A Short Note On Hydrogenation

A reduction reaction that results in the addition of hydrogen is known as hydrogenation (usually as H2). When an organic substance is hydrogenated, the hydrogen atoms become more “saturated.” Because hydrogenation occurs only at high temperatures, the process usually necessitates the presence of a catalyst. Nickel, platinum, and palladium are the most common catalysts.

What Is Hydrogenation and How Does It Work?

Hydrogenation is a chemical process that occurs when molecular hydrogen reacts with an element or molecule, usually with the help of a catalyst. The process could be one in which hydrogen merely adds to a double or triple bond joining two atoms in the molecule’s structure, or one in which hydrogen causes the molecule to dissociate (break up) (called hydrogenolysis, or destructive hydrogenation). Typical hydrogenation reactions include the formation of ammonia from hydrogen and nitrogen, as well as methanol or hydrocarbons from hydrogen and carbon monoxide, depending on the catalyst used.

In the presence of a catalyst, nearly all organic molecules having numerous bonds connecting two atoms can react with hydrogen. Hydrogenation of organic molecules (through addition and hydrogenolysis) is an important industrial reaction. The addition of hydrogen to liquid oils is used to produce edible fats. The destructive hydrogenation of hydrocarbons is used in many operations in the petroleum industry, including the production of gasoline and petrochemical compounds. The hydrogenation of coal to produce liquid fuels has become a popular alternative to petroleum extraction in the late twentieth century. The hydrogenation method gained industrial importance in 1897, when French chemist Paul Sabatier found that adding a trace of nickel as a catalyst enhanced the addition of hydrogen to carbon compound molecules.

In most hydrogenation reactions, three components are required: the substrate, the hydrogen supply, and the catalyst. Depending on the catalyst and substrate utilised, the reaction is carried out at different temperatures and pressures. An alkene is converted to an alkane by hydrogenation. Hydrogen is added to compounds in a syn addition manner, with hydrogen being added to the same face of the compound and entering from the least hindered side. By hydrogenation, alkenes become alkanes, alkynes become alkenes, aldehydes and ketones become alcohols, esters become secondary alcohols, and amides become amines.

Hydrogenation Reaction Examples

• Alkene: Ethene (C₂H₄) reacts with hydrogen at 150  ͦC to produce ethane (C₂H₄).

C₂H₄ + H₂ → C₂H₆

• Cycloalkene: Cyclohexene (C₆H₁₀) converts into cyclohexane (C₆H₁₂) by reacting with hydrogen in the presence of palladium (Pd) catalyst.

C₆H₁₀ + H₂ → C₆H₁₂

What Products Are Made by The Process Of Hydrogenation?

In the industry, hydrogenation is commonly employed. Hydrogenation is used to solidify, preserve, or purify a variety of products, raw materials, and substances. Hydrogenation is used to treat ammonia, fuels (hydrocarbons), alcohols, medicines, margarine, polyols, different polymers, and chemicals (hydrogen chloride and hydrogen peroxide).

Vegetable oil is the most typically hydrogenated product. Vegetable oil is converted from a liquid to a solid or semi-solid fat through hydrogenation. D-sorbitol syrup is created by hydrolyzing starches to produce dextrose, which is subsequently hydrogenated to produce sorbitol, or sugar alcohol. Hydrocracking, a process that breaks heavy crude’s long hydrogen carbon chains into lighter petroleum products like diesel, gasoline, and jet fuel, uses hydrogenation in the petroleum industry.\

Sources Of Hydrogen

H2 gas, which is normally accessible commercially within the storage medium of a pressurised cylinder, is the apparent source of hydrogen for hydrogenation. The hydrogenation process frequently takes more than one atmosphere of H2, which is normally supplied by cylinders and supplemented by “booster pumps.” Steam reforming is a technique that produces gaseous hydrogen from hydrocarbons in the industrial sector.   Hydrogen is transported from donor molecules such as formic acid, isopropanol, and dihydroanthracene in numerous applications. These hydrogen donors are dehydrogenated to carbon dioxide, acetone, and anthracene, respectively. Transfer hydrogenations are the name for these processes.

Hydrogenation Catalysts

Without metal catalysts, hydrogenation reactions between hydrogen and organic molecules will not occur below 480 degrees Celsius. Catalysts are responsible for attaching the H2 molecule and enabling the hydrogen-to-substrate conversion. Platinum, palladium, rhodium, and ruthenium are active catalysts that can function at low temperatures and pressures. Non-precious metal catalysts with similar activity at lower temperatures and pressures are now being researched. Raney nickel and other nickel-based catalysts have been created, although they still require high temperatures and pressures.

Catalysts are divided into two categories: homogeneous and heterogeneous catalysts.In the solvent containing the unsaturated substrate, homogeneous catalysts are soluble. In industry, heterogeneous catalysts are more frequent, and they are not soluble in the fluid containing the substrate.

Conclusion

Hydrogenation is used in petrochemical processes to saturate alkenes and aromatics, making them less poisonous and reactive. Because most vegetable oils are made up of polyunsaturated fatty acids, hydrogenation is also vital in their processing.

The hydrogenation technique is used to create ghee (saturated fat) from vegetable oils in the industrial world (unsaturated fat).