Electroanalysis of hydrazine and related compounds by oxidation promoted with MN4 macrocyclics

Abstract

Hydrazines and related compounds are hazardous chemicals widely used in the laboratory and in industry. Hydrazine, a colorless liquid, is considered a human carcinogen. This substance is a powerful reducing agent and is employed in many industrial applications as a reagent, catalyst, and corrosion inhibitor. Hydrazine and its derivatives have been used as rocket fuels and as oxygen scavengers in boilers. Other uses include the manufacture of metal films, blowing agents for plastics, photographic chemicals, insecticides, explosives, and pharmaceuticals. The compounds have been used as intermediates in the synthesis of different types of drugs, including nifuroxazide, carbidopa, hydralazine, dihydralazine, isoniazid, and iproniazid. Hydrazine itself, in the form of the sulfate salt, has been used in the treatment of tuberculosis, sickle cell anemia, and various chronic illnesses. The determination of hydrazine and its alkyl substituted analogs is challenging because of their volatility, low molecular weight, high polarity, tendency to oxidize, lack of chromophores, and (in the case of hydrazine) the absence of any carbon atoms. Nonetheless, the quantitative determination of these compounds is of great analytical importance, due to their multiple applications and their recognition as carcinogenic and hepatotoxic agents, and has attracted the interest of many researchers. The analytical methods that are commonly used for hydrazine and its alkyl substituted analogs include high performance liquid chromatography (HPLC), gas chromatography (GC), ion chromatography (IC), thin layer chromatography (TLC), high performance thin layer chromatography (HPTLC), spectrophotometry, capillary electrophoresis (CE), micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). These conventional techniques are sensitive, reliable, and precise. However, despite their advantages, they require skilled analysts and the use of expensive instrumentation. They are also time-consuming and difficult to adapt for use in field analyses. An alternative is to use simple, inexpensive methods based on the electrochemistry of N4 macrocyclic complexes. These complexes offer many advantages: they are cheap and easy to synthesize, show good stability at different pH, and can catalyze a myriad of electrochemical reactions. Tuning of the formal potential of the active site can be achieved by placing appropriate groups on the ligand in order to alter the electron density of the metal center. This chapter provides a comprehensive discussion of various aspects of hydrazine and related compounds, focusing on their analysis using electrochemical methods based on N4 macrocyclic complexes. The catalytic properties of MN4 metallomacrocyclics in the oxidation of hydrazine and related compounds are discussed, together with the different factors affecting catalytic activity, such as the effects of the central metal and the ligand on hydrazine electrooxidation.