F. H. Greenberg State University College Buffalo, New York 14222
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Natural Products kolafi~n-orang.
Oil
An undergraduate organic experiment
There are a number of natural products whose isolation is adaptable to elementary organic experiments.' One such natural product experiment, apparently not utilized previously in the undergraduate organic lab, is the isolation of orange oil from orange peel and identification of the major component, (+)limonene. This experiment, as described below, illustrates steam distillation, extraction, gas chromatography, refractive index, micro boiling pomt, and polarimetry and introduces ir and nmr spectra. The peel of one orange is ground in a Waring blendor2 with 200 ml of water such that individual pieces of peel can still be seen.a The mixture is poured into a 500-ml distilling flask with the aid of a powder funnel. An additional 50 ml of water is used to wash the remaining contents of the blendor into the flask and the mixture is distilled into a 125-mI separatory funnel graduated at 10-ml intervals. The student should observe the temperature a t which distillation occurs and the odor and appearance of the liquid. Approximately 20-50 ml of distillate is collected. After three extractions with 10ml portions of methylene chloride, the combined extracts are dried (Na2S04)and filtered through cotton (or decanted) into a weighed 50-ml Erlenmyer containing a boiling chip. The sodium sulfate and cotton are washed with 5 ml methylene chloride and the solution is concentrated on a steam cone until vigorous boiling ceases (about 1 ml remaining). Residual solvent is removed a t reduced pressure; the flask is attached to an aspirator by a #2 rubber stopper, immersed in a warm water bath, and swirled gently. The average
yield from 20 and 50 ml of distillate is 0.3 and 0.5 g, respectively. Gas chromatographic analysis on a 6-ft X 1/4-in. column nacked with 20% Carbowax 6000 on Chromosorb W-'Aw at 160°C if~owsthree components4 with the major peak as 97% of orange oil. The student is asked to find this percentage from peak areas. If methylene chloride is present, the oil is returned to the aspirator and then re-examined by gas chromatography. When the oil appears free of solvent the refractive index'and boiling point5 are det,ermined.
Name &"d structure
' O ' C o n ~ o n ,R.,
J. CHEM.EDUC.,42, 491 (1965). NELSON, THOMPSON, E., "Laboratory Projects in Organic Chemistry," Allyn and Bacon, Boston, 1966, p. 106. I n this manual literature references are given for isolation procedures of 49 natural products. 2A Wering blendor is not essential although it does result in imoroved vields. The eel mav be cut bv hand. takine care that the pieces are small enough to be removed from the distillaton flask at the end of t,he experiment,. 3 If the peel is ground to a purhe, frothing occurs on distillation and some of t,he pot mixture may be carried int,o the receiver. Resol~~t,ion of 14 hydrocarbon and 12 oxygen-cont,aining components in orange oil has been achieved by irseof preparative and open tnbular colllmn gas chromatography. TERANISHI, R., el al., J. Food Science, 28, 541 (1963); TERANISHI, R., e l al., J . Agr. Food Chem., 14, 447 (1966). The D-limonene content of pressed California. and Florida orange oil is reported to be 87.5 and respectively. I K E I ~ AR,. M., STANLEY, W. L., RULLE,L. A,, AND VANNIER, S. II., J. Food Science, 27, 593 (1962). T h e method empluyed is that of SEIRINER, R. L., FasoN, R. C., A N D CURTIN,U. Y., "The Systematic Identification of Organic Componnds," (5th ed.), John Wiley and Sons, Inc., New York, 1964, pp. 37-38.
K. L.
AND
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Adapted from "IIandhook of Chemiatryand Physics," (47th d l , Chemical Rubber Co., Cleveland, Ohio, 1966.
Volume 45, Number 8, August 1968
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537
The infrared spectrum of the oil is then recorded, and the student is to identify, with the aid of the text: the absorptions a t 3.19, 3.42, 6.08, and 11.27p as alkane carbon-hydrogen stretching, alkene carbon-carbon stretching, etc. Usually there is not sufficient time for every student to record the ir spectrum of his sample and a reproduction7 is used. After finding the empirical and molecular formulas from % composition (% C = 88.30; Yo H = 11.78) and molecular weight, the student is given reproductions of the actual nmr spectrum8 and a simulated nmr spectrum without spin-spin ~ p l i t t i n g . From ~ the table of ten CloHlscompounds, given above, the student is to identify the structure of the major component of orange oil.
538 / lournol of Chemicol Educofion
The structure assignment may he corroborated by determination of the optical rotation of technical (+)limonenel0 (assumed to be 88% optically pure) and calculation of the specific rotation. MORRISON, It. T., and BOYD,R. N., "Organic Chemist,ry," Allyn and Bacon, Boston, 1966, pp. 452-453. R O ~ E R TJ.~D., , A N D C.~SERIO, M. C., "Basic Principles of Organic Chemistry," W. A. Benjamin, Inc., New York, 1965, p. 150. The ir and nmr spectra are given by I l m a , J. R., "Applications of Absorpbion Spectroscopy of Organic Compounds," Prentice Hall, Inc., Englewood Cliffs, N. J., 1965, D. 49 and v. 87. See footnote 7. The experiment is nsoally performed before spin-spin splittine has been exvlained in the lecture. l ; ; ~ a s t m a n~ ; , d a k#T 1980, 1 kg, $2.75.
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