Reduction reactions can be defined by two concepts :
- Classical or old concept.
- Electronic concept or new concept.
Classical Concept of Reduction Reactions
According to the classical concept, reduction reaction is defined as the addition of hydrogen or removal of oxygen.
To depict the classical concept of reduction, let us look at the following example :
Cl2+ H2 → HCl In the above reaction, Hydrogen is added to chlorine to form hydrogen chloride. Thus, chlorine gas is getting reduced to form hydrochloric acid.
H2S + Cl2 → 2HCl + S
Same as the first example, Hydrogen is added to chlorine by hydrogen sulfide, thereby reducing chlorine.
Reducing Agent
A substance which provides or supplies hydrogen or removes oxygen is said to be a reducing agent according to the classical concept. So, in the above example, since hydrogen sulfide is providing hydrogen to chlorine, Hydrogen sulfide is the ‘reducing agent’.
ZnO + C → Zn + CO
In the above reaction, carbon removes oxygen from zinc oxide, thereby reducing the zinc oxide.
This, carbon here is the reducing agent.
Fe2O3+ 3CO → 2Fe + 3CO2
Carbon monoxide acts as a reducing agent and takes away oxygen from Fe2O3.
Electronic Concept of Reduction
A new concept, the electronic concept explains reduction reaction more clearly. These are defined in terms of electron transfer between the reactants, known as electronic concept of oxidation and reduction.
According to this concept, reduction is a process in which an atom or group of atoms taking part in chemical reaction gains one or more number of electrons. The eventual gain of electrons results in the decrease in positive charge or increase of negative charge of the species.
Examples of Reduction Reactions
Gain of electrons resulting in decrease in positive charge
Fe3+ + e- → Fe2+
Iron (III) ion gains one electron and changes to Iron (II) ion, and hence gets reduced.
Sn4+ + 2e-→ Sn2+
Tin (IV) gets reduced to tin (ii) ion, with the addition of electrons.
Gain of electrons resulting in increase in negative charge
MnO4-+ e-→ MnO4 2-
With the gain of electrons, MnO4- is reduced to MnO4 2-.
With the increase in negative charge, the oxidation number is decreased.
Reduction Reaction Example
Na + Ag+ → Na+ + Ag
In this reaction, sodium reduces silver ion to silver. So, sodium is the reducing agent.
Silver ion, on the other hand, has oxidized sodium to sodium ion (increase in oxidation number). Silver, therefore, is the oxidizing agent. This is a redox reaction since reduction and oxidation take place together.
Reduction reaction in organic chemistry
You can reduce aldehyde and ketone by using Raney Nikel at 413k to given 1 and 2 alcohol compound.
G.R; CHO / R-COR -> alcohol
Also we can reduce carboxylic acid by using LiAlH4 as reducing agents its give alcohol and also by using NaBH4 we also reduce acid to get alcohol compund
Also by using Na-Hg/H2O as reducing catalyst provide nescent hydrogen which can reduce carbonyl compound to produce alcohol molecules .