A continuous-flow resonator-type microwave reactor for high-efficiency organic synthesis and Claisen rearrangement as a model reaction

Abstract

We have developed a single-mode microwave reactor for continuous-flow synthesis with various methods of operation. This device measures the resonant frequency and modulates the oscillation frequency accordingly to maintain the maximum electric field intensity in the cavity. It can be operated either using constant applied irradiation power or using new programs which change the electric power (E-GRA) and change the flow rate (Fl-GRA), in order to rapidly screen various reaction conditions. As a model reaction, the Claisen rearrangement reaction of allyl 1-naphthyl ether 1 was rapidly optimized in this device, affording the desired product 2-allylnapthalen-1-ol 2 in high (91%) yield and up to 20 g/h productivity.

High Efficiency Microwave Flow Chemistry Towards Synthesis of Functional Materials and Pharmaceutical Cores

“…5, left, center) with calibration as previously described. 6 The surface temperature increased in a non-linear fashion and the surface temperature of locations near the reactor exit were in agreement with the internal exit temperature (Fig. 5, right).…”

“…5, right). Together with the dielectric constant of the Duran pipe ( r' = 4.6, 1 MHz, 25 o C) 6 being much lower than NMP ( r' = 14.2, 2.45 GHz, 25 o C), this indicates the surface temperature is similar to the internal temperature and confirms the direct nature of radiative heating of the reaction mixture by MW. CH requires much higher surface temperatures (locations 5,15, Fig.…”

“…This 'thermal' MW effect is less pronounced for the C60/indene conjugation reaction, where heating of the Duran reactor tube and o-Xylene occurs in competition (such an effect has been previously reported for Duran and CPME). 6 Dielectric properties may change at elevated temperatures, so a 'non-thermal' microwave effect cannot be exclusively ruled out. Table 4.…”

“…Elsewhere, AFT-MW CF technology has been leveraged for the OFAT-type optimization of a Johnson-Claisen rearrangement 16 and the synergy of AFT MW CF with software programs that automatically vary the flow rate and MW power has been employed to rapidly optimize an ortho-Claisen rearrangement reaction of allyl 1-napthyl ether. 6 3 Summary…”

Effective Application of Microwave Resonant Cavity System to Flow Chemistry

“…Norikane group of AIST applied the system using Xylene as solvent to C60 derivative conjugation. The group reports that the reaction temperature reaches at 270 C, and yield and productivity are improved a lot ,…”