Fabrication of a Monolith Reactor in a Copper Tube by Polymerization of Acetylene for Flow Catalysis

Continuous-flow processing is considered as a disruptive technology in the synthesis of active pharmaceutical ingredients and other fine chemicals. However, it remains extremely challenging to immobilize heterogeneous catalysts in the channels of microreactors in a facile and flexible manner. In the present investigation, a polymer monolith coiled copper reactor was fabricated by Cu-catalyzed polymerization of acetylene at atmospheric pressure in the temperature range of 290–370 °C. The polymerization yielded a cotton-like structure of carbonaceous fibers, which were able to assemble by themselves to form a monolith inside the copper tube. The characterization results revealed that unsaturated C═C groups, which are favorable for post-surface modification, were present on the carbonaceous fibers. After air oxidation at 160 °C for 10 h, a fraction of the C═C groups were converted to C═O groups. By strong interaction with C═O groups, Pd was immobilized in the polymer monolith by circulating an ethanol solution of palladium acetate through the copper tube. A 1000 mm-long monolith tube reactor with an inner diameter of 2 mm with a Pd loading of 1.15 wt % was fabricated and used in the continuous Suzuki–Miyaura coupling reaction. An ethanol–water (2:1 in volume) solution of iodobenzene (0.0125 M), phenylboronic acid (0.0188 M), and potassium carbonate (0.0250 M) was used as the feed, and the reaction took place at 100 °C and 1.0 MPa. The selectivity to biphenyl was kept at >99% with complete conversion of iodobenzene in a 100 h run.