The reactions under CO2 pressured conditions were carried out in a stainless steel reactor (SUS 304, 30 mL, TVS-5 type). Thus, butylamine (2.9 g, 40 mmol), Ph3SbO (370 mg, 1.0 mmol), P4S10 (890 mg, 2.0 mmol), and benzene (20 mL) were charged into the reactor, and then CO2 was introduced at a pressure of 4.9 MPa (50 kg cm-2, ca. 65 mmol) at room temperature. The reactor was heated at 80 ℃ in a temperature-regulated incubator for 12 h. When a reaction temperature higher than 100 ℃ was necessary, an oil bath was used. After the heating, the reactor was cooled and carefully decompressed. The contents were treated with hot benzene (3×20 mL) and filtered to remove an insoluble residue containing the catalyst and phosphoric acid derivatives. The collected benzene solution was then concentrated to dryness in vacuo with cooling. Pure 1,3-dibutylurea was isolated by recrystallization from ligroin (yield 2.99 g, 88%).
