Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

• Main Authors: Shinichi Yamabe, Wei Guan, Shigeyoshi Sakaki
• Format: Article
• Language: English
• Published: Beilstein-Institut 2013-01-01
• Series: Beilstein Journal of Organic Chemistry
• Subjects: basic hydrolyses; DFT calculations; ethyl benzoate; N-ethylbenzamide; reactive intermediates; transition states
• Online Access: https://doi.org/10.3762/bjoc.9.22

Reaction paths of base-catalyzed hydrolyses of isoelectronic substrates, Ph–C(=O)–X–Et [X = O (ethyl benzoate) and X = NH (N-ethylbenzamide)], were traced by DFT calculations. To simulate bond interchanges accompanied by proton transfers, a cluster model of Ph–C(=O)–X–Et + OH−(H2O)16 was employed. For X = O, three elementary processes and for X = NH four ones were obtained. The rate-determining step of X = O is the first TS (TS1, the OH− addition step), while that of X = NH is TS2. TS2 of X = NH leads to a novel Mulliken charge-transfer complex, Ph–(OH)(O=)C∙∙∙N(H2)–Et. The superiority or inferiority between the direct nucleophilic process or the general base-catalyzed process for TS1 was examined with the model Ph–C(=O)–X–Et + OH−(H2O)n, n = 3, 5, 8, 12, 16, 24 and 32. The latter process was calculated to be more favorable regardless of the number (n, except n = 3) of water molecules. The counter ion Na+ works unfavorably on the ester hydrolysis, particularly on TS1. A minimal model of TS1 was proposed and was found to be insensitive to n.