One Part of Chemistry: Synthesis of azo dyes

The diazonium salt is resonance stabilized:
To complete the synthesis of the azo dye, the diazonium salt reacts as an electrophile with an electron-rich coupling component, like a phenol, aniline and a beta-ketoacid derivative, through an electrophilic aromatic substitution mechanism.

Synthesis of Azo Dyes Mechanism of Synthesis of Azo Dyes

Synthesis, characterization and electrochemical studies of azo dyes derived ..

Mechanism of Decolorization of Azo Dyes in Anaerobic …

The diazo-coupling reaction dates back to the 1850s (and a close association with Imperial College via the first professor of chemistry there, ) and its mechanism was much studied in the heyday of physical organic chemistry. Nick Greeves, purveyor of the excellent site, contacted me about the transition state (I have on this aspect of aromatic electrophilic substitution). ChemTube3D recruits undergraduates to add new entries; Blue Jenkins is one such adding a section on dyes.

diazotisation reaction and synthesis of azodyes - …

Initial experiments using only SBP and H2O2 showed that unlike other dyes, CP6R was unable to be degraded by SBP/H2O2 alone (data not shown). It is well known that the presence of redox mediators such as 1-hydroxybenzotriazole (HOBT), veratryl alcohol, violuric acid, 2- methoxyphenothiazone, etc. can dramatically increase the rate of dye degradation[, , , ]. The mechanism involved is well known, wherein, the substrate initially undergoes an one-electron oxidation in the presence of a redox mediator and transforms into a radical cation followed by abstraction of a H-atom from the substrate by the mediator and converting it into a radical, which can then cause the substrate to co-oxidize[].

13/07/2000 · Mechanism of Decolorization of Azo Dyes in Anaerobic Mixed Culture ..
14/05/2017 · Synthesis of Azo Dyes The synthesis of an azo dye requires two organic compounds: 1) ..

The chemistry of isatins: a review from 1975 to 1999 - …

to form a diazonium salt.
the positively charged diazonium ion serves as the electrophile towards activated aromatic substrates,
Y can be –OH (phenol) or –NR2 (arylamine)

Factors Affecting Synthesis of Azo Dyes


The nitroanilines and naphthols are highly toxic.

The Chemistry of Isatins: a Review from 1975 to 1999


They are always prepared as needed under acidic conditions with good stirring, kept at or near zero degrees celcius
To minimize the thermal decomposition of diazonium ion and used immediately in the coupling reaction.
The pH of solution is quite important in azo coupling step

Temperature
pH

Phenols are usually coupled in alkaline conditions:

Anionic species are more water soluble than the phenol itself.
_O- group is more electron releasing than the _OH group and hence much strongly activates the ring towards electrophilic substitution.
Aromatic amines are coupled under mildly acidic or neutral conditions:
Because the amine is converted substantially into more water soluble protonated form (ArNH3+), but there is a significant equilibrium concentration of the free amine (ArNH2) which is more reactive towards azo coupling.
Reactive methylene based coulping components undergo azo coupling via the enolate anion, the concentration of which increases with increasing pH.
Combinatorial Synthesis of Azo Dyes
Azo dyes have vivid colours, especially reds, oranges, and yellows.
This diversification can be derived from both arenes.

Program | 6th World Congress and Expo on …

Bioremediation of azo dyes remains as a critical industrial and environmental issue in the 21st century. Azo dyes, characterized by the presence of azo bonds (-N = N-), remain as the largest group, 60-70% of commercially produced synthetic dyes that do not occur naturally (; ). The resistance of azo dyes to biological or chemical degradation is due to the azo linkages, the aromatic moieties and sulfonated substitutions that resulted in colour fastness and structural stability (). The lack of proper degradation of dyes presents other environmental hazard as the dyes and their metabolites may leach into the water bodies and pose health hazard ().