Process for the preparation of methylene diphenylene diisocyanates and polymethylene polyphenylene poly (diisocyanates)

摘要

An improved process is provided for the preparation of methylene diphenylene diisocyanates (MDI) and polymethylene polyphenylene poly (diisocyanates) by the thermal decomposition of a methylene diphenylene bis (dialkylurea) or a polymethylene polyphenylene poly (dialkylurea) in a solvent in the presence of a tertiary amine hydrohalide, such as pyridine hydrochloride, as a promoter for conversion of the urea groups to the corresponding isocyanate.