Saponification substituent effect

Table 6.6 shows that saponifications according to the BAC2 mechanism are also slowed down when the esters are derived from sterically demanding alcohols. However, this structural variation takes place at a greater distance from the reaction center than the structural variation of Table 6.5. The substituent effects in Table 6.6 are therefore smaller.

Tab. 6.5 Substituent Effects on the Rate of the BA[2 Saponification of Different Ethyl Esters...

The combined results of kinetic studies on condensation polymerization reactions and on the degradation of various polymers by reactions which bring about chain scission demonstrate quite clearly that the chemical reactivity of a functional group does not ordinarily depend on the size of the molecule to which it is attached. Exceptions occur only when the chain is so short as to allow the specific effect of one end group on the reactivity of the other to be appreciable. Evidence from a third type of polymer reaction, namely, that in which the lateral substituents of the polymer chain undergo reaction without alteration in the degree of polymerization, also support this conclusion. The velocity of saponification of polyvinyl acetate, for example, is very nearly the same as that for ethyl acetate under the same conditions. ... 

The use of cycloaddition reactions for the synthesis of partially reduced heterocyclic systems was shown to be an attractive approach to dihydrobenzimidazoles, dihydroquinazolines, and dihydro-//n-benzopurines (Scheme 14) <86JOC6i6>. The dihydroxylation of the Diels-Alder adduct dimethyl 3,6-dihydrophthalate (128) with 0s04 and NMO followed by protection of the diol as the iso-propylidene derivative afforded compound (129). Saponification, dehydration with ethoxyethyne, and rearrangement with TMS—N3 effected conversion to the substituted tetrahydroisatoic anhydride (130), and subsequent treatment with formamidine acetate yielded compound (131). The substituents at the 6,7-positions of compound (131) were not amenable, however, for annelation of an imidazole. 

Ropp and Raaen (1954) compared the molar radioactivities of product after 3% and after 100% reaction for the saponification of a series of 0-oarbonyl-labeled ring-substituted ethyl benzoates at 25°0, and for the formation of the 2,4-dinitrophenylhydrazones of a series of ring-substituted carbonyl-labeled acetophenones. In both series of reactions studied the isotope effects k jk) for the carbon-14-labeled reactants varied with the ring substituent, the greater the electron-donating ability of the substituent, the smaller k jk and thus the larger the isotope effect. 

The presence of acetate substituents on the side chain at C-6 is very common. Compounds (40) and (41) were isolated by Drewes et al from the bark of Cryptocarya latifolia trees in their investigations of the chemistry of plants used for magical and medicinal purposes by the Zulu people (55). The CD spectra of these two compounds show a positive Cotton effect and hence they possess the (67 )-configuration. Saponification followed by acetonide formation of (40) afforded two acetonides (42) and (43) (50). A (2 7 ,6 5)-stereochemistry followed from application of the MTPA determination rule (24) to the (/ )- and (5)-MTPA esters of these acetonides. A (4 5)-stereochemistry was assigned from the syn-diol relationship of the two acetal oxygen atoms in (42) and (43) as determined from their C NMR spectra (57). Thus the acetonide rings in both compounds possessed chair conformations with the alkyl... 

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