The Chemistry of Formazan Dyes. Synthesis and Characterization of a Stable Verdazyl Radical and a Related Boron-Containing Heterocycle

• Autores: David E. Berry, Robin G. Hicks, Joe B. Gilroy
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 86, Nº 1 (January), 2009, págs. 76-79
• Idioma: inglés
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• Resumen

  • This experiment describes the synthesis and characterization of a formazan dye, and its subsequent conversion to a stable verdazyl radical and a boron–nitrogen heterocycle (boratatetrazine). Each of these compounds is intensely colored and is prepared and handled under aerobic conditions, which often surprises students as free radicals are generally described as short-lived, highly reactive species and compounds containing boron are often assumed to be air-sensitive. The prepared compounds are studied by 1H and 13C NMR, UV–vis, and EPR spectroscopy. The UV–vis spectra introduce an opportunity to discuss the different energy transitions that may give rise to intense colors, and interpretation of the EPR spectrum requires the student to carefully consider the bonding within the verdazyl radical; that is, is the radical centered on one atom or is it shared over several atoms within the structure? In addition the crystal structures of the formazan and the boratatetrazine are viewed in detail, expanding the students knowledge of bonding in delocalized systems.