Glass microreactors

Reaction conditions 0.1 g of the zeolite Y modified catalyst, tested in a conventional glass microreactor with racemic butan-2-ol (7.35 x 10" mol h-1), prevaporized in a nitrogen diluent (6.2 -6.7 x 10" mol h-1). Products were analyzed using on-line GC with a 40m capillary y- cyclodextrin colimm with trifluoroacetyl stationary phase, temperature programmed from 25-70 "C with a split ratio of 120 1. 

Wilson, N. G., McCreedy, T., On-chip catalysis using a lithographically fabricated glass microreactor - the dehydration of alcohols using sulfated zirconia,... 

Fig. la-e. Selected microreactors, a Stainless steel microreactor system designed by Ehrfeld Mikrotechnik. b Glass microreactor (Watts and Haswell 2005). c Stainless steel microreactor of the CYTOS Lab system (http //www.cpc-net.com/cytosls.shtml). d Silicon-based microreactor designed by Jensen (Ratner et al. 2005). e Glass microreactor of the AFRICA System... 

Examples of using metal, polymer, and glass microreactors appear in other chapters of this volume. The present chapter focuses on microreactors created in silicon, a material that has high mechanical strength,... 

WUes and Watts [48,53] have reported the use of a rather successful heterogenic catalytic system to carry out these reactions. They have tested a borosilicate glass microreactor (dimensions 3.0 x 3.0 x 0.6 cm) consisting of two etched layers with two inlets, mixing channels, a larger etched region and the outlet. A solid-supported catalyst was dry-packed in this structure (Fig. 4). 

Figure 2.4 Photographs of the glass microreactors (a) larger (100 mm wide x 50 mm deep) channels and (b) smaller (50 mm wide x 20 mm deep) channels [64].

Baxendale et al. (2008) reported a bifurcated approach to the synthesis of thiazoles and imidazoles by coupling a glass microreactor and a packed-bed reactor to achieve a base-mediated condensation reaction. As Scheme 32 illustrates, reactions focused on the use of ethyl isocyanoacetate 123, as the cyanide source, with variations made via the isothiocyanate reagent, as illustrated in Table 13. 

Table 27 Photochemical [2 + 2] cycloaddition conducted in a FORTURAN glass microreactor...

Scheme 58 An early example of the photochemical generation of singlet oxygen within a glass microreactor.

Compared with the above examples, whereby an array of pharmaceutically important molecules have been synthesized under pressure-driven flow, Garcia-Egido et al. (2002) reported the synthesis of fanetizole (207), an active compound for the treatment of rheumatoid arthritis, utilizing EOF. Employing a borosilicate glass microreactor fabricated at The University of Hull, the authors demonstrated the first example of a heated EOF-controlled reaction. As Scheme 60 illustrates, using... 

Scheme 77 Photooxygenation of (-)-p-citronellol (279) conducted in a glass microreactor and the subsequent use of hydroperoxide 278 in the synthesis of (-)-rose oxide (200).

The same group also investigated the photochemistry in a glass microreactor, and reported that the reaction was completed within a short time period (Scheme 4.61) [91]. 

Ducry and Roberge reported controlled nitration of phenol in a glass microreactor with a channel width of 500 pm and an internal volume of 2.0 ml [2]. Nitration was most efficient and controlled under nearly solvent-free conditions at 20 °C without the addition of sulfuric acid or acetic acid (Scheme 4.2). Under these concentrated conditions, autocatalysis spontaneously started in the mixing zone, allowing safe control of the reaction. Undesirable polymer formation, which is significant in batch reactions, was effectively suppressed by a factor of 10. 

The combination of fluoride ions and enol silyl ethers provides a useful method for the generation of enolate anions [9]. Watts, Haswell and coworkers applied a borosilicate glass microreactor, having channel dimensions of 100 pm x 50 pm and equipped with an electrosmotic flow (EOF) pumping system, to the C-acylation of enolate anions, which leads to 1,3-diketones [10,11]. A THF solution of tetrabutyl-ammonium fluoride (TBAF) was placed in reservoir A, a THF solution of benzoyl... 

A borosilicate glass microreactor (152 pm (width), 51pm (depth) and 2.3 cm (length)) that was connected to a T-shaped PEEK (poly(ether-ether-ketone)) unit (MicroTee, Upchurch Scientific) was used for the formation of sodium enolate of... 

Haswell and coworkers carried out the Wittig reaction of 2-nitrobenzyl triphenylpho-sphonium bromide with methyl 4-formylbenzoate in a microflow system [17,18]. They used a borosilicate glass microreactor with T-shaped channels (width = 200 pm and depth = 100 pm), and the reagents were added via EOF by applying a constant... 

Fernandez-Suarez and coworkers investigated a domino reaction using a glass microreactor with a channel 74 pm in width [24], The reaction of citronellal with... 

Microreaction technology has also been applied to peptide synthesis. Haswell and coworkers demonstrated that, using a borosilicate glass microreactor, the desired... 

Another enzyme that was studied extensively in microreactors to determine kinetic parameters is the model enzyme alkaline phosphatase. Many reports have appeared that differ mainly on the types of enzyme immobilization, such as on glass [413], PDMS [393], beads [414] and in hydrogels [415]. Kerby et al. [414], for example, evaluated the difference between mass-transfer effects and reduced effidendes of the immobilized enzyme in a packed bead glass microreactor. In the absence of mass-transfer resistance, the Michaelis-Menten kinetic parameters were shown to be flow-independent and could be appropriately predicted using low substrate conversion data. 

Catalytic testa have been carried out in a continuous-flow fixed-bed glass microreactor at atmospheric pressure equipped with on-line gas chromatographs. Other details on the apparatus were reported previously [6,7], Unless otherwise indicated, the standard reaction conditions were 0.8% 1-butene, 20% 02 and 20% H20 in helium. The total flow at STP was 3,6 LA with 2,5 g of catalyst. 

Catalytic Experiments Catalytic measurements were carried out by means of a vibrating glass microreactor [4]. The rotating vibration of the reactor simulates fluidized bed conditions. The composition of the reaction products and the methyl chloride conversion was measured by on-line gas chromatography. Under the assumption of a differential behavior of the reactor, initial reaction rates were calculated from the methyl chloride conversion as a measure of the catalytic activity of the contact masses. The selectivity of the reaction is not a matter of discussion in this paper and will be mentioned only exceptionally. 

In most cases microwave reactions have been conducted in a batch system, but very recently the use of a microflow system for microwave reactions has been reported. For example, Suzuki-Miyaura coupling of aryl halides with phenylboronic acid to form biaryls is promoted by microwave irradiation of the supported Pd catalyst (Table 5.1). A thin, gold film patch located on the outside surface of the base of a glass microreactor is quite effective for absorbing microwaves. 

S. Mukherjee, M.K. Hatalis, M.V. Kothare, Water Gas Shift Reaction in a glass microreactor, Catal. Today 120 (2007) 107. 

F. Trachsel, C. Hutter, P.R. von Rohr, Transparent silicon/glass microreactor for high-pressure and high-temperature reactions, Chem. Eng. J. 135 (2008) S309. 

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