Abstract cis-β-Phenoxyacrylic acid and several of its ring-substituted derivatives were prepared, and their ionization constants were determined in 50% ethanol–water at 25 °C. The Hammett ρ value for the ionization of these acids, 0.439, is smaller than that reported for cis-β-phenylthioacrylic acids, 0.531. The greater efficiency of the sulfur atom in transmitting the substituent effects is explainable in terms of the “through-conjugation” of the sulfur atom in the thioacrylate anions formed.
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Kajimoto et al. (1973) studied this question.