Abstract
Microreactors have found widespread use for continuous flow synthesis and reaction optimization. Flow rates are critical factors with respect to the latter application because they are used to set screening parameters such as reaction time and stoichiometric ratios. However, the set flow values of pumps for nanoliter to microliter volume reactors are quite often not sufficiently accurate. In this paper we present a generally applicable chromatographic method to analyze flow rates during microreactor reaction screening. By adding flow markers to all reactant and reagent flows and performing conventional GC analysis on all samples, an accurate flow rate was calculated. The deviation between the set flow values and the measured flow rates was shown for a standard continuous flow experiment. The implications of this deviation for reaction optimization were demonstrated via a model Swern-Moffatt oxidation reaction, which showed that accurately measured flow rates are critical for correct data interpretation.
Highlights
The interest in using microreactors for synthesis has increased enormously in recent years [1,2,3,4,5,6]
In order to simulate flow parameters in a real reaction kinetics experiment, the set flow rates were calculated from linear arrays of ratios and residence times
Swern-Moffatt oxidationd aThe complete data set can be found in S3 and S4 of the Supporting Information. bAfter setting the appropriate flow rate, the outflow needle was placed in a waste container. cSolution of flow markers A and B, respectively, in CH2Cl2 (2% v/v). dFor flow A: Solution of benzyl alcohol (0.5 M), dimethyl sulfoxide (DMSO) (2.5 M) and a flow marker A (2% v/v) in CH2Cl2
Summary
The interest in using microreactors for synthesis has increased enormously in recent years [1,2,3,4,5,6]. Most setups consist of syringes loaded on syringe pumps and connected to a microreactor via tubing. This leads to a continuous flow system, i.e. reactants and reagents are continuously pumped into the microreactor and a stable outflow of starting material, products and possibly by-products is obtained. The flow rates in combination with the reactor’s internal volume determine parameters such as reaction time and reagent stoichiometry. Since these parameters are often the subject of the investigation (e.g. in the optimization of a reaction), it is crucial to exactly control and know the flow rates
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