Question

What happens when vegetable oils are hydrogenated? Name catalyst used.

Answer 1

Hint: Vegetable oils are basically polyunsaturated fatty acids. Unsaturated fatty acids are converted into saturated fatty acids by the hydrogenation process. Unsaturated fatty acids are liquids while saturated fatty acids are solids. Hydrogenation of vegetable oils is carried out by passing out hydrogen gas (${H_2}$) into the heated oil in the presence of a catalyst that does reduction.

Complete Solution :
- Hydrogenation is a process that reduces unsaturated fatty acids of triglycerides by attaching hydrogen atoms at the point of unsaturation in the presence of a catalyst. Hydrogenation of vegetable oils is carried out by passing out hydrogen gas (${H_2}$) into the heated oil in the presence of ‘powdered nickel as catalyst’. After hydrogenation vegetable oil is heated and the catalyst is recovered by filtration. The hydrogenation reaction of vegetable oil or unsaturated fatty acids can be shown as:

- Thus when vegetable oils which are polyunsaturated fatty acids are hydrogenated, double bonds get converted to single bonds or we get saturated compounds like vegetable ghee.
- Hydrogenation of vegetable oils (example: cotton seed oil, corn oil, or soybean oil) convert these liquids into solids having consistency comparable to that of butter. This process is also known as hardening of oil.
Also, hydrogenation of oil slows down the development of rancidity by decreasing the number of double bonds.
Hence, this is the required answer.

Note: In nearly all the naturally occurring unsaturated fatty acids, the double bonds are in cis-configuration. Trans fatty acids are produced by the partial hydrogenation of oils. Trans fatty acids are the result of side chain reaction with the catalyst of hydrogenation reaction.