Cl[C:2]1[C:3]([O:5][C:6](=[O:8])[CH:7]=1)=[O:4].[Cl:9][C:10]1=[C:11](Cl)[C:12](O[C:15]1=O)=O.C=CC(Cl)=C.Cl>C1C2NC3C(=CC=CC=3)SC=2C=CC=1.ClC1C=CC=CC=1.O>[Cl:9][C:10]1[CH2:15][C:7]2[C:6](=[O:8])[O:5][C:3](=[O:4])[C:2]=2[CH2:12][CH:11]=1
A 3-necked 50 mL flask was equipped with a pressure equalizing additional funnel, a thermocouple well with a thermocouple, a water cooled condensor and a magnetic stir bar. The flask was charged with 6.62 g (0.05 mol) of monochloromaleic anhydride contaminated with approximately 0.005 mol of dichloromaleic anhydride, 6.1 g of monochlorobenzene and 100 mg of phenothiazine. The contents of the flask were heated to 92° C. and 4.42 g (0.05 mol) of chloroprene was added over 15 to 30 minutes. HCl gas was observed evolving from the reactor. After 16 hours at 92° C., the solvent was removed in-vacuo and triturated with 10 mL of diethyl ether to yield 4.6 g (50% of theoretical) of 4-chloro-3,6-dihydrophthalic anhydride. High resolution mass spectrometry (MS) of the solid resulted in the following analysis: Calculated mass=183.99271; observed mass=183.9924. 13C and 1H nuclear magnetic resonance (NMR) spectra were consistent with the assigned structure.
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