Guanidinium derivatives, carboxylate

Figure 2.13 Carboxylate anion binding by (a) guanidinium and (b) amidinium derivatives.

As expected for lipophilic guanidinium cations/ both 13 and 14 extract carboxylates from aqueous into organic phases, presumably exchanging for chloride. As hoped, this can happen with significant enantioselectivity for amino acid derivatives. Table 4 summarises the results from a series of experiments employing A -acetyl a-amino carboxylates 15. The selectivities are not exceptional, but are close to the best previously reported for extractions of amino acid derivatives. Considering the variations possible on the theme of 12, we can reasonably hope for improved performance in future, more refined versions of the system. 

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