Complex formation between poly(vinyl alcohol) and metallic ions in aqueous solution
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Abstract As the basic research for the study of complex reactions in polymers, the complex formation of poly(vinyl alcohol) (PVA) with copper and other metals was tried. Spectroscopy, pH titration, and elementary analysis were employed in the reaction of PVA and Cu(II) ions in aqueous solution. The complexing protonation was found in the higher pH region (above 7.0), and the maximum absorptions at 640 and 260 nm were observed. These ϵ max were proportional to the concentrations of Cu(II) ions bound to the hydroxyl groups of PVA. Formation constants of the PVA–Cu(II) complexes were measured by applying a modified Bjerrum's method. The effects of the ratio Tcu 2+ /T HL , the anions in copper salts, and the degree of polymerization on the formation constants were studied. Four hydroxyl groups combined with one Cu(II) ion in the pH range above 7.0. The stability constants for the complexes of PVA with bivalent transition metallic ions were in agreement with the Irving‐William's series. The changes in viscosity, solubility, tacticity, mechanochemical phenomenon, and the other properties based on the complex formation are discussed.Keywords:
Vinyl alcohol
This investigation examines the protonation of diiron dithiolates, exploiting the new family of exceptionally electron-rich complexes Fe(2)(xdt)(CO)(2)(PMe(3))(4), where xdt is edt (ethanedithiolate, 1), pdt (propanedithiolate, 2), and adt (2-aza-1,3-propanedithiolate, 3), prepared by the photochemical substitution of the corresponding hexacarbonyls. Compounds 1-3 oxidize near -950 mV vs Fc(+/0). Crystallographic analyses confirm that 1 and 2 adopt C(2)-symmetric structures (Fe-Fe = 2.616 and 2.625 Å, respectively). Low-temperature protonation of 1 afforded exclusively [μ-H1](+), establishing the non-intermediacy of the terminal hydride ([t-H1](+)). At higher temperatures, protonation afforded mainly [t-H1](+). The temperature dependence of the ratio [t-H1](+)/[μ-H1](+) indicates that the barriers for the two protonation pathways differ by ∼4 kcal/mol. Low-temperature (31)P{(1)H} NMR measurements indicate that the protonation of 2 proceeds by an intermediate, proposed to be the S-protonated dithiolate [Fe(2)(Hpdt)(CO)(2)(PMe(3))(4)](+) ([S-H2](+)). This intermediate converts to [t-H2](+) and [μ-H2](+) by first-order and second-order processes, respectively. DFT calculations support transient protonation at sulfur and the proposal that the S-protonated species (e.g., [S-H2](+)) rearranges to the terminal hydride intramolecularly via a low-energy pathway. Protonation of 3 affords exclusively terminal hydrides, regardless of the acid or conditions, to give [t-H3](+), which isomerizes to [t-H3'](+), wherein all PMe(3) ligands are basal.
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Protonation states of amino and hydroxyl phosphoroorganic derivatives have been studied. Based on the presented calculations we can state that mono- and di-protonated species on nitrogen are dominating states in solution. The protonation on phosphoryl oxygen occurs only as an effect of dynamic equilibrium between protonated species. The double and tripple protonation lead to very strong acid and thus such states are rather not present even in strong acidic media.
Brønsted–Lowry acid–base theory
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13C nuclear magnetic resonance study of the protonation of 2,2,4-trimethyl-1,5,9-triazacyclododecane
13 C N.m.r. spectroscopy has been used to investigate the protonation of 2,2,4-trimethyl-1,5,9-triazacyclododecane. The chemical shifts which occur upon protonation are interpreted as indicating that each protonation step results in the protonation of only one nitrogen atom, and that the sequence is probably N-5, N-9, and then N-1. There is some evidence indicating that a hydrogen bond is formed between N-1 and N-9 during the second protonation step. Chemical shifts observed are due to protonation of the nitrogen atom and to conformational changes within the molecule. The significance of these results for the determination of the protonation sequence of aliphatic polyamines is discussed.
Nitrogen atom
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Hydrogen atom
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Reactivity
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The protonation behaviour of several triamines having the general formula H2N[CH2]mNH[CH2]nNH2 with m⩽n has been studied by 13C and 1H n.m.r. techniques. In all cases, in the first two protonation steps, only primary amino-groups are involved. The protonation of the secondary amino-group starts only after the protonation of the primary ones is complete.In the case of symmetrical triamines, in the first step, the proton is shared by the two primary nitrogens to an equal extent. Unsymmetrical triamines having m < 3 are initially protonated on the primary nitrogen atom attached to the longer aliphatic chain. However the unsymmetrical triamine spermidine, having m= 3 and n= 4. behaves like the symmetrical ones.
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Copper(Ⅱ) complexes with N,N'-oxalylbis(salicylaldehydehydrazone), N,N'-malonylbis(salicylaldehydehydrazone) and N,N'-succinylbis(salicylaldehydehydrazone) have been prepared in 95% DMF. Their protonation and stability constants were investigated by potentiometric titration. We observed that MBSH ligand showed the largest protonation constant. The values of the protonation constants among three different ligands were increased as following order SBSH
Base (topology)
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The protonation of some polynuclear carbonyl complexes in concentrated sulphuric acid has been studied and the new complexes [HRu3(CO)12]PF6 and [HOs3(CO)12]PF6 have been isolated. The kinetic isotope effect observed in these protonation reactions has been investigated and the new complex HOsCo3(CO)12 has been prepared.
Kinetic isotope effect
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