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William F. Coleman Wellesley College Wellesley, MA 02481
Molecules of Interest to Chemists and Consumers: Melamine, DEET, and Vanillin William F. Coleman Department of Chemistry, Wellesley College, Wellesley, Massachusetts 02481
[email protected] w This paper contains enhanced objects available on the Internet at http://pubs.acs.org/jchemeduc. n
JCE Featured Molecules for May 2010 Several articles in the current issue share the common theme of describing some aspect of the synthesis or properties of molecules of wide interest to students and the general public. These papers range from the analysis of melamine to the enzymatic synthesis of several antioxidants (1-3). All three of these papers contain information that would be of interest to students at all levels of the chemical curriculum. Structures of a variety of the species discussed in these papers are shown in Figure 1 and 3D rotatable images in MOL format are available in the HTML version of this paper for these 12 molecules: cyanuric acid, cyanuric acid tautomer, melamine, and melamine-cyanuric acid adduct (1); N,N-diethyl-3-methylbenzamide (DEET), oxalyl chloride (cis and trans), and m-toluic acid (2); apocynin, diapocynin, vanillin, and divanillin (3). Featured molecules from past issues are available in the molecule collection at the JCE Digital Library (4). In the paper by Doris Renate Kimbrough and Anna Chick Jensen on the analysis of melamine in foodstuffs (DOI: 10.1021/ ed800174h), the authors discuss several aspects of the melamine structure that provide useful problems for students in organic and physical chemistry courses (1). The authors point out that one of the tautomers of cyanouric acid, the enol tautomer, is aromatic. Students could perform molecular orbital calculations on this tautomer and on the keto form, and compare the molecular orbitals obtained to those of more standard aromatic compounds such as benzene, pyridine, or one of the triazines. Do these calculations provide additional evidence of aromaticity? Students in physical chemistry could verify the statement that the keto form is more stable than the enol form, and using computed thermodynamic parameters or partition functions, could calculate an equilibrium constant for this tautomerism. This paper also provides a good opportunity for a discussion of the intersection of scientific and business ethics, and the role of regulation in fields such as public health. Jean Christophe Habeck, Lamine Diop, and Michael Dickman describe two routes to the synthesis of DEET (DOI: 10.1021/ed800169h). This approach leads smoothly to a discussion of which synthesis has the higher atom economy, the nature of the byproducts of the two routes, the solvent used, and which of the two pathways would be considered “greener”. Perhaps we have reached the point where the green aspects of all reactions should be described and discussed in laboratory procedure manuals. For students in classes in which computational chemistry is stressed, a comparison of the energetics of the rotational conversion from cisto trans-oxalyl chloride with the similar conversion in 1,3-butadiene, provides insights into a number of aspects of conformational stability and energy surfaces. 564
Journal of Chemical Education
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Figure 1. Molecules of interest to chemists and consumers: melamine (1), DEET (2), and vanillin (3).
Rachel T. Nishimura, Chiara H. Giammanco, and David A. Vosburg address the question of green synthesis head on in their paper (DOI: 10.1021/ed8001607) describing the use of horseradish peroxidase as a catalyst in the enzymatic synthesis of divanillin and diapocynin (3). Students in various courses might be intrigued by the complexities of the molecular changes that occur on going from green vanilla beans to the roasted vanilla beans whose flavors are familiar to them. Literature Cited 1. Kimbrough, D. R.; Jensen, A. C. J. Chem. Educ. 2010, 87, DOI: 10.1021/ed800174h. 2. Habeck, J. C.; Diop, L.; Dickman, M. J. Chem. Educ. 2010, 87, DOI: 10.1021/ed800169h. 3. Nishimura, R. T.; Giammanco, C. H.; Vosburg, D. A. J. Chem. Educ. 2010, 87, DOI: 10.1021/ed8001607. 4. JCE Featured Molecules from June 2002 until December 2009 are available at the JCE Digital Library, http:/www.jce.divched.org/ JCEWWW/Features/MonthlyMolecules/.
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Vol. 87 No. 5 May 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed800177n Published on Web 04/13/2010
