NMR对MDI在稀溶液中水解反应机理的表征

采用核磁共振波谱(NMR)研究了二苯基甲烷二异氰酸酯(MDI)在稀溶液中的水解反应机理.将同一MDI样品分别溶解在氘代氯仿、氘代丙酮和加入少量水分的氘代二甲基亚砜溶剂(DMSO)中,进行核磁共振氢谱(1H NMR)、核磁共振碳谱(13C NMR)测试.结果显示,MDI在含水的DMSO溶剂中测得的谱图与氘代氯仿、氘代丙酮中的差别显著.对该溶液进行了13C-1H异核近程相关(HMQC)、13C-1H异核远程相关(HMBC)及碳原子级数(DEPT 135)测试,并利用经验公式对其进行了详细归属,确认了反应产物的结构.分析得知MDI在含水溶剂中迅速反应,异氰酸酯基转化为脲基和氨基基团.异氰酸酯与水反应生成氨基基团,其与异氰酸酯反应活性比水高,对位取代氨基与水的竞聚率比值为7.1,邻位为1.4,对位取代氨基活性约是邻位的5倍.

Characterization of Hydrolyzing of Diphenylmethane Diisocyanate in Dilute Solution by NMR

The mechanism of the hydrolysis reaction of diphenylmethane diisocyanate(MDI) in dilute solution was studied by NMR.MDI was dissolved in CDCl3,(CD3)2CO and deuterated diphenyl sulfoxide(DMSO) containing a small quantity of water,respectively,and then were analyzed by 1H NMR and 13C NMR,respectively.The results indicated that the NMR spectrum of MDI in water-containing DMSO solvent was quite different from those in CDCl3 and (CD3)2CO solvents.MDI in DMSO solvent was further studied by 13C-1H heteronuclear multiple-quantum coherence(HMQC),13C-1H heteronuclear multiple-bond correlation(HMBC) and distortionless enhancement by polarization transfer(DEPT 135),respectively,and its corresponding spectra were assigned with the aid of empirical formula.The structures of the products were also confirmed.It was found that MDI reacted rapidly with the water in DMSO,and the isocyanate group transformed into para-/ortho-substituted urea group and para-/ortho-substituted amino group.The reactivity of water with amino group produced from the reaction of isocyanate with water was higher than that of water with isocyanate.The reactivities of water with para-and ortho-substituted amino group were 7.1 and 1.4,respectively.Hence,the effect of water content should be taken into consideration when water-containing DMSO is used as solvent for NMR analysis.