Hydrolysis rate prediction

Preservation and formation of readily biodegradable organic substrate, Ss, is a major characteristic that is observed under anaerobic conditions in wastewater. An experimental procedure that can be applied for this purpose is crucial for the prediction of the anaerobic transformation of the organic matter and particularly as a basis for estimation of the anaerobic hydrolysis rate (cf. Figure 6.10). 

Chemical/Physical. Hydrolysis in distilled water at 25 °C produced l-chloro-2-propanol and HCl. The reported half-life for this reaction is 23.6 yr (Milano et al., 1988). The hydrolysis rate constant for 1,2-dichloropropane at pH 7 and 25 °C was determined to be 5 x 10 Vh, resulting in a half-life of 15.8 yr. The half-life is reduced to 24 d at 85 °C and pH 7.15 (Ellington et al., 1987). A volatilization half-life of 50 min was predicted from water stirred in an open container of depth 6.5 cm at 200 rpm (Dilling et al., 1975). Ozonolysis yielded carbon dioxide at low ozone concentrations (Medley and Stover, 1983). 

Decrease of separation and increase of solute permeability predicted by the oxidation or hydrolysis rate data are shown in Figure Ig. If we increase the concentration of NaOCl from 2 mg/1 to U mg/l, decrease of separation is accelerated because the deterioration rate is proportional to the square of the concentration of the solute. The dotted line shows the tendency of solute decline of the first stage membranes of Toray s spiral wound module which was tested at the Chigasaki Laboratory of Water Reuse Promotion Center over 9 OOOhours( )... 

These conclusions have several implications for pesticide waste disposal considerations. For incidental or accidental disposal of pesticides in natural aquatic systems, the results suggest that model calculations using aqueous solution values for abiotic neutral hydrolysis rate constants can be used without regard to sorption to sediments. For alkaline hydrolysis, on the other hand, models must explicitly include sorption phenomena and the correspond ng rate reductions in order to accurately predict hydrolytic degadation. 

Experimental and predicted volatilization rate constants for the five pesticides are listed in Table II. It should be noted that, despite low H values for the pesticides, experimental volatilization rates for diazlnon and parathlon are fairly rapid from water under the conditions of our tests (t> of 4.2 and 9.6 days, respectively). When compared to their hydrolysis rate constants (Table I), volatilization can be seen to be a more important route of loss than hydrolysis for diazlnon, parathlon, and methyl parathlon. The relative volatilization rates reported here for diazlnon and parathlon are in good agreement with those reported by Lichtenstein (14). 

Thirty different esterases and lipases were tested. The rate of release of 14 in the wells of standard microtiter plates was monitored by fluorescence (70,86). Control experiments ensured that the apparent rate of release of 14 is directly proportional to the rate of acetate hydrolysis. The predicted and observed E and ee values (as checked by standard HPLC assay on a chiral phase) were found to match within + 20%. Only in one case was a larger discrepancy observed, a result that was believed to be caused by the occurrence of an unusually low value of Km for one of the enantiomers. 

There are at least two cases where experimental results are not consistent with the above approach. In both cases, hydrolysis remains homogeneous but the weight-loss rate is higher than predicted. This means that the hydrolysis rate is higher on chain ends than on internal network segments K > K. Many possible causes can be proposed for such a behavior ... 

Methods to predict the hydrolysis rates of organic compounds for use in the environmental assessment of pollutants have not advanced significantly since the first edition of the Lyman Handbook (Lyman et al., 1982). Two approaches have been used extensively to obtain estimates of hydrolytic rate constants for use in environmental systems. The first and potentially more precise method is to apply quantitative structure/activity relationships (QSARs). To develop such predictive methods, one needs a set of rate constants for a series of compounds that have systematic variations in structure and a database of molecular descriptors related to the substituents on the reactant molecule. The second and more widely used method is to compare the target compound with an analogous compound or compounds containing similar functional groups and structure, to obtain a less quantitative estimate of the rate constant. 

Recent years have seen limited advances in formulating quantitative prediction correlations for hydrolysis rate constants. Fortunately numerous experimental studies provide pH-dependent hydrolysis rate constants for one or more compounds in most classes of organics that might be of environmental concern. Estimation of reactivity by comparison with structural analogs within a given class is often the fastest and most reliable approach. 

Predicting Hydrolysis Rate Difference Based on Substituents Sizes PROBLEM Based on Taft steric parameters, how much faster than ethyl acetate would you expect ethyl formate to hydrolyze ... 

Note r = correlation coefficient n = number of compounds analyzed, p = net charge on P, Kcorr = hydrolysis rate corrected for fraction of compound sorbed to sediment. K"corr represents a sediment-catalyzed transformation and rates of hydrolysis in the overlying water phase will be much lower than predicted using these QSARs. 

Each compound (i.e., unprotonated and protonated species) in an aqueous solution undergoes acid-base catalyzed degradation (i.e., hydrolysis) as predicted in Equation (5.156a), Equation (5.156b), and Equation (5.156c). The pseudo-first-order degradation rate constant is ... 

Figure 7.14 Model prediction of ADP concentration and inorganic phosphate concentration in cytoplasm as a function of ATP hydrolysis rate in the healthy subjects. Data are from [106] solid lines are prediction of model of Wu et al. [213],...

Collette, T.W. (1990) Ester hydrolysis rate constant prediction from infrared interferograms. Environ. Sci. Technol. 24, 1671-1676. 

Since we are considering the hydrolysis of dmgs it might seem that an obvious way to reduce the breakdown would be to replace some or all of the water in the system with a solvent such as alcohol or propylene glycol. As we will see in this section, however, this is effective only in certain systems and in others it can, in fact, increase the rate of breakdown. The equation that allows us to predict the effect of the solvent on the hydrolysis rate is... 

The data and mechanistic conclusions summarized above come from work with aryl phosphomonoesters as predicted by the steep jSlg value, alkyl ester dianions react at very slow rates. A recent study of methyl phosphate found the rate of the dianion hydrolysis to be below the threshold of detectability, with an estimated rate constant of 2 x 10 20 s 1 at 25 °C.3 Since this value is close to the rate predicted from an extrapolation of the Bronsted plot of aryl phosphomonoester dianions, a similar mechanism is likely to be followed for alkyl and aryl esters. 

A pediatric formulation of lincomycin - 2 - phosphate at pH 7.5 containing sucrose, sorbitol, glycerin, alcohol, saccharin, preservatives, flavor and color yielded hydrolysis rate constants in reasonable agreement with those predicted from the simple aqueous buffer kinetic data (19). 

Zhang, H Qu, X. and Ando, H. (2005) A simple method for reaction rate prediction of ester hydrolysis./. Mol. Struct. (Theochem), 725, 31-37. 

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