Aquation Rate Research Articles

H2O/Triton X-100 solvent effect in the micellar catalysis of the aquation of tris-(3,4,7,8-tetramethyl-1, 10-phenanthroline)iron(II)

The effect of triton X-100 micelles on the aquation of Fe(Me4phen)2+3 has been investigated with triton X-100 as solvent. In liquid triton X-100, over a range of [H2O]T(0.2–2.0 mol dm–3), significant rate enhancement factors of 35–140 are observed. Acid inhibits the rate of aquation at fixed [H2O]T. A mechanism based on effective solvent participation in a chemical environment similar to that in reversed micelles is proposed in liquid triton X-100 with dispersed water pockets. This mechanism predicts direct H2O substitutions into the coordination sphere of Fe(Me4Phen)2+3 in the highly polar water pockets or cavities where the FeII complex molecules are solubilized. Changes in the tumbling rate, mobility, structure, nucleophilicity and activity of water are suggested to account for the observed changes in the rate of aquation as a function of [H2O]T, in the peculiar chemical environment of the water pockets. All kψ–[H2O]T profiles are structured and exhibit maxima with kψ(max) shifted to progressively higher [H2O]T as the fixed concentration of [H+]T is increased.

TWO CONTROLLING PROCESSES IN BACK-EXTRACTION OF TRIS (BENZOYLACETONATO )IRON (III ) FROM CARBON TETRACHLORIDE INTO AQUEOUS ACID SOLUTIONS

ABSTRACT By spectrophotometry experiments, the aquation of tris (benzoylacetonato )iron (III ), [Fe (bza)3 ], in aqueous acid perchlorate solutions is found to be controlled by the dissociation of the last ligand from the [Fe (bza ) ]2+ species and accelerated by hydrogen ions. However, two controlling processes are found in the back-extraction of this complex in carbon tetrachloride into similar aqueous solutions. When the acid concentration is high, a rapid process takes place in the early stage and slow one follows thereafter but when the acid concentration is low, the former is not clearly observed and only the latter is found. This is explained in terms that the rapid process corresponds to the dissociation of two ligand anions among three in the [Fe (bza )3 ] species in the aqueous phase while the slow process corresponds to the dissociation of the last ligand from the [Fe (bza ) ]2+ species after a transient equilibrium is established among the rest of complexes in the system. From these, it is concluded that the higher acid concentration in the washing solution is favorable in order to shorten the time for the back-extraction because it enhances the rate of aquation of the complexes and also increases the total amount of the charged complexes in the aqueous phase.

ChemInform Abstract: Synthesis, Characterization, and Aquation Kinetics of (N‐(o‐Carboxyphenyl)iminodiacetato)(glycinato)chromate(III) Complex Ion in Acidic Media.

AbstractThe rates of aquation of the title complex (I) in aqueous perchloric acid are reported as a function of acid concentration and temperature.

ChemInform Abstract: Quantitative Estimates of Steric Effects: Intramolecular Strain Energy Effects on the Activation Energy for Aquation of Some trans‐Dichlorotetraaminecobalt(III) Complexes

Abstract In an effort to quantitatively estimate steric contributions to the aquation rates of a series of structurally related cobalt(III) tetraamine complexes, strain energy minimization calculations have been performed on the reactant and some plausible transition state structures. Free energies of activation Δ G * obs , are factored as: Δ G * obs , = Δ G * bb + Δ G * strain + Δ G * CF + Δ G * solvation + … where Δ G * bb is the free energy change associated with bond breaking, Δ G * solvation is the solvation free energy difference between the reactant and a proposed transition stare, Δ G * CF is the difference in crystal field stabilization between the reactant and a proposed transition state, and Δ G * strain is the strain energy difference between the reactant complex and a proposed transition state. The activation energy for the aquation of a hypothetical ‘strain free’ complex is defined as Δ G * int and reflects the energy required for the bond breaking step with all other terms. For the cations trans -( RR,SS )-dichloro-1,8- diamino-3,6-diazaoctanecobalt(III)( trans [Co(2,2,2- tet)Cl 2 ] + ), trans -(RR,SS)- or trans -( RS )-dichloro-1.9- diamino-3,7-diazanonanecobalt(III)(trans [Co(2,3,2- tet)Cl 2 ] + and trans -( RS )-dichloro-1,10-diamino-4,7- diazadecanecobalt(III)( trans [Co(3,2,3-tet)Cl 2 ] + ) Δ G * int is found to be a constant 123 kJ/mol. For the trans -dichlorocobalt(III) complexes with the ligands 1,4,7,10-tetraazacyclotridecane([13]-ane-N 4 ), 1,4,8, 11-tetraazacyclotetradecane([14]-ane-N 4 ), 1,4,8,12- tetraazacyclopentadecane([15]-ane-N 4 ) and 1,5,9,13- tetraazacyclohexadecane([16]-ane-N 4 ), Δ G * int lies in the range 133–139 kJ/mol.

Effect of solvent on the reactions of coordination complexes. Part 1.—Kinetics of solvolysis of cis-(bromo)(benzimidazole)bis(ethylenediamine)cobalt(III) in methanol–water media

The kinetics of the solvolytic aquation of cis-(bromo)(benzimidazole)bis(ethylenediamine)cobalt(III) have been investigated at 35, 40, 45, 50.2 and 54.8 °C in aqueous methanol media of methanol content 0–80 wt %. The pseudo-first-order rate constant decreases with increasing methanol content. Plots of log ksaqvs. D–1s(where Ds is the dielectric constant of the solvent mixture) and log ksaqvs. the Grunwald–Winstein Y parameter or revised YCl(1-adamantyl Chloride) parameter are non-linear. The plot of log ksaqvs. the molefraction of methanol (XMeOH), which deviates from linearity at 35, 40 and 45 °C, is an excellent straight line (r= 0.998) at 50 and 54.8 °C over the entire composition range studied. It is evident that the solvation phenomenon plays dominant role and that the rate of aquation is mediated by the dual solvent vectors, the overall basicity and acidity of the solvent mixtures. At 25 °C the calculated values of the transfer free energy of the dissociative transition state, cis-{[Co(en)2(bzmH)]3+}*, relative to that of the initial state, cis-[Co(en)2(bzmH)Br]2+, for the transfer of the ions from water to the mixed solvent were positive at all solvent compositions (except 80 % MeOH), exhibiting a maximum at XMeOH= 0.46. This reflects the propensity of the said tripositive transition state and the dipositive initial state towards solvation interaction with the medium. In contrast to the activation free energy, which varies linearly with XMeOH, the plots of activation enthalpy and entropy against XMeOH exhibit maxima at XMeOH= 0.12 and 0.46 and minima at XMeOH= 0.02 and 0.25; thereafter both ΔH‡ and ΔS‡ decrease steeply to significantly low values at XMeOH= 0.69 (ΔH‡= 80.1 ± 4.3 kJ mol–1 and ΔS‡=–91 ± 13 J K–1 mol–1), manifesting the effect of solvent-shell reorganisation around the complex ion both in the initial state and in the transition state as the composition is varied.

The reactions of some pentaammine(o-substituted benzoato)chromium(III) cations in perchloric acid and water

The reactions of pentaammine(o-fluorobenzoato)-, pentaammine(o-bromo-benzoato)- and pentaammine(o-nitrobenzoato)chromium(III) cations in 0.01 M perchloric acid solution and water have been studied at 21dgC. It was found that the reaction in acid was the release of ammonia but in water it was aquation to the pentaammineaquachromium(III) cation. The aquation rates in water decrease in the order o-fluorobenzoate, o-bromobenzoate and o-nitrobenzoate complexes, suggesting an associative mechanism.

Synthesis, characterisation, and aquation kinetics of [N-(o-carboxyphenyl)iminodiacetato](glycinato)chromate(III) complex ion in acidic media

The potassium salt of the [N-(o-carboxyphenyl)iminodiacetato](glycinato)chromate(III) complex has been synthesised and characterised. In acidic media, the complex has been shown to aquate to diaqua[N-(o-carboxyphenyl)iminodiacetato]chromium(III) and protonated glycine as the ultimate products. The rates of aquation of the complex in aqueous perchloric acid media are reported as a function of acid concentration and temperature. The variation of the observed pseudo-first-order rate constants with acid concentration suggests the operation of two concurrent paths with kobs.=k0+kH[H+], where k0 and kH are the appropriate rate constants for uncatalysed and acid-catalysed pathways respectively. The production of a metastable bidentate glycinato-O,O′ ligand configuration in the aquation process is proposed to explain the reactivity of the chromate(III) complex.

Micellar effects upon the reactions of complex ions in solution. Retardation of the base hydrolysis of cis-(azido)(imidazole)bis(ethylenediamine)cobalt(III) by sodium dodecyl sulphate

The kinetics of base hydroloysis of cis-(azido)(imidazole)bis(ethylenediamine)cobalt(III) has been studied in the presence of sodium dodecyl sulphate at 40 °C. Unlike the case for univalent anions, the surfactant strongly retards the base hydrolysis of the complex. The rate data have been satisfactorily analysed by the pseudo-phase ion-exchange model: [graphic ommitted] where Cb+ denotes the imidazole (1–) conjugate base, cis-[(en)2Co(im)N3]+, and W and M stand for the aqueous and micellar pseudo-phases, respectively. The pseudo-phase ion-exchange equilibium has also been verified by measuring the equilibrium constant using a spectrophotometric method. The second-order base hydrolysis path of Cb+ is, however, absent for the fully micelle-incorporated species, Cb+M. Micellar binding of Cb+ also leads to a slowing down of its spontaneous aquation rate to a small extent (by a factor of 2), which may be ascribed to the difference in the polarity of the microenvironment of the reactant in the micellar pseudo-phase and the aqueous phase.

Optically active chromium(III) complexes. VII. Chiroptical and kinetic properties of chloro(1,5-diazahexane)( 1,4,7-triazaheptane)chromium(III) tetrachlorozincate(II), [CrCl(NMetn)(dien)]ZnCl 4

One isomer of [CrCl( N-Me-tn)(dien)]ZnCl 4 has been isolated from the reaction of CrCl 3·6H 2O, dehydrated in DMF, with the polyamines N-methyl- 1,3-diaminopropane and diethylenetriamine. This complex is isomorphous with δλ-( R,S)usft-[CoCl( N-Me-tn)(dien)] ZnCl 4 and thus has the unsym-fac- configuration with the N-Me group trans to the sec-NH group of the coordinated triamine. The Cr(III) complex has been resolved with NH 4BCS and the chiroptical parameters of (-) 488-[CrCl( N-Me-tn)(dien)]- ZnCl 4, derived from the less soluble diastereoisomeride by metathesis, are similar to those obtained for the less soluble (-) 534-λ-( S)- a, cb, edf-Co(III) analogue, of known absolute configuration. Kinetic parameters for the rates of thermal aquation (μ= 1.0 M, HClO 4) and Hg 2+-assisted chloride release (μ= 1.0 M) for usft-[CrCl( N-Me-tn)(dien)]ZnCl 4 are k H= 3.7 × 10 −6 s −1, E a=93 ± 8 kJ mol −1, Δ S 2984t #= −45 ± 16 J K −1 mol −1 and k Hg=2.01 × 10 −3 M −1 s −1, E a=64.2 ± 3.3, Δ S 298 #=−89.5 ± 7, respectively at 298 K.

KINETICS OF DISSOCIATION OF THE MALONATOBISTRIMETHYLENEDIAMINE COBALT(III) COMPLEX IN ACIDIC MEDIA

Abstract The kinetics of dissociation of malonate from the malonatobistrimethylenediaminecobalt(III) complex have been investigated in aqueous perchloric acid media (0.1–1.0 mol dm−3 over a temperature range of 50–70°C at an ionic strength of 2.2 mol dm−3 adjusted with sodium perchlorate. The variation of observed pseudo-first-order rates on [acid] suggests the operation of two concurrent paths with kobs = ko + kH + [H+]. where ko and kH+ are the rate constants for uncatalysed and acid-catalysed pathways respectively. Under identical conditions the malonato complex was found to dissociate 103 times faster rate than that of corresponding oxalato complex. The influence of basicity and chelate ring size of the carboxylate and diamine groups on the aquation rate has been discussed. Analysis of rate data corresponding to kH+ suggests a dissociative mechanism involving the protonated complex.

Quantitative estimates of steric effects: Intramolecular strain energy effects on the activation energy for aquation of some trans-dichlorotetraaminecobalt(III) complexes

In an effort to quantitatively estimate steric contributions to the aquation rates of a series of structurally related cobalt(III) tetraamine complexes, strain energy minimization calculations have been performed on the reactant and some plausible transition state structures. Free energies of activation Δ G* obs, are factored as: Δ G* obs, = Δ G* bb + Δ G* strain + Δ G* CF + Δ G* solvation + … where Δ G* bb is the free energy change associated with bond breaking, Δ G* solvation is the solvation free energy difference between the reactant and a proposed transition stare, Δ G* CF is the difference in crystal field stabilization between the reactant and a proposed transition state, and Δ G* strain is the strain energy difference between the reactant complex and a proposed transition state. The activation energy for the aquation of a hypothetical ‘strain free’ complex is defined as Δ G* int and reflects the energy required for the bond breaking step with all other terms. For the cations trans-( RR,SS)-dichloro-1,8- diamino-3,6-diazaoctanecobalt(III)( trans [Co(2,2,2- tet)Cl 2] +), trans-(RR,SS)- or trans-( RS)-dichloro-1.9- diamino-3,7-diazanonanecobalt(III)(trans [Co(2,3,2- tet)Cl 2] + and trans-( RS)-dichloro-1,10-diamino-4,7- diazadecanecobalt(III)( trans[Co(3,2,3-tet)Cl 2] +) Δ G* int is found to be a constant 123 kJ/mol. For the trans-dichlorocobalt(III) complexes with the ligands 1,4,7,10-tetraazacyclotridecane([13]-ane-N 4), 1,4,8, 11-tetraazacyclotetradecane([14]-ane-N 4), 1,4,8,12- tetraazacyclopentadecane([15]-ane-N 4) and 1,5,9,13- tetraazacyclohexadecane([16]-ane-N 4), Δ G* int lies in the range 133–139 kJ/mol.

ChemInform Abstract: Rate of Aquation of the Fluoropentaaquochromium(III) Ion in Concentrated Perchloric Acid.

Chemischer InformationsdienstVolume 17, Issue 11 Physical Inorganic Chemistry ChemInform Abstract: Rate of Aquation of the Fluoropentaaquochromium(III) Ion in Concentrated Perchloric Acid. J. W. VAUGHN, J. W. VAUGHNSearch for more papers by this authorE. L. KING, E. L. KINGSearch for more papers by this author J. W. VAUGHN, J. W. VAUGHNSearch for more papers by this authorE. L. KING, E. L. KINGSearch for more papers by this author First published: March 18, 1986 https://doi.org/10.1002/chin.198611031Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue11March 18, 1986 RelatedInformation

Isonicotinamide as entering ligand on trans-[Ru(NH 3) 4P(OR) 3(H 2O)]2 2+, (R = Me, Pr, iPr and Bu)

trans-[Ru(NH 3) 4P(OR) 3(H 2O)] 2+ (R = Me, Pr, iPr, and Bu) reacts with isonicotinamide at second-order- specific rates k 1 of 1.2, 2.3, 7.4 and 8.1 M −1 s −(25 °C, μ = 0.10 NaCF 3COO/CH 3COOH), respectively, for R = Me, Pr, iPr and Bu. The products trans- [Ru(NH 3) 4P(OR) 3isn](PF 6) 2 have been isolated and characterized by micro analysis, cyclic voltammetry, and electronic spectral data. The aquation rates k −1 for the isonicotinamide (isn) derivatives are 5.2 × 10 −2, 5.9 × 10 −2, 2.0 × 10 −1 and 3.4 × 10 −1 s −1 for R= Me, Pf, Bu and iPr, respectively. The activation parameters for the forward and backward reactions indicate the same mechanism for all of them. The substitution proceeds by a dissociative mechanism with a significant outer-sphere association of trans-[Ru(NH 3) 4P(OR) 3(H 2O)] 2+ complexes with isn. Assuming k 1 as indicative of the lability of the coordinated water molecule on the monophosphite complexes, the following sequence of increasing trans-effect mav be proposed: P(OMe) 3 <P(OEt) 3 <P(OPr) 3 <P(O iPr) 3 <P(OBu) 3. The affinity of the monophosphite complexes for isn increases according to P(OMe) 3 ⋍ P(O iPr) 3 < P(OEt) 3 < P(OPr) 3 ⋍ P(OBu) 3.

E.M.F. and kinetic studies of the ion-pairing effects on the rate of aquation of chloropentamminechromium(III) perchlorate in different dicarboxylate medium

Rate coefficients, k, for aquation of [Cr(NH3)5Cl]2+ in 10% ethanol solutions of some dicarboxylates have been determined by potentiometric titration methods. The dissociation constants of ion-pairs so formed have been obtained from e.m.f.s. of a cell comprising glass and calomel electrodes. A wide range of k(ion) and k(ion-pair) values and dissociation constants has been obtained and a new correlation between k(ion-pair) and association constants among the dicarboxylate series studied has been established.

Kinetics and mechanism of acetate and succinate anations ofcis-tetraamminediaquacobalt(III) in aqueous acidic media

The complexcis-tetraamminediaquacobalt(III) reacts with acetate ion to formcis-tetraamminediacetatocobalt(III). Kinetic evidence shows that the reaction proceeds in a single step process in the pH range 4.0–5.2, but it splits to a biphasic one at pH 5.4. The acetate anation is governed by the rate law: $${\text{k}}_{{\text{obs}}} = {\text{k}}_{\text{0}} + \frac{{{\text{kQ[OAc}}^ - {\text{]}}}}{{1 + {\text{Q[OAc}}^ - {\text{]}}}}$$ where kobs, k0, k and Q denote the observed rate constant, the back aquation rate, the interchange rate and the ion-pair formation constant, respectively. The ΔH≠] and ΔS≠ values associated with the interchange rate are 137 ± 8 kJ mol−1 and 137 ± 12 JK−1mol−1, respectively. The title complex reacts with succinate ions (HSuc−1 and Suc2−) to form tetraamminesuccinatocobalt(III) and no evidence has been obtained for any significant build-up of the monodenate succinato intermediate. It is concluded that the step in which the succinate ion chelates is rapid. The kinetics of the first stage of the reaction involving coordination of succinate ion to cw-[Co(N-H3)4(OH2)2]3+ have been investigated at pH=2.5–4.0, I=0.5 mol dm−3 (NaClO4) and at temperatures 30–50 °C. The interpretation given is consistent with the formation of ion-pairs between the diaqua complex and the succinate ions, HSuc− and Sue2−. The reaction is believed to proceed through a dissociative interchange mechanism.

Micellar inhibition of the aquation of tris-(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) by sodium dodecyl sulphate in aqueous acid medium

The inhibition of the aquation of Fe(Me4phen)2+3 by sodium dodecyl sulphate (SDS) in aqueous acid media has been investigated and a mechanism which explains the pronounced inhibition and pre-micellar activity at low [SDS]T has been proposed. Inhibition is due to favourable thermodynamic-/hydrophobic/electrostatic binding between the FeII complex and SDS monomer aggregates. The bound FeII complex is stabilised with respect to dissociation and binding takes place between the ridges of the Stern layer. The partitioning of the substrate between the bulk-water phase and the micellar phase is in favour of the latter at low [H+]T and low [SDS]T. From the rate law obtained and the observed kinetic data, the micelle–complex binding constant (K1) and micelle–acid binding constant (K3) were calculated to be (2.81 ± 0.08)× 105 and (13.80 ± 0.16) dm3 mol–1, respectively, in acid media. Using the Scatchard method, K1 values of (3.95 ± 0.08)× 105 and (3.04 ± 0.16)× 105 dm3 mol–1 were calculated for the binding in neutral medium (distilled water) and 2 × 10–5 mol dm–3 H+, respectively. The decrease in K1 in acid media is attributed to competition between H+ and the complex ion for the binding sites on the micelle. The kψ–[SDS]T profiles are structured owing to the evolution (size, geometry, aggregation number, etc.) of the micelle. The inhibition of the aquation rate by HSO–4 and SO2–4 ions which form a negative field around the FeII complex is only significant at high acid concentrations. The micelle-bound complex and micelle-bound protons have opposing effects on the aquation rate. The degree of inhibition is therefore sensitive to the ratio of the concentration of these bound species.

A common dissociative interchange (I d) mechanism for the aquations of penta-aminechloro-cobalt(III) and -chromium(III) complexes

The rate of aquation of [Cr(NH2Me)5Cl]2+ is slower than that of [Cr(NH3)5Cl]2+ because of a shorter Cr–Cl bond in the ground state of [Cr(NH2Me)5Cl]2+, which is consistent with an Id mechanism.

Rate of aquation of the fluoropentaaquochromium(III) ion in concentrated perchloric acid

Rate of aquation of the fluoropentaaquochromium(III) ion in concentrated perchloric acid

Axial ligand anation and aquation reactions in diplatinum(III) complexes. Comparison of aquation rates between hexachloroplatinate(IV) anion and diplatinum(III) chloro complexes having .mu.-phosphato or .mu.-pyrophosphito ligands

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAxial ligand anation and aquation reactions in diplatinum(III) complexes. Comparison of aquation rates between hexachloroplatinate(IV) anion and diplatinum(III) chloro complexes having .mu.-phosphato or .mu.-pyrophosphito ligandsRamadan El-Mehdawi, Samuel A. Bryan, and D. Max RoundhillCite this: J. Am. Chem. Soc. 1985, 107, 22, 6282–6286Publication Date (Print):October 1, 1985Publication History Published online1 May 2002Published inissue 1 October 1985https://doi.org/10.1021/ja00308a020RIGHTS & PERMISSIONSArticle Views69Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (629 KB) Get e-Alerts Get e-Alerts

Kinetics of the acid catalyzed aquation of cis- and trans-diacetatobis(1,2-propanediamine)cobalt(III) cations

The aquation of both cis- and trans-Co(pn) 2(AcO) 2 + is catalyzed by H +, in aqueous solutions. The observed pseudo first-order rate constant, k obsd, shows a linear dependence on [H +] and there is kinetic, and in the case of the trans isomer spectrophotometric, evidence for a pre-equilibrium association of the complex cation with the proton. The kinetics obey the rate law −dln[complex]/dt = α Q[H +]/1 + Q[H +] (where Q = the pre-equilibrium constant for protonation and α = the aquation rate constant for the protonated species). The cis diacetato cation aquates with complete retention of configuration yielding cis-Co(pn) 2(AcO)(H 2O) 2+. Aquation of the trans diacetato proceeds with stereochemical change to yield an equilibrium mixture of cis- and trans-Co(pn) 2(AcO)(H 2O) 2+ in the ratio 3:1, respectively. Both cis- and trans-Co(pn) 2(AcO(H 2O) 2+ isomerize to an equilibrium mixture that is 75% cis and 25% trans.