Electrochemically Generated Iodine Cations from a Glassy Carbon Electrode for Highly Selective Iodination of Anisole

Abstract

The synthesis of aryl iodides from commercially available raw chemicals by simple, cheap and green strategies is of fundamental significance. Aryl iodides can undergo a series of homo-/cross-coupling reactions for the synthesis of important industrial chemicals and materials. Traditional methods require the electrophilic substitution on aromatic compounds by iodine or hypervalent iodine compounds, which suffers from the use of erosive halogens or hazardous oxidants. With the development of green chemistry in the field of electrochemical synthesis, anodic oxidation-derived I⁺ cations have been used for substitution reactions. However, the selectivity of the iodination by these electrochemical methods remains unsatisfactory. We believed that the anolyte is contaminated by trace platinum species from the working electrode. Herein, we report the generation of active I⁺ species from the anodic oxidation of I₂ in acetonitrile using a glassy carbon electrode. With the presence of H⁺, electrolyte prepared with a glassy carbon anode can react with anisole to selectively form 4-iodoanisole with a yield as high as 97%. On contrast, the electrolytes prepared from Pt and graphite anodes finished the reaction with yields of 16% and 60% for 4-iodoanisole, respectively. This electrochemical method also applies to the iodination of toluene, benzonitrile and bromobenzene, delivering the target para-iodination products with 92%, 84%, and 73% yields, respectively. Thus, an atom-efficient and highly selective aryl iodination method was developed without the use of excessive oxidants.

Keywords

Iodination / Electrochemistry / Anodic oxidation / Aryl iodides / Selectivity

References

[1] Varenikov A, Shapiro E, Gandelman M Decarboxylative halogenation of organic compounds. Chem Rev, 2021, 121(1): 412-484.

[2] Gallardo I, Soler S Electrochemically promoted arylation of iodoaromatics. J Electroanal Chem, 2017, 799: 9-16.

[3] Cheng LJ, Mankad NP Copper-catalyzed carbonylative coupling of alkyl halides. Acc Chem Res, 2021, 54(9): 2261-2274.

[4] Merritt EA, Olofsson B Diaryliodonium salts: a journey from obscurity to fame. Angew Chemie Int Ed Engl, 2009, 48(48): 9052-9070.

[5] Han YM, Bai LB, Lin JY, et al. Diarylfluorene-based organic semiconductor materials toward optoelectronic applications. Adv Funct Mater, 2021, 31(47): 2105092.

[6] Möckel R, Hilt G Synthesis of polysubstituted iodobenzene derivatives from alkynylsilanes and 1, 3-dienes via Diels-Alder/oxidation/iodination reaction sequence. Org Lett, 2015, 17(7): 1644-1647.

[7] Dong CP, Nakamura K, Taniguchi T, et al. Synthesis of aryl iodides from arylhydrazines and iodine. ACS Omega, 2018, 3(8): 9814-9821.

[8] Ilangovan A, Satish G Direct amidation of 2'-aminoacetophenones using I₂-TBHP: a unimolecular domino approach toward isatin and iodoisatin. J Org Chem, 2014, 79(11): 4984-4991.

[9] Dahiya A, Sahoo AK, Chakraborty N, et al. Updates on hypervalent-iodine reagents: metal-free functionalisation of alkenes, alkynes and heterocycles. Org Biomol Chem, 2022, 20(10): 2005-2027.

[10] Chandra A, Yadav NR, Moorthy JN Facile synthesis of isatins by direct oxidation of indoles and 3-iodoindoles using NIS/IBX. Tetrahedron, 2019, 75(14): 2169-2174.

[11] Yue X, Zhao W, Wang S, Zou Y Selective electrocatalytic hydrogenation of 5-hydroxymethylfurfural to 2,5-dihydroxymethylfuran on bimetallic PdCu alloy. Chinese J Struct Chem, 2022, 41(5): 2205063-2205069.

[12] Malapit CA, Prater MB, Cabrera-Pardo JR, et al. Advances on the merger of electrochemistry and transition metal catalysis for organic synthesis. Chem Rev, 2022, 122(3): 3180-3218.

[13] Yoshida JI, Shimizu A, Hayashi R Electrogenerated cationic reactive intermediates: the pool method and further advances. Chem Rev, 2018, 118(9): 4702-4730.

[14] Miller LL, Watkins BF Scope and mechanism of aromatic iodination with electrochemically generated iodine(I). J Am Chem Soc, 1976, 98(6): 1515-1519.

[15] Miller LL, Kujawa EP, Campbell CB Iodination with electrolytically generated iodine(I). J Am Chem Soc, 1970, 92(9): 2821-2825.

[16] Midorikawa K, Suga S, Yoshida JI Selective monoiodination of aromatic compounds with electrochemically generated I⁺ using micromixing. Chem Commun, 2006, 36: 3794-3796.

[17] Möckel R, Hille J, Winterling E, et al. Electrochemical synthesis of aryl iodides by anodic iododesilylation. Angew Chem Int Ed, 2018, 57(2): 442-445.

[18] Kataoka K, Hagiwara Y, Midorikawa K, et al. Practical electrochemical iodination of aromatic compounds. Org Process Res Dev, 2008, 12(6): 1130-1136.

[19] Chen R, Yang CJ, Cai WZ, et al. Use of platinum as the counter electrode to study the activity of nonprecious metal catalysts for the hydrogen evolution reaction. ACS Energy Lett, 2017, 2(5): 1070-1075.

[20] Imada Y, Okada Y, Noguchi K, et al. Selective functionalization of styrenes with oxygen using different electrode materials: olefin cleavage and synthesis of tetrahydrofuran derivatives. Angew Chemie Int Ed Engl, 2019, 58(1): 125-129.

[21] Rafiee M, Mayer MN, Punchihewa BT, et al. Constant potential and constant current electrolysis: an introduction and comparison of different techniques for organic electrosynthesis. J Org Chem, 2021, 86(22): 15866-15874.

[22] Ji S, Kim H, Park C, et al. Underestimation of platinum electrocatalysis induced by carbon monoxide evolved from graphite counter electrode. ACS Catal, 2020, 10(18): 10773-10783.

[23] Song GY, Yang L, Li JS, et al. Chiral arylated amines via C-N coupling of chiral amines with aryl bromides promoted by light. Angew Chemie Int Ed Engl, 2021, 60(39): 21536-21542.

[24] Yang L, Lu HH, Lai CH, et al. Light-promoted nickel catalysis: etherification of aryl electrophiles with alcohols catalyzed by a Ni ^II-aryl complex. Angew Chem Int Ed Engl, 2020, 59(31): 12714-12719.