In ongoing efforts to replace traditional organic chemistry laboratory experiments with greener versions, two synthetic transformations were targeted for updating. The first was the nitration of methyl benzoate used by many teaching laboratories across the nation as a representative electrophilic aromatic substitution (EAS) reaction. This classic experiment has many redeeming characteristics including a 1H NMR with both meta and ortho aromatic coupling constants observable as well as spectacular crystals. However, the use of this strongly acidic and oxidizing reagent mixture has resulted in documented accidents in teaching laboratories and the use of nitric acid is strongly discouraged by our Department of Environmental Health and Safety (DEHS). A second experiment to be replaced was the Grignard synthesis of triphenylmethanol. Though a few examples of greener Grignard reactions have been reported, we sought to model carbon-carbon bond forming reactions through the Suzuki-Miyaura transformation, commonly used in industry. In this presentation, a two-step synthetic reaction sequence will be described that has been successfully performed multiple semesters in our organic teaching laboratories which successfully addresses the goals outlined above. In the first step of the sequence, vanillin is iodinated using Oxone and potassium iodide in refluxing water. Students are tasked with determining the position of substitution through 1H NMR spectroscopy. The tan, effervescent solid product isolated lends itself to analysis by 13C NMR spectroscopy with well separated signals. The iodinated product is then used in a Suzuki-Miyaura reaction using 10 % Pd/C as a catalyst and p-methylphenylboronic acid in water. 1H NMR is again featured as both para and meta coupling constants are present. These experiments highlight a potentially renewable feedstock, water as a reaction solvent, catalysis, and use of safer chemicals.

Starting with vanillin: Two-step synthetic sequence illustrating green chemistry principles

255th National Meeting (2018)

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