Carbon and its Compounds · Lesson 9 of 13
Oxidation, Addition Reaction And Substitution Reaction
“Carbon compounds can gain oxygen, add hydrogen or swap atoms depending on the bond.”
• Explain oxidation of ethanol to ethanoic acid. • Define oxidising agent and identify the agents named in the chapter. • Explain addition reactions and hydrogenation of unsaturated compounds. • Explain the role of catalysts such as nickel or palladium. • Distinguish addition reactions from substitution reactions.
Carbon compounds do more than burn. Their bonds and functional groups also allow characteristic reactions such as oxidation, addition and substitution. The reaction type often depends on whether the compound is saturated or unsaturated.
Oxidation
Carbon compounds can be oxidised during combustion, but oxidation can also occur without complete burning. Alcohols can be converted into carboxylic acids by adding oxygen.
An Oxidising Agent is a substance that adds oxygen to another substance or otherwise brings about its oxidation.
The chapter identifies alkaline potassium permanganate and acidified potassium dichromate as oxidising agents that convert ethanol to ethanoic acid.
Addition Reaction
An Addition Reaction is a reaction in which atoms are added across a multiple bond of an unsaturated compound, producing a more saturated product.
Unsaturated hydrocarbons can add hydrogen in the presence of catalysts such as nickel or palladium. The multiple carbon-carbon bond is converted toward single bonding as hydrogen atoms are added.
A Catalyst changes the rate of a reaction without itself being consumed in the overall reaction.
Hydrogenation Of Vegetable Oils
Vegetable oils generally contain long unsaturated carbon chains. Hydrogenation adds hydrogen in the presence of a nickel catalyst and converts unsaturated regions toward saturated structures. This industrial process changes the physical character of the oil.
Substitution Reaction
A Substitution Reaction occurs when one atom or group in a molecule is replaced by another atom or group.
Saturated hydrocarbons are relatively unreactive, but chlorine reacts rapidly with them in sunlight. In methane, one hydrogen atom is replaced by chlorine.
With higher alkanes, repeated replacement can produce several chlorinated products because more than one hydrogen atom may be substituted.
| Reaction | Typical Starting Material | Main Change |
|---|---|---|
| Oxidation | Alcohol | Oxygen added; alcohol can become carboxylic acid |
| Addition | Unsaturated hydrocarbon | Atoms add across C=C or C≡C |
| Substitution | Saturated hydrocarbon | One atom or group replaces another |
How To Distinguish Addition And Substitution
Addition reduces unsaturation by adding atoms across a multiple bond. Substitution keeps the basic saturated carbon framework but replaces one attached atom with another. The reactant structure therefore gives a strong clue to the reaction type.
Quiz
Which substances are named as oxidising agents for ethanol?
What happens during hydrogenation?
What is the role of nickel in hydrogenation?
Which reaction is a substitution reaction?
Which type of hydrocarbon most characteristically undergoes addition reactions?
Practice Problems
- Explain why conversion of ethanol to ethanoic acid is an oxidation reaction.
- Define oxidising agent and name the two oxidising agents used for ethanol in the chapter.
- Explain hydrogenation of an unsaturated hydrocarbon using a catalyst.
- Compare saturated vegetable fats and unsaturated vegetable oils using the bonding idea from the chapter.
- Explain the chlorination of methane as a substitution reaction.
- Create a comparison table for oxidation, addition and substitution reactions using one example for each.
Key Takeaways
• Ethanol can be oxidised to ethanoic acid using suitable oxidising agents. • Alkaline potassium permanganate and acidified potassium dichromate are oxidising agents named in the chapter. • Addition reactions add atoms across multiple bonds of unsaturated compounds. • Nickel or palladium can catalyse hydrogenation. • Substitution reactions replace one atom or group with another, as in chlorination of methane in sunlight.