Abstract The oxidation of antimony(III) by tetrachloraurate(III) has been studied in aqueous hydrochloric acid medium at 27°C. The reaction follows the rate law ks = k1K1K2K3K4[Cl]/[H3O+]([H3O+ ] + K1) (i) (i) where K1;K2,K3 and K4 are the respective equilibrium constants of the reactions (ii) to (v) and kj is the rate constant of the slow complementary two HAuCl4 + H2O ⇄ AuCl4- + H3O+ K2 (ii) AuCl4-+H2O⇄ AuCl3 (OH)- + H3O+ + Cl- K2 (iii) SbCl4- + Cl- ⇄ SbCl52- K3 (iv) SbCl52- + Cl- ⇄ SbCl63- K4 (v) electron transfer step of the reaction between the active species AuCl3(OH)- and SbCl63- of the reactants. The enthalpy and entropy of activation were found to be 19.2 ± 1 kj mol-1 and - 182.5 ± 4 JK-1 mol -1 respectively,suggesting a chorobridged electron transfer.
{"title":"Kinetics of Oxidation of Antimony(III) by Tetrachloroaurate(III) in Aqueous Hydrochloric Acid Media","authors":"R. M. Babshet, G. Gokavi","doi":"10.1515/irm-2001-0108","DOIUrl":"https://doi.org/10.1515/irm-2001-0108","url":null,"abstract":"Abstract The oxidation of antimony(III) by tetrachloraurate(III) has been studied in aqueous hydrochloric acid medium at 27°C. The reaction follows the rate law ks = k1K1K2K3K4[Cl]/[H3O+]([H3O+ ] + K1) (i) (i) where K1;K2,K3 and K4 are the respective equilibrium constants of the reactions (ii) to (v) and kj is the rate constant of the slow complementary two HAuCl4 + H2O ⇄ AuCl4- + H3O+ K2 (ii) AuCl4-+H2O⇄ AuCl3 (OH)- + H3O+ + Cl- K2 (iii) SbCl4- + Cl- ⇄ SbCl52- K3 (iv) SbCl52- + Cl- ⇄ SbCl63- K4 (v) electron transfer step of the reaction between the active species AuCl3(OH)- and SbCl63- of the reactants. The enthalpy and entropy of activation were found to be 19.2 ± 1 kj mol-1 and - 182.5 ± 4 JK-1 mol -1 respectively,suggesting a chorobridged electron transfer.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"26 1","pages":"75 - 82"},"PeriodicalIF":0.0,"publicationDate":"2001-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79728707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The kinetics and mechanism of Cr(VI) oxidation of D-glucose in the presence and absence of picolinic acid (PA) in aqueous acid media have been carried out under the conditions, [D-glucose]T ⋟ [Cr(VI)]T at different temperatures. Under the kinetic conditions, HCrO4- has been found kinetically active in the absence of PA while in the ΡΑ-catalysed path Cr(VI)-PA complex has been established as the active oxidant. In the ΡΑ-catalysed path, Cr(VI)-PA complex receives a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition (through 2e transfer) leading to lactone (oxidised product) and Cr(IV)-PA complex. Then Cr(IV)-PA complex participates further in the oxidation of D-glucose and ultimately is converted into Cr(III)-PA complex. In the uncatalysed path, Cr(VI)-substrate ester experiences an acid catalysed redox decomposition (2e transfer) at the rate determining step. The uncatalysed path shows a second-order dependence on [H+], Both the paths show first-order dependence on [D-glucose]T and [Cr(VI)]T. The ΡΑ-catalysed path is first-order in [PA]T. These observations remain unaltered in the presence of externally added surfactants. Effect of cationic surfactant (i.e. cetylpyridinium chloride, CPC) and anionic surfactant (i.e. sodium dodecyl sulfate, SDS) on both the uncatalysed and ΡΑ-catalysed path has been studied. CPC inhibits both the uncatalysed and ΡΑ-catalysed path while SDS catalyses the reactions. The observed micellar effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. Applicability of different kinetic models, e.g. pseudo-phase ion exchange (PIE) model, Menger-Portnoy model, Piszkiewicz cooperative model, has been tested to explain the observed micellar effects. Effect of [surfactant]T on the activation parameters has been explored to rationalise the micellar effect.
{"title":"Micellar Effect on Chromium(VI) Oxidation of D-Glucose in the Presence and Absence of Picolinic Acid in Aqueous Media: A Kinetic Study","authors":"A. Das, S. Mondal, D. Kar, M. Das","doi":"10.1515/irm-2001-0107","DOIUrl":"https://doi.org/10.1515/irm-2001-0107","url":null,"abstract":"Abstract The kinetics and mechanism of Cr(VI) oxidation of D-glucose in the presence and absence of picolinic acid (PA) in aqueous acid media have been carried out under the conditions, [D-glucose]T ⋟ [Cr(VI)]T at different temperatures. Under the kinetic conditions, HCrO4- has been found kinetically active in the absence of PA while in the ΡΑ-catalysed path Cr(VI)-PA complex has been established as the active oxidant. In the ΡΑ-catalysed path, Cr(VI)-PA complex receives a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition (through 2e transfer) leading to lactone (oxidised product) and Cr(IV)-PA complex. Then Cr(IV)-PA complex participates further in the oxidation of D-glucose and ultimately is converted into Cr(III)-PA complex. In the uncatalysed path, Cr(VI)-substrate ester experiences an acid catalysed redox decomposition (2e transfer) at the rate determining step. The uncatalysed path shows a second-order dependence on [H+], Both the paths show first-order dependence on [D-glucose]T and [Cr(VI)]T. The ΡΑ-catalysed path is first-order in [PA]T. These observations remain unaltered in the presence of externally added surfactants. Effect of cationic surfactant (i.e. cetylpyridinium chloride, CPC) and anionic surfactant (i.e. sodium dodecyl sulfate, SDS) on both the uncatalysed and ΡΑ-catalysed path has been studied. CPC inhibits both the uncatalysed and ΡΑ-catalysed path while SDS catalyses the reactions. The observed micellar effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. Applicability of different kinetic models, e.g. pseudo-phase ion exchange (PIE) model, Menger-Portnoy model, Piszkiewicz cooperative model, has been tested to explain the observed micellar effects. Effect of [surfactant]T on the activation parameters has been explored to rationalise the micellar effect.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"17 1","pages":"63 - 74"},"PeriodicalIF":0.0,"publicationDate":"2001-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85099116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Multiwavelength stopped-flow spectrophotometry has been used to investigate the rates and mechanisms of reactions of solvates of Co(II), Ni(II), Cu(II) and Zn(II) with 2,2':6',2"-terpyridine (terpy) and its 5-methyl-, 4-(4-tolyl)-, 4'-(4-tolyl)-, 4'-phenyl/ 4'-(4-f-butyIphenyl)-, 4'-(4-nitrophenyl)-, 4'-(4-pyridyl)-, 4'-(l-naphthyl)-, and 4'-(2-naphthyl)-derivatives. The reactions of Co(II), Ni(II) and Zn(II) with 4'-(l-naphthyl)terpy were also investigated by stopped-flow fluorimetry. Using excess ligand, a single pseudo-first-order rate process is observed for reactions with either Co(II), Ni(II) or Zn(II) that corresponds to the rate of formation of the mono(ligand)metal(II) ion, followed by rapid conversion of the monoto the bis-(terpy)metal(II) complexes. However, using excess Co(II), Ni(II) and Zn(II), intermediates are observed prior to the formation of the mono(terpy)metal(II) species, in a two-step consecutive first-order process. The results are consistent with the formation of an intermediate mono(ligand)metal(II) complex in which the terpy acts as a bidentate 2,2'-bipyridine (bipy) donor, followed by a measurable final chelate-ring-closure step. For the intermediates involved in the reactions of Z n 2 + with terpy and 4'-phenylterpy, at 25 °C the kinetically determined equilibrium constants, estimated from the ratios of slopes/intercepts of plots of kobs versus [Zn 2 + ] , are logifCj/dm 3 ι η ο Γ 1 ) = 5.14 ± 0.08 and 4.80 ± 0.12 respectively. These values of K-[ are too small for the formation of mono(terpy)zinc(II) complexes, but are as expected for the formation of a mono(ligand)zinc(II) complex in which the terpy acts as a bidentate (bipy) donor. The kinetics of the reaction of [Cu(OH2)g] with excess terpy in water buffered at pH 6.1 are more complex, with several kinetic steps observed. The first, very rapid stage involves the largest absorbance changes, and is attributed to the formation of mono(terpy)Cu(II) (at 25 °C, 1 0 ~ 7 k f = 1.2 ± 0.1 d m 3 m o l 1 s ). Subsequent reactions are attributed to the rapid formation and slow rearrangement of a five-coordinate bis(terpy)copper(II) intermediates, with one terpy acting as a terdentate donor and the other terpy as a bidentate ligand. Reaction of pre-formed [Cu(terpy)(OH2)2l + with excess terpy also revealed the rapid formation and slow rearrangement of bis(terpy)copper(II) species. 1 7 0 NMR and ESR line broadening were used to determine the rate of water exchange with [Cu(terpy)(OH2)2l ; assuming [Cu(terpy)(OH2)2] + has a trigonal bipyramidal geometry with both solvent molecules in equivalent positions in the equatorial plane, and that they undergo solvent exchange at the same rate, for each coordinated solvent the following results were obtained: 10"8fcex = 6.6 ± 0.9 s" 1 : ΔΗ* = 20.7 ± 2 k j
采用多波长停流分光光度法研究了Co(II)、Ni(II)、Cu(II)和Zn(II)溶剂化物与2,2′:6′，2′-三吡啶(terpy)及其5-甲基-、4-(4-甲苯基)-、4′-(4-甲苯基)-、4′-(4-硝基)-、4′-(4-丁基苯基)-、4′-(4-硝基苯基)-、4′-(4-吡啶基)-、4′-(1 -萘基)-和4′-(2-萘基)衍生物的反应速率和反应机理。用停流荧光法研究了Co(II)、Ni(II)和Zn(II)与4′-(l-萘基)三元化合物的反应。使用过量配体，观察到与Co(II)， Ni(II)或Zn(II)反应的单一伪一级速率过程，对应于单(配体)金属(II)离子的形成速率，然后将单(配体)金属(II)配合物快速转化为双(terpy)金属(II)配合物。然而，使用过量的Co(II)， Ni(II)和Zn(II)，中间体在形成单(terpy)金属(II)之前被观察到，在一个连续的两步一级过程中。结果与中间单(配体)金属(II)配合物的形成一致，其中terpy作为双齿2,2'-联吡啶(bipy)供体，随后是可测量的最终螯合环闭合步骤。对于zn2 +与terpy和4′-苯基terpy反应的中间体，在25°C时，根据kobs与[zn2 +]曲线的斜率/截距比值，动力学确定的平衡常数分别为logifCj/dm 3 ι η ο Γ 1) = 5.14±0.08和4.80±0.12。这些K-[的值对于形成单(terpy)锌(II)配合物来说太小了，但是对于形成单(配体)锌(II)配合物来说，正如预期的那样，其中terpy充当双齿(bipy)供体。在pH为6.1的缓冲水中，[Cu(OH2)g]与过量terpy的反应动力学更为复杂，观察到几个动力学步骤。第一个非常快速的阶段吸光度变化最大，这是由于单(terpy)Cu(II)的形成(在25°C, 10 ~ 7 k f = 1.2±0.1 d m 3 m 1 s)。随后的反应归因于五坐标双(terpy)铜(II)中间体的快速形成和缓慢重排，其中一个terpy作为双齿供体，另一个terpy作为双齿配体。预形成的[Cu(terpy)(OH2)2l +与过量的terpy反应也揭示了其(terpy)铜(II)的快速形成和缓慢重排。采用NMR和ESR谱线展宽法测定了与[Cu(terpy)(OH2)2l的水交换速率;假设[Cu(terpy)(OH2)2] +具有三角双锥体的几何结构，两种溶剂分子在赤道平面上的位置相等，并且它们以相同的速率进行溶剂交换，对于每一种配位溶剂，得到如下结果:10”8fcex = 6.6±0.9 s”1:ΔΗ* = 20.7±2 k j
{"title":"Kinetic and Mechanistic Studies of Substitution Reactions of Solvated Cobalt(II), Nickel(II), Copper(II) and Zinc(II) Ions with 2,2′:6′,2″-Terpyridine and Several 2,2′:6′,2″-Terpyridine Derivatives. Evidence for the Formation of Intermediates","authors":"Gleb U. Priimov, P. Moore, L. Helm, A. Merbach","doi":"10.1515/irm-2001-0102","DOIUrl":"https://doi.org/10.1515/irm-2001-0102","url":null,"abstract":"Multiwavelength stopped-flow spectrophotometry has been used to investigate the rates and mechanisms of reactions of solvates of Co(II), Ni(II), Cu(II) and Zn(II) with 2,2':6',2\"-terpyridine (terpy) and its 5-methyl-, 4-(4-tolyl)-, 4'-(4-tolyl)-, 4'-phenyl/ 4'-(4-f-butyIphenyl)-, 4'-(4-nitrophenyl)-, 4'-(4-pyridyl)-, 4'-(l-naphthyl)-, and 4'-(2-naphthyl)-derivatives. The reactions of Co(II), Ni(II) and Zn(II) with 4'-(l-naphthyl)terpy were also investigated by stopped-flow fluorimetry. Using excess ligand, a single pseudo-first-order rate process is observed for reactions with either Co(II), Ni(II) or Zn(II) that corresponds to the rate of formation of the mono(ligand)metal(II) ion, followed by rapid conversion of the monoto the bis-(terpy)metal(II) complexes. However, using excess Co(II), Ni(II) and Zn(II), intermediates are observed prior to the formation of the mono(terpy)metal(II) species, in a two-step consecutive first-order process. The results are consistent with the formation of an intermediate mono(ligand)metal(II) complex in which the terpy acts as a bidentate 2,2'-bipyridine (bipy) donor, followed by a measurable final chelate-ring-closure step. For the intermediates involved in the reactions of Z n 2 + with terpy and 4'-phenylterpy, at 25 °C the kinetically determined equilibrium constants, estimated from the ratios of slopes/intercepts of plots of kobs versus [Zn 2 + ] , are logifCj/dm 3 ι η ο Γ 1 ) = 5.14 ± 0.08 and 4.80 ± 0.12 respectively. These values of K-[ are too small for the formation of mono(terpy)zinc(II) complexes, but are as expected for the formation of a mono(ligand)zinc(II) complex in which the terpy acts as a bidentate (bipy) donor. The kinetics of the reaction of [Cu(OH2)g] with excess terpy in water buffered at pH 6.1 are more complex, with several kinetic steps observed. The first, very rapid stage involves the largest absorbance changes, and is attributed to the formation of mono(terpy)Cu(II) (at 25 °C, 1 0 ~ 7 k f = 1.2 ± 0.1 d m 3 m o l 1 s ). Subsequent reactions are attributed to the rapid formation and slow rearrangement of a five-coordinate bis(terpy)copper(II) intermediates, with one terpy acting as a terdentate donor and the other terpy as a bidentate ligand. Reaction of pre-formed [Cu(terpy)(OH2)2l + with excess terpy also revealed the rapid formation and slow rearrangement of bis(terpy)copper(II) species. 1 7 0 NMR and ESR line broadening were used to determine the rate of water exchange with [Cu(terpy)(OH2)2l ; assuming [Cu(terpy)(OH2)2] + has a trigonal bipyramidal geometry with both solvent molecules in equivalent positions in the equatorial plane, and that they undergo solvent exchange at the same rate, for each coordinated solvent the following results were obtained: 10\"8fcex = 6.6 ± 0.9 s\" 1 : ΔΗ* = 20.7 ± 2 k j","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"57 1","pages":"1 - 24"},"PeriodicalIF":0.0,"publicationDate":"2001-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84869874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Hypochlorite oxidation of the Schiff base complex of chromium(IIl), Cr(salen)(H20)2 has been investigated at pH 9.0 to understand the mechanism of formation of oxochromium(V) species, which has been implicated in the apoptotic cell death brought about by Cr(salen)(H2)O2 . The reaction exhibited a two stage kinetic profile due to the formation of oxochromium( V) species and its subsequent decay. The final product has been unambiguously identified as Chromate. The overall stoichiometry of lfCr(III)]: 1.5[OCl ] has been established for the reaction. The thermodynamic parameters for the formation of oxochromium( V) species are ΔΗ 9.9 ± 1.8 Kcal mol 1 and ΔS 24.5 ± 8.0 e.u. Reaction schemes have been proposed invoking Cr(V) and Cr(IV) dimeric species as possible intermediates. An inner sphere mechanism has been invoked in the formation of oxochromium( V) intermediate.
{"title":"Hypochlorite Oxidation of a Chromium(III) Schiff Base Complex","authors":"R. Rajan, B. Nair, T. Ramasami","doi":"10.1515/irm-2000-0401","DOIUrl":"https://doi.org/10.1515/irm-2000-0401","url":null,"abstract":"Abstract Hypochlorite oxidation of the Schiff base complex of chromium(IIl), Cr(salen)(H20)2 has been investigated at pH 9.0 to understand the mechanism of formation of oxochromium(V) species, which has been implicated in the apoptotic cell death brought about by Cr(salen)(H2)O2 . The reaction exhibited a two stage kinetic profile due to the formation of oxochromium( V) species and its subsequent decay. The final product has been unambiguously identified as Chromate. The overall stoichiometry of lfCr(III)]: 1.5[OCl ] has been established for the reaction. The thermodynamic parameters for the formation of oxochromium( V) species are ΔΗ 9.9 ± 1.8 Kcal mol 1 and ΔS 24.5 ± 8.0 e.u. Reaction schemes have been proposed invoking Cr(V) and Cr(IV) dimeric species as possible intermediates. An inner sphere mechanism has been invoked in the formation of oxochromium( V) intermediate.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"61 1","pages":"247 - 256"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86609152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The oxidation of thiocyanate by periodate has been studied in alkaline media. A microamount of Os( VIII) is sufficient to catalyse the reaction. The active species of catalyst and oxidant in the reaction are understood to be OsO4 (OH)22- and IO-4. The autocatalysis exhibited by one of the products i.e., cyanate is attributed to adduct formation between cyanate and periodate. A composite mechanism and rate law are proposed. The reaction constants involved in the mechanism are evaluated.
{"title":"Osmium(VIII) Catalysed Oxidation of Thiocyanate by Periodate in Aqueous Alkaline Medium","authors":"G. A. Hiremath, N. Halligudi, S. Nandibewoor","doi":"10.1515/irm-2000-0407","DOIUrl":"https://doi.org/10.1515/irm-2000-0407","url":null,"abstract":"Abstract The oxidation of thiocyanate by periodate has been studied in alkaline media. A microamount of Os( VIII) is sufficient to catalyse the reaction. The active species of catalyst and oxidant in the reaction are understood to be OsO4 (OH)22- and IO-4. The autocatalysis exhibited by one of the products i.e., cyanate is attributed to adduct formation between cyanate and periodate. A composite mechanism and rate law are proposed. The reaction constants involved in the mechanism are evaluated.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"28 1","pages":"301 - 308"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73657660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract A formula for the calculation of formation constants for ion-triplets in contact, KIT, is derived on the basis of a thermodynamic argument. This approach also yields an expression for the association constants for ion-pairs, ΚIP, within the same approximation, leading to a modification of the familiar Fuoss equation. The formula for K1T is compared with literature data for transition metal cyano complexes.
{"title":"Theoretical Estimates of Association Constants for Contact Triple-Ion Formation","authors":"Willem Η. Mulder, T. Dasgupta, G. Stedman","doi":"10.1515/irm-2000-0402","DOIUrl":"https://doi.org/10.1515/irm-2000-0402","url":null,"abstract":"Abstract A formula for the calculation of formation constants for ion-triplets in contact, KIT, is derived on the basis of a thermodynamic argument. This approach also yields an expression for the association constants for ion-pairs, ΚIP, within the same approximation, leading to a modification of the familiar Fuoss equation. The formula for K1T is compared with literature data for transition metal cyano complexes.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"71 1","pages":"257 - 264"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86597545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The kinetics and mechanism of the oxidation of hydroxylamine by tris(pyridine-2-carboxylato)manganese( III) in Na(pic)-picH [where Na( pic) = sodium salt of pyridine-2-carboxylic acid (picH)] has been studied in the pH range 4.89-6.10. The rate of the reaction increases with increasing [substrate] but with decreasing acidity. A rate expression has been derived from which the dissociation constant of the equilibrium NH3OH+ ⇄ NH2OH + H+ has been computed at different temperatures. Activation parameters for the slow rate determining step have been evaluated. Manganese(III) complex is reduced by the hydroxylammonium ion by an inner sphere mechanism. The reaction appears to proceed through the intermediate formation of free radicals to give products of oxidation.
{"title":"Inner Sphere Reduction of Tris(pyridine-2- carboxylato)manganese(III) by Hydroxylammonium Ion in Sodium Picolinate-Picolinic Acid Buffer Media","authors":"K. Gupta, B. Pal","doi":"10.1515/irm-2000-0403","DOIUrl":"https://doi.org/10.1515/irm-2000-0403","url":null,"abstract":"Abstract The kinetics and mechanism of the oxidation of hydroxylamine by tris(pyridine-2-carboxylato)manganese( III) in Na(pic)-picH [where Na( pic) = sodium salt of pyridine-2-carboxylic acid (picH)] has been studied in the pH range 4.89-6.10. The rate of the reaction increases with increasing [substrate] but with decreasing acidity. A rate expression has been derived from which the dissociation constant of the equilibrium NH3OH+ ⇄ NH2OH + H+ has been computed at different temperatures. Activation parameters for the slow rate determining step have been evaluated. Manganese(III) complex is reduced by the hydroxylammonium ion by an inner sphere mechanism. The reaction appears to proceed through the intermediate formation of free radicals to give products of oxidation.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"15 1","pages":"265 - 272"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73753871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bharti Goyal, M. Mehrotra, A. Prakash, R. Mehrotra
Abstract The title reaction proceeds through the formation of an intermediate [CoIII W... N3]6 formed between [ComIIIW]5- and N3- and not between [CoIIIW]5 and HN3. The absorbance measurements of the intermediate at various [HN3] yield an equilibrium constant Κ = 0.012 ± 0.001 at 35° C which compares well with the value 0.011 obtained at that temperature from the kinetics data. The reaction is first-order with respect to [ComIIIW]5- and HN3. The pH dependence of kobs, the pseudo-first-order rate constant ([HN3] > [CoIIlW]5-), is consistent with the linearity of the plots between kobs-1 and [H+] with intercepts on the rate ordinate. The inverse correlation between kobs and [H+] is traced to the equilibrium HN3 ⇄ N-3 + H+ followed by [CoIIIW]5 + N3 ⇄ [CoIIIW... N3]6 andnot through the equilibria [CoIIlW]5 + HN3 ⇄ [ColIIW ...N3]6- + H+. The high reactivity of the N-3 ion is traced to the presence of an unshared pair of electrons as in the case of NH2OH and N2H4 which seems to imply an inner-sphere mechanism with the substrate binding to the oxidant via this pair of electrons. However, in view of the well-protected nature of the central CoIII atom in [ColIIW]5- ion there is difficulty in visualising the coordination of the substrate with the Co1" ion. That the electron transfer is outer-sphere is substantiated by excellent agreement between the experimental rate of electron-transfer, 0.305 dm3 mol-1 s-1 , and the one (0.339 dm3 mol-1 s-1) calculated by the application of Marcus equations.
{"title":"Kinetics and Mechanism of Oxidation of Azide Ion by 12-Tungstocobaltate(III), [CoW12O40]5-, Ion","authors":"Bharti Goyal, M. Mehrotra, A. Prakash, R. Mehrotra","doi":"10.1515/irm-2000-0406","DOIUrl":"https://doi.org/10.1515/irm-2000-0406","url":null,"abstract":"Abstract The title reaction proceeds through the formation of an intermediate [CoIII W... N3]6 formed between [ComIIIW]5- and N3- and not between [CoIIIW]5 and HN3. The absorbance measurements of the intermediate at various [HN3] yield an equilibrium constant Κ = 0.012 ± 0.001 at 35° C which compares well with the value 0.011 obtained at that temperature from the kinetics data. The reaction is first-order with respect to [ComIIIW]5- and HN3. The pH dependence of kobs, the pseudo-first-order rate constant ([HN3] > [CoIIlW]5-), is consistent with the linearity of the plots between kobs-1 and [H+] with intercepts on the rate ordinate. The inverse correlation between kobs and [H+] is traced to the equilibrium HN3 ⇄ N-3 + H+ followed by [CoIIIW]5 + N3 ⇄ [CoIIIW... N3]6 andnot through the equilibria [CoIIlW]5 + HN3 ⇄ [ColIIW ...N3]6- + H+. The high reactivity of the N-3 ion is traced to the presence of an unshared pair of electrons as in the case of NH2OH and N2H4 which seems to imply an inner-sphere mechanism with the substrate binding to the oxidant via this pair of electrons. However, in view of the well-protected nature of the central CoIII atom in [ColIIW]5- ion there is difficulty in visualising the coordination of the substrate with the Co1\" ion. That the electron transfer is outer-sphere is substantiated by excellent agreement between the experimental rate of electron-transfer, 0.305 dm3 mol-1 s-1 , and the one (0.339 dm3 mol-1 s-1) calculated by the application of Marcus equations.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"122 1","pages":"289 - 300"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77096670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The water-soluble complex RUCl2(TPPTS)3 has been prepared. In aqueous solution the complex undergoes both CI and TPPTS dissociation, but has been characterized in solution. The reaction with H2 occurs readily through at least two separate mechanisms. The slower step is independent of [CI ] and probably involves direct reaction of H2 with RUCl2(TPPTS)3. A much more rapid step is strongly inhibited by [CI"] and probably involves CI dissociation, perhaps two CI dissociations. In the presence of excess CI the kinetics are well-behaved showing a first-order dependence on [RUCl2(TPPTS)3] and [H2].
{"title":"The Complex Aqueous Chemistry of RUC12(TPPTS)3 and its Reaction with Dihydrogen","authors":"D. Phaho, J. Atwood","doi":"10.1515/irm-2000-0404","DOIUrl":"https://doi.org/10.1515/irm-2000-0404","url":null,"abstract":"Abstract The water-soluble complex RUCl2(TPPTS)3 has been prepared. In aqueous solution the complex undergoes both CI and TPPTS dissociation, but has been characterized in solution. The reaction with H2 occurs readily through at least two separate mechanisms. The slower step is independent of [CI ] and probably involves direct reaction of H2 with RUCl2(TPPTS)3. A much more rapid step is strongly inhibited by [CI\"] and probably involves CI dissociation, perhaps two CI dissociations. In the presence of excess CI the kinetics are well-behaved showing a first-order dependence on [RUCl2(TPPTS)3] and [H2].","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"41 1","pages":"273 - 280"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86788574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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