Carbamate Synthesis on Pd/C Catalysts:  Gas−Solid versus Slurry Processes

Abstract

Carbamate synthesis has been studied over NaI-Pd/C in slurry, gas-solid, and tubular reactors at 373-438 K and 0.41-7.61 MPa. The gas-solid carbamate synthesis process in which the CO, O 2 , methanol, and aniline reactants are present in the gas phase and the catalyst is in solid form occurs at a significantly higher rate than the slurry-phase synthesis in which CO and O 2 dissolve in the liquid methanol/aniline mixture. The high rate of the gas-solid carbamate synthesis compared with that of the slurry-phase synthesis can be attributed to (i) the intimate contact between the NaI promoter and the Pd on the carbon surface, (ii) the absence of solubility limitations in the gas-solid synthesis, and (iii) the slowing of the sintering of the Pd particles. Reaction pathway studies show that the direct oxidative carbonylation of aniline with methanol is the most effective pathway for carbamate synthesis. A low-cost, environmentally benign carbamate synthesis for the replacement of the isocyanate synthesis from phosgene/amine can be developed by coupling the high rate of the gas-solid synthesis with its intrinsic advantage of ease of catalyst recovery.

One Pot Synthesis of Methyl N-Phenyl Carbamate from Aniline, Urea and Methanol

“…Synthesis of isocyanate via a phosgene free route has attracted much interest of researchers due to the drawbacks originated by phosgene [1]. Preparing isocyanate by a decomposition method from carbamate is commended as a promising way among the reported nonphosgene routes.…”

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

“…Numerous examples of homogeneous and heterogeneous catalysts have been shown to exhibit high selectivities toward carbamates in oxidative carbonylation of aniline or aliphatic amines. [3][4][5][6][7][8][9][10][11][12][13][14] The reaction of oxidative car-bonylation of aniline to the desired carbamate can be written as follows:…”

“…Reviewing previous studies, most carbonylation reactions have been carried out batchwise; little has been done for the continuous process, and reports regarding the recovery of catalysts as well as the deactivation phenomenon are also rather rare. Recently, Toochinda and Chuang 13 have reported a gas-solid oxidative carbonylation reaction in a semibatch fixed-bed reactor wherein a two-step synthe-sis via diphenyl urea was carried out using NaI-Pd/C catalyst. The semi-continuous carbamate synthesis proceeded for only two hours with 80.2% of aniline conversion and 74.8% carbamate yield.…”

Síntese e emprego do [Pd(dmba)(NCO)(PPh3)] em processos catalíticos envolvendo a preparação de derivados da uréia e de alcoxicarbonil complexos

“…Reações entre nitrocompostos e aminas, quando catalisadas por compostos de platina [3][4][5][6], sofrem influência significativa do sistema empregado. Assim, quando um complexo de platina (II) é utilizado com cloreto de estanho (IV) e trietilamina, resultam produtos com altos rendimentos.…”

“…A ausência do cloreto de estanho (IV) ou trietilamina, diminui drasticamente o rendimento da reação catalítica. A temperatura ideal para estas reações segundo a literatura [3][4][5][6] é 140 ºC, sendo constatado um decréscimo acentuado no rendimento a 100 ºC.…”