2.3 Sample analysis
After the reaction was quenched, a 1 mL sample was collected in a 10 mL centrifuge tube. The internal standard method was used to quantify the composition of the products. A known quantity of nitrobenzene was added to the centrifuge tube as the internal standard, and then methanol was added to dilute the mixture. After the sample was evenly mixed, a small amount of the sample was extracted and analyzed by ultra-performance liquid chromatography (UPLC) using an ACQUITY UPLC I-Class system (Waters, USA) equipped with an ACQUITY UPLC BEH C18 column (2.1 × 100 mm, 1.7 μm). The injection volume was 1 μL. The mobile phase consisted of methanol (50%) and water (50%), and its flow rate was 0.2 mL/min. The column temperature was 30 °C. The detection wavelength of the UV detector was 200-300 nm. For the peaks observed for each substance by UPLC, please refer to the Supporting Information (Figure S1 ).
In the internal standard method, standard curves were obtained by varying the proportions of each substance and the internal standard can be found in the Supporting Information (Figure S2 ). The correction factor for each substance was calculated with Equation (1), and the mass of the various substances in the sample was calculated with Equation (2). The goodness of fit (R2) for each standard reached 0.999.
The subscript i represents CB, o -NCB, p -NCB, m -NCB or DNCB. The subscript s represents nitrobenzene, f is the correction factor obtained from the standard curve, A is the liquid chromatographic peak area, and m is the mass of the substance in the sample.
The CB conversion can be calculated with the following equations:
where c is the molar concentration of the substance in the sample, M is the molar mass of the substance, andX CB is the CB conversion.
The selectivity of each product can be calculated with the following equations:
where S NCB is the selectivity of mononitrochlorobenzene and S DNCB is the selectivity of DNCB.
The residence time in the capillary is calculated with the following equation:
where V is the volume of the capillary andQ or and Q ac are the volumetric flow rates of the two solutions, respectively.