Comparative Study between 2‐Furonitrile and 2‐Cyanopyridine as Dehydrants in Direct Synthesis of Dialkyl Carbonates from CO₂ and Alcohols over Cerium Oxide Catalyst

Abstract

The shift of equilibrium by removing water with nitrile dehydrants is crucial for CeO2‐catalyzed synthesis of dialkyl carbonates from CO2 and alcohols. Two nitriles – 2‐cyanopyridine and 2‐furonitrile – were previously found as effective dehydrants, yet their detailed comparison as well as exploration of potential of 2‐furonitrile remain insufficient. Herein, the performance of 2‐cyanopyridine and 2‐furonitrile was compared in the synthesis of various dialkyl carbonates. 2‐furonitrile was found to be superior to 2‐cyanopyridine in the synthesis of dialkyl carbonates from CO2 and bulky or long‐chain (≥C3) alcohols. Namely, the yield of diisopropyl carbonate (up to 50 %) achieved using CeO2 and 2‐furonitrile is comparable to or even higher than previously reported ones. Meanwhile, 2‐cyanopyridine acted as a better dehydrant than 2‐furonitrile in the synthesis of dimethyl carbonate and diethyl carbonate. The adsorption experiments and density functional theory calculations have indicated that the better performance of 2‐furonitrile compared to 2‐cyanopyridine in the synthesis of dialkyl carbonates from bulky or long‐chain alcohols is due to the weaker interaction of 2‐furonitrile with the CeO2 surface. Such weak interaction of 2‐furonitrile offers a larger reaction field on the catalyst surface for both CO2 and alcohols.

Sustainable synthesis of diethyl carbonate from carbon dioxide and ethanol featuring acetals as regenerable dehydrating agents

“…5 Compared to traditional procedures such as Bayer phosgenation, 6 ENIChem oxidative carbonylation, 7,8 and Asahi-Kasei indirect trans -esterification, 9 the direct synthesis of DEC from CO 2 and ethanol (EtOH) offers the benefit of higher sustainability, with DEC yield strongly depending on the catalyst-dehydrating agent combination due to the severe limitation originated from chemical equilibrium. 10 High DEC yields were achieved by combining CeO 2 as a catalyst 11 with 2-cyanopyridine, 12 2-furonitrile, 13,14 acetonitrile, 15 benzonitrile, 16 butylene oxide, 17 chloroacetate, 18 and orthoesters 19 as dehydrating agents, although the efficient regeneration of these agents remains challenging.…”

Dialkyl Carbonate Synthesis Using Atmospheric Pressure of CO2

“…The development of catalysts lowering the activation energy is one of the important factors to effectively convert inert CO 2 into DRC . Thus, the combination of catalysts and dehydrating agents has been explored and includes Ti­(IV) compounds, Sn­(IV) compounds, or CeO 2 –ZrO 2 with acetal, − choline hydroxide/MgO or CeO 2 with epoxide, − CeO 2 with 2-cyanopyridine, Cu-doped CeO 2 with methyl trichloroacetate, CeO 2 with orthoester, and CeO 2 with 2-furonitrile . Imidazolium bicarbonate has been reported to function as both a dehydrating agent and a catalyst. , Despite the significant efforts devoted to this research area, achieving high yields of DRC using low-pressure CO 2 remains a challenging task.…”