A linear solvation energy relationship study for the reactivity of 2‐(4‐substituted phenyl)‐cyclohex‐1‐enecarboxylic, 2‐(4‐substituted phenyl)‐benzoic,and 2‐(4‐substituted phenyl)‐acrylic acids with diazodiphenylmethane in various solvents

The reactivities of 2‐(4‐substituted phenyl)‐cyclohex‐1‐enecarboxylic acids, 2‐(4‐substituted phenyl)‐benzoic acids, and 2‐(4‐substituted phenyl)‐acrylic acids with diazodiphenylmethane in various solvents were investigated. To explain the kinetic results through solvent effects, the second‐order rate constants of the examined acids were correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The signs of the equation coefficients support the proposed reaction mechanism. The solvation models for all investigated carboxylic acids are suggested. The quantitative relationship between the molecular structure and the chemical reactivity is discussed, as well as the effect of geometry on the reactivity of the examined molecules. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 430–439, 2010     

Solvent and structural effects on the kinetics of the reactions of 2‐substituted cyclohex‐1‐enylcarboxylic and 2‐substituted benzoic acids with diazodiphenylmethane

The rate constants for the reaction of 2‐methyl‐cyclohex‐1‐enylcarboxylic, 2‐phenylcyclohex‐1‐enylcarboxylic, and 2‐methylbenzoic and 2‐phenylbenzoic acids with diazodiphenyl‐methane were determined in 14 various solvents at 30°C. To explain the kinetic results through solvent effects, the second‐order rate constants of the examined acids were correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The quantitative relationship between the molecular structure and the chemical reactivity has been discussed, as well as the effect of geometry on the reactivity of the examined molecules. The geometric data of all the examined compounds corresponding to the energy minima in solvent, simulated as dielectric continuum, obtained using semiempirical MNDO‐PM3 energy calculations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 664–671, 2007     

Solvent and structural effects on the kinetics of the reactions of cycloalkenylcarboxylic and cycloalkenylacetic acids with diazodiphenylmethane

The rate constants for the reaction of different cycloalkenylcarboxylic, cycloalkenylacetic acids, and phenylacetic acid with diazodiphenylmethane were determined in 12 aprotic solvents at 30°C. In order to explain the kinetic results through solvent effects, the second‐order rate constant of the examined acids was correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The opposite signs of the electrophilic and the nucleophilic parameters are in agreement with the well‐known mechanism of the reaction of carboxylic acids with diazodiphenylmethane. The quantitative relationship between the molecular structure and the chemical reactivity is also discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 361–367, 2005     

Solvent and substituent effects on the electrochemical oxidation of substituted benzylamines in 2‐methylpropan‐2‐ol/water medium

Electrochemical oxidation of various para‐ and meta‐substituted benzylamines in different mole fractions of 2‐methylpropan‐2‐ol in water has been investigated in the presence of 0.1 M sulfuric acid as supporting electrolyte. The oxidation potential data of benzylamines correlates well with Hammett's substituent constants affording negative reaction constants (?1.112 < ρ > ?1.529). The correlation of the oxidation potential values with macroscopic solvent parameters is nonlinear, suggesting the operation of both specific and nonspecific solvent–solvent–solute interaction mechanisms. Correlation of the experimental data with Kamlet–Taft solvatochromic parameters is excellent (100r² > 98%) and the results reveal that the reactivity is influenced by the preferential solvational effects. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 371–377, 2007     

Linear free‐energy relationships in chromium(VI) oxidation of substituted benzylamines in nonaqueous media

The kinetics of oxidation of 11 para‐ and meta‐substituted benzylamines by imidazolium fluorochromate (IFC) in different organic solvent media has been investigated in the presence of p‐toluenesulfonic acid (TsOH). The reaction was run under pseudo‐first‐order conditions. The rate of the reaction was found to be first order in IFC and found to increase with increase in [TsOH]. Solution IR studies in combination with kinetic measurements were used to get a better insight into the mechanism of the oxidation process. The product analysis was carried out using GC–MS. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species benzylamines reaction (k₂) correlates with Hammett's substituent constants affording positive reaction constants. The rate data failed to correlate with macroscopic solvent parameters, such as ε_r and E^N_T, while showing satisfactory correlation with Kamlet–Taft's solvatochromic parameters (α, β, and π*) which suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 362–369, 2007     

Solvent and Structural Effects on the Activation Parameters of the Reaction of Carboxylic Acids with Diazodiphenylmethane

The kinetics of the reaction of benzoic, 2‐methylbenzoic, phenylacetic, cyclohex‐1‐enecarboxylic, 2‐methylcyclohex‐1‐enecarboxylic, and cyclohex‐1‐eneacetic acids with diazodiphenylmethane was studied at 30, 33, 37, 40, and 45°C in a set of 12 protic and aprotic solvents. The reactions were found to follow the second‐order kinetics. The activation energy as well as the activation parameters, such as the standard entropy, the standard enthalpy, and the standard Gibbs energy of the activation, was calculated from the second‐order rate constants. The solvent and structural effects on the activation energy and the standard Gibbs energy of activation, for each examined compound, were analyzed. The results of Kamlet–Taft multiple correlation analysis show that the specific solvent–solute interactions play a dominant role in the governing of the reaction. The signs of the equation coefficients support the proposed reaction mechanism.     

Solvent and substituent effects on the electrochemical oxidation of para‐ and meta‐substituted anilines

Electrochemical oxidation of 15 para‐ and meta‐substituted anilines in different mole fractions of water in 2‐methylpropan‐2‐ol has been investigated in the presence of 0.1 M sulfuric acid as a supporting electrolyte. The oxidation potential data of anilines correlate well with the Brown–Okamoto's substituent constants affording a negative reaction constant. The effect of para‐ and meta‐substituents on the oxidation potential confirms to Swain's F and R, affording negative reaction constants. The oxidation potential values also correlate satisfactorily with macroscopic solvent parameter such as relative permittivity, ε_r. The results of Kamlet–Taft multiple correlation analysis show that specific solute–solvent interactions play a dominant role in governing the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 289–297, 2007     

A LFER Kinetic Study of The Reaction of 5‐Substituted Orotic Acids with Diazodiphenylmethane

Linear free energy relationships (LFER) were applied to the kinetic data for the reaction of 5‐substituted orotic acids, series 1 , with diazodiphenylmethane (DDM) in N,N–dimethylformamide and compared with results obtained for 2‐substituted benzoic acids, series 2 . The correlation analysis of the kinetic data with σ substituent parameters was carried out using SSP (single substituent parameter) methods. From the sign and value of proportinality constant ρ, lower sensitivity to the substituent effect was obtained in series 1 , 0.876, than in the series 2 , 1.877. Evaluation of substituent “ortho‐effect” was performed using the Charton model, which includes the steric substituent parameter, and Fujita and Nishioka's model, which describes the total ortho‐effect as contribution of ordinary polar effect, the ortho‐steric and ortho‐polar effects. Results of correlations, obtained by using the Charton model, showed highest contribution of the polar effect, 0.861 vs. 2.101, whereas the steric effect is of lowest significance, 0.117 vs. 0.055, for series 1 and 2 , respectively. Also, a low negative value of coefficient with the steric effect, –0.08, obtained from the Fujita–Nishioka model indicated low steric effect, influencing a decrease of the reaction rate in series 1 . The structural and substituent effects were also studied by using the density functional theory method, and together with kinetic data, it gave a better insight into the influence of the effect of both geometry and substituent on the π?electron density shift induced reactivity of investigated acids.     

Studies on the kinetics of imidazolium fluorochromate oxidation of some meta‐ and para‐substituted anilines in nonaqueous media

The imidazolium fluorochromate (IFC) oxidation of meta‐ and para‐substituted anilines, in seven organic solvents, in the presence of p‐toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta‐ and para‐substituted anilines at 299–322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species‐anilines reaction (k₂) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ε_r and E^N_T. A correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166–175, 2006     

Kinetics and mechanism of the oxidation of substituted benzaldehydes by hexamethylenetetramine‐bromine

The oxidation of thirty‐six monosubstituted benzaldehydes by hexa‐methylenetetramine‐bromine (HABR), in aqueous acetic acid solution, leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to HABR. Michaelis‐Menten–type kinetics were observed with respect to aldehyde. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of hexamethylenetetramine on the reaction rate. The oxidation of [²H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the solvent. The rates of oxidation of meta‐ and para‐substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho‐substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para‐substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho‐ and meta‐substituted compounds displayed a greater dependence on the field effect. The positive value of γ suggests the presence of an electron‐deficient reaction center in the rate‐determining step. The reaction is subjected to steric acceleration when ortho‐substituents are present. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 615–622, 2000     

Kinetic investigation on the reactions of p‐toluenesulfonyl chloride with p‐substituted benzoic acid(s) in the presence of triethylamine in aprotic solvents

Second‐order rate constants of the reactions of p‐toluenesulfonyl chloride with p‐substituted benzoic acids in the presence of triethylamine in acetonitrile/acetone under equimolar and pseudo‐first‐order conditions have been determined by the conductometric method using the Guggenheim principle at 25, 30, 35, and 40°C. The reactions follow second order with respect to the whole and first order with respect to each of the reactants. The order of reactivity of the substituents in benzoic acid is rationalized. Activation parameters are obtained by applying the usual methods. The Hammett plot has been found nonlinear, whereas the Bronsted plot shows good correlation. This may be explained on the basis of electronic effects of substituents on the reaction center. Kinetic data and the product analyses indicate that the reaction proceeds through direct nucleophilic attack on the sulfur center. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 303–308, 2009     

Solvent hydrogen bonding and structural effects on nucleophilic substitution reactions: Part 3. Reaction of benzenesulfonyl chloride with anilines in benzene/propan‐2‐ol mixtures

Substitution reactions of 13 para‐ and meta‐substituted anilines with benzenesulfonyl chloride in varying mole fractions of benzene in propan‐2‐ol have been investigated conductometrically. The second‐order rate constants correlate well with pK_a values of anilines and with the Hammett's equation. The negative Hammett reaction constant indicates the formation of an electron‐deficient transition state. The rate data correlate satisfactorily with macroscopic solvent parameters such as relative permittivity, ε_r, and polarity, E_T^N. Correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that both the specific and nonspecific solute–solvent interactions influence the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 657–663, 2007     

Solvent and substituent effects on the reaction of 2‐ and 4‐chloro‐3,5‐dinitrobenzotrifluorides with substituted anilines

The solvent effect on a nucleophilic substitution reaction of 2‐ and 4‐chloro‐3,5‐dinitrobenzotrifluoride with substituted anilines was studied in methanol, acetonitrile, and toluene at 25°C. This reaction is of second order, except 2‐chloro‐3,5‐dinitrobenzotrifluoride in toluene shows third order. The k_A values are found to be dependent on the substituent in aniline and give good Hammett correlations. The obtained ρ values are ?4.07 and ?4.62, for the reaction of anilines with 2‐chloro‐3,5‐dinitrobenzotrifluoride in methanol and acetonitrile, respectively. The ρ values for the reaction of the anilines with 4‐chloro‐3,5‐dinitrobenzotrifluoride are ?3.38, ?4.11, and ?4.34 in methanol, acetonitrile, and toluene, respectively. The reaction of the former compound with anilines in toluene shows a second order in aniline. The dependence of the reaction on the external base such as DABCO suggests a proton transfer controlling step. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 777–786, 2009     

Scavenging activity of C4‐hydroxyphenyl‐ and polyhydroxyphenyl‐1,4‐dihydropyridines toward free radicals

The radical‐scavenging ability of synthesized C4‐phenolic‐substituted 1,4‐dihydropyridines (1,4‐DHPs) toward 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) and alkyl/alkylperoxyl ABAP‐derived radicals at pH 7.4 was assessed by UV–visible spectroscopy. Reactivity of 1,4‐DHPs toward DPPH^? was measured by following the decay of the absorption corresponding to the radical λ_max at 525 nm, permitting the calculation of EC₅₀, t_EC50, and antiradical efficiency values. Pseudo–first‐order kinetic rate constants for the reactivity between the C4‐phenolic‐substituted 1,4‐DHP compounds and alkyl/alkylperoxyl ABAP‐derived radicals were followed by the decrease in λ_max at 356 nm corresponding to 1,4‐DHP moiety. C4‐phenolic‐substituted 1,4‐DHPs were more reactive toward alkyl free radicals than the other tested radicals. The 3,4,5‐trihydroxyphenyl‐1,4‐DHP was the most reactive derivative toward this radical with a kinetic rate constant value of 513.2 s^?1. Also, this derivative was the most effective toward the DPPH^? radical with the lowest EC₅₀ value (5.08 µM). Comparative studies revealed that synthesized 1,4‐DHPs were more reactive than commercial 1,4‐DHPs. The scavenging mechanism involves the contribution of both pharmacophores, that is, hydroxyphenyl and 1,4‐DHP rings, which was supported by the identification of the reaction products. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 810–820, 2012     

Microwave‐assisted synthesis of novel 4‐N,N‐dimethylamino‐ and 4‐cycloamino‐ substituted 1,2,4‐triazole‐3‐thiones

4‐N,N‐Dimethylamino‐ and 4‐cycloamino‐5‐phenyl‐1,2,4‐triazole‐3‐thiones 1–13 have been synthesized from benzhydrazides and substituted methyl dithiocarbazates under various conditions including short microwave irradiations. The last method seemed faster than the classical refluxing one. The influence of base and solvent types on the reaction direction has been also examined. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:188–195, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20594     

Quantum chemistry aspects of the solvent effects on the ene reaction of 1‐Phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene

A density functional theory study was used to investigate the quantum aspects of the solvent effects on the kinetic and mechanism of the ene reaction of 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene. Using the B3LYP/6–311++ G(d,p) level of the theory, reaction rates have been calculated in the various solvents and good agreement with the experimental data has been obtained. Natural bond orbital analysis has been applied to calculate the stabilization energy of N18? H19 bond during the reaction. Topological analysis of quantum theory of atom in molecule (QTAIM) studies for the electron charge density in the bond critical point (BCP) of N18? H19 bond of the transition states (TSs) in different solvents shows a linear correlation with the interaction energy. It is also seen form the QTAIM analysis that increase in the electron density in the BCP of N18? H19, raises the corresponding vibrational frequency. Average calculated ratio of 0.37 for kinetic energy density to local potential energy density at the BCPs as functions of N18? H19 bond length in different media confirmed covalent nature of this bond. Using the concepts of the global electrophilicity index, chemical hardness and electronic chemical potentials, some correlations with the rate constants and interaction energy have been established. Mechanism and kinetic studies on 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene ene reaction suggests that the reaction rate will boost with interaction energy enhancement. Interaction energy of the TS depends on the solvent nature and is directly related to electron density of the bonds involved in the reaction proceeding, global electrophilicity index and electronic chemical potential. However, the chemical hardness relationship is reversed. Finally, an interesting and direct correlation between the imaginary vibrational frequency of the N18? H19 critical bond and its electron density at the TS has been obtained. © 2014 Wiley Periodicals, Inc.     

Solvent effect on the alkaline hydrolysis of 2‐thiophenyl‐ 3,5‐dinitropyridine

The kinetics of the alkaline hydrolysis of 2‐thiophenyl‐3,5‐dinitropyridine were studied spectrophotometrically in different aquo‐organic solvents such as methanol, ethanol, n‐propyl alcohol, iso‐propyl alcohol, t‐butyl alcohol, acetonitrile, dimethyl sulfoxide, dioxane, and acetone at 30°C with various solvent compositions up to 80% (v/v) of organic components. An increase in the organic solvent percentage (v/v) has different effects on the reaction rate constants presumably due to hydrogen bond donor HBD and acceptor HBA of the medium and other solvatochromic parameters. Linear and nonlinear plots of log k against the reciprocal of the dielectric constant of the solvent were obtained. The effects are too complex to be analyzed in terms of a single parameter, but an approach using the Kamlet–Taft solvatochromic parameters is applied successfully to six mixed aquo‐organic solvent systems. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 159–165, 2006     

Single‐Electron Transfer in σ‐Complexation Reactions of 2,6‐Dimethoxy‐3,5‐dinitropyridine with Para‐X‐phenoxide Anions in Aqueous Solution

Second‐order rate constants have been measured spectrophotometrically for reactions of 2,6‐dimethoxy‐3,5‐dinitropyridine 1 with 4‐X‐substituted phenoxide anions (X = OMe, Me, H, Cl, and CN) 2a–e in aqueous solution at various temperatures. The effect of phenoxide substituents on the reaction rate was examined quantitatively on the basis of kinetic measurements, leading to nonlinear correlations of Δ^≠H and Δ^≠S with Hammett's substituent constants (σ). Each Hammett plots exhibits two intersecting straight lines for the reactions of 1 with the phenoxide anions 2a–e , whereas the Yukawa–Tsuno plots for the same reactions are linear. The large negative ρ values (?4.03 to ?3.80) obtained for the reactions of 1 with the phenoxide anions possessing an electron‐donating group supports the proposal that the reactions proceed through a single‐electron transfer mechanism.