Cross-Course Collaboration in the Undergraduate Chemistry Curriculum: Primary Kinetic Isotope Effect in the Hypochlorite Oxidation of 1-Phenylethanol in the Physical Chemistry Laboratory

Abstract

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, k H, 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 k H/k D, 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.

Cross-Course Collaboration in the Undergraduate Chemistry Curriculum: Isotopic Labeling with Sodium Borodeuteride in the Introductory Organic Chemistry Laboratory

“…Acetophenone was selected as a substrate for two reasons. First, the secondary alcohol product is preferred over a primary alcohol for use in the KIE companion experiment . The latter would present overoxidation issues via the corresponding aldehyde.…”

“…In an effort to develop a cross-course collaboration between the organic and physical chemistry laboratories, an isotopic labeling experiment was sought whereby the students in the organic class would produce a compound which would then be handed off to the physical chemistry students for use in a kinetic isotope effect (KIE) experiment. , This labeling experiment would have to be appropriate for chemistry majors as well as nonmajors, and would have to be suitable for use in the first semester of the organic course since KIE appears in the first semester of the physical chemistry course. In addition to clarifying and reinforcing the students’ understanding of isotopes and KIE, the organic experiment would have to provide, because of its early appearance in the course, a straightforward, yet substantive, introduction to any applicable characterization techniques such as NMR spectroscopy, IR spectroscopy, and MS.…”

“…Reported here is an experiment in which students use either NaBH 4 or NaBD 4 to reduce acetophenone to 1-phenylethanol (Scheme ) and compare analytical data for each product. The deuterated alcohol is then provided to the physical chemistry students who perform a KIE experiment involving hypochlorite oxidation back to the original ketone . These students report their experimental findings to the organic students later in the semester.…”

Incorporating Interlab Collaborations into the Organic Chemistry Teaching Laboratories

“…Examples of group work in general chemistry, − organic chemistry, − and advanced chemistry laboratories − have been reported. Traditionally, students from the same lab section (and course) work together, although collaborations across courses have also been reported. − For example, to model drug discovery, students in organic and biochemistry courses synthesized an antibiotic and tested its biological properties . In a similar vein, biochemistry students studied the kinetics of enzyme–substrate reactions with substrates synthesized by organic chemistry students .…”

Hands-On Electrospray Ionization Mass Spectrometry for Undergraduate Biochemistry Students: Peptide Identification by Ladder Sequencing

“…Experimental applications of mass spectrometry in analytical and/or instrumental undergraduate courses include the detection of essential oil in citrus fruits, 5 analysis of environmental samples for identification and measurement of pollutants in the environment, 6 analysis of caffeine, 7 and identification of components in gasoline. 8 Mass spectrometry has been used in undergraduate physical chemistry laboratories to study the primary kinetic isotope effect in a household bleach, 9 measure gas-phase basicities of amino acids, 10 and investigate structures and bonding configurations of inorganic compounds. 11 With the rise of mass spectrometry for biochemical analysis, the educational need is pushed beyond instrumental analysis into other chemical subfields, including biochemistry.…”