Date of Award

6-1989

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Abstract

The reactions of the esters of trimethyl acetic acid (pivalic acid) have been followed kinetically (Walrath 1977 and Watkins 1986) in the presence of alkali in a 3:1 ethyl cellosolve: water solvent at 64°C. Through the use of both optically active pivaloates and O18 as a tracer, the positions of bond fission during saponification for several pivolates have been determined. With the secondary butyl ester bimolecular attack on both the acyl- and the alkyl- carbon atom is observed in the presence of alkali. Partial racemization of the product secondary butyl alcohols suggests that for a saponification of secondary butyl pivaloates a combination of the common Bac2 saponification mechanism and the rarer Bal2 saponification mechanism may occur in a purely aliphatic ester. In contrast to the secondary butyl ester, O18 studies show that the methyl ester undergoes biomolecular attack at only the acyl carbon atom in the presence of alkali. Apparently both the α tertiary butyl group and the secondary alcohol group are necessary to mask nucleophilic attack at the acyl carbon atom. The absence of a secondary alkyl group in methyl pivaloate allows nucleophilic attack at the acyl carbon to occur quite readily. Solvolysis experiments employing phenoxide ion (ՓO-) are under way to investigate the effect of the attacking nucleophile’s size on the reaction mechanism. Experiments employing O18 as a tracer for the saponification of ethyl-, n-butyl-, and secondary butyl pivaloate will begin shortly. This work should provide a more quantitative measure of the relative extent if each mechanism that occurs during the saponification of secondary butyl pivaloate and should provide insight into the effect of varying alkyl substituents on the mechanism of saponification of pivaloate esters.

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In Copyright - Educational Use Permitted.