Second-order alkaline hydrolysis rate

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. 

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) ... 

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 15. Relative rates of the second-order alkaline hydrolysis of aromatic amino esters .

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... 

The alkali- and acid-catalyzed hydrolysis of the isomeric pyridine monocarboxamides was examined. In the second order alkaline process, the calculated Hammett a-values agreed well with constants obtained by molecular orbital calculations. The methods were extended to the acid-catalyzed process where Hammett constants are not available for comparison. The rate of acid-catalyzed hydrolysis of picolinamide and -methylpicolinamide is somewhat decreased by Cu(II) ions. " ... 

CycHc esters show accelerated hydrolysis rates. Ethylene sulfate compared to dimethyl sulfate is twice as fast ia weak acid (first order) and 20 times as fast ia weak alkaH (second order) (50). Catechol sulfate [4074-55-9] is 2 x 10 times faster than diphenyl sulfate ia alkaline solution (52). Alcoholysis rates of several dialkyl sulfates at 35—85°C are also known (53). 

Decomposition kinetics of five compounds by alkaline hydrolysis were measured. For three compounds, second-order reaction rate constants and activation energies were given. These five compounds andd be divided two groups with high and low decomposition rates. 

In a study of the alkaline hydrolysis of ethyl 2-methylpropenoate in 84.7% ethanol, Thomas Watson (JACS 77 3962, 1956) obtained the data of the first two columns of the table, t in sec, NaOH titre/cc. The initial concentrations of both ester (A) and alkali (B) were 0.058 mol/liter. 10 cc of the reaction mixture were removed from the vessel at the time stated, pipetted into 10 cc of 0.0668 mol/liter HC1 and the excess titrated with 0.0511 nol/liter NaOH. Find the mean value of the second order specific rate. 

Chemical/Physical. Hydrolyzes in water to o-phthalic acid (via the intermediate 2-ethyl-hexyl hydrogen phthalate) and 2-ethylhexyl alcohol (Kollig, 1993 Wolfe et al., 1980). Although no pH value was given, the reported hydrolysis rate constant under alkaline conditions is 1,400/M-yr (Ellington et al., 1993 Kollig, 1993). A second-order rate constant of 1.1 x 10 /M-sec was reported for the hydrolysis bis(2-ethylhexyl) phthalate at 30 °C and pH 8 (Wolfe et al., 1980). 

CASRN 1928-44-5 molecular formula C16H22CI2O3 FW 333.25 ChemicaPPhysical The second-order hydrolysis rate constants at 24 °C and pHs 8.88, 10.04, and 10.39 were 4.8, 3.1, and 4.4/M-sec, respectively. In the presence of dissolved humic substances, the overall hydrolysis rate decreased. It was concluded that the humic-bound 2,4-D, / -octyl ester was protected from hydrolysis under alkaline conditions by a factor equal to the fraction of ester associated with the humic substances (Perdue and Wolfe, 1982). 

Chlorpyrifos. As was the case for the neutral hydrolysis studies, the most detailed kinetic investigations of alkaline hydrolysis kinetics in sediment/water systems have been conducted using chlorpyrifos (10). As can be seen from Figure 2, alkaline hydrolysis of chlorpyrifos is not second-order, so the value selected for k cannot be calculated from the pH and a second-order rate constant. Nevertheless, since aqueous kinetics at alkaline pH s for chlorpyrifos was always pseudo-first order, careful pH measurements and Figure 2 can be used to select accurate values for k at any pH. 

Most of the characteristics invoked to explain rate accelerations and rate retardations by micelles are valid for vesicles as well. For example, the alkaline hydrolysis of A-methyl-A-nitroso-p-toluenesulfonamide is accelerated by cationic vesicles (dioctade-cyldimethylammonium chloride). This rate acceleration is the result of a higher local OH concentration which more than compensates for the decreased polarity of the vesicular pseudophase (compared to both water and micelles) resulting in a lower local second-order rate constant. Similar to effects found for micelles, the partial dehydration of OH and the lower local polarity are considered to contribute significantly to the catalysis of the Kemp elimination " by DODAB vesicles. Even the different... 

Sulfates having alkyl groups from methyl to pentyl have been examined. With methyl as an example, the hydrolysis rate of dimethyl sulfate increases with the concentration of the sulfate. Typical rates in neutral water are first order and are 1.66 x 10-4 s-1 at 25°C and 6.14 x 10-4 s-1 at 35°C (46,47). Rates with alkali or acid depend on conditions (42,48). Rates for the monomethyl sulfate [512 42-5] are much slower, and are neady second order in base. Values of the rate constant in dilute solution are 6.5 x 10 5 L/(mol-s) at 100°C and 4.64 x 10-4 L/(mol-s) at 138°C (44). At 138°C, first-order solvolysis is ca 2% of the total. Hydrolysis of the monoester is markedly promoted by increasing acid strength and it is first order. The rate at 80°C is 3.65 x 10-4 s-1 (45). Alkaline solvolysis has been studied by a calorimetric method (49). Heat of hydrolysis of dimethyl sulfate to the monoester under alkaline conditions is 106 kj/mol (25 kcal/mol) (51). 

Fig. 21. Logarithmic plot of the second-order rate coefficients k2) for catalysis by imidazole of the hydrolysis of various esters, against the rate coefficients for alkaline hydrolysis. The most reactive compound is acetic anhydride the other open circles represent results for acetate esters of phenols, except for the two least reactive compounds, trifluorethyl acetate, and the acetate of acetone-oxime. The closed triangles represent data for ethyl esters with activated acyl groups, with the exception of the least reactive compound, which is ethyl acetate.

Simpler evidence for the presence of a tetrahedral intermediate is adduced from a study of the kinetics of alkaline hydrolysis of amides such an anilides26-28, chloroacetamide30, N,N-diacylamines31, and urea32. The rate equations for these reactions contain both first- and second-order terms in hydroxide ion. A reasonable explanation is that the hydrolysis mechanism involves a tetrahedral intermediate, rather than that the second-order term is due to base catalysis of the addition of the hydroxide ion to the carbonyl group. Such a mechanism is... 

This alkaline hydrolysis shows a rate term that is second order in hydroxide ion concentration, which is indicative of a stepwise mechanism involving a TBPI with a hypervalent sulfur atom. Reversible attack of the hydroxide ion on a /3-sultam generates a monoanionic TBPI-, which requires deprotonation by a second hydroxide ion before the intermediate can collapse to products. 

Table 12 Second-order rate constants for the alkaline hydrolysis of /V-benzoyl /3-sultams...

Sydnones and sydnonimines are stable in acid solution at room temperature but are subject to rapid hydrolysis in basic solution. The kinetics of alkaline hydrolysis of 3-alkylsydnonimines was found to be third order, first order in sydnonimine and second order in hydroxide ion at pH 8 (63ZOB3699). The mechanism shown in Scheme 3 rationalizes the kinetics of the hydrolysis. The nitrosonitrile (29) is hydrolyzed to the nitrosoamide at higher pH (65KGS328). The rate law for 3-arylsydnonimines is fc[syd][OH-]. 

The activation parameters for more complex reactions show similar patterns to that outlined above. For example, in the alkaline hydrolysis of ethyl acetate in aqueous mixtures (Tommila et al.t 1952), the second-order rate constant decreases with increasing mole fraction of ethyl alcohol, while AG increases, and AH falls to a minimum near x2 = 0-1 (Fig. 52), 5m AS having a minimum in the same region. A similar trend is observed in aqueous acetone and in... 

Now we can return to our reaction the alkaline hydrolysis of various meta- and para-substituted ethyl benzoates. The rate constants for this second-order reaction have been measured and shown here is a graph of log (kx/kn) versus O, where /cx is the rate constant for the reaction with the substituted benzoate and kn is that for the unsubstituted reaction (X = H). 

As in the case of the base-catalyzed hydrolysis, the observed rate constant for the reaction of ester 9c in the presence of amine 5a was found to decrease with increasing concentration of CTAB. Using equation (28), the second order rate constants for the aminolysis and those for the alkaline hydrolysis were calculated as a function of CTAB concentration and were found to be decreased by factors of 30-6 and 13-3, respectively, by micellar CTAB. These results can be interpreted by an explanation analogous to that for the alkaline hydrolysis in the absence of amines. However, the magnitude of the inhibition for the aminolysis (30-6) as compared to that for the hydroxide ion-catalyzed hydrolysis (13-3) is not readily explicable. It is conceivable, however, that deep penetration of ester into the micelle could result in an environment for the ester group in which the amino group is either not suitably oriented for nucleophilic attack or is excluded to a greater extent than water and hydroxide ion. 

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