Thiol-Pendant Crown Ethers

Separate investigations of the effect of alkaline-earth metal ions on rates of deacetylation of the thiol acetate and of acetylation of the parent thiol under single 

The control experiments reported in Table 5.5 show that (a) thiolysis of pNPOAc in the absence of metal ions is only 5 x faster than the very slow background reaction (fi/2 3 days) and (b) remarkable accelerations are brought about by the metal salts alone, which is ascribed to the formation of reactive metal bound methoxide species in equilibrium with the tiny amount of free methoxide in the buffered solution [Eq. (la)]. Whereas these large accelerations are interesting per se, here it suffices to emphasize that mixtures of 10 and m + are much more effective than either thiol or metal ion alone. The reactivity order Ca Sr Ba found in the acylation step closely parallels that found in deacylation. 

The superiority of the 18-crown-6 scaffold in 10 and 12 to the 19-crown-6 scaffold in 9 and 11 is apparent from a comparison of acylation and deacylation rates in the presence of Ba + (footnote c in Tables 5.4 and 5.5). 

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Breccia, P., Cacciapaglia, R.. Mandolini. L. and Scorsini, C. (1998) Alkaline-earth metal complexes of thiol pendant crown ethers as turnover catalysts of ester cleavage. J. Chem. Soc., Perkin Trans., 2, 1257. 

Another plausible strategy consists of the functionalization of CNTs via covalent attachment of selected groups. This is the case of thiol and thiol-plus macrocyclic ///-crown-/ ether ( = 12, n = 4, and zn = 15, = 5)-functionalized single-wall CNTs (// C SI la-SWNT) prepared by Alvaro et al. (2007). The functionalization process and the structure of pendant units are depicted in Figure 7.21. Attachment of such... 

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