Metal Exchange and Displacement

Rate laws for the exchange of Y + with yttrium(m) complexes of the aminocarboxylate ligands edta, cydta, and dtpa have terms in hydrogen ion concentration and in yttrium(in) concentration. The terms in which hydrogen ion concentration, or its square, appears relate to dissociation of mono- and di-protonated forms of the complex. Terms in yttrium(ra) concentration relate to bimolecular attack by the incoming Y +. Yttrium(m) exchange with its hedta complex has a rate law in which the yttrium(m) ion concentration does not appear, so the mechanism here must be purely dissociative.  

References to kinetic studies of the displacement of one metal cation from its complex with a multidentate ligand by another metal cation are listed in Table In general these reactions proceed either by dissociation of the 

Lead(ii)-edta, -hedta, -cydta, -dtpa Nickel(ii) 409 

Nozaki, K. Kasagu, and K. Koshiba, Nippon Kagaku Kaishi, 1972, 568 Chem. Abs., 1972, 76, 145 394k). 

Kopanica and V. Stard, Coll. Czech. Chem. Comm., 1972, 37, 80. 

Dragulescu, A. Nimara, E. Princz, A. Balint, and I. Julean, Rev. Roumaine Chim., 1976,21, 1171. 

For other ligand abbreviations see the list at the start of this volume. 

For the exchange of i Tb + with [Tb(edta)] in 0.025 mol 1 ammonium acetate the observed rate constant, k, is given by the following expression, with the term dominant  

A similar study of the exchange of Ce with its polyaminecarboxylate complexes involves the formation of a more labile chloro-complex in a chloride medium. Negative volumes of activation are reported for the displacement of Ce, Eu and Tb from their cydta complexes by Er, but the mechanistic significance of these results is uncertain. Reaction of (Eu(edta)] with the actinides Cm Bk , and Cfi involves acid-catalysed dissociation and the formation of dinuclear intermediates. Transfer of the ligand 7V-(hydroxyethyl)ethylenediaminetriacetate from its lead(ii) and iron(in) complexes to gallium(m) proceeds by a simple dissociative mechanism, whereas for edta, cydta, and dtpa dinuclear intermediates are involv-ed. Dinuclear intermediates of nickel(n) and copper(n) arc also reported wth the multidentate ligands ttha and NiV -bis-(2-picolyl)cthylenediamine.  

Neeiakantan and R. E. Jervis, Inorg. Nuclear Chem. Letters, 1974,10, 67. C. I. Balcombe and B. Wiseall, 7. Inorg. Nuclear Chem., 1974, 36, 881. 

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X = halogen which is displaced hy the metal. Exchange and trapping temperature. 

The formation of more replaced compounds in studied conditions is not have place. Maximal yield on surface polyurethane foam of salts is observed by pH 2-6. By pH<2 the equilibrium ionic exchanges was displaced left and by pH<0,5 the sorbent practical completely was regenerated. It was studied the influence of the weight of sorbent, the nature of cations of light alkali and alkali earth metals and any other factors on the coefficient concentration ofM(I). 

For the halogen-metal exchange reaction of bulkier halopyrimidines, steric hindrance retards the nucleophilic attack at the azomethine bond. As a consequence, halogen-metal exchange of 5-bromo-2,4-di-r-butoxypyrimidine (43) with n-BuLi could be carried out at -75 °C [20]. The resulting lithiated pyrimidine was then treated with n-butylborate followed by basic hydrolysis and acidification to provide 2,4-di-f-butoxy-5-pyrimidineboronic acid (44). 5-Bromopyrimidine 43 was prepared from 5-bromouracil in two steps consisting of a dehydroxy-halogenation with phosphorus oxychloride and an SnAt displacement with sodium r-butoxide. 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

Most cation exchange occurs in estuaries and the coastal ocean due to the large difference in cation concentrations between river and seawater. As riverborne clay minerals enter seawater, exchangeable potassium and calcium are displaced by sodium and magnesium because the Na /K and Mg /Ca ratios are higher in seawater than in river water. Trace metals are similarly displaced. 

On one hand, systematic analysis of the reaction medium liquid phase by H and C NMR in the presence of a standard has shown that siloxy (-OSiMe3, -OSiEts) Hgands are easily displaced from the metallic centers and leach during the reaction. Their de-coordination by exchange with the alkyl hydroperoxide is irreversible because they form condensation products such as R3SiOSiR3 and R3SiOO Bu with... 

Exps. 9 and 10 are convincing illustrations of the high lrineiic acidity of the ethynyl proton. In principle, there are four reaction pathways if l-bromo-5-hexyne and a strongly basic reagent are allowed to interact abstraction of the acetylenic proton, Br-metal exchange, displacement of Br by the "nucleophilic" part of the base, and elimination of HBr with formation of HCsC(CH2)2CH=CH2- Only the first process takes place under the conditions of this experiment. The kinetic stability of the intermediate LiOC(CH2)4Br is sufficient to allow for successful functionalizations with a number of reagents. For alkylations with most of the alkyl halides, the polarity of the medium will usually be insufficient. 

Although most other cations have little effect on the activity of a-D-mannosidase, certain bivalent cations, notably Cu2+, Cd2+, and Co2+, combine firmly with the enzyme, displacing Zn2+ and causing inactivation in every case.39,46,60 Unlike the metalloenzyme carboxy-peptidase86 (EC 3.4.2.1), a-D-mannosidase in the metal-free state cannot combine with substrate so as to prevent subsequent restoration of activity by the metal metal-free preparations are immediately activated by Zn,2+ even in the presence of substrate.39,48,60 On the other hand, substrate combines so firmly with metal complexes of a-D-mannosidase, regardless of whether the metal ion is Zn2+ or an inactive cation, that it lessens dissociation (and, consequently, metal exchange) to small proportions. 

The typical reactions of halogenothiophenes can be classified under the following headings nucleophilic displacement, halogen-metal exchange, reductive dehalogenation and formation of thienyl radicals. 

The results and experience that have accumulated from studies of the exchange reactions of the aminopolycarboxylates of different lanthanides are very useful in the assessment of the kinetic stabilities of the Gd3+ chelates. In the body fluids where the CAs are administered, the Gd3+ chelates are surrounded by various endogenous metal ions and ligands. Some of these metal ions can react with the Gd3+ chelate by displacing Gd3+ in a metal-metal exchange reaction ... 

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