One-pot catalytic synthesis of urea derivatives from alkyl ammonium carbamates using low concentrations of CO2

To reduce anthropogenic carbon dioxide (CO2) emissions, it is desirable to develop reactions that can efficiently convert low concentrations of CO2, present in exhaust gases and ambient air, into industrially important chemicals, without involving any expensive separation, concentration, compression, and purification processes. Here, we present an efficient method for synthesizing urea derivatives from alkyl ammonium carbamates. The carbamates can be easily obtained from low concentrations of CO2 as present in ambient air or simulated exhaust gas. Reaction of alkyl ammonium carbamates with 1,3-dimethyl-2-imidazolidinone solvent in the presence of a titanium complex catalyst inside a sealed vessel produces urea derivatives in high yields. This reaction is suitable for synthesizing ethylene urea, an industrially important chemical, as well as various cyclic and acyclic urea derivatives. Using this methodology, we also show the synthesis of urea derivatives directly from low concentration of CO2 sources in a one-pot manner.


General information S2
Synthesis of ammonium carbamate salts using high purity CO2 gas S2 Synthesis of 2-ammonioethylcarbamate from CO2/N2 mixed gas (v:v = 15:85) or ambient air S6 Determination of conversion yield for ethylenediamine during CO2 bubbling S10 Catalyst performance for ethylene urea synthesis S11 Investigation of activation energy for ethylene urea synthesis S12 Synthesis of urea derivatives S13 Copies of NMR spectra for urea derivatives S17 One-pot synthesis of urea derivatives S27 Pressure change during reaction of 3a synthesis S27 Supplementary References S28

General Information
All commercial amines and catalysts except Cp2Ti(OTf)2 were purchased from TCI, FUJIFILM Wako Pure Chemical or Sigma-Aldrich and used without any purification. Cp2Ti(OTf)2 were synthesized according to the literature method 1 and stored in a glove box. EtOH and n-hexane for ammonium carbamate salts synthesis were purchased from FUJIFILM Wako Pure Chemical as a special grade and used without further purifications. Solvents for urea synthesis except DMI, NMP, and 2-pyrroridone were purchased from FUJIFILM Wako Pure Chemical as super dehydrated grade and used in a glove box without any purifications. DMI, NMP and 2-pyrroridone were purchased from TCI, and used in a glove box after drying with activated molecular sieve 4A purchased from Kanto Chemical
After filtration, washing with n-hexane and drying under reduced pressure for 4 h, this compound was obtained as white powder.

Benzylammonio benzylcarbamate (2a)
This compound was synthesized from 44.5 g (415 mmol) of benzylamine in 300 mL of n-hexane at an 500 mL eggplant flask for 10 min CO2 bubbling. After filtration to afford a precipitate, CO2 was bubbled to the filtrate again.
These operations were conducted three times. Then, washing the obtained solid with n-hexane and drying under reduced pressure, this compound was obtained as white powder.

S11
Catalyst performance for ethylene urea synthesis.

Investigation of activation energy for ethylene urea synthesis
Activation energy Ea for ethylene urea synthesis were calculated from Arrhenius plot ( Supplementary Fig. 3 and Eq. 1), which was based on reaction results using 95.8 mg (200 mol, 10mol%) of Cp2Ti(OTf)2 as a catalyst, 208 mg

Synthesis of urea derivatives
All urea derivatives were synthesized by a similar method. Therefore, a procedure of 2-imidazolidinone is shown as an example for typical urea derivative synthesis herein. The different aspects such as substrate amount are described in sections for each compound. 1.04 g (10.0 mmol) of 1a, 95.2 mg (200 mol, 2 mol%) of Cp2Ti(OTf)2 and 4.5 mL of DMI were added to an 5 mL autoclave reactor vessel and completely shielded with a stainless plate gasket. The vessel was dunked in a heated oil bath, and the reaction solution was stirred at 170 ºC for 24 h. After reaction, the vessel was removed from the oil bath and cooled to room temperature. The reaction mixture was extracted with MeOH (ca. 20 mL) and 1,3,5-trimethylebenzene (~100 mg) was added as an internal standard for 1 H NMR to determine NMR yield.