Article Title

Iodination of Anisole

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As a rule direct iodinations do not proceed readily, often explained as due to the unfavorable equilibrium attained with the reverse reaction of hydrogen iodide upon the iodo-compound. Iodine is more commonly introduced into an aromatic nucleus through the Sandmeyer reaction by the addition of potassium iodide to a diazotized primary aromatic amine. Thus p-iodoanisole has been prepared from p-anisidine.1 A procedure of direct iodination for the preparation of iodoaromatic compounds would appear to offer important advantages. In 1901, Brenans2 reported such a process in the preparation of p-iodoanisole through the interaction of an absolute ethyl alcohol solution of anisole with mercuric oxide and iodine. Later in 1912, Kauffmann3 used the same procedure for the iodination of resorcinol dimethyl ether to produce l-iodo-2, 4-dimethoxybenzene, although he made no reference to the earlier work of Brenans. Blicke and Smith4 in 1928 modified the Brenans procedure for preparation of p-iodoanisole for which they claimed more desirable results. As a result of our experience, we have adopted a procedure more nearly like that of Brenans, giving a better yield and product than would appear from his report, and less involved procedure than that of Blicke and Smith. One mol quantity of anisole is dissolved in about four weight quantities of absolute ethanol, three fourths mol quantity of commercial mercuric oxide is added and slightly more than one mol quantity of iodine introduced in five portions with mechanical shaking between portions until the color of iodine nearly vanished. Finally the whole mixture is shaken for about eight hours on a mechanical shaker. The undissolved mercury compounds are filtered, washed with ethanol, the ethanol removed by distillation, the residual oil dissolved in ether and filtered again if necessary, the ether solution washed with a potassium iodide solution, the ether evaporated, the residual oil steam distilled, and the organic part of distillate crystallized from about 85 per cent ethanol. A yield of 85 per cent, melting at 50.5-51.5 (corrected), was obtained. Some speculation with reference to the role of HgO as a catalyst for this iodination is given. 1 Reverdin, Ber. 29, 1000 (1896). 2 Brenans, Bull. Soc. Chim. [3] 25, 819 (1901). 3 Kauffmann, Ber. 45, 2334-35 (1912). 4 Blicke and Smith, J. Am. Chem. Soc. 50, 1229·30 (1928).

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Proceedings of the Iowa Academy of Science





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©1940 Iowa Academy of Science, Inc.



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