Notes Notes Bull. Korean Chem. Soc. 2008, Vol. 29, No. 7 1395 A Ferrocene Derivative Redox Sensor for Mercuric Ion: Synthesis and Electrochemical Study Nhat-Nguyen Bui, Jong-Tai Hong, Sun-il Mho, and Hye-Young Jang * Division of Energy Systems Research, Ajou University, Suwon 443-749, Korea. * E-mail: hyjang2@ajou.ac.kr Received May 21, 2008 Key Words : Ferrocene, Mercuric ion, Electrochemistry, Redox sensor The sensitive detection of mercuric ion is currently a task of prime importance for environmental or biological con- cerns. To develop sensitive mercuric ion sensors, various receptors consisting of a mercuric ion recognition unit and a probe exhibiting physical responses upon the coordination of mercuric ion have been reported. 1 Among them, ferrocene derivatives are often applied to redox sensors due to the unique electrochemical property. 2 In the presence of mer- curic ions, the ion-recognition event induces the significant electrochemical changes at the redox active ferrocenyl moiety. In addition, the ease of functionalization of ferro- cene leads to the synthesis of assorted ferrocene derivatives possessing the metal ion binding unit. 2 Recently, our research has focused on the development of new ferrocene complexes as redox sensors for the mercuric ion detection. In this account, we report the synthesis and electrochemical analysis of 2-(ethylthiomethyl)-N-ferrocenylmethyl aniline in the presence of various metal ions, illustrating this ferrocene complex as a sensitive and selective redox sensor for the detection of mercuric ion. As shown in Scheme 1, 1-(bromomethyl)-2-nitrobenzene 1 was treated with ethanthiol with sodium metal to afford ethyl(2-nitrobenzyl)sulfide 2 in 72% yield. Subsequent reduction of compound 2 provided 2-(ethylthiomethyl)- aniline 3 which reacted with ferrocene carboxaldehyde 4, forming imine 5. Due to the instability of compound 5 on the silica gel, compound 5 was not isolated and subject to the reduction conditions using NaB(OAc) 3 H to give 2-(ethyl- thiomethyl)-N-ferrocenylmethyl aniline 6 in 80% yield. With compound 6 in hand, electrochemical properties of compound 6 were evaluated in the absence of any metal ion via cyclic voltammetry (CV). In the range of 0.0 to 2.0 V, two oxidation peaks appear at 0.41 V and 1.04 V during the anodic scan, and no reduction peak was observed in the reverse scan, shown in Figure 1. When the anodic scan was reversed at 0.80 V subsequent to the 1 st oxidation at 0.41 V, the reversible reduction peak at 0.30 V was detected, with the peak separation of ca. 0.11 V. Accordingly, the first oxidation peak at 0.41 V was speculated to be the oxidation of the ferrocene entity of compound 6. The second oxidation Scheme 1. Synthesis of 2-(ethylthiomethyl)-N-ferrocenylmethyl aniline 6. Figure 1. Cyclic voltammograms of compound 6 obtained in 0.1 M LiClO4 acetonitrile solution at a scan rate of 100 mV/s.