Synthesis of Methyl N-Phenyl Carbamate Catalyzed by Ionic Liquid-Promoted Zinc Acetate

Enhanced Performance of Zirconium-Doped Ceria Catalysts for the Methoxycarbonylation of Anilines

The methoxycarbonylation of anilines stands as an attractive method for the phosgene-free production of carbamates. Despite the high yields obtained for ceria catalysts, the reduction of the amount of side products and the prevention of catalyst deactivation still represent major hurdles in this chemistry. One advantage of ceria is the possibility of tuning its reactivity by doping its lattice with other metals. In the present work, a series of doped ceria-based materials, prepared by substitution with metals, are evaluated in the methoxycarbonylation of 2,4-diaminotoluene with dimethyl carbonate. Among all catalysts, containing Eu, Hf, La, Pr, Sm, Tb, Y or Zr, ceria promoted with 2 mol % Zr exhibited 96 % selectivity towards the desired carbamates, improving the pure CeO₂ catalyst. Density functional theory demonstrates that two descriptors are needed: 1) a geometric factor that governs the reduction of energy barriers for carbamate formation through ureas; 2) catalyst basicity as N-H bonds need to be activated. Assessment in subsequent reaction cycles revealed that the CeO₂ -ZrO₂ catalyst is more stable than bulk CeO₂ , along with the reduction of fouling processes.

An Escape from Noble Metals for Generating Urethanes via Reductive Carbonylation of Nitroarenes over FeSe2/γ-Al2O3 †

The reaction of FeCl3, SeO2, and Pyridine (Py) in the presence of methanol (MeOH) under CO pressure generates a black precipitate, which has been confirmed as ferric di-selenide, FeSe2 through different structure characterization methods. Furthermore, impregnation of 5 wt% of FeSe2 onto γ-Al2O3 exhibits better catalytic performance than FeSe2 due to the highly dispersed and smaller particle sizes ca. 200–300 nm. The reductive carbonylation of nitrobenzene (NB) was investigated over FeSe2/γ-Al2O3 as a heterogeneous catalyst, delivering an excellent yield and high selectivity of methyl-N-phenyl carbamate (MPC). Moreover, a set of reactions was performed with variation in the reaction time, temperature, and pressure to investigate the effects of these factors. In particular, FeSe2/γ-Al2O3 is highly stable and can be recycled for up to five cycles without significant loss in catalytic performance. A mechanistic study was also conducted on this low-cost catalyst system, especially proposing a crucial role of FeSe2 (μ-CO) active species.

Zn/Al/Pb Mixed Oxides as Efficient Heterogeneous Catalysts for the Synthesis of Methyl N-Phenyl Carbamate

Dimethyl carbonate aminolysis is an effective and green pathway for the synthesis of methyl N-phenyl carbamate (MPC), which is an important intermediate for the synthesis of polyurethanes and many other chemicals. In this work, we demonstrate the fabrication of Zn/Al/Pb mixed oxides as efficient and stable heterogeneous catalysts for MPC synthesis. The catalysts are prepared via facile coprecipitation and subsequent thermal annealing. Their micromorphology and physical-chemical properties are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM (STEM), X-ray photoelectron spectroscopy (XPS), and NH3-TPD. The results show that rather than being doped into ZnO and/or Al2O3, PbO is highly dispersed in the ZnO/Al2O3 base forming ultrafine nanoparticles. Despite the weak interactions within the mixed oxides, the high density of active sites generates outstanding catalytic activity and cycling stability for MPC synthesis, with an aniline conversion of almost 100% and MPC yield of up to 90% during six repeated tests, providing great potential for their further application.

Bmim[OAc]-Cu2O/g-C3N4 as a multi-function catalyst for sonophotocatalytic degradation of methylene blue

In this study, ionic liquid, 1-butyl-3-methylimidazolium acetate (Bmim[OAc]) modified cuprous oxide immobilized over graphitic carbon nitride (Bmim[OAc]-Cu₂O/g-C₃N₄) as an efficient heterogeneous catalyst was successfully prepared by depositing Bmim[OAc]-Cu₂O over the surface of g-C₃N₄. The deposition of cuprous oxide over the surface of g-C₃N₄ leads to the formation of a heterojunction that promotes the charge separation. Cu₂O enhances the degradation capability owing to its dual function where it acts as a photocatalyst and Fenton like catalyst. Bmim[OAc] plays a vital role in trapping the photogenerated electrons, which in turn reduce the chances of electron-hole pairs recombination. Sonophotocatalytic degradation of methylene blue (MB) was investigated using the prepared Bmim[OAc]-Cu₂O/g-C₃N₄ at room temperature and pH = 7 in presence of ultraviolet (UV, 6 W, λ = 254 nm) and ultrasonic (US, 20 kHz) as a dual irradiation system and H₂O₂ as an oxidant. Only 30 min of dual irradiation was enough for Bmim[OAc]-Cu₂O/g-C₃N₄ (0.1 gL^-1) to achieve a complete degradation using 10 mM H₂O₂ at 25 °C and pH = 7. The value of band gap of tested catalyst plays a vital role in boosting the degradation capability of the sonophotocatalytic system through the generated reactive radicals especially the hydroxyl radicals and superoxide radicals, which play a major role in the system. The kinetics of the reaction was investigated and the activation energy was calculated from the slope of the Arrhenius plot and found to be 19.77 kJ/mol.

Zr-MOF-808@MCM-41 catalyzed phosgene-free synthesis of polyurethane precursors

Zr-MOF-808@MCM-41 exhibited high catalytic activity, selectivity and stability for the synthesis of aromatic carbamates from aromatic amines and dimethyl carbonate.

Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors

Methyl N-phenyl carbamate (MPC) is an important intermediate for the green synthesis of methylene diphenyl diisocyanate (MDI) as well as many other important products. In the present work, Zn/Al/Ce mixed oxides derived from hydrotalcite-like precursors were employed as effective and recoverable heterogeneous catalyst for MPC synthesis via DMC aminolysis. Zn/Al/Ce hydrotalcite-like precursors prepared via coprecipitation method and the resulting catalysts were characterized by means of XRD, BET, SEM and XPS. Strong interactions within the Zn/Al/Ce mixed oxides were observed via the addition of appropriate amount of cerium. The mixed oxides containing 2.5% cerium showed high DMC aminolysis activity giving aniline conversion of 95.8%, MPC selectivity of 81.6% and MPC yield of 78.2%. Moreover, as a heterogeneous catalyst, it also exhibited superiorities of easy recovery and recyclable stability for MPC synthesis.

Zn/Al/Ce mixed oxides derived from hydrotalcite-like precursors were employed as effective and recoverable heterogeneous catalyst for MPC synthesis via DMC aminolysis.

Ionic liquid-mediated solvothermal synthesis of 4,4′-methylenediphenyl diisocyanate (MDI): an efficient and environment-friendly process

Mechanism for MDI synthesis via decomposition of MDC catalyzed by Zn(OAc)₂–[EAmim]BF₄.

Efficient and recyclable heterogeneous zinc alkyl carboxylate catalyst for the synthesis of N-phenyl carbamate from aniline and dimethylcarbonate

A heterogeneous salt catalyst with zinc alkyl carboxylate chemically bonded on silica was highly active and recyclable in the synthesis of MPC.