Submitted to: Dr.

MUREED ABBAS

Submitted by: MUHAMMAD ASIF

Class: B.S. Chemistry

Semester: 6th (Morning)

College Roll # 115

University Roll # 222603

Session: 2018-2022

Course Code: CHM-506

Course Title: Physical Chemistry-III

Government Postgraduate College Samanabad Faisalabad

Topic:

Azo dyes and their applications

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Azo dyes and their applications
Introduction to azo dyes:
Azo dyes contain at least one nitrogen-nitrogen
double bond (N=N); however, many different structures are possible. Monoao dyes have only
one N=N double bond, while diazo and triazole dyes contain two and three N=N double bonds,
respectively. The azo groups are generally connected to benzene and naphthalene rings, but can
also be attached to aromatic heterocycles or ionizable aliphatic groups. These side groups are
necessary for imparting the color of the dye, with many different shades and intensities being
possible. A common example of an azo dye. When describing a dye molecule, nucleophiles are
referred to as auxochromes, while the aromatic groups are called chromophores. Together, the
dye molecule is often described as a chromogen. Synthesis of most azo dyes involves
diazotization of a primary aromatic amine, followed by coupling with one or more nucleophiles.
Amino- and hydroxy- groups are commonly used coupling components. Because of the diversity
of dye components available for synthesis, a large number of structurally different azo dyes exist
and are used in industry. Worldwide production of organic dyes is currently estimated at nearly
450,000 tons, with 50,000 tons being lost in effluents during application and manufacture.

Applications of azo dyes:

1. In biological system:
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 Azo dyes acquired wide interest in application to
biological system and indicator in complexometric titration of analytical chemistry. Azo
dyes are the most important group of synthetic colorants. They are generally considered
as xenobiotic compounds that are very recalcitrant against biodegradative processes.
Aromatic azo compounds especially are used as acid-base indicators, also used in
biological strains and commercial colorants for clothing, plastics, cosmetics and food
beverages. Color changes are caused by change in extent of delocalization of electrons.
More delocalization shifts the absorption max to longer wave lengths and makes the light
absorbed redder, while less delocalization shifts the absorption max to shorter
wavelengths.

2. In pharmaceutical:
In pharmaceutical, azo linkage was used to protect drug
from undesirable reaction, such as prontosil was found to protect against, and cure
streptococcal infections in mice. Interestingly prontosil was inactive on bacterial cultures.
Prontosil is totally in active in vitro but possesses excellent activity in vivo. Due to the
highly variable nature of biological treatment systems and especially textile effluents,
there are a number of factors that may affect the biodegradation rate of azo dyes.
Throughout the literature, researchers have discussed various problems associated with
dye biodegradation that may or may not be anticipated or remedied. Non-dye related
parameters such as temperature, pH, type and source of reduction equivalents, bacteria
consortium, and cell permeability can all affect the biodegradation of azo dyes and textile
effluents. Dye related parameters such as class and type of azo dye (i.e., reactive-
monoao), reduction metabolites, dye concentration, dye side-groups, and organic dye
additives could also affect the biodegradability of azo dye wastewaters.

3. In biodegradation:
The azo dye structure can play a significant role in the dye
biodegradation rate. Depending on the number and placement of the azo linkages, some
dyes will biodegrade more rapidly than others. In general, the more azo linkages that
must be broken will cause the reduction rate to be slower. While there are not a large
number of studies that specifically address this factor, Brown and Laboureur5 observed

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 that two poly-azo dyes showed only moderate to variable biodegradation as compared to
four monoao and six diazo dyes. The authors indicate that poly-azo dyes are less likely to
degraded than mono- or diazo dye types.

4. Chemotherapeutic agents:
The azo dye sulfonamides antibacterial drugs
were the first effective chemotherapeutic agents that could be used systemically for the
cure of bacterial infection in humans. A series of azo dyes containing the sulfonamide
functional group were synthesized as potential antimicrobial agents, sulfonamide was
classified into three different types; antibacterial that are aniline-substituted
sulfonamides, prodrug that react to generate active sulfanilamide and non-aniline
sulfonamides. There are also other commonly used drugs that are azo dyes sulfonamides
or sulfanilamide (the diuretic furosemide, the diuretic chlortalidone and the oral
hypoglycemic drug tolbutamide). Today, there are a few sulfonamides and especially
sulfonamide–trimethoprim combination that are used extensively for opportunistic
infection in the patients with AIDS.

5. Miscellaneous applications:
These dyes are the most diverse group of all
synthetic dyes (-N≡N-) they are widely used in the fields of pharmacy, plastics, hypnotic
medicine, living cells cancer and pharmacological activities, biological, in high-tech
applications such as lasers and nonlinear optical systems, thermal transfer printers and
fuel cells. Also sensitized to solar cells, photodynamic therapy, metallochromic indicators
(Marche sky, 1985), dyeing of textiles, leather, paper, food (Dungan, 2019), cosmetics
(Zhi-Gang, 2009) and medicines (Khalid, 2008). The latter result from the combination
of the properties of the azo group and of types of substituted aromatic ligands. These dyes
are also known to be involved in a number of biological reactions such as DNA
inhibition, RNA and protein synthesis, carcinogenesis and nitrogen fixation. Furthermore,
the azo dyes are characterized by their physicochemical stability (Zhao, Y, 2009) and
optical properties with various applications in liquid crystals and the nanotubes. In recent
years, azo functionalized dyes bearing aromatic heterocyclic compounds have attracted
increasing attention due to their wide range of colors, luminosity, the simplicity of

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manufacture and good dyeing performance (Derkowska-Zielinska, 2017). In the
following paragraph, we have presented some recent applications of azo dyes such as
azo- polymer conjugation. The types of bond which favor this conjugation can be
covalent or non-covalent. The preparation of polymeric dyes for technical and industrial
applications is mainly carried out by the polymerization routes of colored monomers and
polymer-like fixing of dye molecules to preformed polymers since the corresponding
materials contain a higher dye concentration. Then, a tinctorial resistance is higher than
the molecular weight derivatives of the unique chromophores (Marechal, E, 1982).

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References

Azo dye - Wikipedia

Azo dye | chemical compound | Britannica

Classifications, properties, recent synthesis and applications ...