydrolysis reactions of inorganic cyclic and linear tri-, tetra-, hexa- and octaphosphates were studied by liquid chromatography. The rate constants in 0.1 M hydrochloric acid and 0.5 M lithium hydroxide solutions at various temperatures were determined. The reaction mechanism is discussed on the basis of the rate constants and the activation energies.

Temperature dependence of the anion-exchange chromatographic behaviour of cyclic phosphate oligomers and their anion-exchange separation

Abstract The temperature dependence of the chromatographic behaviour of a series of cyclic condensed phosphates with degree of polymerization from 3 to 8 on an anion-exchange column was investigated. The efficiency of Janderas equation in predicting the elution behaviour was confirmed and the elution conditions for separating cyclic phosphates were established with the aid of computer simulations. An increase in column temperature resulted in a significant increase in the number of theoretical plates. Conditions for separating the six phosphates were not found at 30°C; however, the computer simulations suggested that suitable conditions for their separation existed at 70°C and this was confirmed experimentally. The enthalpy changes of the ion-exchange reaction of all phosphates were deterimed from the temperature dependences of their retention times and varied in proportion to their anionic charges.The ion-exchange reaction of these cyclic phosphates was governed by the dehydration of the anions and partial dissociation of ion pairs between cyclic phosphate anions and K+ ions in the eluent.

HYDROLYSIS OF CONDENSED PHOSPHATES IN AN ANION-EXCHANGE RESIN

The alkaline hydrolysis of diphosphate, triphosphate and cyclo-triphosphate sorbed into anion-exchange resins has been investigated using 31P NMR spectroscopy. Well resolved 31P NMR spectra of the sample species and their hydrolysis products within the resin phase were observed. For diphosphate and triphosphate systems, the rate constant and activation parameters for each hydrolysis reaction are quite similar, both in the resin phase and in a basic solution. For the cyclo-triphosphate system, however, the hydrolysis is significantly retarded compared to that in a solution of tetramethylammonium hydroxide. This retardation is shown to be entirely due to a much more unfavourable ΔH‡ for the reaction in the resin phase. The relationship between mechanisms and reactivities of the hydrolysis in the resin phase is discussed.

Hydrolysis reaction of inorganic cyclophosphates at various acid strengths

Hydrolysis rate constants of six-, eight-, twelve- and sixteen-membered inorganic cyclophosphates at various acid strengths at 40°C were determined. Six-membered cyclotriphosphate was the most rapidly hydrolyzed at almost all acid concentrations, as a result of its interaction with hydrogen ion, and strain in the six-membered ring structure. The hydrolysis rate of the cyclophosphate which has a stronger affinity with hydrogen ions was faster than that of others. Binding of hydrogen ions renders the phosphorus atoms more susceptible to nucleophilic attack by water molecules.

Study of cation effects on inorganic cyclophosphates hydrolysis in aqueous solutions

Abstract The ionic strength dependence of cyclophosphates hydrolysis rates was investigated at constant acid concentration. The rates decreased with the increase in the ionic strength, and hence the degree of association of cyclophosphate anions with hydrogen ions strongly affects the hydrolysis rates. In alkaline solutions, the hydrolysis rates for each phosphate decrease in the order: LiOH > NaOH > KOH > N(CH 3 ) 4 OH. When copper(II) ion of concentration 5 x 10 −3 M was added, the hydrolysis rates of the phosphates were accelerated. The “metaphosphate abstraction” was briefly discussed.

Effect of copper(II), nickel(II) and aluminum(III) ions on the hydrolysis rates of inorganic condensed phosphate oligomers

Abstract The effects of Cu 2+ , Ni 2+ and Al 3+ on the hydrolysis rates of cyclic and linear condensed phosphate oligomers have been investigated. Al 3+ ions affected the hydrolysis rate most strongly, except for the Al 3+ -cyclo-octaphosphate system at pH 3. Cu 2+ ions accelerated the rate more strongly than Ni 2+ ions. The hydrolysis rate is influenced not only by the degree of complex formation with the cations, but also by the nature of the cation bonding in the complexes.

Study of the acidic hydrolysis of cyclic trimetaphosphate by liquid chromatography

Abstract The hydrolysis of cyclic trimetaphosphate in acidic aqueous solution ([H + ] = 0.1) was investigated by liquid chromatography. The phosphate in the effluent from an anion-exchange column was detected automatically with the use of Mo(V)-Mo(VI) reagent. From the rate constants at 10, 20, 30, 40 and 50°C, the Arrhenius activation energy in 0.1 M hydrochloric acid solution for scission of a P-O-P linkage was estimated as 21.3 kcal/mole.

Potentiometric determination of stability constants of inorganic cyclophosphate complexes with copper(II), cadmium(II) and lead(II) ions

Abstract The stability constants of the complexes of cyclophosphate anions and copper(II), cadmium(II) and lead(II) ions were determined by potentiometry with the use of ion-selective electrodes. For each metal ion, the stability constant of the 1:1 complex increases linearly with the charge on the phosphate ion. For the same cyclophosphate ion, the stability constants also increase with increase in the crystal radii of the cation, i.e. in the order: Cu 2+ 2+ 2+ . These results suggest that the complex formed is a typical outer-sphere type based on electrostatic forces.

Study of the acid hydrolysis of cyclic tetrametaphosphate by liquid chromatography

Abstract The hydrolysis of cyclic tetrametaphosphate in acidic aqueous solution ([H+] = 0.1 M was investigated by automatic liquid chromatography. Anion-exchange separation of tetrametaphosphate from the hydrolysis products was achieved with 0.4 M potassium chloride solution, the pH of which was adjusted to 10.2. From the rate constants at 20, 30, 40, 50 and 60°C, the Arrhenius activation energy in 0.1 M hydrochloric acid for scission of a P—O—P linkage was 24.0 kcal/mole.

31P and 27Al NMR study on the binding isomerism and isomerization equilibrium of aluminium-cyclopolyphosphate complexes in solution

The complexes of cyclo-tri-, cyclo-tetra- and cyclo-hexaphosphate with aluminium in solution were studied using 31P and 27Al NMR spectrometry. For the 1 : 1 Al3+-P3O93− complex, only a four-membered bidentate binding complex was found. For the 1 : 1 Al3+-P4O124− complex, on the other hand, three kinds of the complex isomers (four-membered, six-membered and eight-membered bidentate binding) were found. For the 1 : 1 Al3+-P6P186− complex, four kinds of isomers (four-membered bidentate, six-membered bidentate, 10-membered bidentate and eight-membered tridentate binding) were found. The discovery of new binding isomers is based on the assignment of the 31P and 27Al NMR resonances observed as separate peaks despite the existence of a complexation equilibrium. Furthermore, the stability constants or micro-stability constants and the isomerization constants for the 1 : 1 complexes were evaluated: Kfree1 = 1.1 × 103 for the cyclo-triphosphate complex; Kfree1 = 3.3 × 104, K11–2 = 0.29 and K1–21–3 = 6.7 for cyclo-tetraphosphate complexes; and K11–2 = 8.4, K1–21–4 = 0.91 and K1–41–3–5 = 0.62 for cyclo-hexaphosphate complexes, at an ionic strength of 0.1 and 20°C.