Automated microreactors phases

Many strategies have been and are still being developed to access oligosaccharides by chemical synthesis. This chapter focuses on recent developments in the automated solid-phase synthesis of oligosaccharides and emphasizes the recent advances of novel microreactor techniques for carbohydrate synthesis. 

For the laboratory prototype a Gilson fraction collector was used. The whole setup as depicted was named MICROTAUROS (Fig. 15.14) (microreactor for automated reaction optimisation) and worked fairly well with only a few drawbacks. The length of the tube necessary for reaching every position on the fraction collector rack precluded very short reaction times. Higher pump rates would compromise the advantage of a laboratory system with the rather small amoimts of materials and small syringes. A much more severe drawback is the fact that a three-way solenoid valve had to be used. In the equilibrium phase the material stream is switched to waste and only diverted for collection of analytical samples. 

How this works in practice is detailed as follows. After a compound has been identified for which several hundred to several thousand derivatives would be of value, a synthetic route is chosen that (i) permits linkage to a solid-phase support (ii) utilizes reaction steps that appear possible to optimize to > 90% yield and (iii) affords reagents in each step for which desirable variants can be purchased (or, less optimally, can be made trivially). In the synthesis itself, one of the significant advantages of the microreactor approach becomes evident one can use standard laboratory glassware and equipment to accomplish the library synthesis. There is no need for the automation of liquid-handling steps, and indeed no need for automation at all until rather large libraries are desired (vide supra). 

Quiram DJ, Jensen KF (2007) Integrated microreactor system for gas-phase catalytic reactions. 3. Microreactor system design and system automation. Ind Eng Chem Res 46 8319-8335... 

Second, a study performed by Lonza (Visp, Switzerland), dealing with current benefits and drawbacks of microreaction technology, was presented [5]. The authors depicted the kind of reaction that prevails in the FCPI and classified them in three main classes. Type A, B and C (very fast, rapid and slow reactions, respectively). Thqr reasoned that up to 50% of the reactions performed at Lonza could benefit from continuous processing. For 44% of lhem a microreactor would be the preferred reaction device. However, the handling of solids reduces the number of reaction candidates to less than 20%. The authors therefore emphasized the development of multi-purpose microreactor modules that can deal with solid phases. Further, Roberge et al. [5] emphasized the potential of MRT to reduce labor costs by highly automated and efficient processes. 

Mills PL, Nicole JF Multiple automated reactor systems (MARS). 2. Effect of microreactor configurations on homogeneous gas-phase and wall-catalyzed reactions for 1,3-butadiene oxidation, Ind Eng Chem Rjes 44 6453—6465, 2005b. 

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