azoalkanes

Azoalkanes are organic compounds that contain the functional group R-N=N-R', where R and R' are alkyl or aryl groups. This group is characterized by two nitrogen atoms joined by a double bond, with each nitrogen atom also bonded to a carbon atom of an alkyl or aryl substituent. The general formula for azoalkanes is R1R2N=NR3R4 where R1, R2, R3, and R4 are hydrogen or alkyl/aryl groups. However, the term azoalkane specifically refers to compounds where R and R' are alkyl groups. Azo compounds with aryl substituents are called azoarenes.

Azoalkanes are typically colored compounds, often yellow or orange, due to the presence of the azo group which acts as a chromophore. This coloration is a result of the delocalization of pi electrons across the N=N double bond and into the adjacent carbon atoms. They are generally stable compounds, but can undergo decomposition under certain conditions.

One of the key chemical properties of azoalkanes is their ability to undergo thermal or photochemical decomposition. Upon heating or irradiation with UV light, the carbon-nitrogen bond cleaves, leading to the extrusion of nitrogen gas (N2) and the formation of free radicals. These radicals can then participate in various subsequent reactions, such as dimerization, hydrogen abstraction, or rearrangements. This radical-generating property makes azoalkanes useful as initiators in polymerization reactions, such as the free radical polymerization of alkenes. For example, azobisisobutyronitrile (AIBN) is a commonly used thermal initiator in radical polymerizations.

Azoalkanes are synthesized through various methods. One common route involves the oxidation of hydrazines. Another method is the coupling of diazonium salts with organometallic reagents, though this is more common for azoarenes. The reduction of nitroso compounds or oximes can also lead to the formation of azoalkanes. Their reactivity and ease of generation of radicals make them important intermediates and reagents in organic synthesis.