Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The hypothesis concerning orientational effects of carboxylate in general-base catalysis is discussed, and the first models that allow proton transfer to the syn lone-pair of the carboxylate during intramolecular general-base catalysis are designed, prepared, and tested. These models use a carbon backbone of two aryl groups linked by a two carbon bridge. The syntheses of 2-(2-hydroxyphenylethynyl)benzoic acid (24) and derivatives used in these studies are described. These derivatives were also needed to evaluate the ethynyl group as the bridge linking the aryls and to aid in the design of more complex models. The hydrolysis of the dichloroacetate ester (26) is compared to the hydrolysis of 2-dichloracetoxybenzoic acid (22), Ester 22 has been shown to hydrolyze by an intramolecular general-base mechanism but is constrained by geometry to use the anti lone-pair of the carboxylate in the proton transfer step. The hydrolyses differed in several respects. The kinetic solvent isotope for 26 (2.72) is higher than for 22 (2.17), the rate constant for the solvolysis of 26 in 0.5 mole fraction dioxane is significantly different than the average of the rate constants in H(,2)O and D(,2)O, and the addition of dioxane slows the rate of hydrolysis of 26. These differences support a transition state for the hydrolysis of 26 that involves more than one water molecule, which is consistent with the utilization of the syn lone-pair of the carboxylate in the proton transfer step. The acetate ester (26) of 24 does not hydrolyze but cyclizes to 3- (2-acetoxyphenyl)methylene -1-(3H)-isobenzofuranone. This reaction was studied with other derivatives of 24 and the cyclization is accelerated by groups that are electron withdrawing by inductive effects, while resonance effects do not contribute. X-ray structures for several 2-arylethynylbenzoic acids are examined. In the structures, the carbonyl oxygen and proximal ethyne carbon are closer than the sum of their van der Waals radii. This unexpected result limits the usefulness of the diarylethyne models to esters that hydrolyze relatively fast.

Pages

160

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