Potentiometric titration of monofunctional bases in ion exchanger-aqueous solution medium. Multiple equilibriums

1974 ◽  
Vol 46 (3) ◽  
pp. 344-350 ◽  
Author(s):  
Frederick F. Cantwell ◽  
Donald J. Pietrzyk
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Ion Exchanger

A study of the decomposition behaviour of 12-tungstophosphate heteropolyacid in solution

2003 ◽  
Vol 81 (10) ◽  
pp. 1044-1050 ◽  
Author(s):  
Zhirong Zhu ◽  
Ruan Tain ◽  
Colin Rhodes
Keyword(s):  
Aqueous Solution ◽  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
Potentiometric Titration ◽  
Inductively Coupled Plasma ◽  
High Performance ◽  
Atomic Emission ◽  
Inductively Coupled ◽  
Vis Spectroscopy ◽  
Decomposition Behaviour

In this paper, the decomposition of H3PW12O40 in aqueous solution or in mixed solutions of water–ethanol or water–acetone is investigated by potentiometric titration and 31P NMR. Identification of the products from H3PW12O40 decomposition over a pH range of 1–12 was achieved using preparation high performance liquid chromatography (Pre-HPLC) combined with IR, UV–vis spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP). It is found that H3PW12O40 in aqueous solution decomposes in a stepwise fashion with increasing pH, with the following solution compositions: [PW12O40]3– (at pH ~ 1) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– (at pH 2.2) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– + [P2W19O67]10– (at pH 3.5) [Formula: see text] [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– (at pH 5.4) [Formula: see text] [PW9O34]9– (at pH 7.3) [Formula: see text] PO43– + WO42– (pH > 8.3). In the first stages at pH < 8, H3PW12O40 decomposes partially with removal of W=O units. In the second stage at pH > 8, tungstophosphoric completely decomposes to PO43–. In contrast, the decomposition of H3PW12O40 is reduced, or the stability of the [PW12O40]3– anion is enhanced, in ethanol–water or acetone solution at pH < 8. Key words: 12-tungstophosphate heteropolyacid, decomposition behaviour, potentiometric titration, 31P NMR, preparation high performance liquid chromatography.

Kinetics, stoicheiometry, and mechanism in the bromination of aromatic heterocycles. I. Aqueous bromination of pyrazole, 1-methylpyrazole, and 3,5-dimethylpyrazole

1971 ◽  
Vol 24 (7) ◽  
pp. 1413 ◽  
Author(s):  
BE Boulton ◽  
BAW Coller
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Electrode Potential ◽  
Rate Coefficients ◽  
Molecular Bromine ◽  
Aromatic Heterocycles ◽  
Dilute Aqueous Solution ◽  
Direct Attack ◽  
Rate Behaviour ◽  
Bromide Solutions

A procedure is described for monitoring the reactivity of a substrate towards bromine in aqueous bromide solutions, as a function of extent of reaction, by following the changes of electrode potential with time in the intervals between successive periods of electrolysis. ��� The title compounds show 1 : 1 stoicheiometry with substitution in the 4-position. The observed rate behaviour may be understood in terms of direct attack by molecular bromine on the neutral substrate molecules, rate coefficients for dilute aqueous solution at 25�C being: ����� k20(Br2+pyrazole) = 3.8x105 dm3 mol-1 s-1, kH/kD = 1.39;����� k20(Br2+1.methylpyrazole) = 8.0x105 dm3 mol-1 s-1;����� k20(Br2+3,5-dimethylpyrazole) = 1.4x109 dm3 mol-1 s-1, kH/kD = 1.08 Values of pKa(pyrazole-H+) = 2.58 and pKa(3,5-dimethylpyrazole-H+) = 4.11 were determined by potentiometric titration methods.

Aluminium(III) and Iron(III) 1,2-Diphenolato Complexes: a Potentiometric Study

1985 ◽  
Vol 38 (5) ◽  
pp. 659 ◽  
Author(s):  
JA Kennedy ◽  
HKJ Powell
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Protocatechuic Acid ◽  
Acid System ◽  
Experimental Conditions ◽  
Potentiometric Study ◽  
Hydroxo Complexes ◽  
Equilibrium Reactions ◽  
Ternary Metal ◽  
Metal Ligand

The equilibrium reactions between aluminium(III) and the phenols catechol (LH2), protocatechuic acid (LH3) and catechin (LH4), and between iron(III) and protocatechuic acid have been studied by potentiometric titration in aqueous solution, I 0.10M ( KCl ), 25°C. Stability constants are reported for the mononuclear diphenolato complexes AlLHn-2, Al(LHn-2)2and Al(LHn-2)3, and the hydroxo complexes Al(OH)LHn-2 and Al(OH)(LHn-2)2, n = 2 ( catechol ) or 4 ( catechin ). For protocatechuic acid, the carboxylate -coordinated species lLH22+ and the species AlLH + (carboxyl- protonated ) are also postulated. Analogous species were characterized for the iron(III)- protocatechuic acid system. Stoichiometric end-points were obtained only if an excess of ligand was used (L/M > 4). Monomeric and polymeric aluminium- hydroxo species and ternary metal- ligand - hydroxo species were found to be unimportant under the experimental conditions employed.

Preparation of the 1-(2,5-anhydro-β-d-arabinofuranosyl) derivatives of cytosine and uracil and their cleavage with hydrogen bromide

1982 ◽  
Vol 47 (11) ◽  
pp. 2961-2968 ◽  
Author(s):  
Hubert Hřebabecký ◽  
Josef Brokeš ◽  
Jiří Beránek
Keyword(s):  
Aqueous Solution ◽  
Sodium Hydroxide ◽  
Hydrogen Bromide ◽  
Ion Exchanger ◽  
Alternative Synthesis ◽  
Derivatives Of ◽  
Uracil Derivative

Anhydronucleoside Ia was prepared from chloroarabinofuranosylcytosine IIIc or from 2,2'-anhydro-1-(5-chloro-5-deoxy-β-D-arabinofuranosyl)cytosine by the action of a strongly basic ion exchanger. The anhydro derivative IIa was prepared from 2,2'-anhydro-1-(5-chloro-5-deoxy-β-D-arabinofuranosyl)uracil by treatment with aqueous solution of sodium hydroxide. The action of hydrogen bromide in dimethylformamide on 2',5'-anhydronucleosides Ia and IIa leads both to the cleavage of the anhydro bond under formation of the 5'-bromo derivatives IIIa and IVa and to the cleavage of nucleosidic bond. In case of the uracil derivative IIa, the α-arabinofuranosyl derivative V was also isolated after preceding acetylation. For unambiguous proof of the structure, an alternative synthesis of compound V was performed.

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