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The kinetics of the reaction of n-butyl- and isopropylmagnesium chloride with alkyltriethoxysilanes (RSi(OEt)3) in diethyl ether were determined. The rate constants correlate well with the steric parameters Es(Si). The resulting steric factors δ fit the range of available susceptibility values for the reactions of organosilicon compounds. The thermodynamic activation parameters for six reactions of ethoxysilanes with alkylmagnesium chlorides in dibutyl ether were determined. The entropy values indicated that two Grignard molecules are involved in the transition state of the reaction. From the correlation analysis of the activation enthalpies for the reactions, it appeared that the inductive effect controls the rate of replacement more considerably than steric requirements in the transition state. [ABSTRACT FROM AUTHOR]

Highlights: [•] Kinetic sonication effects were determined for the hydrolysis of 4-methoxyphenyl dichloroacetate in MeCN–H2O mixtures. [•] An experimental evidence of kinetic effects of US presumably in the absence of cavitation was presented. [•] A disturbing impact of cavitation on the ultrasonic acceleration of reactions was found. [Copyright &y& Elsevier]

The kinetics of a tetraethoxysilane reaction with n-butylmagnesium chloride, stoichiometrically monosolvated with isopropyl ether or with methyl tert-butyl ether, was studied in toluene. The pseudo-first-order rate constants determined at a great excess of Grignard reagent were used for separation of the appropriate equilibrium and rate constants. Equilibrium constants for five alkyl ether ligands at the magnesium center are in an excellent correlation with isosteric ES(Si) parameters. It was concluded that these constants should be applicable to all elements of the third period of the periodic table. [ABSTRACT FROM AUTHOR]

Abstract: A LFE (Linear Free Energy) analysis of kinetic data for different organic reactions in various organic aqueous solutions was carried out. The rate constants of these reactions were compared with those for the solvolysis of tert-butyl chloride in the same solvents in terms of the LFE Relationships, and linear plots were observed in a wide range of the co-solvent content. This similarity points to a common nature of the solvent effect in these reactions in variety of water–organic mixtures, regardless of largely different reaction mechanisms. We explain these results by the prevalence of hydrophobic stabilization of the initial state of these reactions in water-rich solvent mixtures. Recently the same conclusion was also made on the basis of investigations into sonication effects in kinetics of organic reactions. A considerable contribution of hydrophobic effects to the Y scale by Grunwald and Winstein was deduced. [Copyright &y& Elsevier]

Kinetic effects of sonication on ester hydrolysis and tert-butyl chloride solvolysis, studied in ethanol–water binary solvent, are discussed in terms of quantitative relationships between their magnitude and the hydrophobicity of reagents. A number of conclusions were drawn from the observed linear free-energy (LFE) relationships. Independent of reaction mechanism, the decrease in reaction rates with increasing ethanol content in the solvent is mainly due to hydrophobic stabilization of the ground state. While hydrophobic species can be hidden in the ethanol clusters present in the region XEtOH > 0.15, at lower ethanol contents hydrophobic reagents are weakly solvated and the hydrophobic stabilization can be easily overcome by sonication. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The kinetics of KCN-catalyzed benzoin condensation of benzaldehyde in water and ethanol−water binary mixtures was investigated both under ultrasound at 22 kHz and without sonication. Thermodynamic activation parameters were calculated from kinetic data obtained at 35, 50, and 65 °C. Evidence that ultrasound can retard reactions is reported and hence a direct proof that sonochemical processes occur in the bulk solution. Former results and literature data for ester hydrolyses and tert-butyl chloride solvolysis are involved in the discussion. A quantitative relationship between sonication effects and the hydrophobicity of reagents is presented for the first time. Ultrasound affects hydrophobic interactions with the solvent, which are not manifested in conventional kinetics. When it suppresses the stabilization of the encounter complexes between reagents, sonication hinders the reaction but accelerates it when it perturbs the hydrophobic stabilization of the ground state of a reagent. [ABSTRACT FROM AUTHOR]

Abstract: Grignard reactions with alkoxysilanes or carbonyl compounds produce alkoxymagnesium halides as by-products. Kinetic measurements for reactions of silanes and of a ketone were performed with Grignard reagents, enriched in alkoxymagnesium halides and taken in a great excess. The alkoxide-type reaction products complex tightly with Grignard reagents and enhance in this way their nucleophilicity, thus accelerating the reaction. However, alkoxides branched at α-C atom exert an unfavorable steric hindrance to reaction resulting in a decrease in the reaction rate. [Copyright &y& Elsevier]

Kinetics of the reactions of phenylmagnesium chloride and bromide and diphenylmagnesium with chlorosilanes were investigated in tetrahydrofurane (THF) and in THF-hydrocarbon mixtures. The reaction in THF is much faster than that in diethyl ether. Assuming coordination of magnesium halides with three molecules of THF, concentrations of all the species involved in Schlenk equilibrium were calculated. In the Grignard reaction, species R2Mg and RMgX react competitively accompanied by additional reaction paths involving electrophilic catalysis by magnesium halide. This conclusion also proved to be valid for the Grignard reaction with a ketone and probably can be expanded to any Grignard reaction. When Schlenk equilibrium is shifted far to the RMgX species, the catalytic pathways are insignificant. Substituents at the silicon center control the rate of the reaction through their inductive and steric effects. [ABSTRACT FROM AUTHOR]

The complexation of MgX2, MeMgX, and Me2Mg (X=Cl, Br) with propyne have been studied both in the gas phase and in the presence of dimethyl ether (Me2O) by means of the density functional theory B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. The complex formation between disolvated magnesium compound and alkyne is connected with replacement of a coordinated solvent molecule by the alkyne, being necessary for the reaction to proceed to the end. The reaction towards end products, an acetylenic Grignard reagent and an alkane, is exothermic. The transition state has a cyclic structure, which is almost triangular with practically linear proton transfer. The transition state resembles more the reagents than the products. [Copyright &y& Elsevier]

Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ethertoluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a fourcenter transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions. [ABSTRACT FROM AUTHOR]

We have investigated the kinetics of the acid-catalyzed hydrolysis of ethyl, propyl, and butyl acetates in aqueous binary mixtures of ethanol and of 1,4-dioxane without sonication and under ultrasound at 22 kHz. Various rate enhancements were found in the region from pure water up to 50 wt % ethanol and 60 wt % dioxane. The calorimetric measurements performed in the same region indicated an insignificant effect of the solvent composition on the ultrasonic power. It was concluded that the sonochemical acceleration of ester hydrolysis in ethanol-water and 1,4-dioxane-water mixtures may be interrelated with the destruction of the molecular structure of the binary solvent and essentially with the perturbation of hydrophobic solute-solvent interactions. The ultrasonic acceleration of polar homogeneous reactions takes place in the bulk reaction medium. This implies the presence of acoustic-field sonochemistry besides the generally accepted hot-spot sonochemistry. [ABSTRACT FROM AUTHOR]

Selectivity problems in preparation of silanes by Gri�gnard reaction were discussed. A quantitative approach in terms of LFE analysis was proposed. It appeared that the inductive effect controls the rate of replacement more considerably than steric requirements in the transition state. Rates of subsequent substitution reactions at silicon decrease stepwise. Only with methylmagnesium halides are the subsequent steps faster. [ABSTRACT FROM AUTHOR]

Selectivity problems in preparation of silanes by Gri?gnard reaction were discussed. A quantitative approach in terms of LFE analysis was proposed. It appeared that the inductive effect controls the rate of replacement more considerably than steric requirements in the transition state. Rates of subsequent substitution reactions at silicon decrease stepwise. Only with methylmagnesium halides are the subsequent steps faster. [ABSTRACT FROM AUTHOR]

Abstract: A revision of quantitative literature data for the reactivity of organosilicon compounds in light of conceptions stemmed from organic chemistry has been carried out. It has been found that in structure-reactivity analysis for organosilicon compounds, differently of carbon compounds, the inductive effect of substituents, at least in nucleophilic displacement reactions at silicon, must be expressed by two terms involving that for electronegativity. A protocol for the correlation analysis in organosilicon chemistry is now available. [Copyright &y& Elsevier]

In this communication we present the results of initial kinetic studies in which we have established that alkoxysilanes and chlorosilanes react with Grignard reagents in entirely different ways. The Grignard reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium centre by silane, followed by a subsequent rearrangement of the complex to the products. Chlorosilanes react without solvent molecule replacement. [Copyright &y& Elsevier]

Review: 101 refs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ultrasonic effects were determined for the hydrolysis of ester in MeCN-H2O mixtures. [•] MD simulation of ethyl acetate solution in acetonitrile–water mixtures was performed. [•] The rate levelling effect by ultrasound was discussed. [Copyright &y& Elsevier]

Abstract: Molecular dynamics (MD) simulation of the structure of ethyl acetate solutions in two water–ethanol mixtures was performed at 280 and 330K. The MD simulations revealed that ethyl acetate was preferentially solvated by ethanol, water being mainly located in the next solvation layer. With increasing temperature ethanol was gradually replaced by water in the first solvation shell. These findings explain the decrease in the rate of ester hydrolysis with increasing molar ratio of ethanol in the solution as the reaction rate was linearly dependent on the relative ethanol content in the first solvation shell of the ester. Predominance of ethanol results in decreased polarity and water activity in the shell and accordingly in a decreased reaction rate. Based on the results of the MD simulations, the principal conclusion of this work is that ultrasound enhances the kinetic energy (the effective temperature) of species in the solution and, in this way, evokes shifts in the solvation equilibria thus affecting the reaction rate. It appears that ultrasound does not completely break down the solvent shells or clusters in the solution as previously believed. Phenomena of thermo-solvatochromism and reaction rate levelling by ultrasound in binary solvents are described. [Copyright &y& Elsevier]

Abstract: Kinetics of the benzoin condensation of benzaldehyde in presence of KCN as the catalyst in water and in ethanol–water binary solutions were investigated without sonication and under ultrasound at 22kHz. A statistically significant 20% decrease of the rate was observed in water. The retardation effect of ultrasound gradually decreases up to 45wt% ethanol content. We report an evidence of ultrasonic retardation of reactions and thereby a direct evidence for sonochemical processes in the bulk solution. Ultrasound can disturb solvation of the species in the solution. If breaking down the stabilization of the encounter complexes between the reagents, sonication hinders the reaction while perturbation of the solvent-stabilization of the reagents accelerates the reaction. [Copyright &y& Elsevier]

Rate constants for the reactions of methylvinyldichlorosilane and tetraethoxysilane with alkylmagnesium chlorides RMgCl (R = Et, n-Bu, i-Bu, i-Pr, s-Bu, t-Bu) in diethyl ether were determined. Excellent correlations of rate data with steric constants ES(Si) by Cartledge and v′ by Charton were found for the reaction of methylvinyldichlorosilane. Linear correlations with break points were obtained for the tetraethoxysilane reaction. It was assumed that this could be referred to a change in the reaction mechanism. [ABSTRACT FROM AUTHOR]

The kinetics of base-catalyzed hydrolysis of 4-nitrophenyl acetate was studied in water and water−ethanol mixtures under ultrasound (21.1 kHz) using a probe equipped with a quartz horn and, by comparison, without sonication. The ethanol concentration was varied from 0 to 50 wt % and pH from 7.5 to 9. The increase of reaction rate was inversely proportional to the strength of substrate interactions with the solvent structure. It was found that the effect of ultrasound could be related to the perturbation of solute−solvent interactions. This conclusion seems to apply to both acid-catalyzed and base-catalyzed hydrolysis reactions. Parallel experiments with a titanium horn revealed the catalytic action of undetermined chemical species formed from dispersed titanium metal. [ABSTRACT FROM AUTHOR]

Pseudo-first-order rate constants were determined for the reactions of tetraethoxysilane with n-butylmagnesium chloride solvated with dibutyl ether, diethyl ether, and THF in toluene. Also isopropylmagnesium chloride and isopropyltriethoxysilane were involved in a similar investigation. Rate and equilibrium constants were calculated for the reactions and the steric effects in the reactions are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Formation reactions of phenylmagnesium chloride and bromide in toluene in the presence of one or two equivalents of diethyl ether or THF were investigated kinetically. Also, the reaction in diethyl ether and in chlorobenzene was addressed. Kinetic features of the reactions are similar to those found previously for the formation of alkylmagnesium halides in toluene and consist of rapid formation of a disolvated Grignard reagent followed by a slower formation of a monosolvated reagent. The latter is able of catalyzing the conversion of different halides into Grignard reagents. However, the contribution of Wurtz-type side reactions is considerable except when THF is used in toluene. Involving the kinetic data and the activation parameters some details of the reaction mechanism were discussed. [Copyright &y& Elsevier]

The solvation effects observed in water-organic solutions were studied by combining data for reaction kinetics and dissolution equilibria by means of a linear free-energy (similarity) analysis. Kinetic data for the pH-independent of (4-methoxyphenyl)-2,2-dichloroacetate measured in this work and solubility data for naphthalene, and other substrates of low polarity, in aqueous binary mixtures of methanol, ethanol, acetonitrile, dimethyl sulfoxide (DMSO), and 1,4-dioxane were used. Linear similarity relationships were discovered for these data over the full range of solvent compositions studied. To gain insight into the similarities observed between these different phenomena, molecular dynamics simulations were carried out for naphthalene and an ester in water-acetonitrile solutions. The results revealed considerable preferential solvation of these substrates by the co-solvent. Linear relationships between the experimental data and the mole fractions of acetonitrile in the solvation shells of substrates were found. Surprisingly, a linear relationship was found between the mole fractions of acetonitrile in the solvation shells of the ester and naphthalene. This linearity indicated that a similar solvation mechanism governs even such different phenomena as dissolution and reaction kinetics. The relationships between the experimental data and the results of the molecular dynamics calculations found in this work explained the solvent effect observed in water-organic solutions on the molecular level. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Kinetics of tetraethoxysilane reaction with n-butylmagnesium chloride, specifically solvated with dibutyl ether, diethyl ether, THF, and triethylamine, was studied in toluene. Also isopropylmagnesium chloride, isopropyltriethoxysilane, and diisopropylketone were involved in a similar investigation. The pseudo-first-order rate constants determined at a great excess of these organomagnesium compounds were used for separation of the appropriate equilibrium and rate constants. An advantage of the method consists in preclusion of non-specific solvation effects when effects of donor solvents are considered. In separate experiments, thermodynamic parameters were determined for rate and equilibrium constants, measured for the reaction of tetraethoxysilane with n-butylmagnesium chloride solvated with dibutyl ether in toluene, and also in bulk dibutyl ether. The implication of steric and solvation effects on this reaction is discussed. [Copyright &y& Elsevier]

Kinetics of the neutral hydrolysis of 4-nitrophenyl chloroacetate was investigated in water and in the presence of 1 mol % of ethanol, propanol, and n-butyl alcohol without sonication and under ultrasound at 25 kHz. Similarly, the kinetics of the acid-catalysed hydrolysis of n-propyl acetate in ethanol—water binary solutions was investigated without sonication and under ultrasound at 22 kHz. The results are discussed together with corresponding data for ethyl and n-butyl acetate from previous works. It was concluded that for ester hydrolyses the solvent effects in an aqueous alcohol binary mixture are limited almost entirely to the hydrophobic ground-state stabilization by the organic co-solvent. [ABSTRACT FROM AUTHOR]

Abstract: Kinetics of reactions of ethyl- and phenylmagnesium chlorides with chlorosilanes, RMeSiCl2, were investigated in diethyl ether under pseudo-first order conditions with a great excess of the Grignard reagent. Rate constants for alkyl substituted silanes correlate well with E s(Si) steric parameters. A good linear correlation of rate data for substituted phenyl derivates with σ 0 inductive constants together with correlations of the literature data rule out the resonance effect of substituents at least in nucleophilic displacement reactions at the silicon center. An attempt to calculate the steric constants for polar substituents was made. It appeared that the inductive constants σ ∗ derived from the carbon chemistry are not applicable to the silicon chemistry. New scales of parameters for description of polar and steric effects in the organosilicon chemistry need to be created. [Copyright &y& Elsevier]

The Schlenk equilibrium involving RMgX, R2Mg, and MgX2 (R = Me, Et, Ph and X = Cl, Br) has been studied both in the gas phase and in diethyl ether (Et2O) and tetrahydrofuran (THF) solutions by means of the density functional theory (DFT) B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. The stabilization due to interaction with solvent molecules decreases in the order MgX2 > RMgX > R2Mg and among the groups (R and X) Ph > Me > Et and Cl > Br. Studied magnesium compounds are more strongly solvated by THF compared to Et2O. The magnesium halide is solvated with up to four solvent molecules in THF solution, assuming that trans-dihalotetrakis(tetrahydrofurano)magnesium(II) complex forms. The formation of cis-dihalotetrakis(tetrahydrofurano)magnesium(II) is energetically less favorable than the formation of corresponding disolvated complexes. The predominant species in the Schlenk equilibrium are RMgX in Et2O and R2Mg + MgX2 in THF, which is consistent with experimental data. [ABSTRACT FROM AUTHOR]