Hydrolytic reactivity

In these equations, Dmax is the larger of the summed values of STERIMOL parameters, Bj, for the opposite pair 68). It expresses the maximum total width of substituents. The coefficients of the ct° terms in Eqs. 37 to 39 were virtually equal to that in Eq. 40. This means that the a° terms essentially represent the hydrolytic reactivity of an ester itself and are virtually independent of cyclodextrin catalysis. The catalytic effect of cyclodextrin is only involved in the Dmax term. Interestingly, the coefficient of Draax was negative in Eq. 37 and positive in Eq. 38. This fact indicates that bulky substituents at the meta position are favorable, while those at the para position unfavorable, for the rate acceleration in the (S-cyclodextrin catalysis. Similar results have been obtained for a-cyclodextrin catalysis, but not for (S-cyclodextrin catalysis, by Silipo and Hansch described above. Equation 39 suggests the existence of an optimum diameter for the proper fit of m-substituents in the cavity of a-cyclodextrin. The optimum Dmax value was estimated from Eq. 39 as 4.4 A, which is approximately equivalent to the diameter of the a-cyclodextrin cavity. The situation is shown in Fig. 8. A similar parabolic relationship would be obtained for (5-cyclodextrin catalysis, too, if the correlation analysis involved phenyl acetates with such bulky substituents that they cannot be included within the (5-cyclodextrin cavity. 

Recently Benkovic and Schrayl28b and Clark and Kirby,26c have investigated the hydrolysis of dibenzylphosphoenolpyruvic acid and mono-benzylphospho-enolpyruvic acid which proceed via stepwise loss of benzyl alcohol (90%) and the concomitant formation of minor amounts (10%) of dibenzylphosphate and monobenzylphosphate, respectively. The pH-rate profiles for release of benzyl alcohol reveal that the hydrolytically reactive species must involve a protonated carboxyl group or its kinetic equivalent. In the presence of hydroxylamine the course of the reaction for the dibenzyl ester is diverted to the formation of dibenzyl phosphate (98%) and pyruvic acid oxime hydroxamate but remains unchanged for the monobenzyl ester except for production of pyruvic acid oxime hydroxamate. The latter presumably arises from phosphoenolpyruvate hydroxamate. These facts were rationalized according to scheme (44) for the dibenzyl ester, viz. 

In general, amides are much less hydrolytically reactive than esters. Typical hydrolysis half-lives under conditions common to aquatic environments range from hundreds to thousands of years. Hydrolysis of amides generally requires acid or base for the reactions to achieve measurable rates. 

Boavida, M.-J., and R. G. Wetzel. 1998. Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural UV. Freshwater Biology 40 285—293. 

The hydrolytic reactivity of a series of vinyl ethers is presented in Table 3 as a function of the Br nsted slope Of, for each vinyl ether. As pointed out by Kresge, the variation in selectivity is small considering the large reactivity range studied. 

Carbon tetrafluoride, CF4, mp — 185 °C, bp — 128 °C, which is the end product of the fluorination of carbon compounds, is a very stable gas. It can also be made by the fluorination of silicon carbide (equation 3). The SiF4 is removed from the CF4 by passing the product gases through 20% aqueous NaOH, which removes the SiF4 as soluble sodium silicate but leaves the CF4 unaffected. This major difference in hydrolytic reactivity of CF4 and SiF4 is a consequence of accessible d orbitals on silicon but not on carbon. 

Very few other studies have been carried out on the hydrolytic reactivity of tris-bidentate complexes. In some instances it is noted that the complexes are prone to decomposition in basic solution. This applies to strained complexes such as those with seven-membered rings 89) or complexes with many axially disposed substituents 162). 

For such inactivators to be effective both in vitro and in vivo, there are several conditions which must be met. First, they must be sufficiently stable that they are not spontaneously hydrolyzed or cleaved by esterases. Second, the acyl-enzymes which they form must be relatively stable to deacylation. Third, they should have good enzyme selectivity. Both the phosphofluoridates and sulphonyl fluorides are too hydrolytically reactive and non-selective to be examined in in vivo models. Recently, several (a-aminoalkyl)phosphonate diphenyl esters were explored [169] in order to address some of these issues. However, as no in vivo results were reported with them, neither they, nor the phosphonyl fluorides nor the sulphonyl fluorides will be discussed further in this review. 

The previous discussion can be used to interpret the hydrolytic behavior of a series of compounds that possess the same acyl group but varied leaving groups. For example, the order of hydrolytic reactivity for an amide, an ester, an anhydride, and an acid chloride is ... 

Reactivity. The reactivities of the bicyclic orthoesters can be compared examining the conditions necessary to form polymer. Although the hydrolytic reactivities were not accelerated, these monomers were Indeed very reactive In polymerization. In contrast to the behavior of the bicyclic acetals, no correlation Is found between the hydrolytic reactivity and the reactivity towards cationic Initiators for the bicyclic orthoesters. The following order can be proposed [2.2.1] > [2.2.2] > [3.2.1] > [3.3.1] which Is the expected order from the ring strains (18-19). 

The a,7-coordinated triphosphate complex [(NH3)4CoP30io] has also been synthesized (121), but little has been reported on its hydrolytic reactivity. 

The polysiloxane formation rate is also dependent on the structure of alkoxysilanes used. Although in the present system koxysilanes such as MTMOS, TMOS, MTEOS and TEOS could be used, the polysiloxane formation rate decreased in the order MTMOS > TMOS > MTEOS > TEOS. It was reported that the polysiloxane formation rate was determined by both hydrolytic reactivity of alkoxysilanes and vapor pressure of alkoxysilanes (boiling point of alkoxysilanes) (6). 

Ono et al. have synthesized series of open acetal surfactants anionics, nonionics, cationics, and amphoterics—and made a systematic study of the influence of the polar head group on hydrolytic reactivity (Fig. 16) [36,37]. The hydrophobic tail as well as the coimecting group was kept constant and the time for complete decomposition was recorded. The results, shown in Table 1, constitute an illustration of the effect of the micelle surface on the hydrolysis rate. With negatively charged micelles the reaction is very fast, with... 

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