The Lewis-acidity of square-planar nickel(II) complexes. III. A kinetic study of the effects of substituents on the addition of 1,10-Phenanthroline to Bis(monothioacetylacetonato)nickel(II) and Bis(dithiophosphato)nickel(II) complexes in toluene

1978 ◽  
Vol 31 (7) ◽  
pp. 1439 ◽  
Author(s):  
MU Fayyaz ◽  
MW Grant
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Activation Parameters ◽  
Adduct Formation ◽  
Second Order ◽  
Lewis Acidity ◽  
Order Rate ◽  
Measured Rate ◽  
Square Planar ◽  
Inductive Effects

The second-order rate constants and activation parameters for the addition of 1,10-phenanthroline to bis(dialkyldithiophosphato)nickel(II) complexes and substituted bis(monothioacetylacetonato)-nickel(II) complexes in toluene have been measured. Rate constants are in the range 102-108 1. mol-1 s-1 at 25°C, while ΔH‡ is in the range 10-50 kJ mol-1 and ΔS‡ is in the range from -30 to -110 J mol-1 K-1. The higher rate constants, smaller ΔH‡ and more negative ΔS‡ values are associated with complexes with electron- withdrawing substituents. The results are related to the thermo- dynamics of adduct formation, the inductive effects of the substituents and the pKa of the ligands.

Kinetic Study on Oxidation of Thiodipropionic Acid by Iron (III)- bipyridine Complex

2016 ◽  
Vol 15 (2) ◽  
pp. 33-44
Author(s):  
John K Adaikalasamy ◽  
Selva A Priya ◽  
Sunaja K R Devi
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Second Order ◽  
Aqueous Acetonitrile ◽  
Order Rate ◽  
Uv Visible

Iron(III)-bipyridine complex was prepared andcharacterized by UV-Visible spectrophotometer. Kineticstudy was carried out by using this iron(III)-bipyridinewith thiodipropionic acid in aqueous acetonitrile solution.The reaction was optimized by studying the effect onsubstrate, solvent, oxidant, acidity and temperature. Firstorder, second order rate constants and activationparameters were calculated. The above reaction wasfound to be second order and proceeded through electrontransfer from thiodipropionic acid to iron(III)-bipyridinecomplex. The product was characterized and confirmedby IR and NMR spectroscopy.Keywords: Thiodipropionic acid, Iron(III)-bipyridine complex,kinetic study of Iron(III)-bipyridyl complexes.

Octahedral cobalt(III) complexes of the chloropentanimine type. XXX. The thallium(III)-induced aquation of some cis-Halogeno(amine)bis(ethylenediamine)cobalt(III) cations in aqueous solution

1973 ◽  
Vol 26 (6) ◽  
pp. 1235 ◽  
Author(s):  
SC Chan ◽  
SF Chan
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Alternative Possibility ◽  
Order Rate ◽  
Leaving Group ◽  
Activated Complex

The second-order rate constants for the thallium(III)-induced aquation of cis-[Co(en)2(RNH2)Cl]2+ cations, where R is H, Me, Et, Prn, and Pri, have been measured in aqueous solution over a range of temperatures, and the activation parameters calculated. The kinetic results are discussed in terms of a rapid pre-equilibrium formation of an activated complex Co-Cl-Tl, followed by a simple rate-determining aquation in which TlCl2+ acts as the leaving group, although the alternative possibility of a rate-determining attack by Tl3+ cannot be excluded. In the case of R = H, the investigations have been extended to the corresponding bromo cation which reacts some 50 times faster than its chloro analogue.

Correlation pKa – activité catalytique des thiols dans la réaction d'hydrolyse de l'acétate de p-nitrophényle

1984 ◽  
Vol 62 (11) ◽  
pp. 2330-2336 ◽  
Author(s):  
Alain Brembilla ◽  
Denis Roizard ◽  
Jacqueline Schoenleber ◽  
Pierre Lochon
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Second Order ◽  
Species Comparison ◽  
Order Rate ◽  
Thiolate Anion ◽  
Group A ◽  
Hydrolysis Of

The kinetic study of the hydrolysis of p-nitrophenylacetate in the presence of primary thiols indicates the thiolate anion as the sole catalytic species. Comparison of the true second order rate constants (kRS−) reveals that purely aliphatic primary thiols behave differently from aromatic α-substituted primary thiols. In the latter group a correlation can be established between the true second order rate constants and the pKSH values by means of the Brönsted equation log kRS− = βpKSH + C, with β equal to 0.40 and C equal to −0.85.

scholarly journals The mechanism of reduction of single-site redox proteins by ascorbic acid

1979 ◽  
Vol 177 (2) ◽  
pp. 641-648 ◽  
Author(s):  
A I Al-Ayash ◽  
M T Wilson
Keyword(s):  
Ascorbic Acid ◽  
Rate Constants ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Reducing Agent ◽  
Second Order ◽  
Single Site ◽  
Redox Proteins ◽  
Order Rate ◽  
Temperature Dependences

The reduction of single-site haem and copper redox proteins by ascorbic acid was studied as a function of pH. Evidence is presented that indicates that the double-deprotonated ascorbate anion, ascorbate2-, is the reducing agent, and the pH-independent second-order rate constants for reduction by this species are given. Investigation of the temperature dependences of these rate constants have yielded the values of the activation parameters (delta H++ and delta S++) for reduction. These values, together with ligand-replacement studies, suggest that ascorbate2- acts as an outer-sphere reductant for these proteins. Reasons to account for the apparent inability of ascorbic acid to reduce the alkaline conformer of mammalian ferricytochrome c are suggested.

scholarly journals Kinetic and High-Pressure Mechanistic Investigation of the Aqua Substitution in the Trans-Aquaoxotetracyano Complexes of Re(V) and Tc(V): Some Implications for Nuclear Medicine

2008 ◽  
Vol 2008 ◽  
pp. 1-9 ◽  
Author(s):  
J. Mattheus Botha ◽  
Andreas Roodt
Keyword(s):  
High Pressure ◽  
Nuclear Medicine ◽  
Kinetic Study ◽  
Rate Constants ◽  
Formation Rate ◽  
Activation Parameters ◽  
Second Order ◽  
Associative Mechanism ◽  
Mechanistic Investigation

A kinetic study of the aqua substitution in the [TcO(OH2)(CN)4]− complex by different thiourea ligands (TU = thiourea, NMTU = N-methyl thiourea, NNDMTU = N, N′-dimethylthiourea) yielded second-order formation rate constants (25∘C) as follows [NNDMTU, NMTU, TU, respectively]: kf = 11.5 ± 0.1, 11.38 ± 0.04, and 7.4 ± 0.1 M−1s−1, with activation parameters: ΔHkf#:55±2, 42±3, 35±5 kJ mol−1; ΔSkf#:−40±8, −84±11, −110±17 J K−1mol−1. A subsequent high-pressure investigation of the aqua substitution in the [ReO(OH2)(CN)4]− and [TcO(OH2)(CN4)]− complexes by selected entering ligands yielded ΔVkf# values as follows: Re(V): −1.7±0.3(NCS−), −22.1±0.9 (TU) and for Tc(V): −3.5±0.3(NCS−), −14±1 (NNDMTU), and−6.0±0.5 (TU) cm3mol−1, respectively. These results point to an interchange associative mechanism for the negative NCS− as entering group but even a pure associative mechanism for the neutral thiourea ligands.

Kinetik der Reaktion von Papain mit Bromacetamid / Kinetics of the reaction of papain with bromoacetamide

1971 ◽  
Vol 26 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Hans-Gerhard Löffler ◽  
Friedhelm Schneider ◽  
Helmut Wenck
Keyword(s):  
Rate Constants ◽  
Turning Point ◽  
Ph Dependence ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Ph Range ◽  
Kinetics Of

The pH-dependence of the second order rate constants of the reaction of papain with bromoacetamide in the pH-range 5,5-8,5 is described by a curve with a turning point corresponding to a pK 7,3 ± 0,1 at 25°. This is the pK of a catalytically essential imidazole residue. The activation parameters of the reaction of papain with bromoacetamide were determined. The second order rate constants at pH 7 for the reaction is 200 times greater than for the reaction of bromoacetamide with simple SH-compounds.

Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ with L-Cysteine and S-Methyl-L-cysteine

2005 ◽  
Vol 58 (7) ◽  
pp. 544 ◽  
Author(s):  
Biljana V. Petrović ◽  
Živadin D. Bugarčić
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Mechanistic Study ◽  
Stopped Flow ◽  
Substitution Reactions ◽  
Order Rate ◽  
Increase With Increase ◽  
Naclo4 Solution ◽  
Entropy Of Activation

The reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) with l-cysteine and S-methyl-l-cysteine were studied in an aqueous 0.10 M NaClO4 solution using stopped-flow and conventional UV-vis spectrophotometry. The second-order rate constants for the reactions of [Pd(dien)H2O]2+ at pH 1.0 are k1298 = (9.11 ± 0.11) × 102 M−1 s−1 for l-cysteine, and k1298 = (33.79 ± 0.63) × 102 M−1 s−1 for S-methyl-l-cysteine. The second-order rate constants for the reactions of [Pt(dien)H2O]2+ at pH 1.0 with l-cysteine is k1298 = (1.28 ± 0.08) × 10−2 M−1 s−1 and for S-methyl-l-cysteine is k1298 = (3.87 ± 0.02) × 10−2 M−1 s−1. Activation parameters were determined for all reactions, and the negative values of entropy of activation support an associative complex formation mechanism. Substitution reactions were also studied at pH 0.5, 1.0, and 1.5. The rate constants increase with increase in pH. These results are discussed in terms of protolitic equilibrium.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

Kinetic Study of the Reaction between Substituted Triphenylmethyl Perchlorates with Pyridines in Nitromethane and 1,2-Dichloroethane Solvents

1975 ◽  
Vol 53 (22) ◽  
pp. 3408-3413 ◽  
Author(s):  
Chang B. Kim ◽  
Kenneth T. Leffek
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Saturation Effect ◽  
Bond Breaking ◽  
Carbonium Ion ◽  
Enthalpy Of Activation ◽  
Substituted Pyridines ◽  
Nitrogen Bond

Second-order rate constants at 25 °C have been measured for the reaction of triphenylmethyl carbonium ion with pyridine and substituted pyridines in nitromethane and 1,2-dichloroethane solvent. The activation parameters are in the range 1 to 3 kcal mol−1 for the enthalpies of activation and −20 to −45 cal mol−1 deg−1 for the entropies of activation. The results are compared to the analogous measurements for Menschutkin reactions and it is concluded that the enthalpy of activation of a Menschutkin reaction results mainly from the bond breaking process and solvation changes associated with it, since the carbon-nitrogen bond making process seems to be entropy controlled.Rate measurements have also been made for 2-methylpyridine reacting with a series of para-substituted triphenylmethyl carbonium ion substrates in 1,2-dichloroethane solvent. A plot of log k2vs ∑σ+ is non-linear and the curvature is interpreted as a saturation effect.

Kinetics of chloride substitution in [Pt(bpma)Cl]+ and [Pt(gly-met-S,N,N)Cl] complexes by thiourea, nitrites, and iodides

2014 ◽  
Vol 68 (1) ◽  
Author(s):  
Adrian Topolski ◽  
Živadin Bugarčić
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Kinetics Of

AbstractSubstitution of chloride in [PtCl(bpma)]+ and [PtCl(gly-met-S,N,N)], where bpma is bis(2-pyridylmethyl)amine and gly-met-S,N,N is glycyl-l-methionine, was studied as a function of the entering nucleophile concentration and temperature. Reactions between the platinum(II) complexes and thiourea (TU), iodides (I−), and nitrites(III) (NO2−) were carried out in aqueous solutions using conventional UV-VIS spectrophotometry. Suitable ionic conditions were reached by an addition of 0.1 M NaClO4 and 0.01 M NaCl (to suppress hydrolysis). The second-order rate constants, k 2, for the studied reactions with NO2− varied between 0.036–0.038 M−1 s−1, and for the reactions with TU between 0.095–1.06 M−1 s−1, respectively. The reaction between TU and the [PtCl(bpma)]+ ion is ten times faster than that of the [PtCl(gly-met-S,N,N)] complex. An analysis of the activation parameters, ΔH ≠ and ΔS ≠, for the selected reactions clearly shows their associative nature.

Sign in / Sign up

Export Citation Format

Share Document