Micromixing microtube reactors

The reaction scope is further enlarged to unsymmetrically disubstituted derivatives. Using one mole equivalent of two different aryllithium precursors at a time in a sequence of four micromixers and microtube reactors (MRi ), it was possible to obtain an unsymmetrically disubstituted final diarylethene. The yield was determined after solvent evaporation and sample purification on the column. 

Yoshida and coworkers also developed a microreaction system for cation pool-initiated polymerization [62]. Significant control of the molecular weight distribution (Mw/Mn) was achieved when N-acyliminium ion-initiated polymerization of butyl vinyl ether was carried out in a microflow system (an IMM micromixer and a microtube reactor). Initiator and monomer were mixed using a micromixer, which was connected to a microtube reactor for the propagation step. The polymerization reaction was quenched by an amine in a second micromixer. The tighter molecular weight distribution (Mw/M = 1.14) in the microflow system compared with that of the batch system (Mw/M > 2) was attributed to the very rapid mixing and precise control of the polymerization temperature in the microflow system. 

Figure 6.7 Microflow system for Friedel-Crafts alkylation of aromatic compounds with an N-acyliminium ion (M, micromixer R, microtube reactor)...

A microstructured fluidic device that is used for conducting chemical reactions is called a microreactor. A microreactor is a reactor containing microstructures for chemical reactions. The size of the microstructure inside a microreactor usually ranges from several micrometers to several hundred micrometers. Various types of microstructured fluidic devices, such as microchip reactors and microtube reactors, have been developed for chemical reactions. Micromixers often serve as microreactors because reactions take place immediately after mixing. In some cases, external energies, such as thermal, photo, and electric energies, are provided in the microspace to promote the chemical reactions. For such purposes, special microreactors have been developed. 

Figure 7.5 Microflow system composed of microtube reactors and micromixers...

When the reaction was performed on a 100 mg scale, the diene was obtained in 55% yield as a mixture of ( )- and (Z)-stereoisomers. However, when the scale was increased to lOOg, various by-products, such as cyclized products or alkyl group-migrated compounds, were produced presumably because of acid-catalyzed reactions of the diene. The formation of such by-products can be reduced using a microflow system composed of a micromixer and a microtube reactor. Thus, a solution of the allylic alcohol in tetrahydrofuran (THF) was mixed with a solution of p-toluenesulfonic acid (p-TsOH) in THF/toluene at 90 °C. After the reaction mixture was allowed to flow for 47 s, the reaction was quenched with a saturated NaHCOs solution at room temperature. In this case the desired diene was obtained in 80% yield. It is noteworthy that the acid-mediated by-products were not detected. This process was applied to the synthesis of pristane, a biologically important natural product that is widely used as an adjuvant for monoclonal antibody production. 

The use of a microflow system composed of a micromixer and a microtube reactor solves the diiodination problem, as shown in Scheme 8.10. The yield of monoiodo compound is 78%, whereas the yield of the diiodo compound is 4%. A significant increase in the product selectivity can also be accomplished for other highly reactive aromatic compounds. 

However, the use of a microflow system composed of a multilamination micromixer and a microtube reactor gives rise to a significant increase in the yield of the cycloadduct (79%) at the expense of the amount of the polymer (ca. 20 % based on styrene). The fast and efficient 1 1 mixing by a micromixer seems to be responsible. The extremely fast mixing might cause the cationic product to be formed at a very low concentration of styrene, which leads to the effective formation of the neutral cycloadduct. Similar mixing effects have also been observed for p-chloro- and p-methylstyrenes. 

Figure 9.2 Microsystem for polymerization. Ml, M2, micromixers Rl, microtube reactor...

A monomer solution and an initiator solution are mixed at a T-shape micromixer Ml and microtube reactor Rl. In this case fast mixing of the two solutions is not important, because radical polymerization does not start until the temperature is elevated sufficiently for thermal decomposition of a radical initiator, such as AIBN. Therefore, the combination of a T-shape micromixer and a short microtube reactor is sufficient for producing a homogeneous solution before polymerization starts. 

Figure 9.9 Microflow system for polymerization. Ml, T-shape micromixer Rl, R2, R3, microtube reactors...

Fig. 4 Flow microreactor system for controlledAiving cationic polymerization of vinyl ether initiated by SnCL. M interdigital multilamination micromixer, R microtube reactor...

Fig. 5 Flow microreactor system for polymerization of vinyl ether initiated by Af-acyliminium ion (cation pool). Ml, M2 micromixers Rl, R2 microtube reactors...

Fig. 8 Flow microreactor system for cationic polymerization of 1,4-diisopropenylbenzene initiated by TfOH. M T-shaped micromixer, /f microtube reactor...

Fig. 14 Flow microreactor system for anionic polymerization of styrene in cyclohexane at 80°C initiated by s-BuLi. M T-shaped micromixer R microtube reactor...

The livingness of the reactive carbanionic polymer end is important for producing end-functionalized polymers and block copolymers. The livingness of the polymer end in a flow microreactor system can be verified as shown in Fig. 17. Solutions of an aUcyl methacrylate and of 1,1-diphenylhexyllithium are mixed in the first micromixer (Ml in Fig. 17) and the polymerization is carried out in the first microtube reactor (Rl in Fig. 17). Then, a solution of the same monomer is introduced at the second micromixer (M2), which is connected to the second micrombe reactor (R2) where the sequential polymerization takes place. By changing the length of Rl with a fixed flow rate, the effect of the residence time in Rl can be examined. The M increases by the addition of the second monomer solution. However, an increase in the residence time in Rl causes an increase in the MJM, presumably because of decomposition of the polymer end (Fig. 18). By choosing an appropriate residence time in Rl (2.95 s for MMA 0.825 s for BuMA), the sequential polymerization can be... 

Continuous nitroxide-mediated block copolymerization of n-butyl acrylate (first monomer) and styrene (second monomer) can be performed using two serial 900-p m inner diameter stainless steel microtube reactors (Fig. 29) [215]. For the second polymerization process, the influence of mixing was examined by changing micromixers. The use of a high-pressure interdigital multilamination micromixer (HPIMM) provided by the Institut fiir Mikrotechnik Mainz (Mainz, Germany), can significantly reduce the polydispersity index = 1.36, 120°C) compared... 

Ziegler-Natta polymerization [241,242] is an important method of vinyl polymerization because it allows synthesis of polymers of specific tacticity. As reported by Santos and Metzger, Ziegler-Natta polymerization can be carried out in a flow microreactor system coupled directly to the electrospray ionization (ESI) source of a quadrapole time-of-flight (Q-TOF) mass spectrometer (Fig. 37) [243]. In the first micromixer (Ml), a catalyst (CP2Z1O2/MAO) and a mmiomer solution are mixed continuously to iiutiate the polymerization. The polymerization occurs in a microtube reactor. The solution thus obtained is introduced to the second micromixer (M2), where the polymerization is quenched by acetonitrile. The quenched solution is fed directly into the ESI source. The transient cationic species... 

---