Kinetic constants hydrolysis reactions

Oh et al. [16] have demonstrated that a microemulsion based on a nonionic surfactant is an efficient reaction system for the synthesis of decyl sulfonate from decyl bromide and sodium sulfite (Scheme 1 of Fig. 2). Whereas at room temperature almost no reaction occurred in a two-phase system without surfactant added, the reaction proceeded smoothly in a micro emulsion. A range of microemulsions was tested with the oil-to-water ratio varying between 9 1 and 1 1 and with approximately constant surfactant concentration. NMR self-diffusion measurements showed that the 9 1 ratio gave a water-in-oil microemulsion and the 1 1 ratio a bicontinuous structure. No substantial difference in reaction rate could be seen between the different types of micro emulsions, indicating that the curvature of the oil-water interface was not decisive for the reaction kinetics. More recent studies on the kinetics of hydrolysis reactions in different types of microemulsions showed a considerable dependence of the reaction rate on the oil-water curvature of the micro emulsion, however [17]. This was interpreted as being due to differences in hydrolysis mechanisms for different types of microemulsions. 

Since the solvent concentration is normally constant, the term kf cse is treated as a first-order rate constant with units of s Also the concentration of A is a known parameter in the experiment, so that the value of k, as a second-order rate constant can be extracted from the relaxation time Tb associated with the back reaction. The same approach is used to determine the kinetics of hydrolysis reactions. The general hydrolysis reaction is written as... 

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

The first-order reaction constants for the hydrolysis of sodium hexadecyl (1 PrO, 2 PrO, 1 BuO, and 2 BuO) sulfates were determined by Weil et al. [60] under the same conditions as for their previous study [58] stated above. These kinetic constants are 0.007, 0.013, 0.010, and 0.018 min-1, respectively. How-... 

Intercalation of BPDE. Several groups have studied the reversible intercalative binding of BPDE to DNA. The fluorescence quantum yield of BPDE is much lower than that of BP derivatives which do not contain an epoxide group and fluorescence techniques have not been widely used to study BPDE physical binding to DNA (4). Association constants for the DNA intercalation of BPDE have been obtained by measuring red shifts in the UV absorption spectra of BPDE which occur upon the formation of intercalated complexes and from fluorescence studies (8) of the kinetics of DNA catalyzed hydrolysis of BPDE. The hydrolysis reaction is conveniently monitored by following the fluorescence of the hydrolysis product, BPT, which has a quantum yield many times greater than BPDE. 

The individual contributions of the H20, H+, and HO- catalysts to the mechanism of the reaction were further evaluated by means of the kinetics parameters (Table 6.4). At neutral pH, Reactions a and c were both dominated by fcH2<> The second-order rate constants ku+ and kHO- were identical, indicating similar efficiencies of the H+ and HO catalysts. Interestingly, the second-order rate constants for the hydrolysis of Gly-D-Val (6.48) to yield Gly and D-Val (6.49) (Reaction b) could also be calculated (Table 6.4). The similarity to the corresponding rate constants of Reactions a and c suggests that the rate of peptide bond hydrolysis is not particularly sensitive to substitution at or protonation of the flanking amino and carboxy groups [69],... 

Recently, the supercritical fluid treatment has been considered to be an attractive alternative in science and technology as a chemical reaction field. The molecules in the supercritical fluid have high kinetic energy like the gas and high density like the Uquid. Therefore, it is expected that the chemical reactivity can be high. In addition, the ionic product and dielectric constant of supercritical water are important parameters for chemical reaction. Therefore, the supercritical water can be realized from the ionic reaction field to the radical reaction field. For example, the ionic product of the supercritical water can be increased by increasing pressure, and the hydrolysis reaction field is realized. Therefore, the supercritical water is expected as a solvent for converting biomass into valuable substances (Hao et al., 2003). 

Helgeson H. C., Murphy W. M., and Aagaard R (1984). Thermodynamic and kinetic constraints on reaction rates among minerals and aqueous solutions, II Rate constants, effective surface area, and the hydrolysis of feldspar. Geochim. Cosmochim. Acta., 48 2405-2432. 

A number of points should be considered to determine the most appropriate experimental conditions for the desired reaction and, to that end, the kinetics of hydrolysis and ionization of 4-methyl-2-phenyl-, 4-benzyl-2-phenyl-, and 4-benzyl-2-methyl-5(4//)-oxazolones have been investigated. Deprotonation of 5(477)-oxazolones in aqueous media, which leads to racemization of optically active 5(477)-oxazolones, is a fast process that competes with the ring opening. The difference between the rate constant for racemization and the ring opening is greater in solvents with dielectric constants less than water and thus, oxazolones racemize faster than they hydrolyze. 

The concept of preassembly as a requirement for substitution may throw light upon the vexed question of the mechanism of the base hydrolysis reaction. It has long been known that complexes of the type, [Co en2 A X]+n can react rapidly with hydroxide in aqueous solution. The kinetic form is cleanly second-order even at high hydroxide concentrations, provided that the ionic strength is held constant. Hydroxide is unique in this respect for these complexes. Two mechanisms have been suggested. The first is a bimolecular process the second is a base-catalyzed dissociative solvolysis in which the base removes a proton from the nitrogen in preequilibrium to form a dissociatively labile amido species (5, 19, 30). 

New data have been presented in the context of a review of the aqueous behavior of silanes which elucidate their behavior, including mixed alkoxysilane hydrolysis kinetics, silane solubility, and the determination of the equilibrium constant for the alkoxy hydrolysis reaction. 

The kinetic order in water for the spontaneous hydrolysis reaction, n, and the hydronium ion catalyzed reaction, m, varies depending on the structure of the silane ester and the solvent conditions [36, 40]. The difficulty in determining the kinetic order of water in aqueous-organic solvents arises from the observation that as the concentration of water is varied, the polarity of the solvent and the activity of the acid change [40], A plot of the logarithm of the rate constant vs. the logarithm of water concentration often does not yield a straight line. These... 

Recently, Pankov and Morgan (1981a,b) emphasized the importance of various mechanisms for regulating kinetics in the aquatic environment. Examples showed the wide range of first- and second order rate constants (kf) and half lifes (ti) for different reactions that might take place in natural waters. The rate constants for several first order trace metal hydrolysis reactions, second order redox- and complexation reactions of interest for aquatic studies are summarized by Hoffmann (1981). His comparison of kinetic data on the oxidation of HS- under only slightly different conditions shows considerable variations e.g., t ranges from 7 -600 min for seawater media. 

Berger and Wolfe (1996) reported a correlation of hydrolysis data for 12 sulfonylurea herbicides. The use of bond strength or Hammett a constants was impossible because of the complex structures of the compounds. The hydrolysis pathways for this class of compounds are also more complex, but the use of quantum mechanical parameters provided the detailed structural information needed to develop a useful correlation. As a result of the many different functional groups, several reaction pathways are available depending on the substituents. Also, there is a complicating pH effect on the pathways and the kinetics of hydrolysis as shown by product studies. The 12 herbicides used in this study are listed in Table 13.4, and the pseudo first-order hydrolysis rate constants are given in Table 13.5. Figure 13.2 shows the basic structure of these compounds. 

Chlorohydrins are compounds characterized by alpha halo-alpha alkoxy groups bound to a common carbon atom. These compounds undergo rapid hydrolysis at this shared carbon atom. Bis(2-chloroisopropyl)ether, a chlorohydrin, has two such carbon atoms, and both react very rapidly with water. In fact, the reactions are so fast that acid and alkaline contributions have not been determined. It is likely, however, that base accelerates the reaction kinetics. The proposed reaction pathway for this compound is based on the reported pathway for bis(chloroethyl)ether (Figure 13.4). The reported rate constant for bis(chlorome-thyl)ether, of 0.23 sec-1 was based on an observed half-life of a few minutes. Similarly, for bis(2-chloroisopropyl)ether, both of the chloro substituents are reactive, and a half-life of a few minutes can be assigned to this compound, as well. 

The rate of steam consumption is equal to the steam flow rate times the steam conversion, and the rate of HBr formation is twice the rate of steam consumption. The formation of HBr at a given reaction time tR depends upon the melt composition. A second-order reaction of CaBr2 was found to match the experimentally measured reaction rates far better than a first-order reaction. The reaction constant is then derived from the rate of HBr formation, which is experimentally measured. The observed kinetic constant was 2.17 10-12 kmol s-1 m-2 MPa-1 (1.30 1CH g-mol min-1 cm-2 bar-1) for the hydrolysis reaction, which is 24 times greater than the constant reported for solid CaBr2 reaction. This higher rate promises to significantly reduce the size and design complexity of the hydrolysis reactor. 

The observed kinetic constant is 24 times greater than the constant reported for solid CaBr2 reaction. This higher rate promises to significantly reduce the size and design complexity of the hydrolysis reactor. 

A related form of an automatic potentiometric titrator is instrumentation that permits the maintenance of the acidity or basicity of a solution over a period of time. Such devices are known as pH-stats, and find application in kinetic studies of hydrolysis reactions. The general approach is (by either manual or automatic means) to add either acid or base such that the pH in the solution is maintained constant over a period of time. Normally the amount of acid or base added as a function of time is sought in order that kinetic measurements may be made for the system. In its simplest form the acidity of the solution is monitored with a pH meter and controlled at a preselected value by the addition of acid or base from a burette the quantity delivered as a function of time is recorded in a notebook. Obviously for the fast reactions this becomes difficult and dependent on the dexterity of the individual. 

The iV-acyl group is easily removed in weakly acidic or basic media, especially from those 1 -acylpyrazoles with electron-withdrawing substituents. The kinetics of hydrolysis and aminolysis of variously substituted acylpyrazoles was studied in great detail by Hiittel,102 using ultraviolet spectroscopy. Rate constants were found for both reactions, and an attempt was made to apply Hammett s equation to substituted pyrazoles. 

Hydrolysis reactions can generally be described using first-order kinetics (Eq. 9) where r, the rate of transformation of a contaminant, is proportional to the contaminant concentration (C), and k is a first-order rate constant [26]. Vogel et al. [26] present the half-lives (t1/2) for hydrolysis of various halogenated compounds ... 

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