Abstract: . . .  call rancid. Partial hydrogenation, of plant oils reduces rancidity because it reduces the number of homoconjugated polyunsaturated fatty acids. Isolated double bonds, as in oleic acid, do not oxidize under ordinary conditions. The joys of olive oil Page 6 6 We have seen that partial hydrogenation of polyunsaturated plant oils produces a spreadable fat, and reduces the tendency toward rancidity, but at the price of increased saturated and trans fatty acids, both of which, some people claim, are not sensible compounds to eat. Only recently are Americans becoming aware of what Italians and Greeks have known for thousands of years: olive oil is good for you. Unlike most plant oils such as soybean, corn, and safflower, which contain triglycerides made with polyunsaturated fatty acids, olive oil is almost pure glyceryl trioleate. It is unique in this respect. For our purposes, we can consider it to contain 80% oleic and 10% stearic acids, randomly distributed at the three OH groups in glycerol. Thus, olive oil solves the dietary problems inherent in other plant oils. It furnishes low- melting-point fatty acids, which do not produce arterial plaque, yet they cannot oxidize because they are monounsaturated. There are not trans fatty acids, and almost no unsaturated ones. THE EXPERIMENT We will use olive oil as a model compound to illustrate the effects of catalytic hydrogenation, using palladium as the catalyst. Its molecular simplicity (monounsaturated fatty acids) makes the calculation of the fatty acid distribution straightforward. Although hydrogenation is usually done with hydrogen gas, we will use transfer hydrogenation, where hydrogen atoms are catalytically transferred from cyclohexene to the fatty acids in the triglyceride. The major component in olive oil is glyceryl trioleate. If there are no complications and the reaction goes to completion, the product is glyceryl tristearate: Page 7 7 H 2 C O C O (CH 2 ) 7 CH = CH (CH 2 ) 7 CH 3 H 2 C O C O (CH 2 ) 16 CH 3 H 2 C O C O (CH 2 ) 7 CH = CH (CH 2 ) 7 CH 3 H 2 C O CO (CH 2 ) 16 CH 3 PROCEDURE I. Hydrogenation of olive oil In a 5 mL conical microflask, place 400 mg of olive oil, 1 mL of cyclohexane, and 100 mg of 5% palladium on charcoal. The active ingredient in the catalyst is very finely divided Pd metal; the charcoal is an inert carrier. Add a boiling stone and a condenser, and reflux gently . . .
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