Billy J. Fairless, Howard E. Dunn, and Daniel O. Foster Indiana State University Evansville Campus Evansville, Indiana
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hstrumentd Techniques Demonstrated by- Analysis of a Reaction Mixture
The organic laboratory experiments in most lab manuals are designed to give only one major product. The product is usually easily separated by distillation or recrystallization and identified by physical constants or by a spectrum. In a real life situation however, one often obtains a mixture of products that are not easily separated by conventional techniques. One example is the reaction of p-toluidine with monobromoethane. The purpose of this experiment is to acquaint the student with not just how one instrument can be used for a structure identification, but how a combination of instruments can be used to separate as well as to identify each component in a reaction mixture. This can be done on a microsized sample. Once the student has identified each component be can better judge how to work up his reaction mixture on a macro scale. Reaction Conditions To a small test tube were added 0.50 g (4.7 mmole) of freshly dist,illed p-toluidine and 0.60 g (3.5 mmole) of monobromoethane. The test tube was shaken until the p-toluidine completely dissolved. The solution was allowed to stand overnight during which time the reaction mixture becomes s. brown solid. The solid was dissolved in 60 ml of 0.1 N HC1 and the aqueous layer washed with ether to remove organic impurities. The acidic layer was then made basic with 2 M KOH and the amines extracted with ether. The ether was removed on a rotary evaporator leaving s red viscous oil. The different compounds in the oil were separated on a. gas chromatograph and each was identified by its infrared and/or nuclear magnet,ie resonance spectrum.
Gas Chromatography Analytical and Preparative.' A Hewlett-Packard Model 700 gas ohromatograph equipped with s W-X thermal conductivity detector was usedin this experiment. Any other similar chromatograph could also be used. For analytical experiments 1-2 p1 of sample were injected into the chromatograph but for preparative work 26-50 111 were required. All other variables were held constant. A '/,-in. copper column 2 m in length was used. I t was packed with 10% (w/w) Apieson L on acid-washed, 60-80 mesh Chromosorb W. The column was conditioned a t 200°C overnight and subsequently used with a helium carrier gas flow of 100 m /min. The chromatograph was operated with the column a t 16OoC, the injector a t 170°C, the detector a t 270°C, the bridge a t 130 p amps, and the attenuator a t 32 mV full scale deflection. A typical chromatogram is shown in Figure 1.
We wish to express our thanks to the National Institute of Health for an educational grant to purchase the nmr spectrometer, ir spectrometer, and the gas chromatograph used in this study. E.J., "Basic Gas ChromatogMCNAIR,H. M., I N D BONELLI, raphy," Vsrisn Aerograph, Walnut Creek, Calif., 1969. BELLMY, L. J., "The Infrared Spectra. of Complex Molecules") (2nd ed.), John Wiley & Sons, Inc., New York, 1966.
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Figure 1. Gar liquid chromotogram of other (11, p-toluidine (21, N-ethylp-toluidine (31, ond N,N-diethyl-p-toluidine (41. The chromatogram was obtained using those conditions described in the text.
Collection of the pure chemicals as they were eluted from the chromatogritph was especially simple. As each of the different peaks eluted a 4-mm outside diameter piece of glass tubing was placed over the exit port using a Teflon tubing connector. The glass tubing should be 10 cm in length to allow sufficientsurface area for sample condensation. Enough sample can be collected from one 25.~1 injection to get an infrared and nuclear magnetic resonance soectrum of each comoonent in the mixture. However. i f morr ..~mpl+ i s dpcirnl rhc r?mc thrrr p i w r . ~ (,f gIa% tt.hinq can I,* ~wmlr , cc~lledfr
