Solvent variations and the rates of ferrocenylmethyl ester solvolyses

Solvent variations and the rates of ferrocenylmethyl ester solvolyses 

More than forty years ago it was shown that triphenylmethyl (trityl) acetate solvolyzes in either aqueous dioxane or methanol almost entirely by alkyl-oxygen bond fission. In addition, a general tendency has been observed towards faster solvolyses of this type in solvents of higher ionizing power, consistent with a dissociative (S l) mechanism, with a carboxylate leaving group. 

Recently, the solvolysis of ferrocenylmethyl acetate has been studied in 2,2,2-trifluoroethanol (TFE)-ethanol mixtures and in aqueous ethanol, acetone, and TFE. For 19 solvents, a fair correlation with OTs values has been obtained. This correlation was much improved when OTs values were replaced with the derived solvent ionizing power (Foac) values. The latter correlation, with a slope close to unity, supported the S l assignment for ferrocenylmethyl acetate solvolyses. The same authors obtained an excellent correlation against their Foac values for a-ferrocenylethyl acetate solvolysis, as well. Since it had previously been shown that the introduction of an a-methyl group into fer- 

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