<p>Mass transfer in a porous solid, partially saturated with asingle solvent and multicomponent liquid mixtures, has beenexperimentally and theoretically studied. A porous materialcontaining single liquids and mixtures of organic solvents wasisothermally dried. Experiments were performed using a jacketedwind tunnel, through which a humidity andtemperature-controlled air stream flowed. The wetted porousmaterial was placed in a cylindrical vessel, whose top isexposed to the air stream until the material became dried to acertain extent. Drying experiments with the single solventswater, methanol, ethanol and 2-propanol, were performed atdifferent temperatures and transient liquid content profileswere determined. In isothermal drying experiments with liquidmixtures,the transient concentration profiles of thecomponents along the cylindrical sample as well as the totalliquid content were determined. The liquid mixtures examinedwere water-methanolethanol and isopropanol-methanol-ethanol.Two different temperatures and initial compositions were usedin the experiments. Mathematical models that describe nonsteadystate isothermal drying of a solid containing single liquidsand multicomponent liquid mixtures were developed. In the solidwetted with a single liquid, capillary movement of the liquidwas the main mechanism responsible for mass transfer. In thesolid containing liquid mixtures, interactive diffusion inliquid phase was superimposed to the capillary movement of theliquid mixture. In addition, interactive diffusion of thevapours in empty pores was considered. The parameters todescribe the retention properties of the solid and thecapillary movement of the liquid were determined by comparingtheoretical and experimental liquid content profiles obtainedduring drying of the solid wetted with single liquids. Tosimulate the transport of the liquid mixtures these parameterswhere weighed according to liquid composition. A fairly goodagreement between theoretical and experimental liquidcomposition profiles was obtained if axial dispersion isincluded in the model when the moisture consists of amixture.</p><p><b>Keywords:</b>Internal mass transfer, capillary flow,multicomponent, diffusion, solvent mixtures</p>

Além do interesse intrínseco pelos seus aspectos mecanísticos, as reações de hidrólise de compostos carbonílicos apresentam também a interessante particularidade da reação pelo próprio solvente, a água. Dentre estas reações, conhecidas como \"reações de água\" (Robertson, 1967; Johnson, 1967), estudou-se neste trabalho a hidrólise de carbonatos, através do cálculo das energias de transferência da fase gasosa para o solvente, de reagentes (R), estado de transição (ET) e produtos (P). O estudo da solvatação de modelos moleculares para R e ET indica uma correlação entre reatividade e estrutura molecular. Os resultados usando o enfoque de \"super-molécula\" mostram maior concordância com os dados experimentais do que o cálculo de solvatação da molécula simples e indicam que a solvatação dos modelos de ET é mais eficiente que para R e, portanto, há um aumento da reatividade. O estudo mais detalhado das estruturas de R, ET e P, em misturas água/acetonitrila para carbonatos de difenila e bis(2,4-dinitrofenila), sugere a existência de duas ligações de hidrogênio: entre o oxigênio da água do \"cluster\" e um dos hidrogênios dos anéis aromáticos (CF e CDNF), e entre o hidrogênio da água e o oxigênio do grupo nitro do outro anel aromático (CDNF). A consequente diminuição da liberdade conformacional em relação à fase gasosa, provocada por estas ligações de hidrogênio (CF e CDNF), expõe um dos hemisférios da carbonila ao ataque da água, provocando então uma aceleração entrópica do processo. Os efeitos eletrônicos, devidos às ligações de hidrogênio, estão de acordo com a maior acidez esperada dos hidrogênios dos anéis do CDNF em relação ao CF. Também mostram uma compensação no CDNF, pouco contribuindo para alterar a densidade eletrônica no seu carbono carbonílico, enquanto que indica uma soma de efeitos no CF, contribuindo então para um aumento desta densidade eletrônica no CF, de acordo com sua conhecida baixa reatividade. O trabalho permite ainda concluir sobre o relativo sucesso do uso de método semi-empírico PM3 e modelo relativamente simples de solvatação (Cramer & Truhlar, 1991), para o cálculo de energia de transferência em misturas de água/acetonitrila, na faixa de fração molar da água (0,40 a 1,00) onde o método apresenta resultados concordantes com os valores experimentais. / In addition to their intrinsic mechanistic interest, hydrolysis reactions of carbonyl compounds in aqueous media exhibit the interesting peculiarity of direct reaction with the solvent itself, i.e., water. In the present work, we have investigated a representative example of one of these \"water reactions\" (Robertson, 1967; Johnson, 1967), the hydrolysis of carbonates, via quantum chemical ca1culation of the free energies of transfer of the reagents (R), the transition state (TS) and the products (P) from the gas phase to water. A model study of the solvation of R and TS points to a correlation between reactivity and molecular structure. Results using the \"super-molecule\" approach show greater agreement with experiment than solvation ca1culations on the isolated molecule and imply that the solvation of the TS is more effective than that of R in increasing reactivity. A more detailed study of the structures of R, TS and P for diphenyl- (DPC) and bis(2,4-dinitrophenyl)carbonates (DNPC) in acetonitrile/water mixtures suggests the existence of two possible types of hydrogen bonds, i.e., between oxygen of the water c1uster and an aromatic ring hydrogen (DPC and DNPC) or, in the case of DNPC, between the protons of water and the oxygens of the nitro group of the second aromatic ring. The decrease in conformational degrees of freedom reI ative to the gas phase provoked by these hydrogen bonds exposes one of the hemispheres of the carbonyl group to attack by water, resulting in an entropic acceleration of the reaction. The electronic effects on the hydrogen bonds are in line with the greater acidity of the aromatic ring hydrogens of DNPC relative to those of DNP. In DNPC, there is a compensation effect, with very little alteration of the electron density on the carbonyl carbon, while in DPC a sum of effects increases the electron density on the carbonyl carbon, in line with the known lower reactivity of the latter. This work points to the relative success of the semi-empirical PM3 method combined with relatively simple solvation models (Cramer & Truhlar, 1991) for ca1culating free energies of transfer involving acetonitrile/water mixtures in the water mole fraction range from 0.40-1.00.

Além do interesse intrínseco pelos seus aspectos mecanísticos, as reações de hidrólise de compostos carbonílicos apresentam também a interessante particularidade da reação pelo próprio solvente, a água. Dentre estas reações, conhecidas como \"reações de água\" (Robertson, 1967; Johnson, 1967), estudou-se neste trabalho a hidrólise de carbonatos, através do cálculo das energias de transferência da fase gasosa para o solvente, de reagentes (R), estado de transição (ET) e produtos (P). O estudo da solvatação de modelos moleculares para R e ET indica uma correlação entre reatividade e estrutura molecular. Os resultados usando o enfoque de \"super-molécula\" mostram maior concordância com os dados experimentais do que o cálculo de solvatação da molécula simples e indicam que a solvatação dos modelos de ET é mais eficiente que para R e, portanto, há um aumento da reatividade. O estudo mais detalhado das estruturas de R, ET e P, em misturas água/acetonitrila para carbonatos de difenila e bis(2,4-dinitrofenila), sugere a existência de duas ligações de hidrogênio: entre o oxigênio da água do \"cluster\" e um dos hidrogênios dos anéis aromáticos (CF e CDNF), e entre o hidrogênio da água e o oxigênio do grupo nitro do outro anel aromático (CDNF). A consequente diminuição da liberdade conformacional em relação à fase gasosa, provocada por estas ligações de hidrogênio (CF e CDNF), expõe um dos hemisférios da carbonila ao ataque da água, provocando então uma aceleração entrópica do processo. Os efeitos eletrônicos, devidos às ligações de hidrogênio, estão de acordo com a maior acidez esperada dos hidrogênios dos anéis do CDNF em relação ao CF. Também mostram uma compensação no CDNF, pouco contribuindo para alterar a densidade eletrônica no seu carbono carbonílico, enquanto que indica uma soma de efeitos no CF, contribuindo então para um aumento desta densidade eletrônica no CF, de acordo com sua conhecida baixa reatividade. O trabalho permite ainda concluir sobre o relativo sucesso do uso de método semi-empírico PM3 e modelo relativamente simples de solvatação (Cramer & Truhlar, 1991), para o cálculo de energia de transferência em misturas de água/acetonitrila, na faixa de fração molar da água (0,40 a 1,00) onde o método apresenta resultados concordantes com os valores experimentais. / In addition to their intrinsic mechanistic interest, hydrolysis reactions of carbonyl compounds in aqueous media exhibit the interesting peculiarity of direct reaction with the solvent itself, i.e., water. In the present work, we have investigated a representative example of one of these \"water reactions\" (Robertson, 1967; Johnson, 1967), the hydrolysis of carbonates, via quantum chemical ca1culation of the free energies of transfer of the reagents (R), the transition state (TS) and the products (P) from the gas phase to water. A model study of the solvation of R and TS points to a correlation between reactivity and molecular structure. Results using the \"super-molecule\" approach show greater agreement with experiment than solvation ca1culations on the isolated molecule and imply that the solvation of the TS is more effective than that of R in increasing reactivity. A more detailed study of the structures of R, TS and P for diphenyl- (DPC) and bis(2,4-dinitrophenyl)carbonates (DNPC) in acetonitrile/water mixtures suggests the existence of two possible types of hydrogen bonds, i.e., between oxygen of the water c1uster and an aromatic ring hydrogen (DPC and DNPC) or, in the case of DNPC, between the protons of water and the oxygens of the nitro group of the second aromatic ring. The decrease in conformational degrees of freedom reI ative to the gas phase provoked by these hydrogen bonds exposes one of the hemispheres of the carbonyl group to attack by water, resulting in an entropic acceleration of the reaction. The electronic effects on the hydrogen bonds are in line with the greater acidity of the aromatic ring hydrogens of DNPC relative to those of DNP. In DNPC, there is a compensation effect, with very little alteration of the electron density on the carbonyl carbon, while in DPC a sum of effects increases the electron density on the carbonyl carbon, in line with the known lower reactivity of the latter. This work points to the relative success of the semi-empirical PM3 method combined with relatively simple solvation models (Cramer & Truhlar, 1991) for ca1culating free energies of transfer involving acetonitrile/water mixtures in the water mole fraction range from 0.40-1.00.

No description available.

Mass transfer in a porous solid, partially saturated with asingle solvent and multicomponent liquid mixtures, has beenexperimentally and theoretically studied. A porous materialcontaining single liquids and mixtures of organic solvents wasisothermally dried. Experiments were performed using a jacketedwind tunnel, through which a humidity andtemperature-controlled air stream flowed. The wetted porousmaterial was placed in a cylindrical vessel, whose top isexposed to the air stream until the material became dried to acertain extent. Drying experiments with the single solventswater, methanol, ethanol and 2-propanol, were performed atdifferent temperatures and transient liquid content profileswere determined. In isothermal drying experiments with liquidmixtures,the transient concentration profiles of thecomponents along the cylindrical sample as well as the totalliquid content were determined. The liquid mixtures examinedwere water-methanolethanol and isopropanol-methanol-ethanol.Two different temperatures and initial compositions were usedin the experiments. Mathematical models that describe nonsteadystate isothermal drying of a solid containing single liquidsand multicomponent liquid mixtures were developed. In the solidwetted with a single liquid, capillary movement of the liquidwas the main mechanism responsible for mass transfer. In thesolid containing liquid mixtures, interactive diffusion inliquid phase was superimposed to the capillary movement of theliquid mixture. In addition, interactive diffusion of thevapours in empty pores was considered. The parameters todescribe the retention properties of the solid and thecapillary movement of the liquid were determined by comparingtheoretical and experimental liquid content profiles obtainedduring drying of the solid wetted with single liquids. Tosimulate the transport of the liquid mixtures these parameterswhere weighed according to liquid composition. A fairly goodagreement between theoretical and experimental liquidcomposition profiles was obtained if axial dispersion isincluded in the model when the moisture consists of amixture. Keywords:Internal mass transfer, capillary flow,multicomponent, diffusion, solvent mixtures

The present thesis investigates the application of pressurized mixtures of imidazolium-based ionic liquids with traditional organic solvents for the dissolution and extraction of lignocellulosic biomass, with bamboo as a specific example of renewable biomass. The approach has been unconventional in that the focus has been on solvent mixtures in which the ionic liquid is the minor component. The objective has been to combine the solvating power of the ionic liquid with a traditional solvent such as ethanol to modulate the outcomes of solubility and extractions by tuning the parameters of fluid composition, temperature, and pressure. Working with mixtures of ionic liquids in traditional solvents as process solvents lowers the viscosity of the medium and thus reduces the transport limitations that are often encountered when working with pure ionic liquids. Among other potential advantages are the reductions in overall process cost that are associated with ionic liquids, potentially easier recovery of post-extraction products, and the recycling of the ionic liquids. This thesis has also addressed another important question regarding the thermal stability of the ionic liquids as a processing medium at elevated temperatures and pressures over time, which may negatively impact their recovery and reuse, and may lead to environmentally unacceptable consequences. The dissolution experiments were carried out in a specially designed high-pressure view-cell equipped with sapphire windows for visual or optical observations. Evaluations were made employing standard characterization tools such as Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis Spectroscopy, and Scanning Electron Microscopy (SEM). Thermal stability studies were carried out using a combination of a view-cell and fiber optic UV-Vis capability at high pressures (up to 350 bar) and temperatures (up to 150 ℃). The dissolution of bamboo was first explored using mixtures of 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) with ethanol at temperatures from 100 to 150 ℃ and pressures from 35 to 350 bar over 4 or 24 h extraction times. The fluid mixtures employed were in the range of 1 - 40 wt % ionic liquid, which is in contrast to relevant dissolution experiments reported in the literature which either use pure ionic liquids or have the ionic liquids as the majority component. The effects of changing the temperature, pressure, and solvent composition on the removal of different components of the bamboo were assessed. Temperature played the most significant role in the amount of material extracted from the bamboo, with higher temperatures resulting in the removal of more lignin than cellulose and greater conversion of crystalline cellulose to the less recalcitrant amorphous form of cellulose. The concentration of ionic liquid in solution was also important, with higher concentrations resulting in more dissolved biomass. Finally, increasing the pressure resulted in higher amounts of dissolved biomass. The next series of studies focused on rigorously assessing the stability of 1-alkyl-3-methylimidazolium acetate and chloride ionic liquids with alkyl chain lengths from 2 to 10 under both isothermal and non-isothermal conditions via thermogravimetric analysis. Isothermal degradation experiments were conducted at temperatures ranging from 100 to 225 ℃ over time periods ranging from two hours to three weeks. Non-isothermal degradation experiments were conducted at heating rates of 5, 10, 15, and 20 ℃/min from room temperature to 650 ℃. The activation energies and pre-exponential factors were assessed with isoconversional integral methods; the activation energies () ranged from 115 to 157 kJ/mol, and the pre-exponential factors (()) ranged from 24-38. The degradation reactions could be described as 1st order, as they often are in the literature, but were best fit by the 3-dimensional reaction model. Ionic liquids with longer alkyl chains on their imidazolium rings decomposed more quickly and at lower temperatures. The thermal stability of the most promising ionic liquids ([EMIM]Ac, [BMIM]Ac, [EMIM]Cl, and [BMIM]Cl) were then assessed more closely at the possible biomass processing conditions that were being considered. The primary interest was determining the effects of various cosolvents on the thermal stability of these ionic liquids at the process temperatures and pressures, from 100 to 150 ℃ and 35 to 350 bar. These evaluations were carried out in the same high-pressure view cell in which the extraction experiments were conducted. To assess the degradation of the ionic liquids, time-evolved UV spectra of the mixtures were generated. It was found that more protic solvents such as water attenuated the degradation of the ionic liquids, whereas aprotic solvents such as DMF significantly exacerbated their degradation. Among the ionic liquids evaluated, it was found that [BMIM]Cl had the greatest stability in ethanol at 150 ℃. The bamboo extraction experiments were then continued with mixtures of [BMIM]Cl in ethanol. The results showed that higher temperatures are necessary to extract lignin and cellulose, with [BMIM]Cl's thermal stability at these temperatures giving it the advantage over [EMIM]Ac. In this system as well it was shown that higher concentrations of ionic liquid facilitated the extraction of more biomass. However, biomass constituents that dissolve into mixtures with lower concentrations of ionic liquid readily precipitate back out of solution when the mixture is returned to room conditions. Along with the results of the studies with [EMIM]Ac, the experiments conducted with [BMIM]Cl show that an increase in pressure results in greater amounts of dissolved biomass holding other conditions constant. The thesis, in summary, presents for the first time (a) the use of ionic liquids as a minor component in organic solvents as a potential biomass processing media, (b) the thermal stability of ionic liquids in a cosolvents at high pressures and temperatures, and (c) experimental results showing that pressure can enhance the amount that can be extracted from biomass with mixtures of ionic liquids in a cosolvent like ethanol. / Doctor of Philosophy / The purpose of the work detailed in the present thesis is to better understand the effects of mixtures of ionic liquids and traditional solvents on woody biomass. Ionic liquids are organic salts with melting points below 100 ℃, and they possess unique physical and chemical properties that can facilitate the dissolution or extraction of otherwise recalcitrant materials. There is a rapidly growing need for greener and more sustainable methods of processing woody biomass, which consist of primarily cellulose, lignin, and hemicelluloses. Industrial use of these liquids as processing solvents for woody biomass is limited by their relatively high viscosity, cost, and the difficulty of separating dissolved materials back out of solution. One method used to address these limitations is to mix the ionic liquids with other solvents, such as ethanol. The studies detailed in this thesis also seek to understand the effects of temperature and pressure on both the dissolution of woody biomass and on the degradation of the ionic liquids. The studies employ both traditional characterization equipment and a custom-designed view-cell which allowed for observation and characterization at high temperatures and pressures. The first part of the study investigated the dissolution of bamboo with mixtures of the ionic liquid 1-ethyl-3-methylimidazolium acetate, [EMIM]Ac, and ethanol. The effects of changing the temperature, pressure, and solvent composition on the removal of different components of the bamboo were assessed. It was found that temperature played the most significant role in the amount of material extracted, with higher temperatures resulting in the removal of more lignin than cellulose. The concentration of ionic liquid in solution was also important, with higher concentrations resulting in more dissolved biomass. Finally, increasing the pressure resulted in higher amounts of dissolved biomass. The next parts of the study focused on the degradation of the ionic liquids at elevated temperatures. The type of ionic liquids used in this study do not boil or evaporate at high temperatures, but instead break down into constituents that are themselves volatile. The thermal degradation of the ionic liquid used in the initial biomass dissolution experiments was investigated along with a series of similar ionic liquids. Their degradation behavior was assessed both by measuring their mass over time at a single constant temperature, and by heating them at a constant rate until they fully degraded. This behavior was mathematically modeled. The thermal stability of the most promising ionic liquids were then investigated in mixtures with other solvents in the high-pressure experimental cell under the same temperature and pressure conditions used in the biomass dissolution experiments. The ionic liquid found to have the best stability in ethanol in those experiments was 1-butyl-3-methylimidazolium chloride, [BMIM]Cl. Further dissolution experiments were carried out with mixtures of this ionic liquid in ethanol. These experiments took the insights gained from the previous investigations to further clarify the effects of temperature, concentration, and pressure on the dissolution of bamboo in mixtures of ionic liquid and ethanol. It was again shown that higher temperatures are necessary to extract lignin and cellulose. It was also shown that higher concentrations of ionic liquid facilitate the extraction of more biomass. However, it was also shown that biomass dissolved into mixtures with lower concentrations of ionic liquid readily precipitates back out of solution when the mixture is returned to room conditions. Pressure was again shown to have a favorable effect on the amount of material extracted.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters. / Ministry of Science and Higher Education of Iran