Rate Constants For Alkaline Hydrolysis Research Articles

A multiple linear regression approach to the estimation of carboxylic acid ester and lactone alkaline hydrolysis rate constants

ABSTRACT Pesticides, pharmaceuticals, and other organic contaminants often undergo hydrolysis when released into the environment; therefore, measured or estimated hydrolysis rates are needed to assess their environmental persistence. An intuitive multiple linear regression (MLR) approach was used to develop robust QSARs for predicting base-catalyzed rate constants of carboxylic acid esters (CAEs) and lactones. We explored various combinations of independent descriptors, resulting in four primary models (two for lactones and two for CAEs), with a total of 15 and 11 parameters included in the CAE and lactone QSAR models, respectively. The most significant descriptors include pK a, electronegativity, charge density, and steric parameters. Model performance is assessed using Drug Theoretics and Cheminformatics Laboratory’s DTC-QSAR tool, demonstrating high accuracy for both internal validation (r 2 = 0.93 and RMSE = 0.41–0.43 for CAEs; r 2 = 0.90–0.93 and RMSE = 0.38–0.46 for lactones) and external validation (r 2 = 0.93 and RMSE = 0.43–0.45 for CAEs; r 2 = 0.94–0.98 and RMSE = 0.33–0.41 for lactones). The developed models require only low-cost computational resources and have substantially improved performance compared to existing hydrolysis rate prediction models (HYDROWIN and SPARC).

The reactivity of propyl esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids

Aim. To study the reactivity of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids.Results and discussion. The reaction rate constants of alkaline hydrolysis of esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids depend on the structure and the length of the hydrocarbon chain at the heterocyclic nitrogen atom. Introduction of hydrocarbon radicals to the structure of the heterocycle slows down the reaction, while the chain extension accelerates it. The effect of the electronic nature of the substituents on the reactivity of propyl esters was quantitatively assessed by Hammett equation. The data obtained suggest that the values of the reaction parameter ρ are positive in the temperature range studied; it is additionally confirmed by the ВАС2 mechanism of this reaction.Experimental part. The concentration of NaOH in the solution was determined by potentiometric titration on an EV-74 ionomer using the standard aqueous HCl solution. The reaction kinetics was performed in triplicates, the experiments contained 6-8 measurements (the depth of the change was not less than 80 %). The accuracy of the results obtained was assessed by the methods of mathematical statistics of small samples with statistical significance of 0.95.Conclusions. The reaction kinetics of alkaline hydrolysis of biologically active propyl esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids has been studied in a wide temperature range; its ВАС2 mechanism has been proven with formation of a highly symmetrical intermediate. The effect of the substituents at the heterocyclic nitrogen atom on the numerous kinetic and activation parameters of the reaction has been analyzed; isokineticity and synchronicity of the reaction have been proven using independent tests.

The reactivity of ethyl esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids

The studies in a series of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids and their derivatives have shown that compounds of the isostructural series exhibit the nootropic, antihypoxic, anabolic activity. Aim. To study the reactivity of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids. Materials and methods. The concentration of NaOH in the solution was determined by potentiometric titration on an EV-74 ionomer using the standard aqueous HCl solution. The reaction kinetics was performed in triplicates, the experiments contained 6-8 measurements (the depth of the change was not less than 80 %). The accuracy of the results obtained was assessed by the methods of mathematical statistics of small samples with statistical significance of 0.95. Results and discussion. The reaction rate constants of alkaline hydrolysis of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids depend on the structure and the length of the hydrocarbon chain at the heterocyclic nitrogen atom. Introduction of hydrocarbon radicals to the structure of the heterocycle slows down the reaction, while the chain extension accelerates it. The effect of the electronic nature of the substituents on the reactivity of ethyl esters was quantitatively assessed by Hammett equation. The data obtained suggest that the values of the reaction parameter ρ are positive in the temperature range studied; it is additionally confirmed by the BAC2 mechanism of this reaction. Conclusions. The reaction kinetics of alkaline hydrolysis of biologically active ethyl esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids has been studied in a wide temperature range; its BAC2 mechanism has been proven with formation of highly symmetrical intermediate. The effect of the substituents at the heterocyclic nitrogen atom on the numerous kinetic and activation parameters of the reaction has been analyzed; isokineticity and synchronicity of the reaction have been proven using independent tests.

Kinetic Study on Alkaline Hydrolysis of 2‐Pyridyl and 4‐Pyridyl X‐substituted‐Benzoates: Effects of Benzoyl Substituent X and Leaving‐Group Basicity on Reactivity and Reaction Mechanism

Second‐order rate constants for alkaline hydrolysis of 2‐pyridyl X‐substituted‐benzoates (4a–4l) and 4‐pyridyl X‐substituted‐benzoates (5a–5l) are reported. The Hammett plots are nonlinear, e.g., substrates possessing a weak electron‐withdrawing group (EWG) or an electron‐donating group (EDG) in the benzoyl moiety deviate negatively from the linear Hammett plots composed of substrates bearing a strong EWG. In contrast, the Yukawa–Tsuno plots exhibit excellent linearity with ρX = 1.57, r = 0.43, and R2 = 0.998 for the reactions of 4a–4l and ρX = 1.47, r = 0.41, and R2 = 0.999 for those of 5a–5l, indicating that the nonlinear Hammett plots are not due to a change in the rate‐determining step (RDS) but are caused by ground‐state (GS) stabilization through resonance interactions. The ρX values found for the reactions of 4a–4l and 5a–5l are similar to those reported previously for reactions that proceed through a stepwise mechanism with formation of an intermediate being the RDS. Small βlg values (e.g., −0.2 ~ −0.3) calculated from the Brønsted‐type correlation of rate constants with leaving‐group basicity also indicate that the reactions proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the RDS.

Isothermal and non-isothermal kinetics of hydrolysis of 1-[2-(2- pentyloxyphenylcarbamoyloxy)-(2-methoxymethyl)-ethyl]- perhydroazepinium chloride (BK 129)

Abstract The substance BK 129 - 1-[2-(2-pentyloxyphenylcarbamoyloxy)-(2-methoxymethyl)-ethyl]-perhydroazepinium chloride was prepared in terms of influence of the connecting chain between the carbamate functional group and the basic part of molecule on biological activity. Such a structural feature is important with regard to its stability. In this work we determined the rate constants of alkaline hydrolysis of this compound at increased temperature under isothermal and non-isothermal conditions. The hydrolysis was also performed in buffer solutions with the purpose of evaluating its stability. Non-isothermal tests of stability enable to reduce the number of analyses. The necessary data for stability of compound are in this way achieved in a short time.

Structure-property relationships of a class of carbamate-based fatty acid amide hydrolase (FAAH) inhibitors: chemical and biological stability.

Cyclohexylcarbamic acid aryl esters are a class of fatty acid amide hydrolase (FAAH) inhibitors, which includes the reference compound URB597. The reactivity of their carbamate fragment is involved in pharmacological activity and may affect their pharmacokinetic and toxicological properties. We conducted in vitro stability experiments in chemical and biological environments to investigate the structure-stability relationships in this class of compounds. The results show that electrophilicity of the carbamate influences chemical stability, as suggested by the relation between the rate constant of alkaline hydrolysis (log k(pH9)) and the energy of the lowest unoccupied molecular orbital (LUMO). Introduction of small electron-donor substituents at conjugated positions of the O-aryl moiety increased the overall hydrolytic stability of the carbamate group without affecting FAAH inhibitory potency, whereas peripheral non-conjugated hydrophilic groups, which favor FAAH recognition, helped decrease oxidative metabolism in the liver.

Kinetics of alkaline hydrolysis and morphologies of novel poly(ethylene terephthalate) micro‐porous hollow fibers and functional characteristics of fabrics

AbstractThis investigation explores the kinetics of the alkaline hydrolysis of regular poly(ethylene terephthalate) (PET) solid fibers and PET micro‐porous hollow fibers, using statistical regression analysis. Statistical regression analysis results concerning the kinetics of the alkaline hydrolysis of regular PET solid fibers and PET micro‐porous hollow fibers yielded a β value of 1. The R2 of the kinetic equation for α values from 1.07 to 1.16 exceeded that for α = 1. The rate constants of alkaline hydrolysis followed the order PET micro‐porous hollow fibers ≫ regular PET solid fibers. A morphology of large pores of diameter 0.1–3.5 μm was observed following alkali treatment of the PET micro‐porous hollow fibers. The weight loss percentage of the hollow fibers was around 20%. The hollowness of the PET micro‐porous hollow fibers after alkali treatment was between 30 and 32%. The PET micro‐porous hollow fibers exhibited simultaneous water‐absorption/release and keep‐warm functions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Kinetic study of hydrolysis of benzoates. part xxvii. ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous Bu4NBr

The second-order rate constants k (in dm3 mol–1 s–1) for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, have been measured spectrophotometrically in aqueous 0.5 and 2.25 M Bu4NBr at 25 °C. The substituent effects for para and meta derivatives were described using the Hammett relationship. For the ortho derivatives the Charton equation was used. For ortho-substituted esters two steric scales were involved: the EsB and the Charton steric (υ) constants. When going from pure water to aqueous 0.5 and 2.25 M Bu4NBr, the meta and para polar effects, the ortho inductive and resonance effects in alkaline hydrolysis of phenyl esters of substituted benzoic acids, became stronger nearly to the same extent as found for alkaline hydrolysis of C6H5CO2C6H4-X. The steric term of ortho-substituted esters was almost independent of the media considered. The rate constants of alkaline hydrolysis of ortho-, meta- and para-substituted phenyl benzoates (X-C6H4CO2C6H5, C6H5CO2C6H4-X) and alkyl benzoates, C6H5CO2R, in water, 0.5 and 2.25 M Bu4NBr were correlated with the corresponding IR stretching frequencies of carbonyl group, (ΔνCO)X.

Determination of reaction mechanism and rate constants of alkaline hydrolysis of phenyl benzoate in ethanol–water medium by nonlinear least squares regression

In the reaction system of alkaline hydrolysis of phenyl benzoate in the ethanol–water media, high performance liquid chromatography-diode array detector (HPLC-DAD) is used to measure the reaction and kinetic profiles are obtained. Nonlinear least squares regression (NLLS) is used to fit the kinetic profiles and then investigate the mechanism. Genetic algorithm (GA) is adopted to optimize the parameters of the postulated mechanisms, and when the minimum standard deviation of mechanical model matches the noise level of measurement, the mechanism of the reaction system can be determined, and parameters, such as rate constants of every reaction step, are resolved simultaneously. The true mechanism of the reaction system that a parallel reaction coexists with a consecutive reaction is determined. In the ethanol–water media, phenyl benzoate hydrolyzes to benzoic acid and phenol, as well as produces a transesterification that ethanyl is substituted for phenyl, and ethyl benzoate, the product of transesterification, consecutively hydrolyzes to benzoic acid and ethanol. The method to resolve online spectroscopic–kinetic data is also studied and the results show that it is hard to obtain the kinetic parameters of all components if their kinetic concentration profiles can be combined linearly in some cases whose pure spectra of components are unknown beforehand.

Estimation of Phosphate Ester Hydrolysis Rate Constants. I. Alkaline Hydrolysis

AbstractSPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition states of a molecule. This difference is a function of the reference rate and internal and external perturbations to the reference rate. The internal perturbations are comprised of electrostatic and resonance effects. The external perturbations quantify solute‐solvent interactions based on the dielectric constant of the solvent and the steric effect of substituent groups. These perturbation models have been tested using 225 reliably measured second order hydrolysis rate constants over a variety of temperatures. The RMS deviation of the calculated versus observed values was 0.401 log M−1s−1.

Preparation and Physical Properties of Hollow Polyester Filaments with High Breathability, Water Absorption and Release Rates

This paper reports the preparation of hollow polyester filaments with high water absorption and release rates, and the study of their physical properties using differential scanning calorimetry, thermogravimetric analysis, density gradient, gel permeation chromatography, rheometry and statistical regression analysis. Four readily soluble poly(ethylene glycol)-modified cationic dyeable poly(ethylene terephthalate) (PEG-CDPET) polymers were prepared, with 3 mol % of the sodium salt of dimethyl 5-sulfo-isophthalate (SIPM). The poly(ethylene glycol) (PEG) contents were 3 and 6 wt% and the number-average molecular weights ([Formula: see text]) of the PEG were 600 and 8000 (g/mol). Blends of regular PET and PEG-CDPET were spun into hollow filaments. These hollow filaments were then drawn and treated with aqueous sodium hydroxide. The crystallinity of the PEG-CDPET polymers declined as the PEG content increased, given a fixed SIPM content. Furthermore, the crystallinity of the PEG-CDPET polymers declined as the [Formula: see text] of the PEG increased for the same SIPM and PEG contents. The SIPM and PEG segments did not change the original PET unit cell. The sodium sulphonate (–SO3Na) functional groups and the PEG molecules were only on the crystal surface and in the amorphous regions. Obviously, the rate constants for alkaline hydrolysis were in the order: PEG-CDPET polymer<<CDPET polymer<regular PET polymer. The water-absorption and release and the heat retention properties of alkali treated PET/PEG-CDPET polyblend hollow filaments were better than those of the regular PET filaments. The porous nature of the large filaments (from 0.02-1 μm in diameter) was observed after alkali treatment of the PET/PEG-CDPET polyblend hollow filaments. Additionally, the hollowness of the PET/PEG-CDPET polyblend filaments was observed to increase from 40 to 42% after alkali treatment.

Physics and kinetics of alkaline hydrolysis of cationic dyeable poly(ethylene terephthalate) (CDPET) and polyethylene glycol (PEG)–modified CDPET polymers: Effects of dimethyl 5‐sulfoisophthalate sodium salt/PEG content and the number‐average molecular weight of the PEG

AbstractThis study investigated the physics and kinetics of three cationic dyeable poly(ethylene terephthalate) (CDPET) and four polyethylene glycol (PEG)–modified cationic dyeable PET (PEG‐modified CDPET) polymers using differential scanning calorimetry, thermogravimetric analysis, the density gradient method, gel permeation chromatography, a rheometer, and statistical regression analysis. The molar ratios of dimethyl 5‐sulfoisophthalate sodium salt (SIPM) for three CDPET polymers were 2, 6, and 10%, respectively. For four PEG‐modified CDPET polymers, with molar ratios of SIPM of 2%, the PEG content and the number‐average molecular weights (Mn) of PEG were 3/6 (wt %) and 400/2000 (g/mol), respectively. Experimental results revealed that the crystallinities of CDPET and PEG‐modified CDPET polymers declined as the SIPM and PEG contents increased. The crystallinity of the PEG400–CDPET polymer exceeded that of the PEG2000–CDPET polymer with the same SIPM and PEG contents. The SIPM and PEG segments did not change the original PET unit cell. The SO3Na functional group and the PEG molecules gathered only on the crystal surface and in the amorphous regions. In the kinetic equation of the alkaline hydrolysis of PET, CDPET, and PEG‐modified CDPET polymers, β equals 1. Furthermore, the R2 of the kinetic equation for α from 1.09 to 1.25 was better than that of α = 1. The rate constants of alkaline hydrolysis were in the order CDPET‐10 > CDPET‐6 > PEG2000‐6‐CDPET‐2 > PEG2000‐3‐CDPET‐2 > PEG400‐6‐CDPET‐2 > PEG400‐3‐CDPET‐2 > CDPET‐2 > PET. Clearly, the rate constant of the alkaline hydrolysis of CDPET and PEG‐modified CDPET polymers increased with SIPM/PEG content and the Mn of the PEG increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 550–556, 2005

Unexpected Rate Retardation in the Formation of Phthalic Anhydride from N-Methylphthalamic Acid in Acidic H2O-CH3CN Medium

Kinetic study on the cleavage of N-methylphthalamic acid (NMPA) in mixed acidic aqueous-acetonitrile solvent reveals the formation of both phthalic anhydride (PAn) (through O-cyclization) and N-methylphthalimide (NMPT) (through N-cyclization). The formation of NMPT varies from similar to 20% to similar to 3% with the increase in the content of acetonitrile from 2 to 70% v/v. Pseudo first-order rate constants for the formation of PAn are more than 4-fold larger than those for the formation of NMPT at 2% v/v CH3CN in mixed aqueous solvents. Pseudo first-order rate constants for alkaline hydrolysis of NMPT reveal a nonlinear decrease with increase in the content of CH3CN in mixed aqueous solvents.

Analysis of physical properties of PET/CD‐PET polyblend hollow fiber and its kinetics of alkaline hydrolysis

AbstractCationic dyeable poly(ethylene terephthalate) (CD‐PET) was formed by copolymerizing dimethylterephthalate (DMT),5‐sodium sulfonate dimethyl isophthalate (SIPM) with a molar ratio of 2% and ethylene glycol (EG). Blends of regular poly(ethylene terephthalate) (PET) and CD‐PET were spun into hollow fibers. The fibers were then treated with aqueous NaOH. This study investigated the physical properties of PET/CD‐PET polyblend hollow fibers and their kinetic behavior of alkaline hydrolysis using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), the density gradient method, a gel permeation chromatograph (GPC), a rheometer, and regression analysis of the statistical method. For the alkaline hydrolysis kinetics equation of PET, CD‐PET, and PET/CD‐PET polyblend materials: − dW/dt = KCαAβ, β values of chip and POY/ FOY hollow fibers are equal to 1. Moreover, R2 of the kinetics equation of chip/POY/FOY for a from 1.09–1.35/1.08–1.32/1.06–1.29 were better than those of a = 1. Experimental results indicate that the rate constant of alkaline hydrolysis was CD‐PET hollow fiber > PET/CD‐PET polyblend hollow fibers > PET hollow fiber and FOY > POY > > Chip. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3601–3610, 2002

Physical Properties of R-PET/CD-PET Polyblended Hollow Filaments and Their Kinetics of Alkaline Hydrolysis

Cationic dyeable poly(ethylene terephthalate) (CD-PET) was formed by copolymerizing dimethylterephthalate (DMT),5-sodium sulfonate dimethyl isophthalate (SIPM) with a molar ratio of 2% and ethylene glycol (EG). Blends of regular poly(ethylene terephthalate) (R-PET) and CD-PET were spun into hollow filaments. The filaments were then treated with aqueous NaOH. This study investigated the physical properties of R-PET/CD-PET polyblended hollow filaments and their kinetic behavior of alkaline hydrolysis using differential scanning calorimetry (DSC), wide angle x-ray diffraction (WAXD), the density gradient method, gel permeation chromatography (GPC), rheometer measurement and statistical analysis using the regression method. Experimental results indicate that the rate constant of alkaline hydrolysis was CD-PET hollow filaments >R-PET/CD-PET polyblended hollow filaments > R-PET hollow filaments. For the alkaline hydrolysis kinetics equation of R-PET, CD-PET/R-PET polyblended and CD-PET hollow filaments: −dW/dt=KCαAβ, β is equal to 1. Moreover, R2 of the kinetics equation for α from 1.06∼1.29 was better than that of α=1.

Use of Rough Sets and Spectral Data for Building Predictive Models of Reaction Rate Constants

A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase mid-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters was used as training compounds. The model is an advance in the development of a generalized system for predicting environmentally important reactivity parameters based on spectroscopic data. By comparison to a previously developed model using the same training set with multiple linear regression (MLR), the rough-sets model provided better predictive power, was more widely applicable, and required less spectral data manipulation. [For the previous MLR model, a standard error of prediction (SEP) of 0.59 was calculated for 88% of the training set data under leave-one-out cross-validation. In the present study using rough sets, an SEP of 0.52 was calculated for 95% of the data set.] More importantly, analysis of the decision rules generated by rough-sets analysis can lead to a better understanding of both the reaction process under study and important trends in the spectral data, as well as underlying relationships between the two.

Infrared spectroscopy-based property-reactivity correlations for predicting environmental fate of organic chemicals

A conventional structure-activity relationship (SAR) has been established between the alkaline hydrolysis rate constants (koh) of 12 alkyl and aryl formates and acetates and the linear combination of the frequencies of the C=o and C—o infrared (IR) absorbance peaks. The inability of this relationship to predict koh values for more structurally diverse carboxylic acid esters led to the development of a prototype of a prediction system that employs multiple linear regression analysis, using points from the Fourier transforms (FTs) of IR spectra. Conventional SARs have also been observed between single IR peak parameters and the microbial degradation rate constants of amides (C=O peak frequencies), 2,4-dichlorophenoxyacetate esters (CH peak intensities), phenols (OH peak frequencies), and anilines (NH stretching peak intensities). These observations indicate the feasibility of extending the FT-based prediction system to microbial degradation when reliable rates are available for additional compounds.

INFRARED SPECTROSCOPY-BASED PROPERTY-REACTIVITY CORRELATIONS FOR PREDICTING ENVIRONMENTAL FATE OF ORGANIC CHEMICALS

A conventional structure-activity relationship (SAR) has been established between the alkaline hydrolysis rate constants (koh) of 12 alkyl and aryl formates and acetates and the linear combination of the frequencies of the C=o and C—o infrared (IR) absorbance peaks. The inability of this relationship to predict koh values for more structurally diverse carboxylic acid esters led to the development of a prototype of a prediction system that employs multiple linear regression analysis, using points from the Fourier transforms (FTs) of IR spectra. Conventional SARs have also been observed between single IR peak parameters and the microbial degradation rate constants of amides (C=O peak frequencies), 2,4-dichlorophenoxyacetate esters (CH peak intensities), phenols (OH peak frequencies), and anilines (NH stretching peak intensities). These observations indicate the feasibility of extending the FT-based prediction system to microbial degradation when reliable rates are available for additional compounds.

Study on the hydrolysis kinetics of vinylsulfonyl reactive dye-fiber bond

The alkaline hydrolysis rate constants k of dyed cotton fiber were measured for a series of vinylsulfonyl reactive dyes and the alkaline hydrolysis rate constants k' of corresponding model dye-fiber compounds were determined. The structure of the reactive dye largely determines the rate of hydrolysis of the dyed fiber. There is a good linear correlation between k and K' for the same reactive groups. The hydrolytic behavior of the dyed cotton fiber can thus be explained by reference to the hydrolysis behavior of the corresponding model dye-fiber compounds, thus enabling studies on the mode of hydrolysis of the vinylsulfonyl reactive dye-fiber bond to be made, using MO theory.

Biodegradability of pesticides in water by microbes in activated sludge, soil and sediment

A relatively simple, aerobic and anaerobic biodegradation test method for pesticides is proposed. The method consists of the inoculation of the test substance to a substrate of non-acclimated microbes in activated sludge, field soil and river sediment in a stirred flask. This method was applied to the evaluation for biodegradability of twelve pesticides. The biodegradation rate constants obtained showed a parabolic correlation with the 1-octanol-water partition coefficients of the pesticides and a linear one with their alkaline hydrolysis rate constants. Therefore, the biodegradability of pesticides can be predicted by these two parameters.