Electrochemical behaviour of 9-methylcaffeinium iodide and in situ electrochemical synthesis of hymeniacidin

• Published in: Electrochimica acta 2018-08, Vol.280, p.71-76
• Main Authors: Pandolfi, Fabiana, Mattiello, Leonardo, Zane, Daniela, Feroci, Marta
• Format: Article
• Language: English
• Subjects: 9-Methylcaffeinium iodide; Animals; Caffeine; Chemical compounds; Chemical synthesis; Cyclic voltammetry; Differential pulse voltammetry; Electrochemical analysis; Electrochemical reduction; Electrolysis; Hymeniacidin; Natural products; Reaction products; Ring opening; Voltammetry
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2018.05.073

9-Methylcaffeinium iodide, a bio-based salt obtained by reaction of caffeine with methyl iodide, is an imidazolium salt. The electrochemical behaviour of 9-methylcaffeinium iodide was studied by means of cyclic voltammetry, differential pulse voltammetry and electrolysis. Its behaviour revealed to be very similar to that of common imidazolium salts. In fact, its cathodic reduction yielded the corresponding N-heterocyclic carbene, which was evidenced by its reaction products with dioxygen and with sulfur, although in low amounts. In fact, this electrogenerated carbene was very unstable and prone to add water, yielding a ring opening product (hymeniacidin) in high yield. Hymeniacidin is a natural product from the marine sponge Hymeniacidon sp. The voltammetric behaviour of isolated hymeniacidin confirmed the in situ formation of this ring opening product, by comparison of the voltammetric peak potentials of starting caffeinium salt and hymeniacidin. This study allowed to determine that hymeniacidin derives from NHC, and not by hydrolysis of the caffeinium salt. [Display omitted] •Caffeine is a bio-based starting material for the synthesis of 9-methylcaffeinium iodide.•Electroreduction of 9-methylcaffeinium iodide gives hymeniacidin in high yield.•Cyclic voltammetry allows to identify the caffeine carbene formation.•DPV highlights diffusional control for carbene oxidation.•Caffeine carbene formation is demonstrated by theacrine isolation.