Alkaline hydrolysis rates

The first was proposed by Iraoto and Otsuji (511) and Otsuji et al (512) and concerned the pK of substituted 2-, 4-, and 5-carboxylic acids and the alkaline hydrolysis rate k of their respective ethyl esters (259, 260, and 261, where Y = Et). When Hammett cr , values were used for... 

In the acidic and alkaline hydrolysis rates of the same ester, the steric and resonance effects. re the same. 

M. Narisada, T. Yoshida, M. Ohtani, K. Ezumi, M. Takasuka, Synthesis and Substituent Effects on Antibacterial Activity, Alkaline Hydrolysis Rates, and Infrared Absorption Frequencies of Some Cephem Analogues Related to Latamoxef (Moxalactam) , J. Med. Chem. 1983, 26, 1577-1582. 

M. Narisada, J. Nishikawa, F. Watanabe, Y. Terui, Synthesis and 3 -Substituent Effects of Some 7a-Methoxy-l-oxacephems on Antibacterial Activity and Alkaline Hydrolysis Rates , J. Med. Chem. 1987, 30, 514-522. 

The hydrolysis half-life in three different natural waters was approximately 48 d at 25 °C (Macalady and Wolfe, 1985). At 25 °C, the hydrolysis half-lives were 120 d at pH 6.1 and 53 d at pH 7.4. At pH 7.4 and 37.5 °C, the hydrolysis half-life was 13 d (Freed et al, 1979). At 25 °C and a pH range of 1-7, the hydrolysis half-life was about 78 d (Macalady and Wolfe, 1983). However, the alkaline hydrolysis rate of chlorpyrifos in the sediment-sorbed phase were found to be considerably slower (Macalady and Wolfe, 1985). In the pH range of 9-13, 3,5,6-trichloro-2-pyridinol and 0,0-diethyl phosphorothioic acid formed as major hydrolysis products (Macalady and Wolfe, 1983). The hydrolysis half-lives of chlorpyrifos in a sterile 1% ethanoFwater solution at 25 °C and pH values of 4.5, 5.0, 6.0, 7.0, and 8.0 were 11, 11, 7.0, 4.2, and 2.7 wk, respectively (Chapman and Cole, 1982). 

For a given pesticide which undergoes hydrolysis, any or all of these hydrolytic pathways may be relevant at various pH s. Organophosphorothioates, for example, have measurable neutral and alkaline hydrolysis rate constants (7). Esters of 2,4-dichlorophenoxyacetic acid (2,4-D), on the other hand, hydrolyze by acid and alkaline catalyzed reactions, but have extremely small neutral hydrolysis rate constants ( ). Thus, any study of the hydrolysis of sorbed pesticides must be prefaced by an understanding of the hydrolytic behavior of individual pesticides in aqueous solution. 

Esters of 2,4-D. Studies of the alkaline hydrolysis of the methyl and n-octyl esters of 2,4-D in sediment/water systems (24), though less detailed than the chlorpyrifos studies, show similar effects. Results from Investigations using EPA-13 at pH s near 10 for the methyl and octyl esters of 2,4-D are summarized in Figure 7. Under the conditons in these experiments, the fractions of the methyl and octyl esters which are sorbed to the sediment are 0.10 and 0.87, respectively. The aqueous hydrolysis half-lives of the methyl and octyl esters at pH=10 are 3.6 and 27 minutes, respectively. In the sediment/water system, the methyl ester, which is mainly in the dissolved phase, hydrolyzes at a rate similar to that expected for the sediment-free system at the same pH. The octyl ester, on the other hand, hydrolyses at a rate which is considerably retarded (and non-first-order) when compared to the expected aqueous phase rate. Though the data are less detailed and do not permit calculations similar to those conducted for chlorpyrifos, it is clear that the effect of sorption is to considerably slow the alkaline hydrolysis rate. 

Ethyl chloroacetate, C4H7CIO2, is used as a solvent and in the synthesis of intermediate dye chemicals. The effluent from a dye synthesis plant is discharged into a wetland, with a pH of 7.3. At this pH, the alkaline hydrolysis rate constant is 1.56 M s . If the alkalinity of the wetland is close to constant, compared with the concentration change of the ethyl chloroacetate, at 0.002 M, what would be the first-order rate constant for ethyl chloroacetate degradation ... 

Alkaline Hydrolysis Rates of Acyl- and Aryl-Substituted Phenyl Benzoates... 

Alkaline hydrolysis rates of a series of thiophenyl 4-X-benzoates (47 X = H, Me, N02) was significantly enhanced in the presence of cyclodextrins (CDs), and this was attributed to strong binding of the benzoyl moiety within the CD cavity and covalent catalysis by secondary hydroxy groups of the CDs (48).63 The effect of MeCN and MeOH on the alkaline hydrolysis of acetylsalicylic acid in aqueous micellar solutions was reported.64 Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and gly-mes) supported the existence of a novel reaction pathway exhibiting a first-order dependence on the concentration of the phase-transfer catalyst and a second-order... 

Equation (30) represents a QSAR for the base-mediated hydrolysis of formates and acetates. The correlation is between the second-order alkaline hydrolysis rate constants and the linear combination of the shifts of the vC=0 and vC-O stretching peaks for 12 of the 41 compounds in Table 13.3. 

Alkaline Hydrolysis Rate Constants (koH, Mr1 s 1, near 25°C) of the Compounds Used in the IR Spectral Frequency Correlations. 

Log of the alkaline hydrolysis rate constant vs. difference in carbon-oxygen stretching frequency for 12 carboxylic acid esters. 

Hydrolysis second-order alkaline hydrolysis rate constant k = 4.2 x 10-3 M-1 s 1 at 27°C (Maquire Hale 1980 quoted, Wolfe 1980) ... 

The kinetics of hydrolysis of energetic material precursors - mono- and dinitro derivatives of pyrazole, imidazole, 1,2,4-triazole, and isoxazole has been studied by the polarographic and photometric methods [647], The alkaline hydrolysis rate constants experimentally determined depend on the nature of the heterocycle. A possible mechanism for hydrolytic transformations of nitroazoles is proposed on the basis of the calculated thermodynamic parameters of the reaction. 

Hydrolysis alkaline hydrolysis rate constant k = 0.182 M s at 25°C in water (Salmi Leimu 1947 quoted, Drossman et al. 1988). 

Hydrolysis alkaline hydrolysis rate constant at 25°C, k = 171 h (Sharma Sharma 1970 quoted, Ellington... 

Reference to Chapter 3 (Scheme 3) shows that the alkaline hydrolysis of aryl carbamate esters has a large Hammett p coefficient (2.54) whereas that for the alkaline hydrolysis of aryl acetate esters is only small (0.67) (Scheme 2). The small p value for alkaline hydrolysis of the acetate case is consistent with little bond fission in the transition structure and the large p for the carbamate case (see Chapter 3 for mechanism) indicates substantial bond fission and a gross difference in mechanism between the two reactions. The simple Hammett relationship only correlates the alkaline hydrolysis rates of the carbamate when meta substituents are employed. Para substituents, which withdraw negative charge by resonance (4-NO2, 4-CN, etcf require values to obtain a good correlation. This is interpreted to mean that the transition structure has sufficient aryl oxide ion character for resonance to occur. In... 

The calculated alkaline hydrolysis rate constant for 4-nitrophenyl acetoacetate is obtained from p, the difference in ct between methyl and acetonyl (CH3COCH2-) and the rate constant for 4-nitrophenyl acetate antilog [2.5 x (0.62 - 0) x 0.978] = 33 M sec ) the large difference between observed (1.32 x 10 M" sec ) and calculated rate... 

The alkaline hydrolysis rates of several aryl phosphorodiamidates (111) have been reported and discussed. 

Wolfe et al. (1978) have developed structure-activity relationships for the hydrolysis of a number of TV-substituted and TV,TV-disubstituted carbamates. An excellent correlation was found between the second-order alkaline hydrolysis rate constant (kb) for the carbamates and the pKa of the alcohol formed upon hydrolysis. The linear free energy relationships for the TV-phenyl and TV-methyl-TV-phenyl carbamates are illustrated in Figure 2.10. These data indicate that only the TV-phenyl carbamates will hydrolyze under environmental conditions. The half-life for the hydrolysis of these chemicals will be less than 6 months at pH 8 at 25°C. 

The disappearance of a plasticizer from water can be the result of a number of abiotic and biotic processes that can transform or degrade the compound into daughter compounds that have different physicochemical properties from the parent compound. Hydrolysis is a family of chemical reactions where a plasticizer reacts with water. Phthalate esters may hydrolyze to form monoesters and then dicarboxylic acid. It has been predicted that di-(2-ethylhexyl) sebacate will form 2-ethylhexanol and decanedioic acid. Wolfe et al experimentally measured second-order alkaline hydrolysis rate constants for dimethyl, diethyl, di-n-butyl, and di-(2-ethylhexyl) phthalates, and it appears that hydrolysis may be too slow to have a major impact on the fate of most dissolved plasticizers. The estimated hydrolysis half-lives at pH 7 for 20 plasticizers were longer than 100 days. No information was located for diallyl, ditridecyl and diundecyl phthalates. Under alkaline conditions, hydrolysis may be important for tricresyl phosphate and tri-(2-ethylhexyl) trimellitate at pH 8 their predicted half-lives are 3.2 and 12 days respectively. 

Table 4.8 Examples of QSAR models for estimating the alkaline hydrolysis rate log hyd correlations with various parameters (X yd. 1 mol- s-O-...

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