Continuous Process for Phase-Transfer-Catalyzed Bisalkylation of Cyclopentadiene for the Synthesis of Spiro[2.4]hepta-4,6-diene

Abstract

The transfer of a highly exothermic phase-transfer-catalyzed bisalkylation of cyclopentadiene with 1,2-dichloroethane from batch to continuous mode using standard and widely available laboratory equipment is presented. Besides the optimization of the reaction temperature and residence time, the efficient mixing of the organic phase (cyclopentadiene, 1,2-dichloroethane, and MeBu3NCl) and the aqueous phase (30% NaOH) was studied in detail and optimized by the use of a simple, homemade “PTFE Raschig ring static mixer” consisting of a PTFE tube filled with small pieces cut from the same PFTE tube. A flow set-up with two PTFE Raschig ring static mixers and three residence time units with a three-stage temperature profile allowed the synthesis of highly energetic spiro[2.4]hepta-4,6-diene in a yield of 95% with a productivity of 15 g/h under safe conditions.