ZnCl₂/Urea Eutectic Solvent as Stable Carbonylation Source for Benign Synthesis of 2–Benzimidazolones and 2–Imidazolones: An Effective Strategy for Preventing NH₃ Gas Evolution

Abstract

The synthesis of 2‐benzimidazolone and 2‐imidazolone derivatives from urea as an inexpensive widely available carbonyl source is usually performed in high boiling organic solvents accompanied by ammonia evolution, due to urea decomposition. In this paper, a sustainable method has been introduced for the synthesis of these N,N‐heterocycles by employing zinc chloride:urea (1 : 3.5) type IV eutectic mixture under mild reaction conditions. No urea was used directly in the reaction owing to the fact that the eutectic mixture (containing urea itself) suffice to provide the carbonylation source. This new concept allowed the smooth conversion of a range of arene‐1,2‐diamines and benzoins to the corresponding N,N‐heterocycle in efficient yields. The remarkable advantage of this green protocol over other conventional heating procedures is that all reactions are conducted under open‐vessel conditions due to the absorption of the evolved ammonia by the eutectic mixture during the reaction process. (© WILEY‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Deep Eutectic Solvents as à-la-Carte Medium for Transition-Metal-Catalyzed Organic Processes

“…Therefore, arene-1,2-diamine derivatives were heated at 100 °C for 4 h in the aforementioned DES, affording seven examples of the corresponding 2-benzimidazolone derivatives in moderate-to-excellent yields. If benzoin derivates were employed instead of the diamine compounds, the corresponding 2-imidazolone products could be obtained in good yields, employing a method that avoids the generation of gas ammonia evolution ( Figure 14 , Table 2 , entry 10) [ 42 ].…”

The methodology for preparing domperidone: strategies, routes and reaction processes

“…2). [23][24][25][26][27][28] However, these catalytic systems have suffered from several drawbacks, such as the use of precious metals (Au, Pb and Ln etc. ), and the complex preparation process of catalysts.…”

Synthesis and Antimycobacterial Activity of 2,5-Disubstituted and 1,2,5-Trisubstituted Benzimidazoles

“…Among the reported methods for obtaining benzimidazoles, some utilize harsh (Gobis et al, 2015;Aghapoor et al, 2019) and others soft reaction conditions (Leutbecher et al, 2011;Sriramoju et al, 2018). Whereas, the former is carried out at a high temperature and with strong acids, the second is performed at or near room temperature (rt) in the presence of soft acids, mainly through heterogeneous catalysis.…”