Heterocyclic Azo Dyes by Oxidative Coupling

A Homage to Siegfried Hünig and His Research

Examples from different research areas of Siegfried Hünig are displayed to remind us that organic chemistry owes much more than Hünig's base to this exceptionally versatile and creative chemist. The main research lines dealing with the synthesis and physical characterization of new dyes, multistage redox systems, and organic metals will be presented as well as his contributions to enamine chemistry, the discovery of diimine as a hydrogenation agent, and nucleophilic acylation with trimethylsilyl cyanide, which are less well-known nowadays. In addition, exotic compounds with parallel C=C and N=N bonds were systematically studied in Hünig's group. Reflecting on the development of his research demonstrates both the importance of a systematic approach and how fruitful entirely unexpected results are if they meet a "well-prepared mind". During Hünig's academic career, teaching played an indisputable role. His efforts in modernizing the chemistry institute at Würzburg and his support of young researchers in the academic system in Germany are also highlighted.

Isolation of a labile homoleptic diazenium cation

Following our interest in nitrogen chemistry, we now describe the synthesis, structure, and bonding of labile disilylated diazene, its GaCl3 adduct, and the intriguing trisilylated diazenium ion [(Me3 Si)2 NN-SiMe3 ](+), a dark blue and highly labile (Tdecomp >-30 °C) homoleptic cation of the type [R3 N2 ](+). Although direct silylation of Me3 Si-N=N-SiMe3 failed, the [(Me3 Si)2 N=N-SiMe3](+) ion was generated in a straightforward two-electron oxidation reaction from mercury(II) dihydrazide and Ag[GaCl4]. Moreover, previous structure data of Me3 Si-NN-SiMe3 were revised on the basis of new data.

A new peroxidase color reaction: oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with its formaldehyde azine. Application to glucose and choline oxidases

Hydrogen peroxide in the presence of horseradish peroxidase effects the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with its formaldehyde azine to form a tetraazapentamethine dye. The blue chromophore, when formed at pH 3.5 and quenched with acetone or 1 N hydrochloric acid, has an extinction coefficient of 69 +/- 2 or 55 +/- 2 mM-1 cm-1, respectively. This chromogen system has been adapted for enzymatic determinations of hydrogen peroxide and of glucose in the 10- to 45-nmol range and of choline in the 5- to 20-nmol range.