Hydrolysis reaction, kinetics

The hydrolysis reaction kinetics using optical absorption spectrometries... 

We have analyzed, both theoretically and experimentally, the reaction chemistry of a variety of metal hydrides and water, and the chemical stability of the organic carriers in contact with metal hydrides and spent hydrides. Since detailed hydrolysis reaction kinetics of the metal hydride/organic carrier slurry is not known, we conducted experiments using a high pressure (13.790 MPa or 2000 psi) and high temperature (232°C) vessel with temperature, pressure, and magnetic stirrer control capabilities (500 cm3 internal volume). Some of the selection criteria for the hydride follow. 

Time Regimes Accessible by Si NMR 3.1 HYDROLYSIS REACTION KINETICS... 

The concentration of phenylacetate can be determined from the kinetics of its pseudo-first-order hydrolysis reaction in an ethylamine buffer. When a standard solution of 0.55 mM phenylacetate is analyzed, the concentration of phenylacetate after 60 s is found to be 0.17 mM. When an unknown is analyzed, the concentration of phenylacetate remaining after 60 s is found to be 0.23 mM. What is the initial concentration of phenylacetate in the unknown ... 

The kinetics of hydrolysis reactions maybe first-order or second-order, depending on the reaction mechanism. However, second-order reactions may appear to be first-order, ie, pseudo-first-order, if one of the reactants is not consumed in the reaction, eg, OH , or if the concentration of active catalyst, eg, reduced transition metal, is a small fraction of the total catalyst concentration. 

If one of the reactants is the solvent, this reactant is present in large excess, so its kinetic participation will not be observed. Thus a bimolecular hydrolysis reaction commonly follows first-order kinetics. This example shows that the reaction order may not be equal to the reaction molecularity. 

The method of evaluation of the rate constants for this reaction scheme will depend upon the type of analytical information available. This depends in part upon the nature of the reaction, but it also depends upon the contemporary state of analytical chemistry. Up to the middle of the 20th century, titrimetry was a widely applied means of studying reaction kinetics. Titrimetric analysis is not highly sensitive, nor is it very selective, but it is accurate and has the considerable advantage of providing absolute concentrations. When used to study the A —> B — C system in which the same substance is either produced or consumed in each step (e.g., the hydrolysis of a diamide or a diester), titration results yield a quantity F = Cb + 2cc- Swain devised a technique, called the time-ratio method, to evaluate the rate... 

In many cases, addition or removal of water proceeds sufficiently slowly that some of the physical properties of unstable species (such as hydrated neutral quinazoline or anhydrous 2-hydroxypteridine) can be observed. In these cases, reaction kinetics can also be examined. Addition of water to pteridine is of special interest in relation to studies of the formation and hydrolysis of Schiflf bases. The reaction proceeds in two reversible stages, 3 4 5 ... 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

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. 

Does 4 act by first undergoing hydrolysis into its components We performed a series of experiments directed at answering this question. We found that in the presence of either hydrazine or formate, there was a drop in reaction kinetics and selectivity (see Table 4). 

PETP flakes produced from used soft drinks bottles were subjected to alkaline hydrolysis in aqueous sodium hydroxide. A phase transfer catalyst (trioctylmethylammonium bromide) was used to enable the depolymerisation reaction to take place at room temperature and under mild conditions. The effects of temperature, alkali concentration, PETP particle size, PETP concentration and catalyst to PETP ratio on the reaction kinetics were studied. The disodium terephthalate produced was treated with sulphuric to give terephthalic acid of high purity. A simple theoretical model was developed to describe the hydrolysis rate. 17 refs. 

However, the pattern is complicated by several factors. The sugar molecules to be hydrogenated mutarotate in aqueous solutions thus coexisting as acyclic aldehydes and ketoses and as cyclic pyranoses and furanoses and reaction kinetics are complicated and involve side reactions, such as isomerization, hydrolysis, and oxidative dehydrogenation reactions. Moreover, catalysts deactivate and external and internal mass transfer limitations interfere with the kinetics, particularly under industrial circumstances. 

Several mechanisms have been proposed for lipase-catalyzed reactions. Kinetic studies of hydrolysis [14,15] and esterification [50] catalyzed by Pseudomonas cepecia lipase, demonstrate that the enzyme has a ping-pong mechanism. 

In our previous work [63], we studied the hydrolysis kinetics of lipase from Mucor javanicus in a modified Lewis cell (Fig. 4). Initial hydrolysis reaction rates (uri) were measured in the presence of lipase in the aqueous phase (borate buffer). Initial substrate (trilinolein) concentration (TLj) in the organic phase (octane) was between 0.05 and 8 mM. The presence of the interface with octane enhances hydrolysis [37]. Lineweaver-Burk plots of the kinetics curve (1/Uj.] = f( /TL)) gave straight lines, demonstrating that the hydrolysis reaction shows the expected kinetic behavior (Michaelis-Menten). Excess substrate results in reaction inhibition. Apparent parameters of the Michaelis equation were determined from the curve l/urj = f /TL) and substrate inhibition was determined from the curve 1/Uj.] =f(TL) ... 

Polymer properties, influence of ions, 258 Polymer surface reactions, kinetics, 322-323 Polymer transformation reactions configurational effect, 38 conformational effects, 38 hydrolysis of polyfmethyl methacrylate), 38 neighboring groups, 37-38 quaternization of poly(4-vinyl pyridine), 37-38 Polymerization, siloxanes, 239... 

Pure parathion is a pale yellow, practically odorless oil, which crystallizes in long white needles melting at 6.0° C. (17). It is soluble in organic solvents, except kerosenes of low aromatic content, and is only slightly soluble in water (15 to 20 p.p.m. at 20° to 25° C.). Peck (35) measured its rate of hydrolysis to diethyl thiophosphate and nitro-phenate ions in alkaline solutions. He found that the reaction kinetics are first order with respect to the ester and to hydroxyl ion. In normal sulfuric acid the rate of hydrolysis was the same as in distilled water. Peck concluded that hydrolysis takes place by two mechanisms—a reaction catalyzed by hydroxyl ions and an independent uncatalyzed reaction with water. He calculated that at a pH below 10 the time for 50% hydrolysis at 25° C. is 120 days in the presence of saturated lime water the time is 8 hours. The over-all velocity constant at 25° C. is k = 0.047 [OH-] + 4 X 10-6 min.-1... 

The slightly exothermic hydrolysis reaction is kinetically hindered, but proceeds rapidly on many single and mixed metal oxides [19,22-25], This means that in practice HNCO is usually hydrolyzed on the SCR catalyst itself, which has to be big enough in order to fulfill the double function [19]. 

Hydrolysis of oximes catalyzed by transition-metal complexes has not been studied prior to a report by Kostic et al. They have reported kinetics of hydrolysis of acetoxime to acetone catalyzed by two palladium(II) complexes, identified active species in the hydrolysis reaction, proposed a reaction mechanism, and fully characterized a bis(acetoxime) complex that is relatively stable toward hydrolysis.458... 

The monomeric metaphosphate ion itself commands a fair amount of attention in discussions of metaphosphates. It is postulated as an intermediate of numerous hydrolysis reactions of phosphoric esters 52 S4,S5) and also of phosphorylation reactions S6> kinetic and mechanistic studies demonstrate the plausibility of such an assumption. In addition, the transient formation of ester derivatives of meta-phosphoric acid — in which the double-bonded oxygen can also be replaced by thio and imino — has also been observed they were detected mainly on the basis of the electrophilic nature of the phosphorus. 

Then the modelization of the hydrolysis kinetics requires at each time the knowledge of a and N. a can be calculated by writing the different relations of dissociation equilibria of water,polyacid and NH3 (produced by the hydrolysis reaction). We have proposed to determine at each reaction step and simulate the whole kinetics by using a Monte-Carlo method. (see ref.8 ). 

Tetrahydroepoxides as models. Since the quantum chemical calculations apply most rigorously to the simple benzo-ring tetrahydroepoxides and since the calculations neglect influences of the hydroxyl groups in the diol epoxides, it is instructive first to examine the benzo-ring tetrahydroepoxides as simplified models for the reactive site in the diol epoxides. Most of the information about tetrahydroepoxide reactivity derives from studies of the kinetics of their hydrolysis reactions, in which cis- and trans-diols, as well as tetrahydroketones can be formed (Equation 5). 

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. 

Catalysis, enzymatic, physical organic model systems and the problem of, 11,1 Catalysis, general base and nucleophilic, of ester hydrolysis and related reactions, 5,237 Catalysis, micellar, in organic reactions kinetic and mechanistic implications, 8,271 Catalysis, phase-transfer by quaternary ammonium salts, 15,267 Catalytic antibodies, 31,249... 

Gagliardi, C. D. Dunuwila, D. Van Vlierberge-Torgerson, B. A. Berglund, K. A. 1992. Reaction kinetics for the hydrolysis of titanium isopropoxide carboxylate complexes. In Better Ceramics Through Chemistry V, edited by Hampden-Smith, M. J. Klemperer, W. G. Brinker, C. J. Mat. Res. Soc. Symp. Proc. 271 257-262. 

C. K. Ingold and E. D. Hughes, "Dynamics and Mechanism of Aliphatic Substitutions," Nature 132 (1933) 933934 C. K. Ingold, E. D. Hughes, and S. Masterman, "Reaction Kinetics and the Walden Inversion. Pt. I. Homogeneous Hydrolysis and Alcoholysis of beta-n-Octyl Halides," JCS 140 (1937) 11961201 and subsequent articles. 

Table 2.4 Kinetic data obtained for esterification/hydrolysis reactions...

In addition to the preceding fluoride transport tests, laboratory-scale tests were conducted to investigate the possibility of containing or removing fluoride from the system to allow more economical materials of construction to be used in the design of the full-scale plant (AEA, 20011). A series of nine tests was to be conducted to obtain kinetic data on the use of calcium as an agent for fluoride removal from the GB simulant, fluorophosphoric acid. Data were to be obtained for the hydrolysis reaction under acidic, neutral, and alkaline conditions. 

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