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Title: Protonation Constants for Triarylphosphines in Aqueous Acetonitrile Solutions

Abstract

No abstract prepared.

Authors:
; ;
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA
Sponsoring Org.:
USDOE Office of Science and Technology (OST) - (EM-50)
OSTI Identifier:
891283
Report Number(s):
IS-J 7084
Journal ID: ISSN 0276-7333; ORGND7; TRN: US200621%%722
DOE Contract Number:
W-7405-Eng-82
Resource Type:
Journal Article
Resource Relation:
Journal Name: Organometallics; Journal Volume: 25
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACETONITRILE; CHEMISTRY; AMES LABORATORY

Citation Formats

Oleg Pestovsky, Andrew Shuff, and Andreja Bakac. Protonation Constants for Triarylphosphines in Aqueous Acetonitrile Solutions. United States: N. p., 2006. Web. doi:10.1021/om060221z.
Oleg Pestovsky, Andrew Shuff, & Andreja Bakac. Protonation Constants for Triarylphosphines in Aqueous Acetonitrile Solutions. United States. doi:10.1021/om060221z.
Oleg Pestovsky, Andrew Shuff, and Andreja Bakac. Wed . "Protonation Constants for Triarylphosphines in Aqueous Acetonitrile Solutions". United States. doi:10.1021/om060221z.
@article{osti_891283,
title = {Protonation Constants for Triarylphosphines in Aqueous Acetonitrile Solutions},
author = {Oleg Pestovsky and Andrew Shuff and Andreja Bakac},
abstractNote = {No abstract prepared.},
doi = {10.1021/om060221z},
journal = {Organometallics},
number = ,
volume = 25,
place = {United States},
year = {Wed Mar 08 00:00:00 EST 2006},
month = {Wed Mar 08 00:00:00 EST 2006}
}
  • Absolute rate constants for reactions of the dichlorine radical anion, Cl{sub 2}{sup {sm_bullet}{minus}}, with unsaturated alcohols and hydrocarbons have been measured at various temperatures. The alcohol reactions were measured in aqueous solutions and the hydrocarbon reactions in 1:1 aqueous acetonitirle (ACN) solutions. The rate constants for two alcohols and one hydrocarbon were also examined as a function of solvent composition. The room temperature rate constants varied between 10{sup 6} and 10{sup 9} M{sup {minus}1} s{sup {minus}1}. The pre-exponential factors, A, were about (1-5) {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1} for the alcohols in aqueous solutions and about (0.1-1) {times}more » 10{sup 9} M{sup {minus}1} s{sup {minus}1} for the hydrocarbons in aqueous ACN solutions. The activation energies, E{sub a}, varied considerably, between 4 and 12 kJ mol{sup {minus}1} for the alcohols and between 2 and 8 kJ mol{sup {minus}1} for the hydrocarbons. The rate constants, k{sub 298}, decrease with increasing ionization potential (IP) of the unsaturated compound, in agreement with an electrophilic addition mechanism. The activation energies for the unsaturated alcohols decrease when the IP decreases from 9.7 to 9.1 eV but appear to level off at lower IP. Most alkenes studied had IP < 9.1 eV and showed little change in E{sub a}. Upon addition of ACN to the aqueous solution, the values of log k{sub 298} decreased linearly by more than 1 order of magnitude with increasing ACN mole fraction. This decrease appears to result from a combination of changes in the activation energy and in the pre-exponential factor. The reason for these changes may lie in changes in the solvation shell of the Cl{sub 2}{sup {sm_bullet}{minus}} radical, which will affect the A factor, in combination with changes in solvation of Cl{sup {minus}}, which will affect the energetics of the reactions as well. 20 refs., 7 figs., 6 tabs.« less
  • Precise vapor pressure data for solutions of Nal in ethanol from 0.04 to 1.9m, and 2-propanol and acetonitrile from approximately 0.06 to 1.5m are communicated and discussed. Polynomials in molalities are given for calculating precise reference values. Osmotic coefficients were calculated by taking into account the second virial coefficients of solvent vapors. Discussion of the data at low concentrations is based on the chemical model of electrolyte solutions and ion-pair association constants are compared to those obtained from other properties of sodium iodide solutions. Pitzer equations are used to reproduce osmotic and activity coefficients at high concentrations; the set ofmore » Pitzer parameters for methanol solutions b = 3.2, ..cap alpha../sub 1/ = 2.0, and ..cap alpha../sub 2/ = 20.0 may be used for ethanol, 2-propanol, and acetonitrile solutions.« less
  • The TALSPEAK process (Trivalent Actinide Lanthanide Separations by Phosphorus-reagent Extraction from Aqueous Komplexes) has been demonstrated in several pilot-scale operations to be effective at separating trivalent actinides (An 3+) from trivalent lanthanides (Ln 3+). However, fundamental studies have revealed undesired aspects of TALSPEAK, such as the significant partitioning of Na +, lactic acid, and water into the organic phase, thermodynamically unpredictable pH dependence, and the slow extraction kinetics. In the modified TALSPEAK process, the combination of the aqueous holdback complexant HEDTA (N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid) with the extractant HEH[EHP] (2-ethyl(hexyl) phosphonic acid mono-2-ethylhexyl ester) in the organic phase has been found tomore » exhibit a nearly flat pH dependence between 2.5 and 4.5 and more rapid phase transfer kinetics for the heavier lanthanides. To help understand the speciation of Ln 3+ and An 3+ in the modified TALSPEAK, systematic studies are underway on the thermodynamics of major reactions in the HEDTA system under conditions relevant to the process (e.g., higher temperatures). Thermodynamics of the protonation and complexation of HEDTA with Ln 3+ were studied at variable temperatures. Equilibrium constants and enthalpies were determined by a combination of techniques including potentiometry and calorimetry. This paper presents the protonation constants of HEDTA at T = (25 to 70) °C. The potentiometric titrations have demonstrated that, stepwise, the first two protonation constants decrease and the third one slightly increases with the increase of temperature. This trend is in good agreement with the enthalpy of protonation directly determined by calorimetry. The results of NMR analysis further confirm that the first two protonation reactions occur on the diamine nitrogen atoms, while the third protonation reaction occurs on the oxygen of a carboxylate group. These data, in conjunction with the thermodynamic parameters of Ln 3+/An 3+ complexes with HEDTA at different temperatures, will help to predict the speciation and temperature-dependent behavior of Ln 3+/An 3+ in the modified TALSPEAK process.« less
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