Introduction to Supported Reagents Organic Experiments

Background: This project was initiated with support from the National Science Foundation as a Leadership in Laboratory Development grant under the Instrumentation for Laboratory Instuction program (ILI-LLD).

A. The object of this project was to develop a new methodology for carrying out experiments in the undergraduate organic chemistry laboratory using supported reagents and catalysts. A major goal was to offer an alternative to the apparatus-intensive technique type of laboratory. Some major features of this approach are:

B. The new methodology was directed primarily toward the large enrollment, service type of laboratory that could come under threat of elimination due to pressures related to costs, safety, or pedagogical inappropriateness. However, as the project developed, additional applications have become apparent. Some of these are:

C. Some more specific areas that have been developed are:

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February 1996.

Lower costs:

The experiments have been developed using polypropylene devices that are marketed for solid phase extraction (SPE) procedures. These have been on the market for several years, and are available from a variety of suppliers. Altech Associates, Inc. of Deerfield, IL is a convenient source of SPE devices. Standard types of small scale laboratory glassware can be used for some supported reagent reactions, but the polypropylene devides have advantages in cost and convenience. One 8mL size resevoir with a frit which serves as a reaction vessel costs about $0.43, compared with a small standard taper flask, or reaction vial, at $8-$10 each. The polypropylene reservoirs are essentially unbreakable, and can be reused. A complete "kit" for running the procedures described here can be assembled for $25-$50 per student. A vacuum manifold for 12-24 students costs $500-$700. Only one of these would be necessary per lab, and usually can be purchased on a supplies budget. The procedures are written at the 10-100 mg level, and correspond with most small or "microscale" experiments. Solvent use is minimum. Most of the supports and many of the supported reagents and catalysts can be recycled or regenerated.

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Reduced Hazards and Waste Minimization:

All of the procedures being developed will avoid the use of carcinogens and highly toxic materials. One major feature of the supporting of reagents is that certain hazards can be reduced in a practical sense. The vapor pressure of volatile and noxious reagents can be reduced. The use of a vacuum manifold can greatly reduce the amount of volatile solvents released into the laboratory. Since most of the supports can be reused or recycled they do not need to be listed as hazardous waste. Regeneration methods can be written into procedures. This has not yet been done with most of the experiments described here, but we intend to do more with this in the future. Users may want to develop methods best suited to their own local situation. In any case, it must be remembered that supporting a toxic or carcinogenic material does not change its hazard in terms of waste disposal. Polymer supported hydrogen chromate is still a carcinogen. The cyanide form of an anion exchange resin is still a highly toxic material.

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Emphasis on Principles:

This methodology for carrying out organic reactions is not intended to teach traditional organic laboratory techniques. Certainly some of the methods presented are important to professional chemists and should be considered for presentation to chemistry majors. (See B.1.) However, a major potential audience for this approach is the large enrollment non-major service organic course. The traditional apparatus-intensive, technique oriented, cookbook procedure laboratory, with emphasis on product yield and purity, and usually not correlated with the lecture, has been criticized as not being the most appropriate for this group of students. With the conviction that laboratory is still a vital part of teaching organic chemistry, methods were developed that could allow a reasonably varied and sophisticated group of reactions to be presented to students. They give an opportunity to involve the student in understanding the reaction principles, the major conditions necessary for the reaction to take place, and the outcome of the reaction. The use of spectroscopic and other instrumental analyical methods are encouraged.

The initial experiments being developed are representative of basic organic processes, and would correlate best with a mechanistic course approach. Areas addressed to date include the following:

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