Kolbe flow scheme

Fig. 6.24 Flow scheme of a simplified rig for performing continuously the aqueous Kolbe-Schmitt synthesis with resorcinol in a microstructured reactor. (Courtesy of the American Chemical Society [39, 40].)...

Another example illustrating the safe operation of micro reactors at elevated temperatures and pressures was reported by Hessel et al. [25], for the industrially relevant Kolbe-Schmidt reaction (Scheme 6.8). Potassium hydrogencarbonate (31) was selected as a raw material as it is cheap and readily available, making it suitable for the industrial-scale preparation of 2,4-dihydroxybenzoic acid (32) water was selected as the reaction solvent as it is inexpensive (100-1000 lh-1). To optimize the continuous flow conditions, the authors employed a stainless-steel capillary reactor and evaluated the effect of pressure for a fixed reaction time of 6.5 min at 120 °C. 

Scheme 6.8 The flow synthesis of 2,4-dihydroxybenzoic acid (32) via the Kolbe—Schmidt reaction of resorcinol (33).

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