Monosodium hydrogen 4-chlorophthalate → 4-Chlorophthalic anhydride

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Reaction Steps

The mixture of commercial 4-chlorophthalic acid monosodium salt (40 g) and thionyl chloride (50 ml) was stirred under reflux for 2 h. From the resulting viscous mass all volatiles were removed at the water aspirator. The residue was heated with benzene (150 ml) and the still hot slurry was filtered by suction. The filter cake was washed twice with benzene (50 ml) and the filtrate was concentrated in vacuo to give a yellowish solid. The crude was recrystallised from n-hexane/benzene 3:1 (filtration of the boiling solution needed) to yield 4-chlorophthalic anhydride (21.1 g) as colourless crystals.

Provenance & Evidence