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

How To Get Isocyanate?

Isocyanate, a pivotal chemical intermediate to synthesize polyurethane with widespread applications in household appliances, automobiles, and construction, is predominantly produced via the phosgene process, which currently holds a paramount status in industrial isocyanate production. Nonetheless, concerns arise from the toxicity of phosgene and the corrosiveness of hydrogen chloride, posing safety hazards. The synthesis of isocyanate using nonphosgene methods represents a promising avenue for future development. This article primarily focuses on the nonphosgene approach, which involves the formation of carbamate through the reaction of nitro-amino compounds with carbon monoxide, dimethyl carbonate, and urea, among other reagents, subsequently leading to the thermal decomposition of carbamate to get isocyanate. This paper emphasizes the progress in catalyst development during the carbamate decomposition process. Single-component metal catalysts, particularly zinc, exhibit advantages such as high activity, cost-effectiveness, and compatibility with a wide range of substrates. Composite catalysts enhance isocyanate yield by introducing a second component to adjust the active metal composition. The central research direction aims to optimize catalyst adaptation to reaction conditions, including temperature, pressure, time, and solvent, to achieve high raw material conversion and product yield.

Reductive Carbonylation of Nitroarenes Using a Heterogenized Phen-Pd Catalyst

The reductive carbonylation of nitroarenes in the presence of MeOH and CO(g) is one of the interesting alternative routes without utilizing toxic phosgene and corrosive HCl generation for the synthesis of industrially useful carbamate compounds that serve as important intermediates for polyurethane production. Since homogeneous palladium catalysts supported by phen (phen = 1,10-phenanthroline) are known to be effective for this catalysis, the heterogenized Pd catalyst was developed using the phen-containing solid support. In this study, we report the synthesis of a phen-based heterogeneous Pd catalyst, Pd@phen-POP, which involves the solvent knitting of a phen scaffold via the Lewis-acid-catalyzed Friedel-Crafts reaction using dichloromethane as a source for linker in the presence of AlCl₃ as a catalyst. The resulting solid material has been thoroughly characterized by various physical methods revealing high porosity and surface area. Similar to the homogeneous pallidum catalyst, this heterogeneous catalyst shows efficient reductive carbonylation of various nitroarenes. The catalytic reaction using nitrobenzene as a model compound presents a high turnover number (TON = 530) and a reasonable turnover frequency (TOF = 45 h^-1), with a high selectivity (92%) for the carbamate formation. According to the recycling study, the heterogeneous catalyst is recyclable and retains ∼90% of the original reactivity in each cycle.