Polysulfide-assisted urea synthesis from carbon monoxide and ammonia in water

Efficient conversion of carbon monoxide into urea in an aqueous ammonia solution was demonstrated through coupling with the elemental sulfur reduction to polysulfides. This reaction starts with a simple mixture of carbon monoxide, ammonia, elemental sulfur, and a small amount of hydrogen sulfide for polysulfide formation, enabling an almost complete conversion of 1 atm of carbon monoxide to urea (95–100% yield) within 216, 64, and 32 h at 35 °C, 50 °C, and 65 °C, respectively. Polysulfides control the overall reaction rate while suppressing the accumulation of a by-product, hydrogen sulfide, to less than 1 Pa. These functions follow simple kinetic and thermodynamic theories, enabling prediction-based reaction control. This operational merit, together with the superiority of water as a green solvent, suggests that our demonstrated urea synthesis is a promising option for sulfur utilization beneficial for agricultural production.