Photodimerization of Maleic Anhydride in a Microreactor Without Clogging

Abstract

Photodimerization of maleic anhydride (MA) gives insoluble precipitated products that can be a trigger to clog a conventional microreactor. To avoid this problem, we devised a microreactor that uses liquid/gas slug flow and ultrasonication. Inert N 2 gas introduced into the reaction solution swept through the reactor tube and transported precipitated products in the liquid segments.Ultrasound vibrations inhibited the adhesion and sedimentation of precipitate in the reactor tube. The combination of gas and ultrasound prevented the tube from clogging. Fluorinated ethylene propylene (FEP) tubes of various sizes were investigated to use as a tube reactor. The tubes were wound around a high-pressure Hg lamp with a Pyrex immersion well which has been using generally as a light source of photoreaction, and the reaction solution was then passed through the tube and irradiated through the tube wall. The slug flow microreactor could be operated for more than 16 h continuously without clogging. Compared to using a batch reactor, this method achieves better product quality, improved conversion, and reduced waste.

9.03 Organic Synthesis in Small Scale Continuous Flow: Flow Chemistry

“…Furthermore, the smaller interstitial path lengths in packed beds prohibit reactions that produce solids, as sonication and other techniques to control particle growth and deposition are ineffective. 79 Lastly, solid-supported catalysts that operate through so-called boomerang mechanisms, where the active species desorbs from the support under reaction conditions and readsorbs on completion of the reaction, are poorly suited to flow conditions.…”

Beyond Organometallic Flow Chemistry: The Principles Behind the Use of Continuous-Flow Reactors for Synthesis

“…These smaller particles are small enough to be transported through the microchannels. This strategy has been used to avoid clogging in C-N cross coupling, 163,164 Suzuki-Miyaura coupling, 165 photodimerization reactions, 166 KMnO4 oxidation reactions 167 and other solids forming reactions. 168, 169…”

Continuous‐flow syntheses of heterocycles

“…As a second synthetic step, the formation of carboxamides under flow conditions was optimized. A standard coupling cocktail for an amide bond synthesis, EDC/ HOBt/DIPEA, at 75 C for 10-min reaction time resulted in complete conversions. Combining the two separate synthetic steps proved to be challenging, because the presence of p-toluenesulfonic acid in the reaction mixture after the cyclization step hindered the amide bond formation in the second step.…”

“…An UV-flow reactor based on the same principle was also developed and used for the synthesis of cyclobutanetetracarboxylic dianhydride by photodimerization of maleic anhydride [75]. However, the formed product tends to precipitate.…”