C. W. Schimelpfenig
North Texos State University Denton
A Gas Chromatography Analysis for the Elementary Organic Laboratory
The search for an appropriate experiment to introduce gas phase chromatography into the elementary organic chemistry course has led to development of a laboratory session in which a class of 12 students prepare and analyze a product mixture in less than two hours. The mixture consists of 2-methyl-1-butene and 2-methyl-2-butene, the dehydration products of 2-methyl-2-butanol. After receiving a short lecture on gas chromatography, each student is given these directions: Add successively to a 50-ml distilling Bask 30 ml of 50% (by weight) sulfuric acid and 10 g of tertpentyl alcohol. Swxl the contents to insure thorough mixing. Immediately distill into a test tube cooled in an ice water bath. Heat the distillation Bask with a hot water bath, not a flame. Stop the distillation when the olefin layer has disappeared from the flask. Wash the turbid distillate by adding 5 ml of cold water to the test tube; cork, and shake vigorously. Remove the water layer with a dropper pipet. Add to the test tube ahout one gram of oaloium chloride, shake, and allow to settle for several minutes. Analyze the liquid above the drying agent by gss chromatography.
The alcohol is Eastman Kodak Co. practical gradc tertpentyl alcohol. With several columns and wit,h the apparatus used, Wilkms Aerograph model A-SOX, only one isomer can be detected. No advantage is gained by using a more expensive grade of alcohol. The volume of the turbid distillate, 7 to 8 ml, depends upon the efficiency of cooling the test tube collector. One water wash followed by treatment with calcium chloride is sufficient to remove water or alcohol which distills with the olefins. With a 10-ft Dow 11 silicone on fire brick column a t 44', a sample of five microliters, and a helium flow rate of 60 ml/min, retention times are 3.6 min for 2-methyl-1-butene and 4.2 min for 2-methyl-2-butene. Under the same conditions water is eluted after 5.3 min and terG pentyl alcohol after 12.9 min. The fraction of the product which is the more volatile, 2-methyl-1-butene
310 / Journol of Chemical Education
(one-tenth to one-twentieth of the total), depends upon keeping the distillate cold. For this reason it is desirable to analyze the product before removing it from the drying agent. Students waiting in line for analyses are advised to keep their samples cold in an ice bath. Yields of dried product are in the range 3.5 to 4.5 g. The theoretical yield is 8.0 g. I n order to answer questions concerning the experiment, the students are referred to the work of Whitmore and his students on this dehydration ( 1 ) and on the polymerization of penteues (S,3). Serious students who are concerned with the mechanism can be directed to recent work on this reaction and on similar systems (4-8). Directions for other laboratory exercises in gas chromatography have appeared in recent years (9-11). One exercise ( 1 1 ) is similar to ours but involves gaseous reaction product,^ and requires different student equipment. Literature Cited (1) WEITMORE, F. C., ET AL.,J. A I I LChenr. Soe., 64, 2970-2 (1942). F. C., AND MOSHER,W. A,, .I. Am. Ch,em. Sor., (2) WHITMORE, 63, 1120-3 (1941). (3) WHITMORE, F. C., A N D MOSHER,W. A,, .I.Am. Chent. Soc., 68, 2 8 1 4 (1946). L. P., J. Am. (4) LEVY,J. B., T A ~R., W., JR., A N D HAMMETT, Chem. Soe., 75, 12534 (1953). (5) BOYD,R. H., ET AL., J. Am. Chem. Soc., 82,4729-36 (1960). I., .I.A m . Chem. Sor., 81,4117-8 (6) S ~ E L LP. , S., AND STARER,
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(7) SILVER,M. S., J. -4nl. Chem. Soe., 83, 3482-6 (1961). V. R., AND WATSON, E. J., J . Chem. Soe., 1302-5 (8) STIMSON, (1961). C., J. CHEM.EDUC., 33, (9) BRENNAN,D., AND KEMBALL. 49&2 (1956). J. M.. J. CHEM.EDUC.. (10), COWAN.P. J.. AND SUGIHARA. . 36.. 246-7 (1959). (11) REILLEY,C. N., A N D SAWYER,D. T., "Experiments for Instrumentd Methods," Mecraw-Hill Rook Co., Inr., New York, 1961, pp. 256-0.
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