Oxygen sensors for flow reactors – measuring dissolved oxygen in organic solvents

Abstract

In an effort to push the boundaries of optical oxygen sensors, this contribution shows the development of a measurement system for high O₂ content in organic solvents specifically designed for flow reactors. Presented sensors were prepared by directly melting an oxygen indicator dye into a highly resistant polymer matrix, leading to the ability to measure oxygen contents up to 59 mmol L⁻¹ in tetrahydrofuran, toluene, acetone, dimethylformamide, cyclohexane and methyl tert-butyl ether. Long-term effects to the solvent were investigated by exposing the sensors for 22 hours to the respective solvent at 25 °C. Linearity according to Stern–Volmer was obtained for every single sensor in order to provide a system that can be easily initialized by two-point calibration into continuous flow reactors. To demonstrate the applicability of the sensor under reaction conditions, an oxidation of a Grignard reagent with molecular oxygen was performed in a flow reactor. The sensors were able to show the oxygen decrease during reaction and allowed online reactant quantification.