Schematic chemical representation of hydrogenation.
Hydrogenation or hardening is a chemical process in which an unsaturated bond is converted to a saturated bond by addition of hydrogen gas, for example a double carbon bond that is converted to a saturated carbon bond. For hydrogenation, nickel powder is usually used as a catalyst. The formation of this saturated alkane is effected by a syn addition to produce cis additive products.
The first catalytic routes to hydrogenate hydrocarbons were found around 1900 (for example, by Paul Sabatier and Jean-Baptiste Senderens), and it became important, inter alia, to expand the scope of vegetable oils in margarines (Wilhelm Normann) ( curing fats and fatty acids).
The role of the catalyst is to weaken the strong covalent bond in the dihydrogen molecule. In the adsorption of hydrogen through a metal crystal, the electron cloud of that bond is partially redistributed to the metal atoms.
In reaction of fats, the reaction from phase 1 (see figure) to phase 2 is reversible. If in the reaction of 2 to 1 another hydrogen atom (in the figure, only one hydrogen atom is drawn to carbon, in practice, there are two hydrogen atoms in carbon) in the catalyst is transferred to the catalyst than the hydrogen atom during the step of 1 to 2 is linked to the double band, the CIS form can pass through this reaction into the TRANS form. If the curing process is not fully continued (partial hardening or hydrogenation), where all double bonds are hydrogenated, the fat contains trans fat. Only fully hardened fat contains no unsaturated fatty acids more and therefore no transfats.
Vegetable oils, such as rapeseed oil, soybean oil, palm oil, olive oil and sunflower oil contain relatively unsaturated fatty acids. As a result, they have a relatively low melting point; at room temperature they are usually liquid. By curing these oils, the melting point is increased. That is an important step in the production of margarine from vegetable oil.
This kind of catalyzed reactions are also used in the production of ammonia.
The reverse reaction, wherein a saturated compound is converted into an unsaturated compound by hydrogen withdrawal, is called dehydrogenation.
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