- Identification of dimethyl sulfide in dimethyl sulfoxide and implications for metal-thiolate disulfide exchange reactions
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The concentration of dimethyl sulfide (DMS) in seven different samples of research grade dimethyl sulfoxide (DMSO), including one deuterated sample, was measured by GC-MS. The average concentration of DMS is 0.48 ± 0.14 mM (range: 0.44-0.55 mM) and ca. 0.
- Garusinghe, Gamage S. P.,Bessey, S. Max,Boyd, Chelsea,Aghamoosa, Mostapha,Frederick, Brian G.,Bruce, Mitchell R. M.,Bruce, Alice E.
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Read Online
- Reactions of O-aryl S-aryl dithiocarbonates with secondary alicyclic amines in aqueous ethanol. Kinetics and mechanism
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The reactions of O-(4-methylphenyl) S-(4-nitrophenyl), O-(4-chlorophenyl) (4-nitrophenyl), O-(4-chlorophenyl) S-phenyl, and O-(4-methylphenyl) S-phenyl dithiocarbonates (1, 2, 3, and 4, respectively) with a series of secondary alicyclic (SA) amines are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically. Under amine excess, pseudo-first-order rate coefficients (kobs) are found. For some of the reactions, plots of kobs vs. free amine concentration at constant pH are linear but others are nonlinear upwards. This kinetic behavior is in accordance with a stepwise mechanism with two tetrahedral intermediates, one zwitterionic (T ±) and the other anionic (T-). In some cases, there is a kinetically significant proton transfer from T± to an amine to yield T-. Values of the rate micro constants k1 (amine attack to form T±), k-1 (its back step), k2 (nucleofuge expulsion from T±), and k 3 (proton transfer from T± to the amine) are determined for some reactions. The Bronsted plots for k1 are linear with slopes β1 = 0.2-0.4 in accordance with the slope values found when T± formation is the rate-determining step. The sensitivity of log k1 and log k-1 to the pK a of the amine, leaving and non-leaving groups are determined by a multiparametric equation. For the reactions of 1-4 with 1-formylpiperazine and those of 3 and 4 with morpholine the k2 and k3 steps are rate determining. Copyright
- Castro, Enrique A.,Gazitua, Marcela,Santos, Jose G.
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supporting information; scheme or table
p. 466 - 473
(2012/01/19)
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- Kinetics and mechanism of the reactions of O-aryl S-(4-nitrophenyl) dithiocarbonates with anilines in aqueous ethanol
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The reactions of O-(4-methylphenyl) S-(4-nitrophenyl) dithiocarbonate and O-(4-chlorophenyl) S-(4-nitrophenyl) dithiocarbonate with a series of anilines are subjected to a kinetic investigation in 44wt% ethanol-water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically at 420nm (appearance of 4-nitrobenzenethiolate anion). Under excess amine, pseudo-first-order rate coefficients (kobs) are found. For the reactions of both substrates with anilines, plots of k obs versus free amine concentration at constant pH are nonlinear upwards, according to a second-order polynomial equation. This kinetic behavior is in agreement with a stepwise mechanism consisting of two tetrahedral intermediates, one zwitterionic (T±) and the other anionic (T-), with a kinetically significant proton transfer from T ± to an aniline to yield T-. The rate equation was derived from the proposed mechanism. By nonlinear least-squares fitting of the rate equation to the experimental data, values of the rate micro-coefficients involved in both steps were determined. Copyright
- Castro, Enrique A.,Gazitua, Marcela,Santos, Jose G.
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scheme or table
p. 176 - 180
(2010/08/20)
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- Reactions of O-aryl S-aryl dithiocarbonates with pyridines in aqueous ethanol: Kinetics and mechanism
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The reactions of O-(4-methylphenyl) S-(4-nitrophenyl) dithiocarbonate (1), O-(4-chlorophenyl) S-(4-nitrophenyl) dithiocarbonate (2), and O-(4-chlorophenyl) S-phenyl) dithiocarbonate (3) with a series of pyridines were subjected to a kinetic investigation
- Castro, Enrique A.,Gazitua, Marcela,Santos, Jose G.
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scheme or table
p. 1003 - 1008
(2010/07/04)
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- Reactions of phosphate and phosphorothiolate diesters with nucleophiles: Comparison of transition state structures
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A series of methyl aryl phosphorothiolate esters (SP) were synthesized and their reactions with pyridine derivatives were compared to those for methyl aryl phosphate esters (OP). Results show that SP esters react with pyridine nucleophiles via a concerted SN2(P) mechanism. Bronsted analysis suggests that reactions of both SP and OP esters proceed via transition states with dissociative character. The overall similarity of the transition state structures supports the use of phosphorothiolates as substrate analogues to probe mechanisms of enzyme-catalyzed phosphoryl transfer reactions. This journal is The Royal Society of Chemistry.
- Ye, Jing-Dong,Barth, Christofer D.,Anjaneyulu, Potluri S. R.,Tuschl, Thomas,Piccirilli, Joseph A.
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p. 2491 - 2497
(2008/02/14)
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- Kinetics and mechanism of the pyridinolysis of S-4-nitrophenyl 4-substituted thiobenzoates in aqueous ethanol
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The pyridinolysis of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO2; 1, 2, and 3, respectively) is studied kinetically in 44 wt % ethanol-water, at 25.0 °C and an ionic strength of 0.2 M (KCl). The reactions are measured spectrophotometrically (420-425 nm) by following the appearance of 4-nitrobenzenethiolate anion. Pseudo-first-order rate coefficients (kobsd) are obtained throughout, under excess of amine over the substrate. Plots of kobsd vs [free amine] at constant pH are linear with the slope (kN) independent of pH. The Bronsted-type plot (log kN vs pKa of the conjugate acids of the pyridines) for the reactions of thiolbenzoate 1 is curved with a slope at high pK a, β1 = 0.20, and slope at low pKa, β2 = 0.94. The pKa value for the center of the Bronsted curvature is pKa0 = 9.7. The pyridinolysis of thiolbenzoates 2 and 3 show linear Bronsted-type plots of slopes 0.94 and 1.0, respectively. These results and other evidence indicate that these reactions occur with the formation of a zwitterionic tetrahedral intermediate (T±). For the pyridinolysis of thiolbenzoate 1, breakdown of T± to products (k2 step) is rate-limiting for weakly basic pyridines and T± formation (k1 step) is rate-determining for very basic pyridines. The k2 step is rate-limiting for the reactions of thiolbenzoates 2 and 3. The smallest pK a0 value for the reaction of 1 is due to a the weakest electron withdrawal of H (relative to Cl and NO2) in the acyl group, which results in the smallest k-1/k2 ratio. The pK a0 values for the title reactions are smaller than those for the reactions of secondary alicyclic amines with thiolbenzoates 1-3. This is attributed to a lower leaving ability from the T± of pyridines than isobasic alicyclic amines. The lower pKa0 value found for the pyridinolysis of 2,4-dinitrophenyl benzoate (pK a0 = 9.5), compared with that for the pyridinolysis of 1, is explained by the greater nucleofugality from T± of 2,4-dinitrophenoxide than 4-nitrobenzenethiolate, which renders the k -1/k2 ratio smaller for the reactions of the benzoate relative to thiolbenzoate 1. The title reactions are also compared with the aminolysis of similar thiolbenzoates in other solvents to assess the solvent effect.
- Castro, Enrique A.,Vivanco, Melissa,Aguayo, Raul,Santos, Jose G.
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p. 5399 - 5404
(2007/10/03)
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- Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium
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The ammonolysis of several substituted phenyl thiolacetates is kinetically studied in aqueous medium, 18°C, ionic strength 0.1 M (KCl). By following the leaving groups spectrophotometrically (λmax = 260-410 nm), under excess free ammonia, pseud
- Rajarathnam,Babu,Nadar, P. Ananthakrishna
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- Kinetics and mechanism of the reactions of quinuclidines with ethyl S- aryl thiolcarbonates
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The reactions of quinuclidines with ethyl S-(4-nitrophenyl) thiolcarbonate (NPTC), ethyl S-(2,4-dinitrophenyl) thiolcarbonate (DNPTC), and ethyl S-(2,4,6-trinitrophenyl) thiolcarbonate (TNPTC) are subjected to a kinetic study in aqueous solution, 25.0°C, ionic strength 0.2 (KCl). The reactions are studied by following spectrophotometrically (400 nm) the release of the corresponding substituted benzenethiolate anion. Under quinuclidine excess, pseudo-first-order rate coefficients (k(obsd)) are found. Plots of k(obsd) vs [N] (N is the free substituted quinuclidine) are linear and pH independent, with slope k(N). The Bronsted-type plots (log k(N) vs pK(a) of quinuclidinium ions) are linear, with slope β = 0.85 for NPTC, in agreement with a stepwise mechanism where the breakdown of a tetrahedral addition intermediate (T±) is rate determining, and β = 0.54 and 0.47 for DNPTC and TNPTC, respectively, consistent with a concerted mechanism. By comparison of the reactions under investigation among them and with similar aminolyses, the following conclusions can be drawn: (i) Substitution of the 4-nitrobenzenethio group in T± by 2,4-dinitrobenzenethio or 2,4,6- trinitrobenzenethio destabilizes the tetrahedral intermediate. (ii) Quinuclidines destabilize the tetrahedral intermediate relative to secondary alicyclic amines, anilines, and pyridines. The leaving abilities of isobasic amines from T± follow the sequence pyridines anilines secondary alicyclic amines quinuclidines. (iii) Quinuclidines are more reactive toward the carbonyl group of phenyl 4-nitrophenyl carbonate than that of NPTC.
- Castro, Enrique A.,Munoz, Patricio,Santos, Jose G.
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p. 8298 - 8301
(2007/10/03)
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- Concerted mechanisms of the reactions of ethyl S-aryl thiocarbonates with substituted phenoxide ions
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The reactions of 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6- trinitrophenyl O-ethyl thiolcarbonates with substituted phenoxide ions are subjected to a kinetic study in water, 25.0 °C, ionic strength 0.2 M (KCl). By following the reactions spectrophotometrically, pseudo-first-order rate coefficients (k(obsd)) are found under excess of the nucleophile. Plots of k(obsd) vs phenoxide anion concentration at constant pH are linear, with the slope (k(N)) independent of pH. The Bronsted-type plots (log k(N) vs pK(a) of the phenols) are linear with slopes β = 0.92, 0.77, and 0.61 for the reactions of the 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6-trinitrophenyl derivatives, respectively. For these reactions, a concerted mechanism is proposed since the slope values are similar to those found in the concerted phenolysis of aryl acetates; the slope magnitudes are not consistent with a stepwise mechanism where the formation of a tetrahedral intermediate is rate limiting. Our results are in line with the finding that the reactions of the 2,4-dinitrophenyl and 2,4,6-trinitrophenyl derivatives with secondary alicyclic amines in water are concerted. In contrast, the reactions of the same substrates with pyridines are stepwise, which means that substitution of a pyridine moiety in a tetrahedral intermediate with a benzenethio group by a phenoxy group destabilizes the intermediate.
- Castro,Paves,Santos
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p. 2310 - 2313
(2007/10/03)
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- Photochemistry of nitrobenzenethiol. Selective generation of the thio radical and thione triplet state as a function of solvent polarity
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Transient absorption spectra of p-nitrobenzenethiol (NBSH) have been measured by the nanosecond laser flash photolysis method. In nonpolar and less polar solvents, nitrobenzenethio radical (NBS(·)) was predominantly formed by the homolytic fission of the
- Alam,Ito
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p. 1285 - 1290
(2007/10/03)
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- Dissection of Nucleophilic and General Base Roles for the Reaction of Phosphate with p-Nitrophenyl Thiolacetate, p-Nitrophenyl Thiolformate, and Phenyl Thiolacetate
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Phosphate buffers are well-known to catalyze the decomposition of various active acyl compounds. This study was undertaken to determine the extent to which it acts as a nucleophile and general base toward some activated esters and thiolesters. Thus, the hydrolyses of p-nitrophenyl acetate (3a), p-nitrophenyl thiolacetate (3b), phenyl acetate (4a), phenyl thiolacetate (4b), and p-nitrophenyl thiolformate (5) have been studied in aqueous phosphate, μ = 1.0 (K2SO4). Both phosphate monoanion and dianion are reactive toward the thiolesters 3b, 4b, and 5. For 3b, reaction of the dianion exhibits a solvent kinetic isotope effect (SKIE) of 1.00 ± 0.11 while that for the monoanion is 2.13 plusmn; 1.1. For the reaction of phosphate dianion with 5, the SKIE is 0.8 ± 0.2 and that for the monoanion at pH 3.05 is roughly 1.5. Phosphate dianion reacts with each thiolacetate and its oxygen analogue at comparable rates: the reactivity ratio of the formyl to acetyl thiolesters, 5:3b, toward phosphate dianion is 685. 1H NMR analysis of the 3b hydrolysis mixtures in H2O and D2O containing phosphate shows the transient formation, and subsequent hydrolysis, of acetyl phosphate. Analysis of the kinetics of these processes indicates that in H2O at pH = 8.5, phosphate dianion functions as both a nucleophile and general base toward 3b, the nucleophilic role comprising 80-93% of the reaction. In D2O, the process is entirely nucleophilic. For the reaction of phosphate dianion with 4b, the 1H NMR analysis indicates that the nucleophilic role comprises 40-50% of the reaction, the general base role being 50-60%. The reaction of phosphate dianion with 5 is entirely nucleophilic, while the monoanion reacts as a general base. The data are interpreted in terms of standard carbonyl addition/elimination mechanisms in which the ability of the attacking phosphate di- or monoanion to displace a given leaving group is tied to the pKa of the conjugate acids of the nucleophile and leaving groups.
- Gill, Manjinder S.,Neverov, Alexei A.,Brown
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p. 7351 - 7357
(2007/10/03)
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- Solvent effects on reactions of hydroxide and oximate ions with phosphorus(V) esters
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Second-order rate constants of reactions of OH-, 2,3-butanedionemonooximate and 2-hydroxybenzaldoximate ions with aryl phosphate, phosphinate and thioarylphosphinate esters go through minima with decreasing water content of aqueous acetonitrile, tert-butyl alcohol and N-methyl-2-pyrrolidone. For reactions in H2O-MeCN the solvent effects are analyzed in terms of activity coefficients of the anionic nucleophiles and transition states. In the drier solvents partial desolvation of the nucleophiles increases rates. Nucleophilicities of several oximates and inorganic anions are compared in water.
- Bunton, Clifford A.,Gillitt, Nicholas D.,Kumar, Anurag
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p. 221 - 228
(2007/10/03)
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- Kinetics and Mechanism of the Pyridinolysis of O-Ethyl S-Aryl Thiocarbonates in Aqueous Solution
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The reactions of a series of 3- and 4-substituted pyridines with S-(4-nitrophenyl), 3-(2,4-dinitrophenyl), and S-(2,4,6-trinitrophenyl) O-ethyl thiocarbonates (NPTC, DNPTC, and TNPTC, respectively) are subjected to a kinetic investigation in aqueous solution, 25.0 deg C, ionic strength 0.2 M (KCl). Pseudo-first-order rate coefficients (kobsd) are found under amine excess. Plots of kobsd vs free amine concentration are linear and pH independent. The Broensted-type plot for NPTC is linear whereas those for DNPTC and TNPTC are biphasic with slopes β1 = 0.2 (high pKa) for both, and β2 = 0.9 and 0.8 (low pKa) for DNPTC and TNPTC, respectively. The curvature center on the pKa axis is pKa0 = 8.6 (DNPTC) and 7.3 (TNPTC). The Broensted plots are consistent with the presence of a zwitterionic tetrahedral intermediate on the reaction path where its breakdown is rate determining for NPTC and there is a change in the rate-limiting step for the reactions of the other two substrates. Comparison of the stepwise reactions of the present work with the concerted ones of DNPTC and TNPTC with secondary alicyclic amines shows that the latter amines greatly destabilize T+/- relative to isobasic pyridines. Comparison of the present reactions with other pyridinolysis indicates that substitution of the oxygen phenoxy atom by sulfur increases pKa0 and the change of methyl to ethoxy as the remaining group also enlarges the pKa0 and besides destabilizes T+/-.
- Castro, Enrique A.,Pizarro, Maria I.,Santos, Jose G.
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p. 5982 - 5985
(2007/10/03)
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- Formation of Stable Aryldisulphide Ions in Dimethylacetamide from the Reaction of Sulphur with Thiolate Ions
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The conditions for the formation of aryldisulphide ions, RS2- during the direct reaction of sulphur with thiolate ions RS- have been studied by the use of spectroelectrochemistry in dimethylacetamide.The series of derivatives examined was R = p-tolyl (1), phenyl (2), 8-quinolyl (3), 2- and 4-pyridyl (4), (5), N-oxido 4-pyridyl (6), 2- and 4-nitrophenyl (7), (8), and 2-(5-nitropyridyl) (9).Sulphur reaction leads to RS2- ions and preceded the oxidation to diaryldisulphide RS2R and polysulphide ions Sx-.With derivatives (1)-(3), both reactions are successive and practically stoicheiometric, while for derivatives containing electron-withdrawing groups (6)-(9), the equilibrium constants have been measured.Analysis of the reaction products by methylation of several solutions of thiolate ions in the presence of sulphur confirmed the possibility of obtaining aryldisulphide ions stabilized in aprotic dipolar media.
- Benaichouche, Meriem,Bosser, Gerard,Paris, Jacky,Auger, Jacques,Plichon, Vincent
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- Relative Nucleophilicities of Aryldisulphide and Thiolate Ions in Dimethylacetamide Estimated from their Reaction Rates with Alkyl Halides
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The relative rates of nucleophilic substitution (SN2) of alkyl halides by aromatic thiolates ArS- and aryldisulphide ions ArS2- have been studied in dimethylacetamide by UV-visible spectrophotometry for Ar = 4-nitrophenyl (1), 2-nitrophenyl (2), and 8-quinolyl (3).Rate constants are relative to the rate constants for benzenethiolate ions (4), studied as reference.With Ar = (1), the reaction rate for disulphide ions is ten times higher than that for monosulphide ions stabilized by the elevated delocalization of their charge.With Ar = (2) and (3), the reactivity of disulphide ions is higher than that of the corresponding thiolates.Our study is consistent with the uncomplicated introduction of a disulphide bond into various substrates from aryldisulphide ions stabilized in aprotic dipolar media.
- Benaichouche, Meriem,Bosser, Gerard,Paris, Jacky,Plichon, Vincent
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p. 1421 - 1424
(2007/10/02)
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- The E1cB Mechanism for Thiocarbamate Ester Hydrolysis: Equilibrium and Kinetic Studies
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The alkaline hydrolyses of a series of S-aryl thiocarbamate esters have been measured and the mechanism confirmed to be dissociative.Equilibrium constant for the synthesis of thiocarbamates from thiol and isocyanic acid have been obtained for aqueous media using both kinetic and analytical techniques.Hammett and Broensted parameters for the equilibrium reaction indicate that there is less positive effective charge on the sulphur in the thiocarbamate compared with that on the oxygen in the oxygen analogue.Theoretical arguments are advanced to show that the dissociative reactions of simple carbamate anions involve a planar geometry of the paticipating atoms.
- Bourne, Nicholas,Williams, Andrew,Douglas, Kenneth T.,Penkava, Thomas R.
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p. 1827 - 1832
(2007/10/02)
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- Effect of Solvation on the Nucleophilic Reaction of Stable Carbanions with Diaryl Disulfides
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Stable carbanions react with diaryl disulfides in aqueous solution by direct displacement (SN2) reaction to yield an arylthiol anion and the corresponding sulfide as products.The reaction of 1,3-dicarbonyl carbanions with 5,5'-dithiobis(2-nitrobenzoic acid) is characterized by Broensted βC value of 0.5.Nitroalkane carbanions react 102-104 slower than 1,3-dicarbonyl carbanions of the same pK and are correlated by a Broensted βC of 0.95.The second-order rate constants for the reaction of nitroalkane carbanions increase by factors of 104-106 as the solvent is changed from water to dimethyl sulfoxide.Smaller increases are observed in the rate constants for reaction of 2,4-pentadienone carbanion (102) and malonitrile carbanion (100.6) with the same sulfide.A linear correlation is found between log (kMe2SO4/kHOH) and the increase in pK for the carbon acid ionization on changing the solvent from water to dimethyl sulfoxide.The effect is attributed to large differences in ground-state carbanion solvation which are reduced or absent in the transition state.Parallels are drawn between the nucleophilic reaction of stable carbanions with diaryl disulfides and proton-transfer reactions of the same carbanions.
- Gilbert, H. F.
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p. 7059 - 7065
(2007/10/02)
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