1H NMR analysis of the tolylene-2,4-diisocyanate–methanol reaction

Abstract

Tolylene-2,4-diisocyanate (2,4-TDI) 1 reacts with methanol through two simultaneous paths in the polyurethane reaction, which involve two different intermediates – tolylene-4-carbamatic-2-isocyanate 2 and tolylene-2-carbamatic-4-isocyanate 3, and the final product is tolylene-2,4-dicarbamate 4. The –CH 3 chemical shifts in benzene ring in compounds 1, 2, 3 and 4 can be easily tested and well distinguished, through which those four compounds are quantified and their kinetics are investigated. It shows that four rate constants for the tolylene-2,4-diisocyanate–methanol reaction in CCl 4 at 50 °C are k 1 = 9.6 × 10 −2 h −2 mol −2 min −1, k 2 = 1.4 × 10 −2 h −2 mol −2 min −1, k 3 = 4.0 × 10 −3 h −2 mol −2 min −1, k 4 = 1.4 × 10 −3 h −2 mol −2 min −1. ( k 1 is the reaction rate constant from compounds 1 to 2; k 2 is the reaction rate constant from compounds 1 to 3; k 3 is the reaction rate constant from compounds 3 to 4; k 4 is the reaction rate constant from compounds 2 to 4).