Question

What is(are) true regarding catalytic hydrogenation of alkene and alkyne ?
A. It is exothermic in nature
B. Heterogeneous catalyst may bring about hydrogenation
C. Homogeneous catalyst may bring about hydrogenation
D.Proceeds through a free radical intermediate

Answer 1

Hint: Hydrogenation is a chemical process that occurs when molecular hydrogen reacts with another molecule or element in the presence of a catalyst, such as nickel, palladium, or platinum. Organic molecules are often reduced or saturated using this method. Hydrogenation is the process of adding two hydrogen atoms to a molecule, most often an alkene. The process requires catalysts to be useful; non-catalytic hydrogenation occurs only at extremely high temperatures. Hydrogenation breaks down hydrocarbons' double and triple bonds.

Complete answer:
In most hydrogenation processes, three components are required: the substrate, the hydrogen supply, and the catalyst. Depending on the catalyst and substrate employed, the reaction is carried out at different temperatures and pressures. An alkene is converted to an alkane through hydrogenation. Hydrogen is added to compounds in a syn addition manner, with hydrogen being added to the same face of the molecule 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 of vegetable oils and fatty acids is an exothermic process that releases around 25 kcal/mol. The Horiuti-Polanyi process describes how hydrogenation happens on heterogeneous catalysts. The unsaturated bond attaches to the catalyst first, followed by HYDROGENdissociation onto the catalyst as atomic hydrogen. The hydrogenation process is then irreversibly completed by attaching one hydrogen atom to the substrate in a reversible phase, followed by the attachment of a second atom. By oxidative addition, the metal bonds to hydrogen to form a hydride complex for homogeneous catalysis.
a) All unsaturated hydrocarbon hydrogenation is exothermic.
b) In the hydrogenation process, H/Pt is a heterogeneous catalyst.
c) An example of homogeneous catalysis is hydroboration followed by RCOOH treatment.
d) The reaction is carried out by an adsorption process rather than a free radical mechanism.
As a result, choices A, B, and Care are accurate.

So, the correct answer is “Option A, B and C”.

Note:
The metal attaches to the substrate and then uses migratory insertion to move one of the hydrogen atoms from the metal to the substrate. The metal's second hydrogen atom is transferred to the substrate at the same time that the newly produced alkane is dissociated by reductive elimination.