Hydrocarbons – Preparation and Properties of Alkanes

“Hydrocarbon” is a term that refers to a class of organic compounds made completely of carbon and hydrogen. These gases are produced by different substances and have an easily recognisable smell. LPG, CNG, and lamp fuel – all incorporate a combination of these energy-delivering synthetic compounds.

Hydrocarbons and their subsidiaries account for the greater part of the universe’s mass. For instance, twofold connections among C=C and C-C create extensive chains, bringing about a rubbery surface in normal elastic. Oil and petroleum gas are hydrocarbons. These mixtures are additionally utilised as natural substances in plastics, filaments, and elastic products. These mixtures are likewise utilised as solvents, and they are also used to make explosives.

Classification of Hydrocarbons

They can be divided into three categories based on the carbon-carbon bonds present. The categories are as follows:

(i) Saturated

(ii) Unsaturated 

(iii) Aromatic hydrocarbons

Saturated hydrocarbons

The carbon particles in these hydrocarbons are consolidated by a solitary bond, and there’s nothing more to it. The expression used to portray them is “saturated hydrocarbons.” All the carbon particles in these natural mixtures are connected to four different components to keep away from numerous carbon-carbon bonds. It is critical to distinguish between non-cyclic saturated hydrocarbons and cyclic immersed hydrocarbons.

Properties of Alkanes

• Saturated hydrocarbons are used to refer to alkanes – acyclic hydrocarbons.

• Methane (CH4) is the first member of this family. Methane is a gas found in coal mines and marshy places.

• Adding a hydrogen atom and completing the valency, we get ethane (C2H6), and the next molecules will be C3H8 C4H10.

• The general formula for alkanes is CnH2n+2.
• All carbon atoms in alkanes are sp3 hybridised.

• The melting point and the boiling point of an alkane are directly related to the length of its carbon chain.

• Due to weak Van der Waals forces, alkanes generally have low boiling and melting points.

Examples of Alkanes:

1. Pentane (C5H12)
2. Methane (CH4)
3. Heptane (C7H16)
4. Nonane (C9H20)
5. Ethane (C2H6)
6. Propane (C3H8)
7. Butane (C4H10)
8. Hexane (C6H14)
9. Octane (C8H18)
10. Decane (C10H22)

Cycloalkanes: Many different chemicals have been hybridised with sp3 carbon atoms to form cycloalkanes. Saturated hydrocarbons may have side chains due to the rings being divided. They are chemically similar to alkanes, but their boiling and melting points are higher. The presence of cis- or trans- prefixes distinguishes between geometric isomers.

1. Cyclopropane is also known as trimethylene. It is an explosive, colourless gas often employed as a general anaesthetic in medicine. It is a gas with an odour that is similar to petroleum ether in nature.
2. Cyclobutane: It is a colourless gas commercially accessible as a liquified gas and is utilised in medicinal formulations.
3. Cyclohexane: It is a colourless, flammable liquid with a characteristic detergent-like odour that may be found in large quantities. They are employed in the production of nylon and industrial operations as a solvent.

Alkanes from Alkenes and Alkynes

The hydrogenation process may result in the conversion of alkenes and alkynes into alkanes via a chemical reaction that occurs throughout the process. It is possible to make alkenes when H2 gas is passed over a metal surface, such as platinum, and you get alkanes when nickel is employed as a metal surface.

CH2=CH2  + H2/Ni → CH3-CH3

The above response is characterised as the “Sabatier-Sanderson’s” response. Different impetuses utilised are Pt, Adams impetus (Pt2O), Wilkinson impetus (R3PRhCl), Pd-BaSO4, and so on.

From alkyl halides

Alkyl halides can be converted to alkanes through various methods. They are as follows:

1. Using Zn/Protic solvents
2. Using courts reactions

Note: Alkanes with only an even number of carbons atoms can be produced.

1. Using Reducing Agents: R-X + [H] → R – H

The reducing agents which can be used are LiAlH4, NaBH4, NaNH2, etc.

E2 Mechanism

• Second-order kinetics
• Single-step process

Order and reactivity 1° > 2° > 3° 

Because of steric hindrance

• More favoured in non-polar, aprotic solvents
• Less substituted alkenes formed as a major product

E1 Mechanism

• Two-step process
• 1st order kinetics

Order of reactivity: 3° > 2° > 1°

Because of the stability of carbonation

• More favoured by polar, protic solvents
• Rearrangement is possible
• It gives more substituted alkenes as major products

Conclusion 

Hydrocarbons like isobutane, which are increasingly being utilised in freezers in the United States, will be employed in a wide range of applications in the future. It is expected that refrigerants such as R290 and R600a will continue to be used in the future. A wide variety of items and even businesses will use these hydrocarbons. Hydrocarbons hold a lot of promise.