Unambiguous ¹³C‐NMR assignments for isocyanate carbons of isophorone diisocyanate and reactivity of isocyanate groups in <i>Z</i> ‐ and <i>E</i>‐stereoisomers

Abstract

Abstract Unambiguous 13 C‐NMR assignments for the primary ( prim ‐) and secondary ( sec ‐) isocyanate carbons of isophorone diisocyanate (IPDI) have been made by using two‐dimensional NMR measurements. On the basis of the assignments, relative reactivity of the prim ‐ and sec ‐isocyanate groups with n ‐butanol was studied by quantitative 13 C‐NMR analysis. The individual stereoisomers of IPDI ( Z ‐IPDI and E ‐IPDI) and their equimolar mixture were reacted with n ‐butanol (IPDI/ n ‐butanol = 2/1 molar ratio) at 50°C for 3 days. It was found that the sec ‐NCO is about 1.6 times more reactive than the prim ‐NCO in both Z ‐ and E ‐isomers. Reactivity of the E ‐isomer was found to be slightly higher than that of the Z ‐isomer. When di‐ n ‐butyltin dilaurate (DBTDL) was used as a catalyst, the reactivity of the sec ‐NCO became about 12 times higher than that of the prim ‐NCO with both isomers. In the case of 1,4‐diazabicyclo [2.2.2] octane (DABCO) catalyst, the prim ‐NCO was 1.2 times more reactive than the sec ‐NCO with both isomers.