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JCE Featured Molecules
William F. Coleman Wellesley College Wellesley, MA 02481
Molecular Models Illustrating Properties of Zeolites Linde-type Zeolite A, Selection of Alcohols, and Diphenylmethanol Etherification Product May 2009 Featured Molecules The featured molecules for this month come from two papers describing aspects of the properties of zeolites (1, 2). The first paper describes an experiment to demonstrate the use of zeolites as molecular sieves (1), and the second describes a zeolite-catalyzed etherification reaction (2). All of the nonzeolite molecules used in these experiments have been added to the collection. Only one zeolite structure is included in the collection, the Linde-type zeolite A (LTA). More structures are not included because there are very useful zeolite structure sites on the web (3, 4). The Database of Zeolite Structures (3) is a Java-enhanced site that provides a great deal of information concerning a variety of zeolite systems. Interactive structures are given for the silicate framework of these materials. A student who is just being exposed to molecular structure will be amazed by the variety of structural motifs found in these systems. This database, however, does not include the aluminum ions in the framework structure, designating both Al and Si as T atoms. The second database (4) comes from Imperial College and includes, for many of the structures, both the Al and Si centers. This database uses Chime as the interactive viewer and is thus limited in terms of the browsers it supports. A very nice feature of the Database of Zeolite Structures is the ability to generate a surface showing the channels in the structure. Both sites give the user access to diffraction information on the structure at hand. Included in the collection are also several versions of the LTA structure with an alcohol molecule in one of the channels (Figure 1). Students should examine these structures using several rendering modes to convince themselves that what might
methanol in LTA
appear to fit in a channel in ball and stick or wireframe, will not fit when the structures are rendered in space-filling mode, which approximates the conditions in the experiment. Literature Cited 1. Cooke, J.; Henderson, E. J. J. Chem. Educ. 2009, 86, 606–609. 2. Cooke, J.; Henderson, E. J.; Lightbody, O. C. J. Chem. Educ. 2009, 86, 610–612. 3. Database of Zeolite Structures; http://www.iza-structure.org/ databases/ (accessed Mar 2009). 4. Index—Zeolites; http://www.ch.ic.ac.uk/vchemlib/course/zeolite/ (accessed Mar 2009).
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/May/abs656.html Full text (HTML and PDF) with images in color Links to cited URLs and JCE articles Supplement Find “Molecular Models of Zeolites” in the JCE Digital Library at http://www.JCE.DivCHED.org/JCEWWW/Features/MonthlyMolecules/2009/May/
The molecules added to the collection this month are: from ref 1: Linde-type zeolite A (LTA) methanol and methanol in LTA 2-methyl-2-propanol and 2-methyl-2-propanol in LTA phenylmethanol (benzyl alcohol) 2-propanol (isopropanol) triphenylmethanol and triphenylmethanol in LTA from ref 2: diphenylmethanol and its etherification product
2-methyl-2-propanol in LTA
triphenylmethanol in LTA
Figure 1. Linde-type zeolite A (LTA) structure with various alcohol molecules in one of the channels.
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Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
