The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 20
(2015) pp 154-156
Methylation of Mesitylene Chromium Tricarbonyl – An Undergraduate Advanced Synthesis Experiment
Curtis J. Czerwinski*, Tanya J. Cordes, and Stephanie A. Zorn
Department of Chemistry & Biochemistry, University of Wisconsin – La Crosse, 1725 State Street, La Crosse, WI 54601, email@example.com
Published: 23 June 2015
Abstract. A multistep experiment in transition-metal organometallic chemistry for an advanced synthesis laboratory course is described. In the first part, students synthesize and characterize mesitylene chromium tricarbonyl. In the second part, students react the mesitylene chromium tricarbonyl with n-butyllithium followed by a methyl iodide quench. The two steps can be used independently or connected in a two-step process that involves four laboratory sessions. Overall, the two-step scheme provides a straightforward exercise that illustrates basic principles for safely handling pyrophoric reagents and organometallic compounds, fundamental inert atmosphere techniques, and use of low-temperature baths. The experiment highlights bonding theory in transition metal complexes, with emphasis on IR and proton NMR spectroscopy. In the second part of the scheme, students follow a discovery-based approach, analyzing the product by proton NMR spectroscopy to determine which of two possible reaction routes occurred. Students can achieve high yields and high selectivity of a single final isomer even though this might be their first time working with organometallic compounds, inert atmosphere techniques, and pyrophoric reagents.
Key Words: Laboratories and Demonstrations; organic chemistry; inorganic chemistry; organometallics; aromaticity/aromatics; metal carbonyls; pyrophoric reagents
(*) Corresponding author. (E-mail: firstname.lastname@example.org)
Handouts for students are provided that include pre-laboratory background descriptions, experimental procedures with diagrams, safety precautions, and questions for students. Instructor notes, samples of student IR and NMR spectra of the final product, supplies and equipment list with a budget, answers to questions, and additional discussion of safety and waste collection are also provided (235 KB).