Chip-based on-line nanospray MS method enabling study of the kinetics of isocyanate derivatization reactions

The reaction of propyl isocyanate (2), benzyl isocyanate (3), and toluene-2,4-diisocyanate (4) with 4-nitro-7-piperazino-2,1,3-benzoxadiazole (1) to yield the corresponding urea derivatives 5 was carried out in a continuous flow glass microfluidics chip. Real-time monitoring of the derivatization reactions was done by electrospray ionization mass spectrometry, making use of a recently reported modular chip-MS interface. Rate constants of 1.5 × 104, 5.2 × 104, and 2.4 × 104 M-1 min-1 were determined for 2, 3, and 4, respectively. Using macroscale batch conditions, the rate constants are 3-4 times lower. The faster on-chip kinetics is attributed to the more efficient molecular diffusion in the micrometer-sized channel.