Kinetic Studies on the Reactions of [(TLtBu)PtCl]+ and [Pt(tpdm)Cl]+ Complexes with Some Thiols and Thioethers

2013 ◽  
Vol 66 (5) ◽  
pp. 534 ◽  
Author(s):  
Enisa Selimović ◽  
Biljana Petrović ◽  
Dragan Čcanović ◽  
Živadin D. Bugarčić ◽  
Jovana Bogojeski
Keyword(s):  
Variable Temperature ◽  
Kinetic Studies ◽  
Substitution Reactions ◽  
Tert Butyl ◽  
Naclo4 Solution ◽  
Entropy Of Activation ◽  
Methyl Pyridine

Substitution reactions of the complexes [(TLtBu)PtCl]+ and [Pt(tpdm)Cl]+, where TLtBu = 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine and tpdm = terpyridinedimethane, with nucleophiles: S-methyl-L-cysteine (S-Met-L-Cys), L-cysteine (L-Cys), glutathione (GSH) and L-methionine (L-Met) were studied in aqueous 0.1 M NaClO4 solution in the presence of 10 mM NaCl using variable-temperature UV-vis spectrophotometry. The higher reactivity of the complex with the tpdm ligand could be attributed to the influence of the bulkiness of the tert-butyl-groups from the [(TLtBu)PtCl]+ complex. The order of reactivity of the studied ligands is: S-Met-L-Cys > L-Met > GSH > L-Cys. The thioethers (S-Met-L-Cys and L-Met) are more reactive than the thiols (GSH and L-Cys). This order of reactivity is in relation with their electron properties and structures. The negative values reported for the entropy of activation confirmed the associative mode.

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.

Article

1998 ◽  
Vol 76 (12) ◽  
pp. 1805-1816
Author(s):  
L Ross C Barclay ◽  
Jennifer K Grandy ◽  
Heather D MacKinnon ◽  
Heather C Nichol ◽  
Melinda R Vinqvist
Keyword(s):  
Oxygen Uptake ◽  
Singlet Oxygen ◽  
Sodium Azide ◽  
Lignin Content ◽  
Sodium Dodecyl ◽  
Kinetic Studies ◽  
Product Distribution ◽  
Geometrical Isomers ◽  
Photo Oxidation ◽  
Tert Butyl

3,5-Di-tert-butyl-ortho-quinone, 6, and 1-(3,4-dimethoxyphenyl-2-(2-methoxyphenoxy)-1-propanone, 7, models for oxidized lignin and for lignin, were used as sensitizers of photo-oxidation. Product studies by HPLC from oxidation of methyl linoleate in solution sensitized by 6 or 7, and in sodium dodecyl sulfate (SDS) sensitized by 6, showed a product distribution of six hydroperoxides, the four conjugated 9- and 13-hydroperoxides of the geometrical isomers: trans-10, cis-12 (2), cis-9, trans-11 (3), trans-10, trans-12 (4), and trans-9, trans-11 (5)-octadecadienoates plus two nonconjugated hydroperoxides. The higher cis/trans to trans/trans (ct/tt) of geometrical isomers (2 + 3//4 + 5) compared to ct/tt from known thermal free-radical peroxidations (Type 1) indicate that singlet oxygen (Type 2) oxidation occurs in reactions sensitized by 6 or 7. Kinetic studies by oxygen uptake are reported on oxidations of hydrocarbons 1-phenyl-2-methylpropene,8, and trans-stilbene,9, sensitized by the quinone, 6, or by a dye, Rose Bengal. Quenching studies imply singlet oxygen reactions. Milled wood lignin undergoes self-initiated photo-oxidation in water, and oxygen uptake was quenched by sodium azide. Cellobiose, a cellulose model, undergoes sensitized photo-oxidation using model quinone, 6, in a mixture of tert-butyl alcohol and water or using the sensitizers benzophenone or the lignin model, 7, delivered on a solid support, silica gel, and these oxidations were quenched with sodium azide. These results implicate singlet oxygen in the photo-yellowing of high lignin content wood pulps.Key words: lignin models, ortho-quinone, photo-oxidation, singlet oxygen, lignin, cellobiose.

Rate and equilibrium studies of the deprotonation of benzylic ketones bearing pyridinium cations

1989 ◽  
Vol 67 (3) ◽  
pp. 428-432 ◽  
Author(s):  
John W. Bunting ◽  
Dimitrios Stefanidis
Keyword(s):  
Activation Parameters ◽  
Kinetic Studies ◽  
Similar Data ◽  
Equilibrium Studies ◽  
Hydroxide Ion ◽  
Pyridinium Cation ◽  
Carbon Acids ◽  
Entropy Of Activation ◽  
Pyridinium Cations ◽  
Conjugate Base

Rates and equilibria for the deprotonation of four benzylic ketones containing pyridinium substituents (1, 2, 5, and 6) have been investigated in basic aqueous solution (ionic strength 0.1) over the range 15–45 °C, and thermodynamic and activation parameters have been evaluated. Similar data are also reported for the deprotonation of nitroethane. The kinetic preference for hydroxide ion addition to the carbonyl group in competition with the thermodynamically preferred enolate ion formation, which was previously reported for the 1-methyl-4-phenylacetylpyridinium cation (1) and its 3-phenylacetyl isomer (2), is also found for the 1-(1-methyl-2-oxo-2-phenylethyl)pyridinium cation (6). Rates of equilibration of the 1-(2-oxo-2-phenylethyl)-pyridinium cation (5) with its enolate ion conjugate base are too rapid to allow investigation by stopped-flow spectrophotometry. For the hydroxide ion catalyzed deprotonation of each of 1, 2, 6, and nitroethane, [Formula: see text] is more negative than ΔS0. This difference, which represents the entropy of activation for protonation of the conjugate base of each of these carbon acids by water, is approximately constant at [Formula: see text] = −4.9 ± 0.5 cal deg−1 mol−1. Keywords: carbon acids, kinetic studies, deprotonation, activation parameters, pKa values.

Kinetic studies on the mechanism of the decomposition of a number of β-substituted tert-butyl α, α -dimethylperpropionates

1977 ◽  
Vol 55 (4) ◽  
pp. 612-618 ◽  
Author(s):  
Dennis D. Tanner ◽  
H. Yabuuchi ◽  
H. Lutzer
Keyword(s):  
General Formula ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Neighboring Group ◽  
Group Participation ◽  
Tert Butyl ◽  
Bond Scission ◽  
Neighboring Group Participation

A series of ter-butyl peresters having a general formula corresponding to I were synthesized.[Formula: see text]The thermally initiated rates of decomposition of these peresters were determined at several temperatures and the activation parameters for these thermolyses were calculated.The rates of decomposition were relatively insensitive to the substituents and followed the order I > C2H5 > C6H5S > H > Br > Cl. The activation parameters and product studies were consistent with a simple two bond scission mechanism and no evidence could be found for neighboring group participation in these homolyses.

Pyrrole chemistry. XXVIII. Substitution reactions of 1-(phenylsulfonyl)pyrrole and some derivatives

1985 ◽  
Vol 63 (4) ◽  
pp. 896-902 ◽  
Author(s):  
Hugh J. Anderson ◽  
Charles E. Loader ◽  
Ru Xun Xu ◽  
Nghia Lê ◽  
Niall J. Gogan ◽  
...  
Keyword(s):  
Substitution Reactions ◽  
Tert Butyl ◽  
Directing Group

The preparative value of the 1-(phenylsulfonyl) N-blocking and directing group for the synthesis of 3-acylpyrroles has been further evaluated. Acetylation and benzoylation are strongly regiospecific and give good yields. However, the regiospecificity is not general and other substitution reactions give mixtures of 2- and 3-substitution or even mostly 2-substitution. Friedel and Crafts tert-butylation gives 3-tert-butyl-1-(phenylsulfonyl)pyrrole and provides a useful route to tert-butylpyrrole, but ethylation and isopropylation give mixtures. Acylations of 2- and 3-alkyl-1-(phenylsulfonyl)pyrroles show little evidence of useful regiospecificity.

Sign in / Sign up

Export Citation Format

Share Document