Base-catalyzed Hydrolysis Reactions Research Articles

A nickel hydroxide platform prepared on a hydroxyl-enriched screen-printed carbon electrode for oxidative electrocatalysis.

We report here the preparation of an activation-free Ni electrode (i.e., eventually the formation of NiOOH) through enrichment of hydroxyl functional groups via a base-catalyzed hydrolysis reaction on a "preanodized" screen printed carbon electrode. The as-prepared Ni electrode exhibits good electroanalytic performance for the flow injection analysis of glucose.

Preparation of Silica Nano-Particles by Sol-Gel Method and Its Characterization

Nano silica (SiO2) has an extensive range of products from manufacturing to scientific. The Sol-gel technique in the field of material science is receiving worldwide interest because of its versatility for synthesizing silica nanoparticles. It provides a controlled composition of organic/inorganic hybrid material because of its unique and low-cost processing. The silica nanoparticles were prepared by the sol-gel method via two different routes first is a base-catalyzed hydrolysis reaction and the second is an acid-catalyzed hydrolysis reaction. The prepared silica nanoparticles were characterized by techniques Particle size analysis, Zeta potential, Fourier transform Infrared spectroscopy (FTIR), and X-Ray diffraction spectroscopy (XRD). Particle size analysis showed the nano range of particle and zeta potential proves the stability of prepared sols. Observed peaks from IR spectra are confirming the presence of a silica network. The amorphous silica was verified by the absence of sharp peaks and the presence of a broad peak at a 2θ angle of 23.8 for the XRD analysis structure in the produced NPs.

Mechanistic Investigation of Sol–Gel Reactions Using Alkoxysilane Precursor

The present study has been carried out to investigate the mechanisms of sol–gel reactions using TEOS as precursor in the presence of acid or base catalyst. The gels were prepared by hydrolysis of TEOS using hydrochloride acid or ammonium hydroxide catalyst. The obtained gels were also characterized by FTIR spectroscopy. The results of FTIR spectroscopy indicated the existence of silanol and siloxane bonds; due to the formation of hydrolyzed species as reactive intermediate compounds in initial stage converted by condensation reactions to gels as ultimate products. Accordingly, appropriate mechanisms have been proposed for sol – gel reaction using TEOS as precursor in the presence of acid or base catalyst. These mechanisms involve three-steps SN2 mechanisms for base catalyzed hydrolysis reaction of TEOS and SN1 mechanisms for acid catalyzed hydrolysis reaction of TEOS. Three mechanisms have been also proposed for condensation reaction as second stage in sol-gel process. These mechanisms include alcoxolation, oxolation and oltaion.

Hydrolytic Activation Kinetics of the Herbicide Benzobicyclon in Simulated Aquatic Systems.

Herbicide resistance is a growing concern for weeds in California rice fields. Benzobicyclon (BZB; 3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one) has proven successful against resistant rice field weeds in Asia. A pro-herbicide, BZB forms the active agent, benzobicyclon hydrolysate (BH), in water; however, the transformation kinetics are not understood for aquatic systems, particularly flooded California rice fields. A quantitative experiment was performed to assess the primary mechanism and kinetics of BZB hydrolysis to BH. Complete conversion to BH was observed for all treatments. Basic conditions (pH 9) enhanced the reaction, with half-lives ranging from 5 to 28 h. Dissolved organic carbon (DOC) hindered transformation, which is consistent with other base-catalyzed hydrolysis reactions. BH was relatively hydrolytically stable, with 18% maximum loss after 5 days. Results indicate BZB is an efficient pro-herbicide under aqueous conditions such as those of a California rice field, although application may be best suited for fields with recirculating tailwater systems.

Kinetic study of specific base catalyzed hydrolysis of ethyl acrylate in water-ethanol binary system

Kinetic study of hydroxide anion catalyzed hydrolysis of ethyl acrylate has been carried in ethanol-water (10–50% v/v) binary systems at the temperature range 30 ± 0.1, 35 ± 0.1, 40 ± 0.1, and 45 ± 0.1°C. Calculated specific rate constant values decreases with increasing proportion of ethanol at all temperatures. The observed retardation of a base catalyzed hydrolysis reaction is explained on the basis of fact that the formation of polarized transition state is disfavored with increase in % of ethanol. The relation between the change in dielectric constant due to variation in binary mixtures and change in specific rate constant are explained on the basis of electrostatic and non electrostatic contributions of solvent mixtures. The variation of ΔG*, ΔH*, ΔS* with solvent composition and the specific effect of water on the reaction rate kinetics are also discussed.

Theoretical Study on the Alkaline Hydrolysis of Methyl Thioacetate in Aqueous Solution

A base-catalyzed hydrolysis reaction of thiolester has been studied in both gas and solution phases using two ab initio quantum mechanics calculations such as Gaussian09 and CPMD. The free-energy surface along the reaction path is also constructed using a configuration sampling technique, namely, the metadynamics method. While there are two different reaction paths obtained for the potential profile of the base-catalyzed hydrolysis reaction for thiolester in the gas phase, a triple-well reaction path is computed for the reaction in the solution phase by two quantum mechanics calculations. Unlike the S(N)2 mechanism (a concerted mechanism) found for the gas-phase reaction, a nucleophilic attack from the hydroxide ion on the carbonyl carbon to yield a tetrahedral intermediate (a stepwise mechanism) is observed for the solution-phase reaction. Moreover, the energy profiles computed by these two theoretical calculations are found to be very comparable with those determined experimentally.

Effect of Ultrasound on the Base-Catalyzed Hydrolysis of 4-Nitrophenyl Acetate in Aqueous Ethanol

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.

Investigation of trialkoxysilane hydrolysis kinetics using liquid chromatography with inductively coupled plasma atomic emission spectrometric detection and non-linear regression modeling

A novel approach is demonstrated for measuring rates of the consecutive acid–base catalyzed hydrolysis reactions of (3-glycidoxypropyl)trimethoxysilane (GPTMS) and (3-aminopropyl)triethoxysilane (APTES) in dilute aqueous solution using liquid chromatography with inductively coupled plasma atomic emission spectrometric (ICP-AES) detection. The hydrolysis reactions are monitored by sampling kinetic solutions in a timewise manner and performing liquid chromatographic separations of the parent silane and organosilicon hydrolysis products. The column effluent is fed into the ICP through a direct injection nebulizer for online monitoring of silicon atomic emission at 251.611 nm, producing a series of silicon chromatograms for each kinetic run. Reversed phase separations are effected using acetonitrile–water gradients and are complete in 6 min or less. The systematic changes in peak areas provide information from which the rate constants of the consecutive hydrolysis reactions ( k 1, k 2, and k 3) are obtained by non-linear regression modeling. Using a quenching scheme, hydrolysis half-lives as brief as 3 min for the parent silane can be monitored. For each compound, a series of rate constants are obtained over a range of pH and buffer concentration, permitting estimation of the catalytic constants k H 3O + and k OH − for the consecutive acid–base catalyzed hydrolysis reactions by multiple regression analysis.

Differences in the activity of neutral and ionized β-cyclodextrin on the nitrosation of amines by phenylpropyl nitrites

The influence of β-cyclodextrin (β-CD) on the base-catalyzed hydrolysis reaction of 1-phenyl-1-propyl, 2-phenyl-1-propyl and 3-phenyl-1-propyl nitrites and on the nitrosation of pyrrolidine, piperidine and N-methylcyclohexylamine by the aforementioned alkyl nitrites (RONO) is studied in aqueous buffers of the amines and in an alkaline medium with [OH−] = 0.20 M. The hydrolysis reaction is catalyzed by the presence of β-CD owing to the formation of reactive 1:1 inclusion complexes between the alkyl nitrite and the ionized β-CD; the addition of potential inhibitors, such as dodecyltrimethylammonium bromide monomers, accelerates the reaction even more. The effect is quite significant in the case of 1-phenyl-1-propyl nitrite and is viewed as a case of allostery. In the presence of neutral β-CD, the nitrosation by 1-phenyl-1-propyl nitrite, either of pyrrolidine or piperidine, is inhibited by β-CD addition; however, the nitrosation reaction of piperidine by 2-phenyl-1-propyl nitrite is catalyzed (passing through a maximum) by β-CD, whereas the nitrosation of pyrrolidine promoted by 3-phenyl-1-propyl nitrite exhibits practically no change upon β-CD addition. In alkaline media (containing ionized β-CD) the nitrosation of pyrrolidine by 1-phenyl-1-propyl nitrite is inhibited by the presence of β-CD; in contrast, the nitrosation of both piperidine and N-methylcyclohexylamine is catalyzed in all cases, but the degree of catalysis depends not only on the alkyl nitrite structure, but also on the type and concentration of the amine. Kinetic results are quantitatively interpreted on the basis of the proposed reaction mechanism in each case, and the kinetic rate constants of the different steps are determined. Comparison of the results obtained in aqueous alkaline media and in aqueous buffers of the amines themselves allows us to establish important characteristics of the transition state of the reaction.

Temperature and pH dependence of fluocinolone acetonide degradation in a topical cream formulation.

We investigated the degradation of fluocinolone acetonide (FA) incorporated into an oil-in-water cream base. The study examined the influence of temperature (23 to 80 degrees C) and cream pH (pH 2.3 to 6) on FA degradation rates. FA degradation followed pseudo-first-order kinetics and adhered to the Arrhenius expression over the entire temperature range investigated. At all temperatures, the pH strongly influenced the observed degradation rate constant (kobs) values, with rate minima observed near pH 4. The FA log(degradation rate)-pH profiles were consistent with a reaction mechanism requiring drug hydrolysis catalyzed by hydroxide and hydrogen ions. Taking into account both the temperature and the pH dependence of FA degradation permits calculating kobs values from the following equation: kobs = exp[22.5 - (17,200/RT)] + exp[38.7 - (22,200/RT)] x [H+] + exp[49.5 - (21,100/RT)] x [OH-] where the three bracketed terms represent Arrhenius expressions for neutral, acid-catalyzed, and base-catalyzed hydrolysis reactions. FA degradation in the cream base parallels the degradation of a related steroid (triamcinolone acetonide) in an aqueous alcohol solution. The equivalence between FA and triamcinolone acetonide kinetics in the different reaction media suggests that in the cream base, FA degradation is limited to an aqueous phase largely unperturbed by the presence of nonaqueous constituents that comprise the cream formulation.

Bolaamphiphiles and monolayer lipid membranes made from 1,6,19,24-tetraoxa-3,21-cyclohexatriacontadiene-2,5,20,23-tetrone

The title macrotetrolide contains two maleic diester units that add hydrophilic sulfur nucleophiles, e.g., bisulfite, thioacetic acid, and various thioglycosides, in high yield. Two-headed amphiphiles (“bolaamphiphiles” or “bolytes”) are thus formed. They produce extremely thin (hydrophobic part ~20 A) monolayer lipid membrane (MLMs) vesicles, which have been characterized by electron microscopy. Vesicle MLMs produce well-resolved 1H NMR spectra at room temperature, indicating fluidity. Such thin vesicle membranes can be effectively perforated with monensin pyromellitate to give water channels. They can be made unsymmetric; they resist fusion. The ester linkages are protected against acid- or base-catalyzed hydrolysis reactions within the membrane. Surface monolayer properties of some bolytes and the crystallization of a pure diastereomer of a sugar pentaacetate amphiphile are reported.

Water‐insoluble dextran polymers by grafting of hydrophobic groups. I. Reaction with butyric anhydride and heterogeneous hydrolysis of the partially modified dextran

AbstractA study has been made on the modification reaction of dextran with butyric anhydride using pyridine as catalyst. The structures of the modified polymers were determined by means of IR and 1H‐NMR spectroscopy as well as by chemical analysis. It has been found a linear dependence of the reaction rate on the product of butyric anhydride and pyridine concentrations and a more complex dependence on the alcoholic groups concentration. The activation energy was found to be 7.0 kcal/mol. A partially modified dextran (D.S. 1.34) was hydrolyzed at several pH values and temperatures. The experimental data have been treated as a pseudo‐first‐order reaction with respect to the butyrate concentration. The activation energies obtained from the acid and base catalyzed hydrolysis reactions were 12.5 and 12.0 kcal/mol, respectively.

Energetics of ribonuclease A catalysis. 2. Nonenzymatic hydrolysis of cytidine cyclic 2',3'-phosphate.

Various kinetic aspects of the nonenzymatic hydrolysis of cytidine cyclic 2',3'-phosphate and uridine cyclic 2',3'-phosphate have been studied in order to provide a basis for comparison with the ribonuclease A catalyzed hydrolysis reaction. Studies of the pH dependence of the nonenzymatic reaction reveal mechanisms that are first order in hydroxide concentration and second order in hydrogen ion concentration, in addition to a "water" reaction. The rate constant for the water reaction was found to be very small, approximately equal to 2.5 X 10(-6) min-1. General base catalyzed hydrolysis reactions were also studied with imidazole as the catalyst. At pH values in which both the protonated and neutral forms of imidazole are present, a kinetic mechanism was observed that appears to be second order in total imidazole concentration, thus suggesting that bifunctional catalysis occurs. The activation enthalpy for the hydroxide, hydrogen ion, water, and imidazole catalyzed reactions was determined.