Date of Award

Summer 8-21-2015

Level of Access

Campus-Only Thesis

Degree Name

Master of Arts (MA)

Department

Chemistry

Advisor

Alice E. Bruce

Second Committee Member

Mitchell R. M. Bruce

Third Committee Member

Carl P. Tripp

Abstract

The focus of this work is on the synthesis and characterization of two new ferrocenoyl compounds, 1,1’-ferrocenoyl bis-acylthiosemicarbazide (3) and N,N-dimethyl(5,’5-bis ferrocenoyl-1,3,4-oxadiazol-2-yl)amine (4). The foundation of our investigation in creating a suitable method for both selective and sensitive detection of Hg(II) is the irreversible 1:1 cyclization reaction of an acylthiosemicarbazide with Hg (II). The reaction is performed under mild conditions and yields 1,3,4,oxadiazoles.

Previous research within our group used solid phase extraction (SPE) coupled with FTIR. A promising detection limit of 5 ppb was obtained, however, limitations, such as mass transports were incurred. As an alternative approach, ferrocene was derivatized with an acylthiosemicarbazide and the reaction was investigated in solution by using NMR and electrochemical techniques. Two new ferrocene derivatives, 1-ferrocenoyl-4-dimethyl-3-thiosemicarbazide (1) and N,N-dimethyl(5,’5-bis ferrocenoyl-1,3,4-oxadiazol-2-yl)amine (2) were previously synthesized and characterized. The detection limit of 1 was found to be 1. 3 ppm. To try to improve the sensitivity, compounds 3 and 4 were synthesized. Chapter 1 focuses on the need and importance of a highly selective method for Hg(II) detection, how Hg(II) is currently detected, current literature utilizing derivatives as sensors, and several electrochemical methods used for detection.

Chapter 2 discusses the synthesis and spectral characterization of 3 and 4 utilizing FT-IR, 1H and 13 C NMR, and UV-visible spectroscopy. When 3 is reacted with 2 equivalents of Hg(II), both acylthiosemicarbazides react yielding a disubstituted oxadiazole compound (4). The electrochemical properties of 1-4 were investigated, 3 was found to have two oxidation peaks at 0.844V (assigned to thiosemicarbazide) and 1.010V (assigned to Fe(II)/Fe(III) redox couple), which is the reverse of 1. It was determined that solvent effects influence the anodic peak potential (Epa) of these derivatives. The anodic peak potential (Epa) trend in DMF is 3>4>1>2, while in CH3CN is 4>3>2>1.

Chapter 3 discusses the reactivity of 3 with 1 equivalent of Hg (II), various mercuric salts, and other thiophillic metals. 1 H NMR demonstrated that 3 is selective to Hg2+ over Pb2+, Cd2+, Zn2+, Li+, and Au+. The influence of the mercuric anion was investigated by observing the reaction with the following compounds; Hg(OAc)2, HgCl2, and Hg(NO3)2. The formation of a novel disubstituted ferrocenoyl oxadiazole (4) formed in the presence of all three compounds, however, the reaction was the most efficient with Hg(OAc)2 yielding complete product formation.

The reactivity of 3 with one equivalent of Hg(OAc)2 was explored via cyclic voltammetry (CV) and 1H and 13C NMR. The formation of new peaks in the NMR spectra as well as an anodic potential shift upon the addition of Hg(OAc)2 suggested the presence on an unknown structure 5. The results suggest that Hg(II) is added and sequentially converts one acylthiosemicarbazide to 1,3,4, oxadiazole at a time. Utilizing differential pulse voltammetry (DPV) 3 was found to have a limit of detection of 0.8 ppm. By increasing the substituent, the LOD has been decreased by almost one half. These results are promising and indicate a further step along the research path of making a deployable low detection sensor for on-site field evaluation.

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