Hydrolysis general tendency toward

In general, the greater the thermodynamic stability of the imine complex, the smaller the tendency towards hydrolysis. The hydrolysis of the imine formed from aniline and benz-aldehyde is enhanced 100,000 times in the presence of copper(n). The importance of the electron configuration of the metal ion is seen in the reactions of this same ligand the imine is stabilised with respect to hydrolysis on co-ordination to a d6 iron(n) centre. This may be partially ascribed to the effective back-donation from the low-spin d6 centre (Fig. 4-24). In this case, the free imine is reasonably stable to hydrolysis in the absence of metal ions. 

In contrast to equilibria dominated by chloride complexation, equilibria involving hydrolysis or carbonate complexation are strongly influenced by pH. A cation s tendency towards hydrolysis, and its complexation behaviour in general, can be described in terms of the ratio of its ionic charge squared (z2) to its ionic radius (r) in Angstroms (Turner et al., 1981). Cations with z2/r in the intermediate range, 7 < z/r < 25, have seawater speciation schemes that are strongly influenced by solution pH. Carbonate equilibria of the form... 

For molecules of the general type R—C( = 0)—Z (22), tendencies toward hydrolysis have been found to correlate with the reactivity of the acyl group, thereby reflecting the resonance structures 22a-22c." As the contribution from 22b increases, the acyl carbon becomes more positive and thus more reactive toward nucleophilic attack, e.g., as in hydrolysis. We have recently shown... 

The relative tendencies toward hydrolysis mentioned in Sec. 1.2 above apply generally to complex formation, except for the reversal of the order of and MO2 acording to [K2]... 

The endothermic maxima observed for apolar solutes and salts in water-rich mixtures must also contribute towards the minima in AH for alkaline ester hydrolysis in these mixtures. As before, the tendency for the rate constant to decrease is determined by the behaviour of 5m AS. Plots of AH against AS are complicated but in mixtures for which x2 < xf the data points generally fall on a straight line. Of course, there are new problems in this class of reactions. For example, the possibility arises that the rate constant is a function of quantities describing the equilibrium between, say, RO- and OH". However, the patterns which emerge indicate that this may not usually be an important consideration in water-rich mixtures. One exception may be the alkaline hydrolysis of ethyl acetate and methyl acetate (Tommila and Maltamo, 1955) in methyl alcohol + water mixtures for which AH increases gradually as x2 increases. 

TBDPS ethers are generally cleaved under the same acidic conditions as those used for TBS ethers but longer reaction times are necessary and consequently selective removal of TBS groups in the presence of TBDPS groups is very common [331,332]. The electron-withdrawing effect of the phenyl substituents enhances the electrophilicity of the silicon atom and therefore is more susceptible towards nucleophiles. For this reason it is possible to reverse the tendency of TBS ethers to cleave more easily than TBDPS ethers using ion fluoride or basic hydrolysis [333]. Some examples in glycal derivatives are shown in Scheme 54. 

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