Rates Of Alkaline Hydrolysis Research Articles

Effects of inorganic ions on rate of alkaline hydrolysis of phthalimide in the presence of cationic micelles

Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of phthalimide (PTH) show a monotonic decrease with the increase in the total concentration of cetyltrimethylammonium bromide ([CTABr]T) at a constant [NaOH] and [NaBr]. The pseudophase micellar (PM) model and the pseudophase ion-exchange (PIE) model reveal that the rate of alkaline hydrolysis of PTH is insignificant in the micellar pseudophase compared to that in the aqueous pseudophase under different reaction conditions. The CTABr micellar binding constants (KS) of ionized phthalimide (S−) follow an empirical relationship: KS = K0S/(1 + Ψ[MX]) where MX represents NaOH or NaBr. The value of the empirical parameter Ψ for HO− is nearly 30-fold smaller than that for Br−. The decrease in KS with the increase in [HO−] or [Br−] is attributed to the expulsion of S− ions from the micellar pseudophase to the aqueous pseudophase by HO− or Br−. Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of PTH in the presence of CTABr micelles vary with [MX] (MX = NaBr, KCl and Na2CO3) according to the empirical relationship: kobs = (k0obs + θK[MX])/(1 + K[MX]) where θ and K are empirical parameters. Based upon the values of θ, it is concluded that the respective anions Br−, Cl− and CO32− can expel nearly 100, 60 and 15% of the total amount of micellized S− from the micellar pseudophase to the aqueous pseudophase under the limiting conditions where 1 ≪ K[MX].

Alkaline hydrolysis of ethylp-nitrophenyl chloromethylphosphonate in the reverse micellar AOT—decane—water system

The influence of cluster formation of micelles on the rate of alkaline hydrolysis of ethylp-nitrophenyl chloromethylphosphonate in the reverse micellar sodium bis(2-ethylhexyl) sulfosuccinate (AOT)—decane—water system was found. The applicability of the pseudo-phase model of micellar catalysis below and above the percolation threshold was shown.

Ring Strain VS. Solvent Effects in Phosphate Base Hydrolysis

To determine the factors governing the enhanced reactivity of 5-membered ring phosphates, the lowest activation free-energy profiles for the alkaline hydrolyses of methyl ethylene phosphate (5-MEP), its acyclic analog, trimethyl phosphate (a-TMP), and its 6-membered ring analog, methyl propylene phosphate (6-MPP), have been computed using ab initio and continuum dielectric methods. The calculations yield product distributions and activation free energy differences in accord with experiment. They show that solvent stabilization of the 5-membered ring transition state plays a key role in the million-fold enhanced rates of alkaline hydrolysis of 5-MEP relative to its acyclic or 6-membered ring analogs. Furthermore, strain energy calculations show that ring strain contributes partly to the observed rate enhancement of 5-MEP relative to 6-MPP but not to that of 5-MEP relative to a-TMP.

Kinetic study on acid-base catalyzed hydrolysis of azimsulfuron, a sulfonylurea herbicide

Pseudo-first-order rate constants (kobs) for hydrolysis of a sulfonylurea herbicide, azimsulfuron, AZIM®, {N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbony]-1-methyl-4-(2-methyl-2H-tetrazol-5-yl)-1H-pyrazole-5-sulfonamide} (AZS) follow an empirical relationship: kobs =α1 + α2[−OH] + α3[−OH]2 within the [NaOH] range of 0.1–2.0 M at different temperatures ranging from 40 to 55°C. The contribution of α3[−OH]2 term is small compared with α2[−OH] term and this turns out to be zero at 60°C. Pseudo-first-order rate constants (kobs) for hydrolysis of AZS within the [H+] range from 2.5 × 10−6 to 1.4 M follow the relationship: kobs = (α1K a + B1[H+] + B2[H+]2)/([H+] + Ka) where pKa = 4.37 at 50°C. The value of B1 is nearly 25 times larger than that of α1. The rate of alkaline hydrolysis of AZIM is weakly sensitive to ionic strength. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 253–260, 1999

Base-catalysed hydrolysis of ?-lactones: reactivity-structure correlations for 3-(substituted phenoxy- and thiophenoxymethylene)-(Z )-1(3H )-isobenzofuranones

Rate coefficients were measured for the base-catalysed hydrolysis of a series of substituted 3-(phenoxy- or thiophenoxymethylene)-(Z)-1(3H)-isobenzfuranones (3-phenoxy- or thiophenoxymethylenephthalides) in 70% (v/v) aqueous dioxane at 30.0 °C, in addition to the carbonyl stretching frequencies in chloroform and tetrachloromethane following deconvolution and band separation, when required. The Hammett reaction constants for the alkaline hydrolysis of the 3-/4-substituted phenoxy and thiophenoxy series are ca 0.75 and 1.10, respectively. These results are related to electrostatic field and resonance effects. Successful correlations between the carbonyl stretching frequencies and substituent constants and the rates of alkaline hydrolysis were found. Computational studies using the semi-empirical AM1 method correctly model both the details of the mechanistic pathway and the substituent effects. © 1998 John Wiley & Sons, Ltd.

Effects of ionic and non‐ionic micelles on rate of hydroxide ion‐catalyzed hydrolysis of securinine

The effects of micelles of cetyltrimethylammonium bromide (CTABr), tetradecyltrimethylammonium bromide (TTABr), sodium dodecyl sulfate (SDS) and polyoxyethylene 10 lauryl ether (C12E10) on the rates of alkaline hydrolysis of securinine were studied at a constant [−OH] (0.05 M). An increase in the total concentrations of CTABr, TTABr, SDS and C12E10 from 0.0 to 0.2 M causes a decrease in the observed pseudo-first-order rate constants (kobs) by factors of ca 2.5, 3, 7 and 4, respectively. The observed data are explained in terms of pseudophase and pseudophase ion-exchange (PIE) models of micelle. The binding constants, KS, of securinine with SDS, C12E10, CTABr and TTABr micelles are 32.4, 14.8, 22.1, and 9.1 M−1, respectively. The magnitudes of the second-order rate constants, kM, for the reactions in the micellar pseudophase are negligible compared with the corresponding rate constant, kW, for the reaction occurring in the aqueous pseudophase for CTABr, TTABr, SDS and C12E10. © 1998 John Wiley & Sons, Ltd.

Effects of ionic and non-ionic micelles on rate of hydroxide ion-catalyzed hydrolysis of securinine

The effects of micelles of cetyltrimethylammonium bromide (CTABr), tetradecyltrimethylammonium bromide (TTABr), sodium dodecyl sulfate (SDS) and polyoxyethylene 10 lauryl ether (C12E10) on the rates of alkaline hydrolysis of securinine were studied at a constant [−OH] (0.05 M). An increase in the total concentrations of CTABr, TTABr, SDS and C12E10 from 0.0 to 0.2 M causes a decrease in the observed pseudo-first-order rate constants (kobs) by factors of ca 2.5, 3, 7 and 4, respectively. The observed data are explained in terms of pseudophase and pseudophase ion-exchange (PIE) models of micelle. The binding constants, KS, of securinine with SDS, C12E10, CTABr and TTABr micelles are 32.4, 14.8, 22.1, and 9.1 M−1, respectively. The magnitudes of the second-order rate constants, kM, for the reactions in the micellar pseudophase are negligible compared with the corresponding rate constant, kW, for the reaction occurring in the aqueous pseudophase for CTABr, TTABr, SDS and C12E10. © 1998 John Wiley & Sons, Ltd.

Factors Governing the Enhanced Reactivity of Five-Membered Cyclic Phosphate Esters

Ab initio calculations and continuum dielectric methods have been employed to map out the lowest activation free-energy profiles for the alkaline hydrolysis of a five-membered cyclic phosphate, methyl ethylene phosphate (MEP), its acyclic analog, trimethyl phosphate (TMP), and its six-membered ring counterpart, methyl propylene phosphate (MPP). The rate-limiting step for the three reactions was found to be hydroxyl ion attack at the phosphorus atom of the triester. By performing constrained optimization along the reaction coordinate, defined as the phosphorus to incoming hydroxyl oxygen distance, and computing the solvation free energies of the resulting stationary points, the rate-limiting transition states have been relocated in solution. Dihedral ring constraints in the five-membered ring leading to a more solvent-exposed hydroxyl group and, thus, better solvation of the cyclic transition state compared to its acyclic counter-part was found to be the dominant factor governing the rate enhancement of cyclic MEP relative to acyclic TMP alkaline hydrolysis. However, both ground-state destabilization of MEP relative to MPP, due to ring strain, and transition-state stabilization of the five-membered cyclic phosphate transition state relative to its six-membered ring analog, due to the differential location of the transition states in solution, were found to contribute to the enhanced rates of alkaline hydrolysis of five-membered ring MEP compared to six-membered ring MPP.

Alkaline Hydrolysis of Nonphenolic β-0-4 Model Diastereomers: Substituent Effect on the Leaving Phenoxide

Nonphenolic β-0-4 lignin model diastereomers [erythro or threo 1-(3,4-dimethoxyphenyl)-2-(4-substituted-2-methoxyphenoxy)-propan-1-oll were synthesized and the alkaline hydrolysis rates. and activation parameters for some compounds, determined. These rates and activation parameters were compared to rates determined earlier for similar models with 2-carbon side chains. Unfortunately, the three derivative with an electron-withdrawing formyl substituent could not be synthesized. The unsubstituted and 4'-Me erythro isomers hydrolyzed about one-third faster than the respective threo analogue. The unsubstituted and 4'-Me 3-carbon side chain models, both erythro and threo, hydrolyzed slightly faster than the 2-carbon analogues, while the erythro 4'-CHO diastereomer hydrolyzed approximately 8 times faster than the formyl analogue with a 2-carbon side chain. Both unsubstituted diastereomers had similar activation parameters as the unsubstituted 2-carbon side chain model. The erythro 4'-CHO diastereomer had a similar ΔH * as the 2-carbon side chain analogue. but the ΔS * was much smaller for the 3- than the 2-carbon side chain model. Explanations for the hydrolysis rate differences are proposed.

Studies of reactions within molecular complexes: alkaline hydrolysis of substituted phenyl benzoates in the presence of xanthines

Complexation with caffeine and theophylline-7-acetate depresses the rate of alkaline hydrolysis of substituted phenyl benzoates and is consistent with the formation of molecular complexes with 1∶1 stoichiometry between the hosts and esters; stacking of the xanthines is excluded as an explanation in the range of concentrations studied. Brønsted-type correlations have been determined for the rate and complexation constants and for the transition-state binding constants. Development of effective charge in the transition state of the reactions in bulk solvent is slightly less than that in the host–ester complex, consistent with a similar electronic environment in both states. The negative Brønsted β values for KS indicate that the interactions between ester and hosts involve electron donation to the host from the ester. Inhibition of hydrolysis is attributed to repulsion of the hydroxide ion from the host–ester complex by the extra hydrophobicity engendered by the xanthine host, as well as by the weaker binding of the transition state to the host compared with that in the host–ester complex.

Evaluation of a Sulfobutyl Ether β-Cyclodextrin as a Solubilizing/Stabilizing Agent for Several Drugs

To evaluate the potential use of β-cyclodextrin sulfobutyl ether, 7 sodium salt (SBE7-β-CD) as a drug solubilizing and stabilizing agent, the solubilizing effects of SBE7-β-CD on 22 different poorly water-soluble drugs were compared with those of intact β-CD and heptakis-(2,6-di-O-melhyl)-β-CD (DMCD). SBE7-β-CD was generally a more effective solubilizer for poorly water-soluble drugs than was intact β-CD, but SBE7-β-CD was not as effective as DMCD. The effects of SBE7-β-CD on the acid hydrolysis rate of prostaglandin I2, the alkaline hydrolysis rate of indomethacin, the dehydration of prostaglandin E1, and the isomerization of prostaglandin A1 were also investigated and compared to those for intact β-CD, DMCD, and 2,3,6 partially methylated-β-CD (PMCD). The stabilizing effects of SBE7-β-CD on chemically unstable drugs were generally higher than those of other CDs.

Alkaline Hydrolysis of Nonphenolic α-Carbonyl β-0-4 Lignin Dimers Substituted on the Leaving Phenoxide Ring: Comparison with Benzylic Hydroxyl Analogues

Four α-carbonyl nonphenolic β-0-4 lignin models [2-(2-methoxy-3- or 4- substitutedphenoxy)-1-(3,4-dimethoxyphenyl)-ethan-1-one] were synthesized and the alkaline hydrolysis rates determined. The rates were then compared to rates for α-hydroxyl analogues run earlier. The unsubstituted ketone hydrolyzed slightly slower, about 30%, then the alcohol analogue. The 4'-CHO ketone hydrolyzed much faster than the unsubstituted ketone and had essentially the same hydrolysis rate as the alcohol analogue. No definitive mechanistic conclusions could be made about the alkaline hydrolysis reaction of the ketones. Unsubstituted and 4'-Me substituted α-carbonyl models appear to be susceptible, even at room temperature, to competing alkali-initiated oxidative degradation.

Base-catalysed hydrolysis of ?-lactones: reactivity-structure correlations for 3-(aryl- and alkylmethylene)-(Z)-1(3H)-isobenzofuranones

Rate coefficients were measured for the base-catalysed hydrolysis of a series of γ-lactones, i.e. 39 substituted 3-(aryl- and alkylmethylene)-(Z)-1(3H)-isobenzofuranones (3-aryl- and alkylmethylenephthalides) in 70% (v/v) aqueous dioxane at 30·0 °C. A Hammett reaction constant for the 3- or 4-substituted phenyl series is ca 1·5, whereas those for the 2-substituted phenyl and 4-substituted 1-naphthyl series, using para-σ values, are ca 1·0 and 1·9. These results are related to an electrostatic field effect model. A very successful correlation between the rates of alkaline hydrolysis of all 39 phthalides and the carbonyl stretching frequencies in chloroform was found. Substituent effects in widely different environments give linearly related effects on both reactivity and physical properties. Computational studies using the semi-empirical AM1 method correctly modelled both the details of the mechanistic pathway and the substituent effects. © 1997 John Wiley & Sons, Ltd.

Micellar effects upon the alkaline hydrolysis of 2-(3-nitrophenoxy)quinoxaline. Effects of cationic head groups

The rate of alkaline hydrolysis of the novel compound 2-(3-nitrophenoxy)quinoxaline 1 increases with increasing head group size in a series of cationic micellized surfactants (C 16H 33NR 3Cl and C 16H 33NR 3OH: R = Me, Et, n-Pr and n-Bu). The reactivity increase with increasing head group size is related to the disruption of the hydration of hydroxide ion.

Reexamination of the Kirkwood–Westheimer theory of electrostatic effects. V. Effect of charged substituents on the rates of alkaline hydrolysis of substituted strychnines

The rates of hydrolysis in aqueous sodium hydroxide of the alkaloid strychnine and seven of its derivatives have been determined at 50 and 75 °C. The kinetic data indicate that all the compounds, except strychninesulfoni acid-I, hydrolyze by competing second- and third-order mechanisms, involving one and two hydroxide ions, respectively; strychninesulfonic acid-I hydrolyzes by the second-order mechanism only. The quantitative effect of positively charged groups in enhancing, and negatively charged groups in depressing, the rates of hydrolysis is in rough agreement with calculations using Kirkwood–Westheimer theory. Keywords: Kirkwood–Westheimer theory; strychnine derivatives, hydrolysis of; lactams, hydrolysis of; electrostatic effects on rates of alkaline hydrolysis; alkaloids, reactions of.

Micellar-catalyzed alkaline hydrolysis of n-butyl acetate by cetyltrimethylammonium bromide

The overall reaction rates of alkaline hydrolysis of n-butyl acetate by aqueous sodium hydroxide solutions, with cetyltrimethylammonium bromide (CTMAB) as a micellar catalyst, were measured in an agitated vessel with a flat interface. The overall reaction rates observed with respect to various liquid compositions could be reasonably explained by the theoretical model, allowing for reactions in the micellar and bulk phases and the distribution of the relevant species between the micellar and bulk phases. This alkaline hydrolysis was accelerated by the solubilization of n-butyl acetate and OH − ions to the micelles, but not by an increase in the reaction rate constant in the micellar phase. The maximum catalytic effect of CTMAB micelles at 298 K occurred at 0.07 kmol m −3 CTMAB and 0.2 kmol m −3 NaOH. The maximum value of the ratio of the overall reaction rates of n-butyl acetate with and without micellar catalyst was about 6. The evaluated apparent reaction rate constants were dependent on the concentration of CTMAB micellar catalyst and the ionic strength of the aqueous solution.

Evidence for a trigonal bipyramidal intermediate during nucleophilic substitution at a sulfonyl centre and for a sulfonylium cation in the acid catalysed reaction

The rate of alkaline hydrolysis of a substituted β-sultam shows a dominant term second-order in hydroxide ion, clearly indicating the reversible formation of a monoanionic trigonal bipyramidal intermediate; substituent effects and kinetic parameters for the acid catalysed hydrolysis are indicative of the formation of a sulfonylium ion intermediate.

Reactivity of β-lactams and phosphonamidates and reactions with β-lactamase

Abstract

Characterization of Peracylated .BETA.-Cyclodextrins with Different Chain Lengths as a Novel Sustained Release Carrier for Water-Soluble Drugs.

A new series of peracylated β-cyclodextrins (β-CyDs) with different alkyl chains (acetyl-lauroyl) was prepared in high purity by acylating all hydroxyl groups of β-CyD using acid anhydrides in pyridine, and their physicochemical properties of solubility, hydrolsis and release and interaction capacity were evaluated. The solublity of peracylated β-CyDs in water decreased with lengthening alkyl chain, whereas that in ethanol/water increased with increase in ethanol concentration, but tended to decrease at higher ethanol concentration. The solubility parameter of peracylated β-CyDs was determined by analyzing the peak-solubility phenomenon by a modified Hildebrand equation. The alkaline hydrolysis rate of peracylated β-CyDs decreased with lengthening alkyl chain, and was about 4-fold faster than that of the corresponding fatty acid ethyl esters. The interaction of perbutanoyl-β-CyD (TB-β-CyD) with a water-soluble drug, molsidomine, in the solid state was investigated by differential scanning calorimetry (DSC). The analysis of DSC curves suggested that molsidomine and TB-β-CyD form a binary solid dispersion with a 2 : 1 (drug : TB-β-CyD) molar ratio. The rate of drug release was markedly retarded by the combination with peracylated β-CyDs in the increasing order of the hydrophobicity of host molecules.

Interaction of the chloropentaamminecobalt(III) cation with mixed micelles of anionic and non-ionic surfactants: a kinetic study

Alkaline hydrolysis rates of the cholropentaamminecobalt(III) cation have been studied at 25.0 °C and an ionic strength of 0.05 mol dm–3 in aqueous mixed micelles composed of anionic sodium dodecyl sulfate (SDS) and non-ionic n-dodecylpenta(oxyethylene glycol) monoether (C12E5) surfactants over a wide range of total surfactant concentration (Ct) and SDS mole fraction (α). The critical micelle concentrations (c.m.c.s) of mixtures of the two surfactants over the entire α range have also have been determined and found to follow the regular solution model for non-ideal mixing. The kinetic results have shown that interactions of the cationic cobalt complex with the mixed micelles cause a decrease of the reaction rate with increasing Ct(at constant α) and α(at constant Ct). The estimated binding constant of the complex decreases markedly as α decreases as a result of the reduction of the charge density at the mixed micellar surface. The present findings are compared with those obtained previously concerning the effect of urea and its alkyl derivatives upon the rate of the same hydrolysis reaction in SDS micellar solutions.