Microwave assisted synthesis – a critical technology overview

Laboratory scaled flow-through processes have seen an explosive development over the past decade and have become an enabling technology for improving synthetic efficiency through automation and process optimization. Practically, flow devices are a crucial link between bench chemists and process engineers. The present review focuses on two unique aspects of modern flow chemistry where substantial advantages over the corresponding batch processes have become evident. Flow chemistry being one out of several enabling technologies can ideally be combined with other enabling technologies such as energy input. This may be achieved in form of heat to create supercritical conditions. Here, indirect methods such as microwave irradiation and inductive heating have seen widespread applications. Also radiation can efficiently be used to carry out photochemical reactions in a highly practical and scalable manner. A second unique aspect of flow chemistry compared to batch chemistry is associated with the option to carry out multistep synthesis by designing a flow set-up composed of several flow reactors. Besides their role as chemical reactors these can act as elements for purification or solvent switch.

Flow Chemistry – A Key Enabling Technology for (Multistep) Organic Synthesis

Porous polymer monoliths: amazingly wide variety of techniques enabling their preparation.

The recent invention and successive commercial introduction of monolithic silica columns has motivated many scientists from both academia and industry to study their use in HPLC. The first paper on monolithic silica columns appeared in 1996. Currently about 200 papers have been published relating to applications and characterization of monolithic silica columns, including monolithic capillaries. This review attempts to give an overview covering various aspects of this new column type in the field of high throughput analysis of drugs and metabolites, chiral separations, analysis of pollutants and food-relevant compounds, as well as in bioanalytical separations such as in proteomics. Some of the applications are described in greater detail. The numerous publications dealing with the physicochemical and chromatographic characterization of monolithic silica columns are briefly summarized.

Applications of silica-based monolithic HPLC columns

Monolithic stationary phases for liquid chromatography and capillary electrochromatography.

Monolithic supports have become the subject of extensive study in the past years. Despite their advantageous features and many successful chromatographic applications in the analytical scale, only a very few examples of larger volume monoliths were described. In the case of GMA−EDMA monoliths, this can be attributed to the fact that due to the exothermic polymerization a pronounced temperature increase inside the monolith significantly affects the structure. The temperature increase depends on the thickness of the monolith, and consequently, there is an upper limit that allows the preparation of a unit with a uniform structure. In the present work, we have analyzed a heat release during the polymerization and have derived a mathematical model for the prediction of the maximal thickness of the monolithic annulus having a uniform structure. On the basis of the calculations, two annuluses of different diameters were polymerized and merged into a single monolithic unit with a volume of 80 mL. In addition, a s...

Construction of large-volume monolithic columns.

Esterification of benzoic acid in microwave tubular flow reactor

The characterization of CIM® DEAE monolithic columns in terms of dynamic binding capacity is presented in this paper. Breakthrough experiments were performed for capacity determination. Bovine serum albumin (BSA) was used as a model protein. It is shown that CIM® monolithic columns have good batch-to-batch reproducibility as well as long-term stability. The experiments performed under different linear velocities demonstrated that the dynamic capacity is unaffected at least up to a linear velocity of 2450 cm/h. Furthermore, the breakthrough curve slope is constant, indicating that the capacity would remain constant at even higher linear velocities. The adsorption isotherm of BSA dissolved in 20 mM Tris-HCl buffer shows a constant capacity of around 30 mg/mL of support down to a concentration of 20 μg/mL. The capacity is substantially influenced by the ionic strength; however, 20% of the maximal capacity is still preserved at 0.3 M NaCl.

Tine Koloini

Papers

Construction of large-volume monolithic columns.

Esterification of benzoic acid in microwave tubular flow reactor

Dynamic Capacity Studies of CIM (Convective Interaction Media)® Monolithic Columns

Pressure drop in CIM disk monolithic columns.

Pressure drop characteristics of poly(high internal phase emulsion) monoliths