0-PHTHALYL CHLORIDE, UNSYMMETRICAL

Pure symmetrical o-phthalyl chloride cannot be obtained, even by recrystallization from carbon tetrachloride. A product melting at 16° may be obtained by distilling the unsymmetrical phthalyl chloride at atmospheric pressure. 

It will be recalled that in the case of succinyl chloride both of these forms are obtained, but mostly the symmetrical (p. 282). Now from phthalic anhydride only one phthalyl chloride is obtained. This chloride acts like the unsymmetrical succinyl chloride, not like the symmetrical. The positive proof, however, that phthalyl chloride is the unsymmetrical compound is the following Sodium amalgam reduces phthalyl chloride by replacement of the chlorine with hydrogen. The compound formed is known as phthalide. This phthalide takes up water as anhydrides do and the product is hydroxy-methyl benzoic acid. 

From these relationships it is seen that phthalyl chloride must have the unsymmetrical formula. 

This reaction establishes the constitution of phthalide as a lactone not a di-aldehyde and, therefore, phthalyl chloride has the unsymmetrical... 

Preparation from Phthalic Acid.—In discussing phthalic acid (p. 691) we spoke of the fact that phthalic anhydride or phthalyl chloride with phenol yields phenolphthalein. The reaction takes place in the presence of anhydrous zinc chloride as a dehydrating agent or in the presence of aluminium chloride (Friedel-Craft). Phthalyl chloride being the unsymmetrical compound (p. 692), the two reactions are represented as follows ... 

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