An Undergraduate Organic Chemistry Laboratory: The Facile Hydrogenation of Methyl trans-Cinnamate

Abstract

Handheld, portable data-collection devices allow the realtime monitoring of chemical reactions by students in teaching laboratories. These devices are primarily marketed for high school and college-level general chemistry experiments, but developing labs for organic chemistry would greatly expand their usefulness at the college level. Many organic chemistry laboratory experiments could employ this technology, one of which is described here.Hydrogenation of alkenes is an important reaction in the synthesis of organic molecules. There have been many reports in this Journal on the topic of catalytic hydrogenation experiments (1-23). Despite these reports, a hydrogenation experiment that meets the following criteria has yet to be developed for an undergraduate organic chemistry lab:

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“…The hydrogenation of methyl-trans-cinnamate is an ideal test reaction because high yields can be obtained in 2−3 h at room temperature under 1 atm of hydrogen. 33 The reactants are inexpensive and the products are relatively safe, viz. environmentally friendly.…”

“…The hydrogenation of methyl-trans-cinnamate was selected because it is a facile reaction that produces high yields in short times at room temperature. 33 In a typical reaction, 1−2 mg of Pd/CM was added to 100 mg (1 mmol) of methyl-trans-cinnamate in 5 mL of ethanol in a 100 mL round-bottomed flask. The round-bottomed flask was twice evacuated and backfilled with hydrogen gas.…”

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“…The reverse reaction, the hydrogenation of N-methylindole to N-methylindoline (1, shown below, where the reactivity takes place at the designated bond) over 0.1 mol% Pd/C at 100 C under 1 atm H 2 showed poor conversion and selectivity after 6 h. Pd/C was chosen as the catalyst for these initial screenings because of its reported utility for catalysing such transformations. 15,16 This poor result may be due to the tertiary amine functionality in this molecule; the binding energy between the nitrogen atom and the catalyst may be too high, resulting in irreversible adsorption to, and therefore poisoning of, the catalyst surface. Benzofuran, in contrast, was quantitatively hydrogenated with excellent selectively (no NMR-detectable sideproducts) under these conditions, but dehydrogenation of the resulting saturated compound, 2,3dihydrobenzofuran (2), went poorly.…”

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“…Our solvent-free hydrogenation can be conducted in a 4 h laboratory period. Some hydrogenation reactions have recently been published in this journal, , but to the best of our knowledge, none of them have an experimental scheme analogous to the one presented in this study.…”