The one-pot synthesis of methylene diphenyl-4,4′-dicarbamate

Abstract

Methylene diphenyl-4,4′-dicarbamate (MDC) is an intermediate for the preparation of methylene diphenyl diisocyanate. This paper reports the one-pot synthesis of MDC using aniline, dimethyl carbonate, and formalin as raw materials. Phenyl N-methyl carbamate (MPC) synthesis was carried out in a batch reactor using Zn(OAc)2 as the catalyst, following which, without any separation, an Hβ catalyst and formalin were added to continue to MPC condensation to give MDC. It was found that there were interactions between the MPC synthesis and MPC condensation, such that the presence of aniline could inhibits MPC condensation. Zn(OAc)2 was also found to adsorb on the Hβ surface to form Si–O–Zn bonds during the condensation, decreasing the quantity of strong acid sites on the Hβ and reducing the catalytic performance. Under the optimal conditions for the one-pot synthesis of MDC, aniline conversion was 100% and the MDC yield was 73.9% (based on HCHO). The deactivated catalyst could be easily regenerated by treatment with acetic acid. The filter cake was dried and calcined to obtain regenerated Hβ and the filtrate was dried by vacuum rotary evaporation to obtain Zn(OAc)2. No significant loss in catalytic activity was observed for the regenerated catalyst.