Resumen de Cross-Course Collaboration in the Undergraduate Chemistry Curriculum: Primary Kinetic Isotope Effect in the Hypochlorite Oxidation of 1-Phenylethanol in the Physical Chemistry Laboratory
Robert J. Noll, Richard W. Fitch, Richard A. Kjonaas, Richard A. Wyatt
A kinetic isotope effect (KIE) experiment is described for the physical chemistry laboratory. Students conduct a hypochlorite (household bleach) oxidation of an equimolar mixture of 1-phenylethanol and 1-deuterio-1-phenylethanol to acetophenone. The reaction occurs in a biphasic reaction mixture and follows first-order kinetics with respect to either isotopomer of 1-phenylethanol. Reaction progress is measured by gas chromatography–mass spectrometry (GC–MS). Alternatively, the experiment could be conducted with each isotopomer serially and followed by GC alone. The reaction rate constant for the disappearance of 1-phenylethanol, kH, ranges from 3 × 10–4 to 2 × 10–3 s–1, while kD, for 1-deuterio-1-phenylethanol, ranges from 9 × 10–5 to 5 × 10–4 s–1. The observed KIE, the ratio kH/kD, is remarkably robust, ranging between 2.3 and 3.6, with a mean of 2.9 and standard deviation of 0.4 over three years of student data. The robustness of the observed KIE stems from using competing reactions. The experiment can be completed in about 3 h; GC–MS data is conveniently acquired overnight using an autosampler. The experiment, as presented here, can stand alone, but is well-suited to cross-course collaboration between the organic and physical chemistry laboratories. The preceding companion paper describes the synthesis of 1-phenylethanol and 1-deuterio-1-phenylethanol using borohydride or borodeuteride reduction of acetophenone as an experiment for the organic laboratory.
