What Is Azobenzene?
Azobenzene is an organic compound consisting of two benzene rings linked by an azo group (a nitrogen-nitrogen double bond). Its IUPAC name is diphenyldiazene, with a CAS number of 103-33-3 and a molecular weight of 182.22. Azobenzene has a melting point of 155°F and a boiling point of 560°F, existing as a solid at room temperature. It is insoluble in water, but soluble in organic solvents like ether, benzene, and alcohol.
The term “azobenzene” sometimes collectively refers to a group of aromatic azo compounds with various functional groups on the benzene ring.
Uses of Azobenzene
Azobenzene, including its derivatives, is widely used as a dye or pigment due to its ability to absorb visible light. Its rod-shaped structure also makes it useful as a mesogen group in liquid crystals. Azobenzene and its derivatives exhibit photochromic properties, undergoing trans-to-cis isomerization upon photoirradiation. These compounds are applied in fields such as light control materials, optical recording materials, optical switches, and functional inks.
Principle of Azobenzene
Azobenzene is characterized by its strong absorption of light in the ultraviolet and visible regions, making it suitable for use as a dye. The trans form of azobenzene is yellow, while the cis form is orange. Azobenzene has both cis and trans conformational isomers, with the trans form being more stable due to reduced steric repulsion between the benzene rings.
Light irradiation or heating can control the ratio of these isomers, a process known as photoisomerization and thermal isomerization. Irradiating trans azobenzene with light of 300-400 nm wavelength converts it to the cis form, and vice versa with light of 400 nm or longer.
Chemical Reactions of Azobenzene
Azobenzene is synthesized from nitrobenzene with tin (II) chloride and sodium hydroxide or sodium amalgam. Its oxidation yields azoxybenzene and hydrogenation produces 1,2-diphenylhydrazine. Azobenzene is also known as a metal ligand, forming complexes with metals like nickel.
Types of Azobenzene
Available azobenzene types include standard samples for melting point determination and reagent products in various volumes. Its derivatives are widely used as dyes, with typical compounds being methyl red and methyl orange. Derivatives are usually synthesized through diazo coupling due to the electron-rich nature of the substituted aromatic rings.