Quaternary ammonium hydroxide as a metal-free and halogen-free catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide

Tadashi Ema, Kazuki Fukuhara, Takashi Sakai, Masaki Ohbo, Fu Quan Bai, Jun Ya Hasegawa

Research output: Contribution to journalArticle

72 Citations (Scopus)


Tetrabutylammonium hydroxide (TBAH) and other quaternary ammonium hydroxides catalyzed the cycloaddition of CO2 to epoxides under solvent-free conditions to give cyclic carbonates. When TBAH was exposed to CO2, TBAH was converted into tetrabutylammonium bicarbonate (TBABC), which was a catalytically active species. A D-labeled epoxide and an optically active epoxide were used to study the reaction mechanism, which invoked three plausible pathways. Among them, path A seemed to be predominant; the bicarbonate ion of TBABC attacks the less hindered C atom of the epoxide to generate a ring-opened alkoxide intermediate, which adds to CO2 to give a carbonate ion, and the subsequent cyclization yields a cyclic carbonate. Density functional theory (DFT) calculations successfully delineated the potential energy profile for each reaction pathway, among which path A was the lowest-energy pathway in accordance with the experimental results. The tetrabutylammonium (TBA) cation carries the positive charges on the H atoms, but not on the central N atom, and the positively charged H atoms close to the central N atom form an anion-binding site capable of stabilizing various anionic transition states and intermediates.

Original languageEnglish
Pages (from-to)2314-2321
Number of pages8
JournalCatalysis Science and Technology
Issue number4
Publication statusPublished - Apr 1 2015


ASJC Scopus subject areas

  • Catalysis

Cite this