Pub Date : 2008-01-01DOI: 10.1515/IRM.2008.6.4.337
S. Prasad, R. Naik, V. Chand
{"title":"Kinetics and Mechanism of Uncatalysed Exchange of Cyanide in Hexacyanoferrate(II) by N-Methylpyrazinium Cation","authors":"S. Prasad, R. Naik, V. Chand","doi":"10.1515/IRM.2008.6.4.337","DOIUrl":"https://doi.org/10.1515/IRM.2008.6.4.337","url":null,"abstract":"","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"195 1","pages":"337 - 344"},"PeriodicalIF":0.0,"publicationDate":"2008-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86745896","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}
Pub Date : 2008-01-01DOI: 10.1515/IRM.2008.6.4.287
B. Saha
Vanadium(V) oxidation of lactic acid shows first order dependency on lactic acid, vanadium(V), H+ and HSO4 . These observations remain unaltered in the presence of externally added surfactants. The effect of adding a cationic surfactant (CPC), anionic surfactant (SDS) and neutral surfactant (TX-100) has been studied. CPC inhibits the reactions while SDS and TX-100 accelerate the reaction to different extents. Observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants
{"title":"Micellar Effects on Vanadium(V) Oxidation of Lactic Acid in Aqueous Acid Media: A Kinetic Study","authors":"B. Saha","doi":"10.1515/IRM.2008.6.4.287","DOIUrl":"https://doi.org/10.1515/IRM.2008.6.4.287","url":null,"abstract":"Vanadium(V) oxidation of lactic acid shows first order dependency on lactic acid, vanadium(V), H+ and HSO4 . These observations remain unaltered in the presence of externally added surfactants. The effect of adding a cationic surfactant (CPC), anionic surfactant (SDS) and neutral surfactant (TX-100) has been studied. CPC inhibits the reactions while SDS and TX-100 accelerate the reaction to different extents. Observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"14 1","pages":"287 - 292"},"PeriodicalIF":0.0,"publicationDate":"2008-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89612677","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}
Pub Date : 2007-12-01DOI: 10.1515/IRM.2007.6.3.201
P. Tandon, A. Mehrotra, Manish Srivastava, S. Singh, Satpal Singh
Iridium(III) chloride further catalyses the oxidation of iodide ions by K3Fe(CN)6, catalyzed by hydrogen ions obtained from perchloric acid. Rate when the reaction is catalyzed only by the hydrogen ions was separated from the rate when iridium(III) and H+ions both catalyze the reaction. Separate reactions, studied in the presence as well as in the absence of IrCl3 under similar conditions were found to follow second order kinetics in [I ̄] with direct proportionality in [Fe(CN)6] ̄ and [IrCl3]. Rate was found to follow first order kinetics with respect to [H+] at low concentrations, tending to become second order at higher concentrations of [H+]. Externally added [Fe(CN)6] ̄ ions in the beginning strongly retard the rate effect, but further addition affects the rate to a little extent. Change in ionic strength has no effect on the rate. Arrhenius parameters were calculated and probable mechanisms were proposed.
{"title":"A Novel Aspect of Hexacyanoferrate (III)- Iodide Ion Reaction in Acidic Medium","authors":"P. Tandon, A. Mehrotra, Manish Srivastava, S. Singh, Satpal Singh","doi":"10.1515/IRM.2007.6.3.201","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.201","url":null,"abstract":"Iridium(III) chloride further catalyses the oxidation of iodide ions by K3Fe(CN)6, catalyzed by hydrogen ions obtained from perchloric acid. Rate when the reaction is catalyzed only by the hydrogen ions was separated from the rate when iridium(III) and H+ions both catalyze the reaction. Separate reactions, studied in the presence as well as in the absence of IrCl3 under similar conditions were found to follow second order kinetics in [I ̄] with direct proportionality in [Fe(CN)6] ̄ and [IrCl3]. Rate was found to follow first order kinetics with respect to [H+] at low concentrations, tending to become second order at higher concentrations of [H+]. Externally added [Fe(CN)6] ̄ ions in the beginning strongly retard the rate effect, but further addition affects the rate to a little extent. Change in ionic strength has no effect on the rate. Arrhenius parameters were calculated and probable mechanisms were proposed.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"1 1","pages":"201 - 210"},"PeriodicalIF":0.0,"publicationDate":"2007-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75716269","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.239
M. Ungureșan, G. Niac
The kinetics of reaction between copper(II) and thiosulfate ions and formation of an intermediate complex, CuS2O3 aq, are investigated. The kinetics of fading of the color of this complex has been traced spectrophotometrically using a stoppedflow apparatus. The experimental reaction order (between 2 and 2.5) shows that the mechanism involves, in the first step, fast formation of the complex and, in the second, the reaction between two complex molecules. The influence of temperature on the reaction kinetics has been studied and the reaction’s activation entropy (−214 JKmol) suggests an associative nature for the transition state.
{"title":"Investigation of Copper(II) – Thiosulfate Reaction Kinetics","authors":"M. Ungureșan, G. Niac","doi":"10.1515/IRM.2007.6.3.239","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.239","url":null,"abstract":"The kinetics of reaction between copper(II) and thiosulfate ions and formation of an intermediate complex, CuS2O3 aq, are investigated. The kinetics of fading of the color of this complex has been traced spectrophotometrically using a stoppedflow apparatus. The experimental reaction order (between 2 and 2.5) shows that the mechanism involves, in the first step, fast formation of the complex and, in the second, the reaction between two complex molecules. The influence of temperature on the reaction kinetics has been studied and the reaction’s activation entropy (−214 JKmol) suggests an associative nature for the transition state.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"1 1","pages":"239 - 246"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79931049","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.193
M. Asadi, Z. Asadi
{"title":"Kinetics andMechanism of Adducts Formation of Tetraaza Cobalt (II) Complex with Organic Bases in Dimethylsulfoxide Solvent","authors":"M. Asadi, Z. Asadi","doi":"10.1515/IRM.2007.6.3.193","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.193","url":null,"abstract":"","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"10 1","pages":"193 - 200"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86194346","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.247
Eman S. H. Khaled
The oxidation of the binary complex chromium(III)-uridine, [CrIII (Urd)(H2O)5]3+ and the ternary one chromium(III) uridine aspartic complex, [CrIII (Urd)(Asp) (H2O)3]2+, by periodate have been studied kinetically in aqueous solution to yield CrVI , over 20–40◦C and the 2.62–3.68 pH range. The oxidation of [CrIII (Urd)(H2O)5]3+ by periodate, obeys the rate law, rate = [CrIII urd(H2O)5]3+ [H5IO6]{k4K5 + (k5K6K2/[H+)}, while the reaction of [CrIII (Urd)(Asp)(H2O)3]2+ with periodate following the rate equation d[CrVI ]/dt = (k6K8[CrIII ]T [IO4 ])/ {1 + K8[IO4 ] + ([H+]/K7)}. Thermodynamic activation parameters have been calculated.
{"title":"Inner-Sphere Oxidation of Binary and Ternary Uridine Chromium(III) Complexes Involving Aspartate by Periodate","authors":"Eman S. H. Khaled","doi":"10.1515/IRM.2007.6.3.247","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.247","url":null,"abstract":"The oxidation of the binary complex chromium(III)-uridine, [CrIII (Urd)(H2O)5]3+ and the ternary one chromium(III) uridine aspartic complex, [CrIII (Urd)(Asp) (H2O)3]2+, by periodate have been studied kinetically in aqueous solution to yield CrVI , over 20–40◦C and the 2.62–3.68 pH range. The oxidation of [CrIII (Urd)(H2O)5]3+ by periodate, obeys the rate law, rate = [CrIII urd(H2O)5]3+ [H5IO6]{k4K5 + (k5K6K2/[H+)}, while the reaction of [CrIII (Urd)(Asp)(H2O)3]2+ with periodate following the rate equation d[CrVI ]/dt = (k6K8[CrIII ]T [IO4 ])/ {1 + K8[IO4 ] + ([H+]/K7)}. Thermodynamic activation parameters have been calculated.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"55 1","pages":"247 - 256"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80933878","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.185
R. Naik, A. Srivastava, A. Verma, S. Yadav, Ruchi Singh, S. Prasad
The kinetics and mechanism of oxidation of [Co(II)TTHA]4- (where TTHA = Triehylenetetraaminehexaaceticacid) by periodate ion has been studied in aqueous acidic medium. The reaction has been investigated spectrophotometrically at λmn = 550 nm under pseudo first- order condition by taking large excess of oxidant, [IO4-] at pH = 4.0 + 0.02, 1 = 0.1 M (CH3COONa + Na NO3) and at three different temperatures viz 150 C, 200 C and 250 C. The electron transfer reaction between [Co(II)TTHA]4- and , [IO4-] obeys inner- sphere reaction pathway through the formation of long lived intermediate complex which eventually get converted into a corresponding [Co(III)TTHA]3- complex as final reaction product. The experimental observations have shown that the reaction exhibit first- order dependence in [Co(II)TTHA]4- . The variation of pseudo- first- order rate constant (Kabc) with [IO4-] keeping other reaction variables fixed at constant value is found to obey the following empirical equation. Kabc = a[IO4-]2/b + c[IO4-] This rate law is consistent with a three step mechanistic scheme. The values of (Kabc) are almost invariant with increasing pH and attributed due to the reaction of deprotonated form of [Co(II)TTHA]4- complex and [IO4-] in the whole pH region. Eyring’s equations has been used to calculate the activation parameters and found to be ∆H* = 16.63 KJ mole-1 ; ∆S* = -214.00 JK-1 mole-1. These values are consistent with three step mechanistic scheme as proposed.
{"title":"The Kinetics and Mechanism of Oxidation of Triethylenetetraaminehexaacetatocobaltate(II) Complex by Periodate Ion in AqueousMedium","authors":"R. Naik, A. Srivastava, A. Verma, S. Yadav, Ruchi Singh, S. Prasad","doi":"10.1515/IRM.2007.6.3.185","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.185","url":null,"abstract":"The kinetics and mechanism of oxidation of [Co(II)TTHA]4- (where TTHA = Triehylenetetraaminehexaaceticacid) by periodate ion has been studied in aqueous acidic medium. The reaction has been investigated spectrophotometrically at λmn = 550 nm under pseudo first- order condition by taking large excess of oxidant, [IO4-] at pH = 4.0 + 0.02, 1 = 0.1 M (CH3COONa + Na NO3) and at three different temperatures viz 150 C, 200 C and 250 C. The electron transfer reaction between [Co(II)TTHA]4- and , [IO4-] obeys inner- sphere reaction pathway through the formation of long lived intermediate complex which eventually get converted into a corresponding [Co(III)TTHA]3- complex as final reaction product. The experimental observations have shown that the reaction exhibit first- order dependence in [Co(II)TTHA]4- . The variation of pseudo- first- order rate constant (Kabc) with [IO4-] keeping other reaction variables fixed at constant value is found to obey the following empirical equation. Kabc = a[IO4-]2/b + c[IO4-] This rate law is consistent with a three step mechanistic scheme. The values of (Kabc) are almost invariant with increasing pH and attributed due to the reaction of deprotonated form of [Co(II)TTHA]4- complex and [IO4-] in the whole pH region. Eyring’s equations has been used to calculate the activation parameters and found to be ∆H* = 16.63 KJ mole-1 ; ∆S* = -214.00 JK-1 mole-1. These values are consistent with three step mechanistic scheme as proposed.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"34 1","pages":"185 - 192"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76919538","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.225
J. Shan, L. Fan, S. Huo, H. M. Liu, S. Shen
The kinetics and mechanism of 2,2′-bipyridyl (bpy) catalysis of the chromium(VI) oxidation of lactic acid (Lac) in aqueous acidic medium was studied with spectrophotometry in a temperature range of 25∼40 ◦C. The reaction was found to be pseudo-first order with respect to Cr(VI) and first order to lactic acid. It was found that the pseudo-first order rate constantkobs increased with the increase in [H+] and [bpy]. There is a weak negative salt effect and no free radicals are detected. Thus, HCrO4 is assumed the main existing species of Cr(VI). Based on the experimental results, a probable reaction mechanism of oxidation is proposed. The rate equation derived from the mechanism can explain all the experimental phenomena. The activation parameters, along with rate constants of the rate-determining step, have been calculated.
{"title":"A Kinetic andMechanistic Study of 2,2'- Bipyridyl the Catalyzed Chromium(VI) Oxidation of Lactic Acid","authors":"J. Shan, L. Fan, S. Huo, H. M. Liu, S. Shen","doi":"10.1515/IRM.2007.6.3.225","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.225","url":null,"abstract":"The kinetics and mechanism of 2,2′-bipyridyl (bpy) catalysis of the chromium(VI) oxidation of lactic acid (Lac) in aqueous acidic medium was studied with spectrophotometry in a temperature range of 25∼40 ◦C. The reaction was found to be pseudo-first order with respect to Cr(VI) and first order to lactic acid. It was found that the pseudo-first order rate constantkobs increased with the increase in [H+] and [bpy]. There is a weak negative salt effect and no free radicals are detected. Thus, HCrO4 is assumed the main existing species of Cr(VI). Based on the experimental results, a probable reaction mechanism of oxidation is proposed. The rate equation derived from the mechanism can explain all the experimental phenomena. The activation parameters, along with rate constants of the rate-determining step, have been calculated.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"82 1","pages":"225 - 230"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81024386","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.211
G. C. Dash, B. Dash, P. K. Satpathy, P. Mohanty
The substitution reaction of cyanocobalamin with pentaaquarhodium (III) has been studied spectrophotometrically as a function of pH, [Rh(III)]T and [cyanocobalamin]T . The rate of the reaction increases with increase in [Rh(III)]T but decreases with increase in [H+] ion. The activation parameters H#(55.8 ± 3.4) kJ mol−1 and S#(−136 ± 10) J K−1mol−1 have been calculated from the Eyring plots and anation rate constant ks was compared with the aqua exchange and anation rate constants of analogous substitution reactions. G◦, H◦, S◦ for the outer sphere association process have been calculated from kinetic measurement. The mechanistic pathway for the substitution reaction within the outer sphere complex is consistent with an association interchange (Ia) type of phenomenon.
{"title":"Kinetic and Mechanistic Studies of the Interaction of Hydroxopentaaquarhodium(III) Ion with Cyanocobalamin","authors":"G. C. Dash, B. Dash, P. K. Satpathy, P. Mohanty","doi":"10.1515/IRM.2007.6.3.211","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.211","url":null,"abstract":"The substitution reaction of cyanocobalamin with pentaaquarhodium (III) has been studied spectrophotometrically as a function of pH, [Rh(III)]T and [cyanocobalamin]T . The rate of the reaction increases with increase in [Rh(III)]T but decreases with increase in [H+] ion. The activation parameters H#(55.8 ± 3.4) kJ mol−1 and S#(−136 ± 10) J K−1mol−1 have been calculated from the Eyring plots and anation rate constant ks was compared with the aqua exchange and anation rate constants of analogous substitution reactions. G◦, H◦, S◦ for the outer sphere association process have been calculated from kinetic measurement. The mechanistic pathway for the substitution reaction within the outer sphere complex is consistent with an association interchange (Ia) type of phenomenon.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"32 1","pages":"211 - 216"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88965074","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}
Pub Date : 2007-01-01DOI: 10.1515/IRM.2007.6.3.169
D. Richens, S. Jain, Andrew C. Gale
Reaction of pale-green high spin mer-tris(picolinato)iron(III) with t-butylhydroperoxide in pyridine gives rise to an EPR signal for the t-butylperoxyl radical via a short lived purple intermediate which itself decays eventually to a yellow-brown high spin iron(III) product. The kinetics of the corresponding reaction with hydrogen peroxide have been studied in regard to the dependence of the hydrogen peroxide and picolinic acid concentration on the rate of the initial stages. The results support two rate-determining initial steps (minutes) involving the formation of a short lived purple high spin hydroperoxoor tbutylperoxoiron(III) intermediate (λmax = 530 nm, ε ~ 1,000 dm3 mol-1 cm-1 for the hydroperoxo species) via pre-equilibrium loss of one picolinic acid which then undergoes homolytic Fe-O bond cleavage to give iron(II) and hydroperoxyl (t-butylperoxyl) radical resulting in eventual formation of deep yellow-brown solution which undergoes further complex UV-visible changes over a period of several hours. During this latter timescale these solutions are able to carry out Gif-type catalytic oxygenation of cyclohexane to cyclohexanone in the presence of H2O2 (or O2/pyH/Zn powder) a process which however is completely inhibited in the presence of small amounts of dimethylsulfoxide, an efficient scavenger of the hydroxyl radical. Bis(picolinato)copper(II) was found to be a poor oxygenation catalyst, a finding consistent with its inability to generate the hydroxyl radical via Cu(I) under the same conditions. These results confirm that generation of hydroxyl radicals (via reaction of H2O2 with iron(II) or any other suitably reactive lower valent state) is central to the oxygenation chemistry carried out by these solutions.
{"title":"Kinetics of the Reaction of Mer-Tris(Picolinato) Iron(III) with Hydrogen Peroxide in Pyridine: Role of Hydroxyl Radicals in Subsequent Catalytic Oxygenation of Cyclohexane to the Ketone.","authors":"D. Richens, S. Jain, Andrew C. Gale","doi":"10.1515/IRM.2007.6.3.169","DOIUrl":"https://doi.org/10.1515/IRM.2007.6.3.169","url":null,"abstract":"Reaction of pale-green high spin mer-tris(picolinato)iron(III) with t-butylhydroperoxide in pyridine gives rise to an EPR signal for the t-butylperoxyl radical via a short lived purple intermediate which itself decays eventually to a yellow-brown high spin iron(III) product. The kinetics of the corresponding reaction with hydrogen peroxide have been studied in regard to the dependence of the hydrogen peroxide and picolinic acid concentration on the rate of the initial stages. The results support two rate-determining initial steps (minutes) involving the formation of a short lived purple high spin hydroperoxoor tbutylperoxoiron(III) intermediate (λmax = 530 nm, ε ~ 1,000 dm3 mol-1 cm-1 for the hydroperoxo species) via pre-equilibrium loss of one picolinic acid which then undergoes homolytic Fe-O bond cleavage to give iron(II) and hydroperoxyl (t-butylperoxyl) radical resulting in eventual formation of deep yellow-brown solution which undergoes further complex UV-visible changes over a period of several hours. During this latter timescale these solutions are able to carry out Gif-type catalytic oxygenation of cyclohexane to cyclohexanone in the presence of H2O2 (or O2/pyH/Zn powder) a process which however is completely inhibited in the presence of small amounts of dimethylsulfoxide, an efficient scavenger of the hydroxyl radical. Bis(picolinato)copper(II) was found to be a poor oxygenation catalyst, a finding consistent with its inability to generate the hydroxyl radical via Cu(I) under the same conditions. These results confirm that generation of hydroxyl radicals (via reaction of H2O2 with iron(II) or any other suitably reactive lower valent state) is central to the oxygenation chemistry carried out by these solutions.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"92 1","pages":"169 - 183"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79159215","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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