Abstract: . . .  C 18 C 18 , and C 18 C 18 C 18 should begin to melt at about 5 and be complete by about 25 even if a few percent stearate (C18 saturated) is present in the mixture. Rancidity Polyunsaturated fatty acids such as linoleic and linolenic oxidize easily in air. Thus, linseed oil, which contains a large percentage of linolenic acid, is an excellent vehicle for oil- based paint because oxidation cross-links the fatty acid molecules to form a strong film. However, what is good for paint evidently is not good for you. Just as excessively saturated fats are not part of a sound diet, neither are ones containing excessive amounts of polyunsaturated fatty acids (e.g. linoleic and linolenic). The CH2 interrupted multiple double bonds (called- homoconjugated) encourage oxidation, which breaks the hydrocarbon chains. The fragments, which usually terminate in an aldehyde group, are volatile and smelly. The fat is 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 . . .
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