A Non‐Phosgene Route Synthesis of Carbamate in Continuous Fixed Bed Reactor

Abstract

A non-phosgene route synthesis of carbamate was carried out in a continuous fixed-bed reactor through oxidative carbonylation of aniline using palladium catalysts and sodium iodide as promoter. The activity, selectivity and stability of both carbon and alumina-supported palladium catalysts were evaluated. It was found that the alumina-supported catalyst system exhibited a higher activity and selectivity than that of the carbon-supported system, and an average aniline conversion of 95.6% and carbamate selectivity of 74.6% were achieved for the Se-Pd/Al 2 O 3 catalyst after 91 h on stream. Reclamation analysis of the spent Pd/C catalyst suggested that the deactivation was mainly due to the leaching and sintering of palladium metal and the accumulation of insoluble chemicals on catalyst support also aggravated the decline of catalyst activity. When small amounts of selenium were added to the Pd/Al 2 O 3 catalyst, its activity, selectivity and stability were significantly improved which indicated that a promotional effect existed for carbamate formation on a Pd-Se catalyst system.

Palladium/iodide catalyzed oxidative carbonylation of aniline to diphenylurea: Effect of ppm amounts of iron salts

“…The promoting effect of iodide/iodine was first reported by Fukuoka while employing a heterogeneous catalyst [44][45][46][47], but the activity of this system was quite low. The activity of heterogeneous systems has been later improved by others [48,51,52,54,63,69,71], but the turnover frequencies (TOF) that can be obtained are nevertheless one or two orders of magnitude lower than those achievable with the use of homogeneous palladium catalysts. We thus decided to focus on homogeneous systems.…”