Question

Explain the given reactions with the examples

1. Hydrogenation reaction
2. Oxidation reaction
3. Substitution reaction
4. Saponification reaction
5. Saponification reaction

Answer 1

1. When hydrogen is added to unsaturated hydrocarbons in the presence of a catalyst such as palladium or nickel to give saturated hydrocarbons, this reaction is called hydrogenation. It is commonly used in converting vegetable oils to animal fats.
   

   \[\begin{array}{cc}
   \ce{R}\phantom{.......}\ce{R}\phantom{................}\ce{H}\phantom{....}\ce{H}\phantom{......}\\
   \backslash\phantom{.....}/\phantom{..................}|\phantom{....}|\phantom{......}\\
   \ce{C = C ->[Nickel catalyst][H2] R - C -  C - R}\\
   /\phantom{.....}\backslash\phantom{..................}|\phantom{....}|\phantom{......}\\
   \ce{R}\phantom{......}\ce{R}\phantom{................}\ce{R}\phantom{...}\ce{R}\phantom{......}\\
   \end{array}\]

2. When oxygen is added to the starting material, it is called oxidation. For example, alcohols are converted to carboxylic acid on treating them with oxidising agents such as alkaline potassium permanganate or acidified potassium dichromate. Oxidising agents are capable of adding oxygen to other substances.
   \[\ce{CH3CH2OH ->[Alkaline KMnO4][Acidified K2Cr2O7] CH3COOH}\]
3. When one type of atom or a group of atoms takes the place of another, it is called substitution reaction. For example, chlorine can replace the hydrogen atoms one by one from saturated hydrocarbons when it is added in the presence of sunlight.
   \[\ce{CH4 + Cl2 \overset{sunlight}{->} CH3Cl + HCl}\]
4. When ester is treated with sodium hydroxide, it gives alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.
   \[\ce{CH3COOC2H5 \overset{NaOH}{->}C2H5OH + CH3COONa}\]
5. When a substance burns in oxygen, it is called combustion. Most carbon compounds release a large amount of heat and light on burning. 
   \[\ce{CH4 + 2O2 -> CO2 + 2H2O + Heat and light}\]