Question

An unsaturated fat that is liquid at room temperature, such as olive oil can react in the presence of Pd/C without a hydrogen source to form a solid fat of the same formula. Explain what process besides hydrogenation could be taking place.

Answer 1

Hydrogenation – to treat with hydrogen – is a chemical reaction between molecular hydrogen (H₂) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. Unsaturated fats exposed to air oxidize to create compounds that have rancid, stale, or unpleasant odors or flavors. Hydrogenation is a commercial chemical process to add more hydrogen to natural unsaturated fats to decrease the number of double bonds and retard or eliminate the potential for rancidity. Unsaturated oils, such as soybean oil, which contain unsaturated fatty acids like oleic and linoleic acid, are heated with metal catalysts in the presence of pressurized hydrogen gas. Hydrogen is incorporated into the fatty acid molecules and they become saturated with hydrogen. Oleic acid (C18:1) and linoleic acid (C18:2) are both converted to stearic acid (C18:0) when fully saturated. The liquid vegetable oil becomes a solid saturated fat (shortening with a large percentage of tristearin). By comparison, animal fats seldom have more than 70% saturated fatty acid radicals. Lard, for example, has 54% unsaturated fatty acid radicals.