Typical synthesis of quinazoline-2,4(1H,3H)-dione (3a)

A stock solution of 2-aminobenzonitrile (0.1 M) in DMSO was prepared. The reaction was proceeded by infusing a solution of 2-aminobenzonitrile (flow rate 3–5 μl min⁻¹) to the upper PDMS channel and pure CO₂ gas with flow rate 30–50 μl min⁻¹ to the lower SiNWs channel of microreactor using individual leak proof syringe. Residence time of reactant and flow rate of gas were varied to obtain the product with different yields determined by GC–MS. The highest yield (97%) was achieved at 3 μl min⁻¹ flow rate at 251 s retention time of 2-aminobenzonitrile (Table 2, Entry 3). After completion of reaction, DCM was infused to the outlet of the microreactor. The product (quinazoline-2,4(1H,3H)-dione) was precipitated in DCM to obtain by filtering, while reactant (2-aminobenzonitrile) was dissolved to be drained out. Molar ratio of CO₂ to 2-aminobenzonitrile was varied from 3.1 to 5.2 as calculations are given in Supplementary Methods.