Solvent-Free Synthesis of 2,2′-Dinitrobiphenyl: An Ullmann Coupling in the Introductory Organic Laboratory

Abstract

The formation of carbon−carbon bonds is an essential theme throughout organic chemistry. The use of transition-metal catalysts to form carbon−carbon bonds, once relegated to more advanced texts, is now commonly found in introductory organic textbooks. However, commensurate laboratory experiments for first-year organic students are more limited. The following experiment utilizes a copper catalyst to create a biphenyl compound, a classical Ullmann coupling reaction. In the first step, 1-iodo-2-nitrobenzene is synthesized from 2-nitroaniline in a mortar. The 1-iodo-2-nitrobenzene is then converted into 2,2′-dinitrobiphenyl by heating in a test tube in the presence of copper and sand. The separation, purification, and identification of the aromatic compounds illustrate the techniques of thin-layer chromatography, column chromatography, melting point, and 1H NMR spectroscopy. Both reactions utilize several green chemistry principles including synthesis in a solvent-free environment, minimal time at reaction temperature, and purification with limited solvent usage. The brightly colored compounds and less common reaction techniques contrast nicely with the traditional refluxing experiments that produce the ubiquitous white powder.