Weakly nucleophilic leaving groups. Solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates

Abstract

Kinetic data are reported for solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates in binary aqueous mixtures with acetone, ethanol, and methanol and in 97% trifluoroethanol–water and hexafluoropropan-2–ol-water. Logarithms of solvolysis rates for t-butyl heptafluorobutyrate compared with t-butyl chloride (Figure 3) and with 1-adamantyl heptafluorobutyrate (Figure 4) show the relatively low reactivity of solvolyses of t-butyl heptafluorobutyrate in fluorinated alcohols, consistent with nucleophilic solvent assistance for solvolyses of t-butyl heptafluorobutyrate in the more nucleophilic solvents (e.g. aqueous methanol). In 97% hexafluoropropan-2-ol–water, 1-adamantyl heptafluorobutyrate solvolyses faster than t-butyl heptafluorobutyrate, supporting a recent prediction. Comparisons of relative rates of solvolyses of 1-adamantyl trifluoroacetate with those of 1-adamantyl chloride (Figure 2) and with Y_OTs(Figure 5) show the absence of substantial effects on relative rates due to electrophilic solvent assistance by fluorinated alcohols, other than those already included in the Y values. Solvolyses of triflates are anomalous in comparison with solvolyses involving other weakly nucleophilic leaving groups (perchlorate, trifluoroacetate, and heptafluorobutyrate).