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In organic chemistry, an azo coupling is an reaction between a diazonium compound (R−N≡N +) and another aromatic compound that produces an azo compound (R−N=N−R’).In this electrophilic aromatic substitution reaction, the aryldiazonium cation is the electrophile, and the activated carbon (usually from an arene, which is called coupling agent), serves as a nucleophile.
Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a functional group in a compound, which is typically, but not always, aromatic. Aromatic substitution reactions are characteristic of aromatic compounds and are common ways of introducing functional groups into benzene rings.
Electrophilic nitrogen sources are, however, either toxic or explosive in general. Great care should be taken while handling these reagents. Many electrophilic nitrogen sources do not provide amines immediately, but a number of methods exist to generate the corresponding amines. Tosylamines: tributyltin hydride; Azo compounds: H 2 /Pd
Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to ...
Anisole undergoes electrophilic aromatic substitution reaction at a faster speed than benzene, which in turn reacts more quickly than nitrobenzene.The methoxy group is an ortho/para directing group, which means that electrophilic substitution preferentially occurs at these three sites.
Formylation reactions are a form of electrophilic aromatic substitution and therefore work best with electron-rich starting materials. Phenols are a common substrate, as they readily deprotonate to excellent phenoxide nucleophiles. Other electron-rich substrates, such as mesitylene, pyrrole, or fused aromatic rings can also be expected to react.
Sulfur trioxide or its protonated derivative is the actual electrophile in this electrophilic aromatic substitution. To drive the equilibrium, dehydrating agents such as thionyl chloride can be added: [2] C 6 H 6 + H 2 SO 4 + SOCl 2 → C 6 H 5 SO 3 H + SO 2 + 2 HCl. Historically, mercurous sulfate has been used to catalyze the reaction. [3]
In this process, the diazonium compound is attacked by, i.e., coupled to, electron-rich substrates. When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution: [ArN 2] + + Ar'H → ArN 2 Ar' + H + The deep colors of the dyes reflects their extended conjugation.