Hydrocarbons

Introduction 

Hydrocarbons are organic compounds composed completely of two types of atoms: Carbon and Hydrogen. They are typically colourless gases with extremely faint odours and have simple or moderate complex structures.

Hydrocarbons are divided into four subcategories: alkanes, alkenes, alkynes, and aromatic hydrocarbons. The study of hydrocarbons can reveal information on the chemical characteristics and manufacture of other functional groups. CxHy is the molecular formula for these substances

Hydrocarbons can be found in both plants and trees. Carotenes, for example, are indeed an organic pigment found in green leaves and carrots. Natural crude rubber is made up of 98 percent hydrocarbons. In addition, Liquefied Petroleum Gas (LPG) is made from hydrocarbons like propane and butane and is used as a commercial fuel. They also have a lot of internal energy, which adds to their significance.

Types of Hydrocarbons

The types of hydrocarbons are as followed-

1. Saturated Hydrocarbons– This substance is also known as alkane or paraffin. Paraffin is a Latin term that means “less active,” and these saturated hydrocarbons are called paraffin because of their lower activity. The general formula for a series is   CnH2n+2, where n is the number of members in the series. Organic compounds such as methane, ethane, propane, butane, pentane, and other saturated hydrocarbons have only one covalent bond between their carbon atoms. They have Sp3 hybridized carbon atoms but no Sp2 or Sp hybridized carbon atoms in terms of hybridization.
2. Unsaturated Hydrocarbons- A single, double, or triple bond between carbon-carbon atoms makes up these compounds. Alkenes and alkynes are double-bonded chemicals and triple-bonded compounds, respectively. Alkenes or olefin have the general formula CnH2n, while alkynes have the general formula CnH2n-2 and an example of which is ethane.
3. Cycloalkanes– One or more carbon rings can be found in these compounds. The carbon ring has a hydrogen atom linked to it.
4. Aromatic Hydrocarbons– They are also known as arenes. Arenes are organic compounds with at least one aromatic ring.
5. Aliphatic Hydrocarbons– There are no rings in these straight chain formations.
6. Alicyclic Hydrocarbons– These are the hydrocarbons that have a ring structure. The carbon atoms can be hybridized as Sp, Sp2, or Sp3.

Properties of Hydrocarbons

The empirical formula of hydrocarbons differs from one another due to their various molecular structures. Alkanes, alkynes or alkenes, for example, have less bonded hydrogen in alkenes and alkynes. This is due to carbon’s “self-bonding” or catenation, which prevents the hydrocarbon from becoming completely saturated by forming double or triple bonds. Catenation is the capacity of hydrocarbons to form bonds with one another.

Preparation of Hydrocarbons

1. Alkanes

• Alkanes can be prepared from alkenes and alkynes:

Through hydrogenation, alkanes can be made from alkenes or alkynes. To make alkane, H2 gas is transported over a metal surface such as Ni or Pt, together with the alkenes.

CH2=CH2 → (presence of H2/Ni) CH3-CH3

The reaction mentioned above is known as the “Sabatier-Sender son’s” reaction. Pt, Pd-BaSo4, Adams catalyst (Pt2O), Wilkinson catalyst (R3PRhCl), are some of the other catalysts which can be used in this preparation.

• Alkanes can be prepared by Alkyl Halides– they can be prepared by reduction of haloalkanes, using Grignard’s Reagent and by the Wurtz Reaction.
• From Carboxylic Acid- it includes preparation of alkane by heating it with soda lime, reduction of carboxylic acid, Kolbe’s Electrolysis (a method for the preparation of even number of Carbon atoms). 
• From alcohol, aldehyde and Ketones- In the presence of red phosphorus, when they are reduced with HI, it gives alkanes.

2. Alkenes

• By Haloalkanes- Dehydrohalogenation converts haloalkanes to alkenes. Dehydrohalogenation is the reaction in which a halogen acid such as HCl, HBr, or HI is removed from the neighboring carbon atoms of alkyl halides by reacting with an alcoholic solution of potassium hydroxide.
• From Alcohol- Here alkenes are formed by dehydration in the presence of Al2O3 or concentrated H2SO4.

3. Alkynes

• Preparation of  Acetylene from Calcium Carbide and water.
• From Dihaloalkanes- Ethyne is made by heating geminal dihaloalkanes (those with both halogens connected to the same carbon atom) or vicinal dihaloalkanes (those with halogen atoms attached to neighbouring carbon atoms) in an alcoholic solution of KOH.
• Reaction of alkynides of lower alkynes with primary alkyl halides.

Application of Hydrocarbons

1. They are used as lubricants and grease.
2. Hydrocarbons are used as fuel.
3. Used in manufacture of drugs and dyes.
4. Helps in the manufacture of polymers such as polyethylene, polystyrene etc.

Conclusion

Hydrocarbons are the parent organic compounds, from which other organic compounds can be made by substituting different functional groups for one or more hydrogen atoms.