DESC:FIELD
The present disclosure relates to azo dyes and a process for preparation thereof.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Azo dyes: The term azo dyes includes the compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. IUPAC defines azo dyes as: "Derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g. PhN=NPh azobenzene or diphenyldiazene."
Disperse dyes: The term disperse dyes includes the organic azo compounds, which are free from ionizing groups, are essentially hydrophobic and are almost insoluble in water. These insoluble dyes are applied as very fine dispersions in water and therefore, they are known as “Disperse dyes”.
Liquor ratio: The term liquor ratio is an expression used in dyeing or finishing of textiles which defines the ratio of the weight of material (textiles) being treated to the weight of liquor used.
BACKGROUND
Dyes are colored substances which impart color by selective absorption of light. The coloristic properties of dyes are defined by their chemical structure.
Azo dyes are important raw material in the dye and pigment industry. Azo dyes represented by formula R-N=N-R', wherein R and R' can be either aryl or alkyl. The nature and orientation of substituents R and R' affects the color and dyeing properties of these compounds. Azo dyes absorb visible light resulting in characteristic p-delocalization. Particular delocalization energies correspond to particular wavelengths of visible light, thus resulting in vivid colors, especially reds, oranges, and yellows.
There is felt a need to provide azo dyes, having improved dyeing and printing properties for dyeing and printing various textile material.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide azo dyes.
Still another object of the present disclosure is to provide an azo disperse dye.
Yet another object of the present disclosure is to provide azo disperse dye for dyeing and printing textile material.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to azo dyes and a process for preparation thereof.
In first aspect, the present disclosure provides an azo dye of formula I.

The azo dye of formula I being characterized by having ?max value in the range of 490 to 505 nm.
In accordance with the embodiments of the present disclosure, the azo dye is represented by formula I, wherein ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity.
In accordance with the embodiments of the present disclosure, the azo dye of formula I is selected from the group constisting of:
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (1), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (2), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-acetoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (3), having ?max value of 492 nm and a shade of reddish orange,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propionyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (4), having ?max value of 492 nm and a shade of reddish orange,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-methoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (5), having ?max value of 500 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (6), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (7), having ?max value of 496 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-actoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (8), having ?max value of 493 nm and a shade of reddish orange, and
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propynyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (9), having ?max value of 494 nm and a shade of reddish orange.
In second aspect, the present disclosure provides a dye composition for dyeing textile material. The dye composition comprises,
(i) an azo dye of formula I, having ?max value in the range of 490 to 505 nm; and
(ii) at least one additive selected from the group consisting of a surfactant, a carrier, a thickener, a dispersing agent, and a wetting agent.
The azo dye of formula I is represented as:

The azo dye is represented by formula I, wherein ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity.
The dye composition is in the form of a powder having average particle size in the range of 1 micron to 3 micron.
In accordance with the embodiments of the present disclosure, the weight of the azo compound of formula I in the dye composition is in the range of 20 weight% to 60 weight%.
In accordance with the embodiments of the present disclosure, the azo dye of formula I is at least one selected from the group consisting of compounds 1 to 9.
In accordance with the embodiments of the present disclosure, the dispersing agent is at least one selected from the group consisting of lignosulfonate salts, and naphthalene sulfonate formaldehyde condensate. The weight ratio of lignosulfonate salt to naphthalene sulfonate formaldehyde condensate in the dye composition is in the range of 20:1 to 1:20.
In accordance with the embodiments of the present disclosure, the wetting agent is at least one selected from the group consisting of alkyl aryl ethoxylates.
In third aspect, the present disclosure provides a process for preparation of an azo dye of formula I. The process comprises diazotizing 2-amino-6-alkoxybenzothiazole of formula II with a diazotizing agent to obtain a 6-alkoxybenzothiazol-2-yl diazonium salt of formula III. The diazonium salt is coupled with a coupling component of formula IV in the presence of an aqueous acid having concentration in the range of 20 wt% to 80 wt%, at a temperature in the range of -10 to 10 °C, while stirring for a period of time in the range of 1 to 10 hours to obtain a product mixture comprising azo dye of formula I. The product mixture is treated with a base to adjust the pH of the product mixture to a value in the range of 1 to 5, followed by filtering the base treated product mixture to obtain a crude azo dye of formula I. The crude azo dye is washed with water, and dried at a temperature in the range of 50 to 150 °C to obtain the azo dye of formula I.
In accordance with the embodiments of the present disclosure, the diazotizing agent is nitrosyl sulphuric acid.
In accordance with the embodiments of the present disclosure, the diazonium salt III is in the form of an aqueous solution.
In accordance with the embodiments of the present disclosure, the weight ratio of the coupling component IV and the aqueous acid is in the range of 3:1 to 1:3.
In accordance with the embodiments of the present disclosure, the aqueous acid is selected from the group consisting of aqueous H2SO4 and aqueous HCl.
In accordance with one embodiment of the present disclosure, the aqueous acid is aqueous H2SO4.
In accordance with the embodiments of the present disclosure, the base is at least one selected from the group consisting of soda lye having concentration in the range of 20% to 55%.
In fourth aspect, the present disclosure provides a process for preparation of the dye composition comprising an azo dye of formula I. The process comprises adding an additive to an azo dye of formula I to obtain a mixture. The mixture is milled to obtain the dye composition comprising finely dispersed azo compound of formula I having average particle size in the range of 1 micron to 3 micron.
The step of milling is carried out using a mill selected from the group consisting of ball mill and sand mill.
The step of milling is carried out for a period of time in the range of 1 to 10 hours.
In fifth aspect, the present disclosure provides a process for dyeing or printing textile material using the dye composition of the present disclosure. The process comprises mixing the dye composition, water, and textile material in a dye bath to obtain a dyeing mixture and adjusting the pH of the dyeing mixture to a value in the range of 3 to 6, to obtain a dye bath comprising wetted textile material, wherein the dye composition is uniformly distributed throughout the wetted textile material. The wetted textile material is dyed by heating the dye bath comprising wetted textile material at a temperature in the range of 110 to 150 °C, and for a time period in the range of 0.5 to 2 hours, followed by cooling and reduction clearing to obtain the dyed textile material.
The dye composition of the present disclosure dyes the textile material in shades selected from the group consisting of yellowish-red, reddish orange and combinations thereof.
In accordance with the embodiments of the present disclosure, the textile material is selected from the group of synthetic fabric consisting of polyester (PES), and cellulose acetate.
DETAILED DESCRIPTION
Azo dyes are important raw material in the dye and pigment industry. The present disclosure relates to azo dyes and, more particularly, to azo dyes containing a substituted 6-alkoxybenzothiazole component, and a substituted 4-methyl-2,6-diaminopyridine component. The present disclosure provides azo dyes having improved light fastness, having improved wash fastness, and having improved dyeing and printing properties for textile material. Further, the present disclosure provides a simple, efficient, and economical process for the preparation of these azo dyes. The present disclosure relates to dyeing or printing textile material using the azo dyes of formula I.

In first aspect, the present disclosure provides azo dyes of formula I,

The azo dye of formula I being characterized by having ?max value in the range of 490 to 505 nm.
In accordance with the embodiments of the present disclosure, the azo dye is represented by formula I, wherein ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity.
In the azo dye of formula I, preferably ‘n’ is an integer selected from 2 or 3, preferably R1 is selected from the group consisting of a methyl and an ethyl moiety, preferably R2 is selected from the group consisting of a methyl, an ethyl, an isopropyl, an acetyl and a propionyl moiety, and preferably R3 is a cyano entity.

The azo dye of Formula I is selected from the group constisting of:

(1)
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (1), having ?max value of 495 nm and a shade of yellowish red,

(2)
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (2), having ?max value of 495 nm and a shade of yellowish red,

(3)
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-acetoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (3), having ?max value of 492 nm and a shade of reddish orange,

(4)
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propionyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (4), having ?max value of 492 nm and a shade of reddish orange,

(5)
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-methoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (5), having ?max value of 500 nm and a shade of yellowish red,

(6)
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (6), having ?max value of 495 nm and a shade of yellowish red,

(7)
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (7), having ?max value of 496 nm and a shade of yellowish red,

(8)
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-actoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (8), having ?max value of 493 nm and a shade of reddish orange, and

(9)
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propynyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (9), having ?max value of 494 nm and a shade of reddish orange.
Compounds 1 to 9 of the present disclosure are non-limiting examples of azo dyes of formula I.
The azo dye of formula I is used as a constituent of a dye composition.
In second aspect, the present disclosure provides a dye composition comprising an azo dye of formula I.
The dye composition of the present disclosure comprises:
1. an azo dye of formula I, having ?max value in the range of 490 to 505 nm.
and
2. at least one additive selected from the group consisting of a surfactant, a carrier, a thickener, a dispersing agent, and a wetting agent.
The dye composition of the present disclosure is in the form of a powder having average particle size in the range of 1 micron to 3 micron.
The azo dye of formula I is at least one selected from the group consisting of compounds 1 to 9.
In accordance with the embodiments of the present disclosure, the weight of the azo compound of formula I in the dye composition is in the range of 20 weight% to 60 weight%.
In accordance with one embodiment of the present disclosure, the weight of the azo compound of formula I in the dye composition is 40 weight%.
The dispersing agent is at least one selected from the group consisting of lignosulfonate salts, and naphthalene sulfonate formaldehyde condensate. The weight ratio of lignosulfonate salt to naphthalene sulfonate formaldehyde condensate in the dye composition is in the range of 20:1 to 1:20. In accordance with an exemplary embodiment of the present disclosure, the weight ratio of lignosulfonate sodium salt to naphthalene sulfonate formaldehyde condensate in the dye composition is 1.5:1.
The lignosulfonate salt is water-soluble salt of lignin sulfonate such as sodium salt.
The wetting agent is at least one selected from the group consisting of alkyl aryl ethoxylates. The alkyl aryl ethoxylates are optionally substituted by groups such as sulphonyl and phosphates.
Other additives such as brighteners, pigments, delusterants, inhibitors, stabilizers, and the like are used for preparing the dye composition comprising azo dye of the formula I.
The dye composition of the present disclosure is a disperse dye.
The dye composition of the present disclosure is suitable for dyeing textile material.
In third aspect, the present disclosure provides a process for preparing azo dye of formula I.
The process of the present disclosure for preparing azo dye of formula I involves the following steps:
An amine of formula II is diazotized to obtain a diazonium compound of formula III.

The diazonium compound of formula III is coupled with a coupling component of formula IV in the presence of an aqueous acid having concentration in the range of 20 wt% to 80 wt%, at a temperature in the range of -10 to 10 °C, while stirring for a period of time in the range of 1 to 10 hours to obtain a product mixture comprising azo dye of formula I.

The product mixture is treated with a base to adjust the pH of the product mixture to a value in the range of 1 to 5, followed by filtering the base treated product mixture to obtain a crude azo dye of formula I. The crude azo dye is washed with water, and dried at a temperature in the range of 50 to 150 °C to obtain the azo dye of formula I.
In accordance with the embodiments of the present disclosure, the diazotizing agent is nitrosyl sulphuric acid.
In accordance with the embodiments of the present disclosure, the molar ratio of 2-amino-6-alkoxybenzothiazole of formula II and the diazotizing agent can be in the range of 1:1 to 1:1.2.
In accordance with one embodiment of the present disclosure, the molar ratio of 2-amino-6-alkoxybenzothiazole of formula II and the diazotizing agent is 1:1.05.
In accordance with one embodiment of the present disclosure, the diazonium salt of formula III is in the form of an aqueous solution.
The weight ratio of the coupling component of formula IV and the aqueous acid is in the range of 3:1 to 1:3.
In accordance with one embodiment of the present disclosure, the weight ratio of the coupling component of formula IV and the aqueous acid is 1:1.
The aqueous acid is at least one selected from the group consisting of aqueous H2SO4 and aqueous HCl. Typically, the aqueous acid is aqueous H2SO4 and the concentration of the aqueous acid is 50 wt%.
The step of coupling is carried out for a period of time in the range of 1 to 10 hours, typically 5 hours.
In the coupling step, the rate of addition of the diazonium salt of formula III to the coupling component of formula IV is controlled so as to maintain the temperature of the reaction mixture in the range of 0 °C to 5 °C.
In accordance with one embodiment of the present disclosure, in the step of coupling, the addition of the diazonium salt of the formula III is carried out at 5 °C for 5 hours.
In the step of coupling, the product mixture is treated with a base to adjust the pH of the product mixture.
In accordance with the embodiments of the present disclosure, the base is selected from the group consisting of soda lye having concentration in the range of 20% to 55%.
In accordance with one embodiment of the present disclosure, in the step of coupling, the product mixture is treated with soda lye (25% NaOH) and the pH of the product mixture is adjusted to a value of 2. The product mixture is filtered to obtain crude azo compound of formula I. The crude azo dye of formula I is washed with water to obtain azo dye of formula I that is dried at 90 °C.
The yield of azo dye of Formula I is in the range of 90% to 95%, and the purity of azo dye of the Formula I is in the range of 98% to 99%.
In fourth aspect, the present disclosure provides a process for preparation of the dye composition. The process involves the following steps.
An additive is added to the azo dye of formula I to obtain a mixture. The mixture is milled to obtain the dye composition comprising finely dispersed azo compound of formula I, having average particle size in the range of 1 micron to 3 micron.
The step of milling is carried out using a mill selected from the group consisting of ball mill and sand mill.
The step of milling is carried out for a period of time in the range of 1 to 10 hours.
Optionally, the step of milling is carried out using water. When a fluid medium is used in the step of milling, the dye composition of the present disclosure is obtained in the form of a suspension. The dye composition obtained in the form of suspension is used as such for the process of dyeing.
Optionally, an additional step of drying is performed to remove the fluid medium from the suspension to obtain the dye composition in the form of a powder. The step of drying is accomplished by desirable means, including spray drying.
In fifth aspect, the present disclosure discloses a process for dyeing or printing textile material using the dye composition of the present disclosure. The process comprises following steps;
a. mixing the dye composition of the present disclosure, water, and textile material in a dye bath to obtain a dyeing mixture and adjusting the pH of the dyeing mixture to a value in the range of 3 to 6, to obtain a dye bath comprising wetted textile material, wherein the dye composition is uniformly distributed throughout the wetted textile material;
b. dyeing the wetted textile material by heating the dye bath comprising wetted textile material at a temperature in the range of 110 to 150 °C, and for a time period in the range of 0.5 to 2 hours, followed by cooling and reduction clearing to obtain the dyed textile material.
The dye composition of the present disclosure dyes a textile material in shades selected from the group consisting of yellowish-red, reddish orange and combinations thereof.
The dye composition of the present disclosure shows remarkable affinity for textile material.
The textile material is selected from the group of synthetic fabric consisting of polyester, and cellulose acetate.
The textile material is in the form of fibres, yarns, or fabrics. The fabric is in the woven (knitted), or non-woven form.
The application of the dye composition to the textile material is accomplished in compliance with known dyeing procedures. For example, exhaust process, and thermosol process, and other known dyeing processes.
The conventional dyeing procedure is varied by the substitution of other dispersing agents, surfactants, suspending agents, thickeners, and the like. The temperature and time of the dyeing procedure is also be varied.
The textile material dyed using the dye composition of the present disclosure produces predetermined percent of dyeing on the textile material, based on the weight ratio of the dye to the textile material.
The azo dyes of formulae 1-9 exhibit good to excellent dyeing and printing properties.
The textile materials dyed using the azo dyes of formulae 1-9 exhibit excellent light fastness, and perspiration fastness.
The process of the present disclosure uses commonly available and inexpensive reagents, and fluid media. Hence, the process of the present disclosure is simple, efficient, and economical.
The disclosure will now be described with reference to the accompanying experiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The experiment provided herein can be scaled up to industrial or commercial scale.

EXPERIMENTS
Experiment 1: Synthesis of 5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (1)
2-Amino-6-ethoxybenzothiazole (66 g, 0.34 mol) was diazotized using nitrosylsulfuric acid (1.05 equivalents) to obtain 6-methoxybenzothiazol-2-yl diazonium salt. The diazonium salt was added slowly to a mixture of 2,6-bis(3-ethoxypropylamino)-3-cyano-4-methyl pyridine (124 g, 0.39 mol) and 50% aqueous sulphuric acid (124 g) at 3 °C and the mixture was stirred for 5 hours to obtain a product mixture comprising azo compound of formula 1. Soda lye (25% NaOH) was added to the product mixture and its pH was adjusted to 2. The product mixture treated with soda lye was then filtered to obtain a crude azo compound of formula 1. The crude azo compound was washed with water to obtain sulfate free azo product, and then dried at 90 °C to obtain azo compound of the formula 1 (yield 90%).
The azo dyes of formulae 2-9 are prepared in analogy to the method described in Experiment 1.
The ?max values and shades of azo dyes of formulae 1-9 are summarized in Table-1.
Table 1: ?max values and shades of azo dyes of formula 1-9
Structure number ?max Shade
1 495nm Yellowish red
2 495nm Yellowish red
3 492nm Reddish orange
4 492nm Reddish orange
5 500 nm Yellowish red
6 495nm Yellowish red
7 496nm Yellowish red
8 493nm Reddish orange
9 494nm Reddish orange

Experiment 2: Preparation of dye composition comprising azo dye of formula I
Azo dye represented by formula 1 (40 g), and lignosulfonate sodium salt (36 g, based on 100% pure salt), and naphthalene sulfonate formaldehyde condensate liquid (24 g, based on 100% pure salt) were charged in a sand mill to obtain a mixture. The mixture was milled for 3 hours, and then spray dried to obtain a free flowing powder of the dye composition having a particle size of 1 micron, which is used for dyeing.
Experiment 3: Dyeing polyester fabric using the dye composition of the present disclosure comprising azo compound of formula I
A dye bath was prepared by mixing the dye composition (1 g) obtained in experiment 2, water (2000 ml), and polyester fabric (100 g), to obtain a dyeing mixture having a final liquor ratio of 1:20 w/w. The pH value of the dyeing mixture was adjusted to 4.5 with acetic acid to obtain a dye bath comprising wetted polyester fabric. The wetted polyester fabric in the bath was dyed by heating the dye bath comprising wetted polyester fabric at 130 °C for 60 minutes followed by cooling and then subjecting to reduction clearing in a mixture of a reducing agent and an alkali. The polyester fabric in the reduction clearing mixture was thoroughly washed and air-dried to obtain dyed polyester fabric in brilliant yellowish-red shade.
Similarly, the polyester fabrics were separately dyed using 2g, 3g, and 4g of the dye composition comprising azo compound of formula I, which corresponds to 2%, 3%, and 4% shades of the dye composition, respectively.
The dyed polyester fabrics obtained after dyeing with 2%, 3%, and 4% shades of the dye composition were tested for wash fastness, and perspiration fastness. The dyed textile materials were found to have good to excellent wash fastness, and perspiration fastness.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of;
• azo dyes that provide yellowish-red, and reddish orange shades;
• a simple, efficient, and economical process for the preparation of azo dyes;
• azo dyes having improved dyeing and printing properties; and
• azo dyes that impart good to excellent wash fastness, and perspiration fastness to the dyed textile material.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

,CLAIMS:WE CLAIM
1. An azo dye of formula I:

the azo dye being characterized by having ?max value in the range of 490 to 505 nm; and
wherein, ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity.
2. The azo dye as claimed in claim 1, wherein ‘n’ is an integer selected from 2 and 3.
3. The azo dye as claimed in claim 1, wherein R1 is selected from the group consisting of a methyl and an ethyl.
4. The azo dye as claimed in claim 1, wherein R2 is selected from the group consisting of a methyl, an ethyl, an isopropyl, an acetyl and a propionyl moiety.
5. The azo dye as claimed in claim 1, wherein R3 is a cyano entity.
6. The azo dye as claimed in claim 1, wherein the azo dye is at least one selected from the group consisting of:
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (1), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (2), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-acetoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (3), having ?max value of 492 nm and a shade of reddish orange,
5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propionyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (4), having ?max value of 492 nm and a shade of reddish orange,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-methoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (5), having ?max value of 500 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-ethoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (6), having ?max value of 495 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-isopropoxypropyl)amino]-4-methyl-3-pyridinecarbonitrile (7), having ?max value of 496 nm and a shade of yellowish red,
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-actoxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (8), having ?max value of 493 nm and a shade of reddish orange, and
5-[2-(6-ethoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-propynyloxyethyl)amino]-4-methyl-3-pyridinecarbonitrile (9), having ?max value of 494 nm and a shade of reddish orange.
7. A dye composition for dyeing textile material, said dye composition comprising:
i) an azo dye of formula I, as claimed in claim 1, having ?max value in the range of 490 to 505 nm;
wherein ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity,
and
ii) at least one additive selected from the group consisting of a surfactant, a carrier, a thickener, a dispersing agent, and a wetting agent;
wherein, the dye composition is in the form of a powder having average particle size in the range of 1 micron to 3 micron.
8. The dye composition as claimed in claim 7, wherein the weight of the azo compound of formula I in the dye composition is in the range of 20 weight% to 60 weight%.
9. The dye composition as claimed in claim 7, wherein the azo dye of formula I is at least one selected from the group consisting of compounds 1 to 9 of claim 6.
10. The dye composition as claimed in claim 7, wherein the dispersing agent is at least one selected from the group consisting of lignosulfonate salts, and naphthalene sulfonate formaldehyde condensate; wherein the weight ratio of lignosulfonate salt to naphthalene sulfonate formaldehyde condensate in the dye composition is in the range of 20:1 to 1:20.
11. The dye composition as claimed in claim 7, wherein the wetting agent is at least one selected from the group consisting of alkyl aryl ethoxylates.
12. A process for preparation of an azo dye of formula I,

the azo dye being characterized by having ?max value in the range of 490 to 505 nm; and
wherein, ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity,
said process comprising:
i. diazotizing 2-amino-6-alkoxybenzothiazole of formula II with a diazotizing agent to obtain a 6-alkoxybenzothiazol-2-yl diazonium salt of formula III;

ii. coupling the diazonium salt with a coupling component of formula IV in the presence of an aqueous acid having concentration in the range of 20 wt% to 80 wt%, at a temperature in the range of -10 to 10 °C, while stirring for a period of time in the range of 1 to 10 hours to obtain a product mixture comprising azo dye of formula I;

iii. treating the product mixture with a base to adjust the pH of the product mixture to a value in the range of 1 to 5, followed by filtering the base treated product mixture to obtain a crude azo dye of formula I;
iv. washing the crude azo dye with water, and drying at a temperature in the range of 50 to 150 °C to obtain the azo dye of formula I.
13. The process as claimed in claim 12, wherein the diazotizing agent is nitrosyl sulphuric acid.
14. The process as claimed in claim 12, wherein the diazonium salt III is in the form of an aqueous solution.
15. The process as claimed in claim 12, wherein the weight ratio of the coupling component IV and the aqueous acid is in the range of 3:1 to 1:3.
16. The process as claimed in claim 12, wherein the aqueous acid is selected from the group consisting of aqueous H2SO4 and aqueous HCl.
17. The process as claimed in claim 12, wherein the aqueous acid is aqueous H2SO4.
18. The process as claimed in claim 12, wherein the base is at least one selected from the group consisting of soda lye having concentration in the range of 20% to 55%.
19. A process for preparation of a dye composition comprising an azo dye of formula I,
wherein, ‘n’ ? 3, when R1 and R2 are both CH3, and R3 is a CN entity,
said process comprising:
a) adding an additive to an azo dye of formula I to obtain a mixture; and
b) milling the mixture to obtain the dye composition comprising finely dispersed azo compound of formula I, having average particle size in the range of 1 micron to 3 micron.
20. The process as claimed in claim 19, wherein the step of milling is carried out using a mill selected from the group consisting of ball mill and sand mill.
21. The process as claimed in claim 19, wherein the step of milling is carried out for a period of time in the range of 1 to 10 hours.
22. A process for dyeing or printing textile material using the dye composition as claimed in claim 7, said process comprising:
I. mixing the dye composition, water, and textile material in a dye bath to obtain a dyeing mixture and adjusting the pH of the dyeing mixture to a value in the range of 3 to 6, to obtain a dye bath comprising wetted textile material, wherein the dye composition is uniformly distributed throughout the wetted textile material; and
II. dyeing the wetted textile material by heating the dye bath comprising wetted textile material at a temperature in the range of 110 to 150 °C, and for a time period in the range of 0.5 to 2 hours, followed by cooling and reduction clearing to obtain the dyed textile material,
wherein the dye composition of the present disclosure dyes the textile material in shades selected from the group consisting of yellowish-red, reddish orange and combinations thereof.
23. The process as claimed in claim 22, wherein the textile material is selected from the group of synthetic fabric consisting of polyester (PES), and cellulose acetate.