Michel Wozniak

Acidites et complexes des acides (alkyl-et aminoalkyl-) phosphoniques—IV Acides aminoalkylphosphoniques R1R2N(CH2)nCR3R4PO3H2

The acids under study differed from one another in length of the carbon chain [N + H(3)(CH(2))(n)PO(3)H(-) for n = 1, 2, 3], substitution on the nitrogen atom [R(1)R(2)N + HCH(2)PO(3)H(-) for R(1) = H; R(2) = Me, Et and R(1) = R(2)= Me, Et] or extent of branching on the carbon atom adjacent to functional groups [N + H(3)CR(3)R(4)PO(3)H(-) for R(3) = H; R(4) = Me, Et, nPr, iPr, nBu and R(3) = R(4) = Me]. Acidity constants and overall stability constants of complexes formed with Ca(II), Mg(II), Co(II), Ni(II), Cu(II), Zn(II) were obtained with the multiparametric refinement programs MUPROT and MUCOMP, applied to potentiometric data, obtained at 25 degrees , in a 0.1M potassium nitrate medium. In the most general case, the existing species are MHA(+), MA, M(OH)A(-), MH(2)A(2), MHA(-)(2) and MA(2-)(2), where A(2-) stands for the fully ionized ligand; preliminary examination of results points out some predominant microscopic forms.

Acidites et complexes des acides (alkyl-et aminoalkyl-) phosphoniques—III Alkylphosphonates substitues de calcium(II) et cuivre(II)

The stability constants of some phosphoric acids RPO(3)H(2) [R = CH(3), C(2)H(5), ClCH(2), Cl(2)CH, Cl(3)C, BrCH(2), Br(2)CH, BrCH(2)CH(2), ICH(2), HOCH(2), (CH(3))(3)N + CH2] and their complexes RPO(3)Ca, RPO(3)Cu, RPO(3)Cu(OH)(-) have been determined by multiparametric refinement of potentiometric titration data obtained at 25 degrees , in a 0.1M potassium nitrate medium. Linear relationships are obtained between stability and acidity constants. Formation of five-membered rings stabilize the hydroxymethylphosphonates. Conversely, cation repulsion by the permanent positive charge reduces the stabilities of complexes with trimethylammoniummethylphosphonic acid.

Computerized potentiometric analysis: Part I. Processing of acid—base titration curves without inflexion points

Abstract The automated titration system described consists of standard potentiometric apparatus and a laboratory medium-capacity computer. The computer controls the reagent additions, reads the delivered volume and the potentials, processes the data, and prints or displays the analytical results. Any parameter of the titration can be determined by multiparametric refinement. The system was tested on neutralization curves without inflexion points obtained in titrations of potassium sodium tartrate and of mixtures of fumaric and maleic acids.

An arbitrary correction function for CO2 evolution in acid—base titrations and its use in multiparametric refinement of data

A great number of acid-base titrations are performed under an inert gas flow: in the procedure, a variable amount of CO(2)-from carbonated reactants-is carried away and thus prevents strict application of mass-balance equations. A function for the CO(2) evolution is proposed and introduced into the general expression for the volume of titrant. Use of this expression in multiparametric refinement yields, besides the usual values (concentrations, acidity constants...), a parameter characteristic of this departure of CO(2). Furthermore, a modified weighting factor is introduced to take into account the departure from equilibrium caused by the slow CO(2) evolution. The validity of these functions was successfully tested on three typical examples: neutralization of strong acid by sodium carbonate, of sodium carbonate by strong acid, and of a mixture of hydrochloric acid, 4-nitrophenol and phenol by carbonated potassium hydroxide.

Phosphonate complexes. Part 6. Influence of steric effects, solvation, and chelation on stability

The interaction of some phosphonic acids RPO(OH)2, chosen to introduce different controlling factors (R = But, cyclo-C6H11, Ph, n-C10H21, Me2NCMe2, CH2SEt, CH2CH2CO2–), with CaII and CuII has been investigated by potentiometry at 25 °C, I= 0.1 mol dm–3(K[NO3]). The selection of the species and the refinement of the stability constants illustrates the applicability of a new version of the program MUCOMP. Examination of linear free-energy plots indicates that factors other than polar effects are of significance, i.e. chelate formation with the potentially bidentate ligands and particularly solvation effects which preferentially stabilize the complexes of α-branched-chain phosphonates. Other features (steric hindrance, predominance of some microscopic forms) are discussed.

Phosphonate complexes. Part 5. An improved multiparametric refinement program, MUCOMP, for complex formation studies from potentiometric data

A new version of the refinement program MUCOMP is described. The stability constants of the complex species as well as the parameters liable to comport systematic errors (total concentration of main components and of impurities, and electrodes characteristics) are adjusted so as to minimize the weighted error-square sum of the added volume, the partial derivatives with respect to the unknown parameters being evaluated analytically. A generalized Newton–Raphson method is employed for the simultaneous calculation of the free concentrations and of the added volume. To deal with carbonate-contaminated reagents and the subsequent carbon dioxide evolution which occurs during titrations under nitrogen flow, an appropriate function for carbon dioxide departure is introduced in the proton balance and the corresponding equilibrium defect is taken into account in the weighting procedure.