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Delineating the Mechanism of Ionic Liquids in the Synthesis of Quinazoline‐2,4(1 H ,3 H )‐dione from 2‐Aminobenzonitrile and CO 2
Author(s) -
Hulla Martin,
Chamam Sami M. A.,
Laurenczy Gabor,
Das Shoubhik,
Dyson Paul J.
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201705438
Subject(s) - catalysis , chemistry , ionic liquid , deprotonation , quinazoline , conjugate , medicinal chemistry , conjugate acid , reaction mechanism , base (topology) , ion , combinatorial chemistry , inorganic chemistry , organic chemistry , mathematical analysis , mathematics
Ionic liquids (ILs) are versatile solvents and catalysts for the synthesis of quinazoline‐2,4‐dione from 2‐aminobenzonitrile and CO 2 . However, the role of the IL in this reaction is poorly understood. Consequently, we investigated this reaction and showed that the IL cation does not play a significant role in the activation of the substrates, and instead plays a secondary role in controlling the physical properties of the IL. A linear relationship between the p K a of the IL anion (conjugate acid) and the reaction rate was identified with maximum catalyst efficiency observed at a p K a of >14.7 in DMSO. The base‐catalyzed reaction is limited by the acidity of the quinazoline‐2,4‐dione product, which is deprotonated by more basic catalysts, leading to the formation of the quinazolide anion (conjugate acid p K a 14.7). Neutralization of the original catalyst and formation of the quinazolide anion catalyst leads to the observed reaction limit.