A-PHTHALIMIDO-O-TOLUIC ACID

The precipitate is separated by suction filtration, pressed on the funnel, and washed successively with three 100-ml. portions of water and two 100-ml. portions of 95% ethanol. The product is transferred to a 1-1. Erlenmeyer flask, boiled for 10 minutes with 400 ml. of 60% ethanol with occasional stirring, filtered hot, washed twice with 50-ml. portions of 95% ethanol, and then dried in an oven at 90-100° for 6-12 hours. The crude a-phthalimido-o-toluic acid, which weighs 140-155 g., is divided into two equal portions, and each portion is dissolved in boiling propionic acid (Note 5). Each solution is treated with 1 tablespoon of Norit and filtered through an electrically heated gravity funnel. The filtrates are allowed to cool slowly to room temperature and are then refrigerated overnight. The crystals from the two portions are collected by suction filtration in one funnel and washed on the funnel with 400 ml. of 95% ethanol. The product is dried over potassium hydroxide in a vacuum desiccator. The yield of nearly white crystals of a-phthalimido-o-toluic acid is 126-141 g. (60-67% based on phthalide), m.p. 265.0-266.5°. 

The reaction mixture is most conveniently cooled by allowing it to stand at room temperature overnight. Occasionally the potassium salt of a-phthalimido-o-toluic acid precipitates at this point, but this does not interfere with the subsequent operations. 

Approximately 1.33 1. of propionic acid is required for 78 g. of the crude a-phthalimido-o-toluic acid. Glacial acetic acid may be used as the solvent, but considerably larger volumes are required than when propionic acid is employed. This step should be carried out in a hood, since hot propionic acid vapors are very irritating. 

The present procedure is that described by the submitters.3 a-Phthalimido-o-toluic acid has also been prepared by the acidolysis of the corresponding ethyl ester, obtained from the reaction of ethyl a-bromo-o-toluate with potassium phthalimide.8... 

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