Imidazolium-Catalyzed Synthesis of an Imidazolium Catalyst

• Published in: Origins of life and evolution of biospheres Vol. 49; no. 4; pp. 199 - 211
• Main Authors: Weber, Arthur L., Rios, Andro C.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.12.2019; Springer Nature B.V
• Subjects: Acetic acid; Acetonitrile; Acids; Astronomy; Astrophysics and Astroparticles; Biochemistry; Biomedical and Life Sciences; Catalysis; Catalysts; Earth Sciences; Formaldehyde; Furfural; Imidazoles - chemistry; Life Sciences; Observations and Techniques; Origin of Life; Prebiotic Chemistry; Yield; Catalytic feedback; Imidazolium catalysis; Origins of life; Reflexive catalysis; Maillard reaction; Prebiotic; Benzoin condensation
• ISSN: 0169-6149; 1573-0875
• DOI: 10.1007/s11084-019-09589-2

The chemistry of imidazolium-catalyzed imidazolium synthesis was studied as part of an effort to develop a plausible prebiotic synthesis of a small catalytic molecule capable of catalyzing its own synthesis. Specifically, we investigated the one-pot 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) catalyzed synthesis of 1,3-dibutyl-4,5-difuryl-imidazolium acetate (DBDFIM-Ac) from furfural, n-butylamine, formaldehyde, and acetic acid at 80 °C. Liu et al. ( 2012 ) had previously demonstrated the first reaction of the synthetic process, the EMIM-Ac catalyzed benzoin condensation of furfural that yields furoin. Our early studies established the second reaction of the synthetic process, the multicomponent reaction of furoin, n-butylamine, formaldehyde, and acetic acid that yields the imidazolium salt, DBDFIM-Ac. Studies of the complete two-reaction process that uses furfural for the synthesis of DBDFIM-Ac showed that the highest yield of DBDFIM-Ac was obtained when the mole ratio of n-butylamine, formaldehyde, and acetic acid relative to furfural was respectively (0.5:0.25:0.25:1.0-furfural), or one-half of the stoichiometric ratio (1.0:0.5:0.5:1.0-furfural). A time course study of the process showed transient formation of furoin, the obligatory reaction intermediate. DBDFIM-Ac and the imidazolium side product, 1,3-dibutyl-4,5-trifuryl-imidazolium acetate (DBTFIM-Ac), were stable under the reaction conditions. Imidazolium products (DBDFIM and DBTFIM) and the furoin intermediate were not formed in control reactions (80 °C, 24 h) in which EMIM catalyst was either absent or replaced with an equal volume of acetonitrile or DMF. The imidazolium product, DBDFIM-Ac, was shown to catalyze the synthesis of structurally similar 1,3-dipentyl-4,5-difuryl-imidazolium acetate (DPDFIM-Ac) from furfural, n-pentylamine, formaldehyde, and acetic acid at 80 °C.