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

The transfer of a highly exothermic phase transfer-catalyzed bis-alkylation of cyclopentadiene with 1,2-dichloroethane from batch to continuous mode is presented, using standard and widely available laboratory equipment. Besides the optimization of the reaction temperature and residence time, the efficient mixing of the organic phase (cyclopentadiene, 1,2-dichloroethane, MeBu3NCl) and the aqueous phase (30% NaOH) was studied in detail and optimized by using of a simple, home-made '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-staged temperature profile allowed for 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.