Electrophilic aromatic substitution (EAS) reactions are important synthetic tools used to functionalize aromatic rings. Therefore, many undergraduate organic chemistry laboratory courses include an experiment illustrating this chemistry in their curriculum. A classic experiment performed is the nitration of methyl benzoate using a mixture of nitric and sulfuric acids. We sought to develop a greener EAS experiment which avoided the use of strong acids, corrosive, and noxious reagents, and eliminated the production of hazardous waste. Based on reports from the primary literature, we investigated the bromination and iodination of electron rich benzene rings using oxone in combination with potassium bromide and potassium iodide salts in a variety of green solvents. In this presentation, we will share several successful adaptations of this chemistry amenable to a teaching lab environment. Substrates with multiple substituents can be used for problem-based exploration of directing effects and analysis by 1H NMR spectroscopy highlights the differences in ortho and meta coupling constants of aromatic protons. Most notably, vanillin (4-hydroxy-3-methoxybenzaldehyde) was shown to react with one equivalent each of oxone and potassium iodide in refluxing water to afford the 5-iodovanillin product in approximately one hour. Incorporation into our large sophomore level organic chemistry laboratory course provided a safer and greener experiment for our students as well as a pleasant smelling experience.

Halogenation of vanillin using Oxone® and halide salts for a greener electrophilic aromatic substitution reaction in the organic chemistry laboratory

251st National Meeting (2016)

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