Alkali-metal ion catalysis and inhibition of acetyl transfer from p-nitroaryl acetates to hexanoate ion

Abstract

Deacetylation of 2-acetoxy-5-nitro-1,3-xylylene-18-crown-5 (21 -acetoxy-18-nitro-2,5,8,11,14-pentaoxa[18]metacyclophane) by hexanoate ion in DMF is strongly inhibited by Li⁺ ion, slightly retarded by Na⁺ ion, and significantly promoted by the larger alkali-metal ions. In contrast, the analogous reaction of the simple model p-nitrophenyl acetate is inhibited by all of the alkali-metal ions. These effects are discussed in terms of differential binding of metal ions to reactants and transition states. In line with conclusions from previous works, it is confirmed that coordinative binding of metal ions with the oxygen donors of the polyether bridge of the crown-ether substrate is an effective force for catalysis.