1971 Volume 44 Issue 10 Pages 2771-2776
The chlorinations of propionic acid with chlorine were carried out at 70°C in various solvent mixtures with photo-irradiation or with initiation by benzoyl peroxide. Benzene - CCl4, naphthalene - CCl4, and anthracene -CCl4 mixtures, and sulfur dioxide - CCl4 were used as the solvents. In the benzene - CCl4 mixtures, the relative reactivity, β/α, of the a and the α positions of propionic acid changed from 1.68 (CCl4) to 1.11 (benzene), the ratio being inversely proportional to the electron-donor properties of the solvents. In the naphthalene -CCl4 mixtures, the plot of the relative reactivity, β/α, versus the naphthalene content showed a minimun at ca. 0.1 mol/l of naphthalene; however, the total yield of the chlorinated acids decreased as the content of the naphthalene increased. No chlorinated acids were obtained in the anthracene - CCl4 system. In the presence of sulfur dioxide, the α-position was more readily substituted than the β-position, the β/α ratio decreasing as the molar ratios of C12/SO2 were decreased, from 1.3 (Cl2/SO2=0.286/0.036) to 0.49 (0.286/0.858), by the initiation of benzoyl peroxide. However, dilution with CCl4 or photo-irradiated chlorination cause no change in the selectivity in spite of the presence of sulfur dioxide. A mechanism to account for such a selectivity has been suggested.
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