mixture of 5.04 g. (0.022 mole) of phloroglucinol and 3.96 g. (0.04 mole) of maleic anhydride in 45 cc. of nitrobenzene was cooled to 10°. During the course of 15 minutes 17.42 g. (0.13 mole) of anhydrous aluminum chloride was introduced with mechanical stirring. External cooling was needed to keep the temperature at 30°. After 0.5 hr. the exothermic reaction subsided and the mixture was stirred at room temperature for 0.75 hr. The aluminum complex was decomposed in a mixture of ice and concentrated hydrochloric acid. The crude acid (4 g.) was recrystallized from water; m. p. of light colored acid 262.5°( dec.

The exceptional reactivity of hexachlorocyclopentadiene (I) in the presence of aluminum chloride may be attributed to the pentachlorocyclopentadienyl cation, CbC1s+. The resonance forms of this ion provide a theoretical basis for the susceptibility of I toward addition reactions, either as an addend or augend. The former is illustrated by the addition of chloroform to I to produce a nonachloromethylcyclopentene3 and by the addition of chlorine in the presence of aluminum chloride to form octachlorocyclopentene.4 The latter is illustrated by the addition of I to trichloroethylene to form 5-(l,2,2,2-tetrachloroethyl) -pentachlorocyclopentadiene (II).Both processes are illustrated by the dimerization of I to form a compound C10CI12 (XVI). A summary of the reactions reported in this paper is shown diagrammatically in Fig. 1.

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