edited by GEORGEL. GILBER; Denison University Granville. Ohio 43023
A Demonstration of the Transformation of a Hydrophobic Liquid to a Partially Hydrophilic Semisolid J a m e s F. Nugent Salve Regina-The Newporl College Newporl, R102840 CHECKEDBY
Davld Blackman Unlverslty of the DIr(r1ct ot Columbla Washington, OC 20009 Vegetable oil from the supermarket consists of a mixture of triesters of saturated and unsaturated fatty acids with glycerol. These substances are quite nonpolar and hydrophobic. They can he transformed into a partially hydrophilic mixture by heating with excess glycerol according t o the alcoholysis reaction: RCO$
2?&H
RTO, H
I
R"CO,CH,
+
3 RCO,CH,
I I
CHOH ====
HOCH
CH8H
HOCH,
I
When the product, which is a n equilibrium mixture of mono-, di-, and triacylglycerols, is poured into water, an amorphous semisolid forms. This material suspends in t h e water. T h e behavior of the product is in sharp contrast with the starting veaetable oil. which. a s a h v d r o ~ h o h i cliauid. does not mix with water. T h e moie hydriphilk character o£ t h e ~ r o d u c can t easilv be explained hv the Dresence of the polar hydroxyl groups in the product &xture. This reaction is a commonly used industrial means for converting animal and vegetable fats and oils t o food-grade emulsifier^.',^ In the industrial situation, however, hydrogenated fats and oils are used in order to eliminate t h e possibility of oxidation reactions associated with unsaturation.
82
Journal of Chemical Education
1250-ml heaker 1150-ml heaker 1 Pyrex test tuhe (No. 9800,18 X 150 mm) 1test tube holder 1Fisher burner vegetahle oil (soybean oil was used) glycerol calcium hydroxide boiling chips Procedure To a Pyrex test tuhe add 5.0 g soybean oil (approximately 5.6 mmol assumingaverage fatty acid units of C-la), 3.1 g glycerol (33.7 mmol), and 0.01 g calcium hydroxide. The glyceroland vegetable oil form separate layers. Add a few hailing chips and heat the test tube with aFisher burner flame so that the mixture boils vigorously. The glycerol layer darkens but then dissolves into the oil layer so that there is only one liquid phase. It takes ahout two minutes from the commencement of heating to reach this point. Continue boiling for one additional minute, remove the test tuhe from the flame, and cautiausly dip the test tube into a 250-ml heaker containing 150 ml water to rapidly cool the test tube mixture. Slowly pour the cooled mixture into 100 ml of vigorously stirred water in a 150-ml heaker. The rather slimy product can be cleaned from the glassware with a laboratory detergent such as Alconox. Hazards The test tuhe should he heated carefully with boiling chips to avoid the hazard of splattering glycerol (bp = 290°C). The demonstration should always be done in a hood because of the possible production of acrolein as a by-product. Aerolein is a n irritating, low-boiling liquid which can cause death if high concentrations a r e
'
Markley, Klare S. (Editor). "Fatly Acids: Their Chemistly. Properties, Production, and Uses," Part 2, Interscience Publishers Inc.. New York, 1961, pp. 873-884. Swern, Daniel (Editor), "Bailey's Industrial Oil and Fat Products." 3rd ed., John Wiley and Sons Inc., New York, 1964, pp. 952-957. "Occupational Health Guidelines for Chemical Hazards," U.S. Department of Health and Human Services. 1978, Publication No. 81123.
