What Is Benzene?
Benzene, an aromatic hydrocarbon, is recognized for its simple chemical structure. This colorless liquid, known for its sweet aroma, plays a fundamental role in petrochemistry and is found in crude oil. Its vapors are toxic, affecting hematopoietic function, and hence, it’s considered a hazardous air pollutant. Recent regulations have reduced benzene content in gasoline to less than 1% from approximately 5%.
Uses of Benzene
Benzene serves as a precursor to various aromatic compounds, finding applications in dyes, synthetic rubbers, detergents, pigments, rubber chemicals, pharmaceuticals, fragrances, fibers, resins, agricultural chemicals, explosives, and insect repellents. The styrene monomer, derived from benzene and ethylene, is particularly sought after for producing polystyrene used in electronics casings, insulation, and containers. Benzene also contributes to the production of nylon, polycarbonate, and polyurethane.
Properties of Benzene
With a melting point of 5.5°C and boiling point of 80.1°C, benzene’s volatility and flammability are notable. Its structure, a hexagonal ring (C6H6) with a molecular weight of 78.11 and density of 0.8765 g/cm3, showcases equal carbon bond distances due to delocalized pi-electrons, symbolized at times by a circle within a hexagon. When part of a substituent, this ring is termed a phenyl group or Ph.
Other Information on Benzene
1. Substitution Reaction of Benzene
Benzene primarily undergoes substitution rather than addition reactions. Examples include halogenation, yielding chlorobenzene and bromobenzene; sulfonation, producing benzene sulfonic acid; nitration, leading to nitrobenzene; and processes like alkylation and acetylation.
2. Addition Reaction of Benzene
Under ultraviolet light, benzene reacts with chlorine to form benzene hexachloride, also known as 1,2,3,4,5,6-hexachlorocyclohexane. Hydrogenation of benzene yields cyclohexane.
3. Benzene Synthesis
Benzene is synthesized by catalytic reaction of hydrocarbons with hydrogen, forming aromatic hydrocarbons through ring formation and hydrogen loss. Additionally, benzene and xylene can be derived from toluene, or benzene can be produced from acetylene using a catalyst. This versatility makes benzene an economically significant chemical raw material.