FSc Notes Part 2 Chemistry Important Chemicals Ethane C2H6

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Introduction

Organic compounds which are composed, of only carbon and hydrogen atoms are known as hydrocarbons. Those hydrocarbons in which all the valencies of carbon atom are fulfilled by hydrogen atoms are called Saturated Hydrocarbon or alkenes.

The second member of alkane family composed of two carbon and six hydrogen atoms and is known as Ethane.

Structure of Ethane

Ethane is a saturated hydrocarbon, which is composed of two carbon and six hydrogen atoms. Its molecular formula is C2H6. The structural formula of ethane shows that each carbon contains three hydrogen and single bond is present between two carbon atoms.

H3C – CH3

Each carbon atom of ethane is Sp3 hyberidized which contains four equivalent partially filled Sp3 hybrid orbitals, these hybrid orbitals are arranged at the four corners of regular tetrahedron (tetra hedral structure) with an angle of 109.5º.

Three Sp3 hybrid orbitals of carbon atoms overlap with s atomic orbitals of hydrogen atoms to form a sigma bond between C – H due to the overlapping of Sp3 – S orbitals. The remaining Sp3 hybrid of each carbon atom overlapp with the Sp3 hybrid orbital of other carbon atom to form sigma bond between C – C due to the overlapping of Sp3 – Sp3

Preparation of Ethane

Ethane can be prepared by the following methods.

1. From Ethyl Magnesium Iodide

In presence of dry ether when alkyl halide reacts with magnesium metal then Alkyl Magnesium halide is formed. This compound was first synthesized by a German Chemist Grignard, therefore, it is also known as Grignard’s Reagent.

2. From Reduction of Ethyl Iodide

When Zn – Cu couple reacts with ethanol then nascent Hydrogen is obtained.

Zn – Cu + 2C2H5OH —-> (C2H5O)2Zn + Cu + 2[H]

Nascent Hydrogen acts as strong reducing agent. When methyl iodide is reduced with nascent hydrogen then methane is formed.

C2H5l + 2[H] —-> C2H6 – Hl

3. From Hydrogenation of Ethane

Introduction of hydrogen in a compound is called hydrogenation. In presence of catalyst Nickle, Palladium, when ethen is heated with hydrogen at about 250ºC then hydrogenation takes place as a result ethane is obtained.

C2H4 + H2 —-> C2H6

4. By Wurtz Synthesis

When methyl iodide is treated with dry sodium metal, then ethane is formed, in this reaction other products are also formed.

2CH3I + 2Na —-> C2H6 + 2NaI

Physical Properties of Ethane

1. At ordinary temperature and pressure ethane act as colourless gas.
2. Ethane gas is sparingly soluble in water but easily soluble in organic solvents.
3. Ethane gas is lighter then air.
4. The melting point, boiling point and specific gravity of ethane is greater than methane.

Chemical Properties of Ethane

Reactivity

Ethane is a saturated hydrocarbon, which is composed of two carbon and six hydrogen atoms. Its molecular formula is C2H6. The structural formula shows that all the valencies of carbon atoms are fulfilled by hydrogen atoms and single bond is present between two carbon atoms. Therefore, ethane is chemically unreactive. It does not react with any acid, base or oxidizing agents such as KMnO4 or K2Cr2O7. Under special circumstances ethane shows only substitution reaction.

Some important reactions of ethane are given below.

1. Halogenation

Introduction of halogen in a compound is called halogenation. In presence of sunlight when ethane reacts with chlorine (halogen) then chlorination (halogenation) takes place. As a result hydrogen atom of ethane is replaced by chlorine atom to form a substituted product, mono chloro ethane or ethyl chloride.

C2H6 + Cl2 —-> C2H5Cl + HCl

In presence of sunlight and excess chlorine further substitution takes place till all the hydrogen atoms are replaced by chlorine atom.

2. Combustion

When ethane is heated in presence of air or oxygen then carbondioxide and water are formed with the evolution of large amount of heat energy.

C2H6 + 5/2O2 —-> 2CO2 + 3H2O