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

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 te...