Claims:

WE CLAIM
1. An azo disperse dye comprising:
i) azo compound of formula (I) having ?max value of 495 nm; and

ii) at least one additive;
wherein, the azo disperse dye is in the form of powder having average particle size in the range of 1 micron to 3 microns.
2. The azo disperse dye as claimed in claim 1, wherein the weight of the azo compound of formula (I) in the azo disperse dye is in the range of 20 weight% to 60 weight%.
3. The azo disperse dye as claimed in claim 1, wherein the additive is at least one selected from the group consisting of dispersing agent, and wetting agent.
4. The azo disperse dye as claimed in claim 3, wherein the dispersing agent is at least one selected from the group consisting of lignosulfonate salts, and naphthalene sulfonate formaldehyde condensate.
5. The azo disperse dye as claimed in claim 3, wherein the wetting agent is at least one selected from the group consisting of alkyl aryl ethoxylates.
6. A process for preparation of the azo disperse dye as claimed in claim 1, said process comprising:
a) adding at least one additive to the azo compound of formula (I) to obtain a mixture; and
b) milling the mixture to obtain the azo disperse dye comprising finely dispersed azo compound of formula (I), having average particle size in the range of 1 micron to 3 microns.
7. A process for dyeing synthetic fabric using the azo disperse dye as claimed in claim 1, said process comprising:
I. mixing the azo disperse dye, water, and synthetic fabric in a dye bath to obtain a dye bath comprising wetted fabric; wherein the azo disperse dye is uniformly distributed throughout the wetted fabric; and
II. dyeing said wetted fabric to obtain dyed synthetic fabric; wherein the azo disperse dye colors the synthetic fabric in yellowish-red shades.
8. The process as claimed in claim 7, wherein the synthetic fabric is selected from the group consisting of polyester (PES), and cellulose acetate.
, Description:
FIELD
The present disclosure relates to an azo disperse dye and a process for preparation of the same.
DEFINITIONS
As used in the present disclosure, the following term is 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 compounds: The term azo compounds 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 compounds as: "Derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g. PhN=NPh azobenzene or diphenyldiazene."
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
Azo compounds are important raw material in the dye and pigment industry.
Organic azo compounds, which are free from ionizing groups, are essentially hydrophobic and are almost insoluble in water. Insoluble dyes can be applied in the form of very fine dispersions in water and therefore, they are known as “Disperse dyes”.
There is, therefore, felt a need to provide azo disperse dye, having improved dyeing and printing properties for dyeing various synthetic fibres.

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 an azo disperse dye.
Still another object of the present disclosure is to provide a process for the preparation of an azo disperse dye.
Still another object of the present disclosure is to provide an azo disperse dye for dyeing and printing of synthetic fibers.
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 an azo disperse dye and a process for preparation of the same.
In accordance with the present disclosure, the azo disperse dye comprises an azo compound of formula (I) having ?max value of 495 nm, and at least one additive.

The azo disperse dye is in the form of powder having average particle size in the range of 1 micron to 3 microns.
In accordance with the embodiments of the present disclosure, the weight of the azo compound of formula (I) in the azo disperse dye is in the range of 20 weight% to 60 weight%.
In accordance with the embodiments of the present disclosure, the additive is at least one selected from the group consisting of dispersing agent, and wetting agent.
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.
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 accordance with the present disclosure, the process for preparation of the azo disperse dye comprises the step of adding at least one additive to the azo compound of formula (I) to obtain a mixture. The mixture is milled to obtain the azo disperse dye comprising finely dispersed azo compound of formula (I), having average particle size in the range of 1 micron to 3 microns.
In accordance with the present disclosure, the process for dyeing synthetic fabric using the azo disperse dye comprises the step of mixing the azo disperse dye, water, and synthetic fabric in a dye bath to obtain a dye bath comprising wetted fabric. The azo disperse dye is uniformly distributed throughout the wetted fabric. The wetted fabric is dyed to obtain dyed synthetic fabric. The azo disperse dye colors the synthetic fabric in yellowish-red shades.
In accordance with the present disclosure, the synthetic fabric is selected from the group consisting of polyester (PES), and cellulose acetate.
DETAILED DESCRIPTION
Azo compounds are important raw material in the dye and pigment industry. The present disclosure envisages a simple, efficient, and economical process for the preparation of an azo disperse dye having improved dyeing and printing properties for synthetic fibers.
In first aspect, the present disclosure provides a process for preparing an azo compound of formula (I).

IUPAC name: 3-Pyridinecarbonitrile, 5-[2-(6-methoxy-2-benzothiazolyl)diazenyl]-2,6-bis[(3-methoxypropyl)amino]-4-methyl-
CAS number: 56113-12-3
The process of the present disclosure for preparing azo compound of formula (I), involves the following steps:
2-Amino-6-methoxybenzothiazole (III) is diazotized to obtain 6-methoxybenzothiazol-2-yl diazonium salt (IV).

The diazonium salt (IV) is coupled with 2,6-bis[(3-methoxyalkyl)amino]-3-cyano-4-methyl pyridine (V), in the presence of an aqueous acid, to obtain a product mixture comprising the azo compound of formula (I).

Azo compound of formula (I) is separated from the product mixture.
The azo compound of formula (I) of the present disclosure is characterized by a melting point in the range of 168 °C to 170 °C.
The azo compound of formula (I) of the present disclosure has characteristic ?max of 495 nm in toluene.
The azo compound of formula (I) of the present disclosure has characteristic yellowish-red hue.
The process of the present disclosure provides azo compound of formula (I) with purity of 98.5% by HPLC analysis.
In accordance with the embodiments of the present disclosure, the weight ratio of 2,6-bis[(3-methoxyalkyl)amino]-3-cyano-4-methyl pyridine (V) and the aqueous acid is in the range of 5:1 to 1:5, typically 1:1.
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.
The concentration of the aqueous H2SO4 is in the range of 20 wt% to 80 wt%, typically 50 wt% H2SO4.
In accordance with the embodiments of the present disclosure, the step of coupling is carried out at a temperature in the range of -10 °C to 10 °C, typically at 3 °C.
In accordance with the embodiments of the present disclosure, the step of coupling is carried out for period of time in the range of 1 to 10 hours.
In the coupling step, the diazonium salt (IV) is added slowly to 2,6-bis[(3-methoxyalkyl)amino]-3-cyano-4-methyl pyridine (V). The rate of addition of the diazonium salt (IV) is controlled in such a way that the temperature of the reaction mixture is maintained in the range of 0 °C to 5 °C.
In accordance with the preferred embodiment of the present disclosure, diazonium salt (IV) is in the form of a mixture with water.
In second aspect, the present disclosure provides an azo disperse dye comprising azo compound of formula (I). The azo disperse dye of the present disclosure comprises:
1. azo compound of formula (I), having ?max value of 495 nm; and
2. at least one additive.
The azo disperse dye of the present disclosure is in the form of powder having average particle size in the range of 1 micron to 3 microns.
In accordance with the embodiments of the present disclosure, the weight of the azo compound of formula (I) in the azo disperse dye 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 azo disperse dye is 40 weight%.
The additive is at least one selected from the group consisting of dispersing agent, and wetting agent. Other additives such as carrier and dyeing assistant can also be used for preparing the azo disperse dye.
The dispersing agent is at least one selected from the group consisting of lignosulfonate salts, and naphthalene sulfonate formaldehyde condensate.
The wetting agent is at least one selected from the group consisting of alkyl aryl ethoxylates. The alkyl aryl ethoxylates may be substituted by groups such as sulphonyl and phosphates.
The dispersing agent is a mixture of lignosulfonate sodium salt, and naphthalene sulfonate formaldehyde condensate. The weight ratio of lignosulfonate sodium 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.
In third aspect, the present disclosure provides a process for preparation of the azo disperse dye of the present disclosure. The process involves the following steps.
A mixture comprising the azo compound of formula (I) and at least one additive is provided. The mixture is milled to obtain the azo disperse dye comprising a finely dispersed azo compound of formula (I), having average particle size in the range of 1 micron to 3 microns.
The step of milling can be carried out using various means, including ball mill and sand mill.
In accordance with one embodiment of the present disclosure, the step of milling is carried out using sand mill.
The step of milling is carried out for a period of time in the range of 1 to 10 hours.
In accordance with one embodiment of the present disclosure, the step of milling is carried out for 3 hours.
Optionally, a fluid medium is used in the step of milling. In accordance with the embodiments of the present disclosure, the fluid medium is water. Other fluid media can also be used for milling. When a fluid medium is used in the step of milling, the azo disperse dye of the present disclosure is obtained in the form of a suspension. The azo disperse dye 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 azo disperse dye in the form of powder. The step of drying is accomplished by various means, including spray drying.
In fourth aspect, the present disclosure provides a process for dyeing synthetic fabric using the azo disperse dye of the present disclosure. The process for dyeing synthetic fabric using the azo disperse dye of the present disclosure comprises following steps;
a. mixing the azo disperse dye of the present disclosure, water, and synthetic fabric in a dye bath to obtain a mixture and adjusting the pH of the mixture to a desired value to obtain a dye bath comprising wetted fabric, wherein the azo disperse dye is uniformly distributed throughout the wetted fabric;
b. dyeing the wetted fabric by heating the dye bath comprising wetted fabric at a predetermined temperature, and for a predetermined time period, followed by cooling and reduction clearing to obtain the dyed synthetic fabric.
The azo disperse dye of the present disclosure dyes a synthetic fabric in yellowish-red shades.
The liquor ratio is a ratio of the weight of the synthetic fabric to the weight of liquor of the disperse dye. In accordance with the embodiments of the present disclosure, the liquor is water.
In accordance with the embodiments of the present disclosure, in the step of mixing, the liquor ratio is in the range of 1:5 to 1:50 w/w.
In accordance with one embodiment of the present disclosure, in the step of mixing, the liquor ratio is 1:20 w/w.
The weight ratio of the azo disperse dye to the synthetic fabric is in the range of 0.1:100 to 10:100.
In accordance with one embodiment of the present disclosure, the weight ratio of the azo disperse dye to the synthetic fabric is 1:100.
In the step of mixing, the pH of the mixture comprising the azo disperse dye is adjusted in the range of 4 to 6.
In accordance with one embodiment of the present disclosure, in the step of mixing, the pH of the mixture comprising the azo disperse dye is adjusted to 4.5.
The synthetic fabric is selected from the group consisting of polyester (PES), and cellulose acetate.
In accordance with one embodiment of the present disclosure, the synthetic fabric is polyester (PES).
The pH of the dye bath is adjusted using acid, typically acetic acid.
The step of mixing is carried out at a temperature in the range of 15 °C to 45 °C.
The step of mixing is carried out for a period of time in the range of 0.5 hours to 10 hours.
The predetermined temperature is in the range of 70 °C to 150 °C.
In accordance with one embodiment of the present disclosure, the predetermined temperature is 130 °C.
During the step of dyeing, some dye particles may remain on the fabric surface, leading to reduced color fastness on washing and rubbing. To overcome these shortcomings, the step of reduction clearing is carried out.
The reduction clearing is carried out using various reagents.
In accordance with one embodiment of the present disclosure, the reduction clearing is carried out using a mixture of a reducing agent and an alkali.
The reducing agent is sodium dithionite or sodium hydrosulfite. Other reducing agents can also be used for reduction clearing.
The step of reduction clearing is carried out at a temperature in the range of 40 °C to 60 °C for a time period in the range of 10 minutes to 40 minutes.
After the step of reduction clearing, the synthetic fabric is thoroughly washed and air-dried.
The polyester fabric dyed using 1%, 2%, 3%, and 4% shade of the azo disperse dye of the present disclosure were found to have good to excellent wash fastness, and perspiration fastness.
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 azo compound of formula (I)
2-Amino-6-methoxybenzothiazole (66 g, 0.37 mol) was diazotized to obtain 6-methoxybenzothiazol-2-yl diazonium salt. The diazonium salt was added slowly to a mixture of 2,6-bis(3-methoxypropylamino)-3-cyano-4-methyl pyridine (113 g, 0.39 mol) and 50% aqueous sulphuric acid (113 g), at 3 °C and the mixture was stirred for 5 hours to obtain a product mixture comprising azo compound of the formula (I). 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 the formula (I). 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 (I) (166 g, yield 91.9%, 0.34 mol). The azo compound of the formula (I), was characterized by a melting point in the range of 168 °C to 170 °C and a ?max of 495 nm in toluene. Purity of the azo compound was found to be 98.5% by HPLC.
Experiment 2: Preparation of azo disperse dye of azo compound (I)
Azo compound represented by formula (I) as wet cake (40 g on 100%), lignosulfonate sodium salt (36 g), and naphthalene sulfonate formaldehyde condensate as liquid (24 g on 100%) 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 azo disperse dye having a particle size of 1 micron, which is used for dyeing.
Experiment 3: Dyeing polyester fabric using the azo disperse dye comprising azo compound (I)
A dye bath was prepared by mixing the azo disperse dye (1 g) obtained in experiment 2, water (2000 ml), and polyester fabric (100 g), to obtain wetted fabric having a final liquor ratio of 1:20 w/w. The pH value of the bath comprising wetted fabric was adjusted to 4.5 with acetic acid. The wetted fabric in the bath was dyed by heating the dye bath to 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 polyester fabric in brilliant yellowish-red shade.
Similarly, the polyester fabrics were separately dyed using 2g, 3g, and 4g of the azo disperse dye comprising azo compound (I), which corresponds to 2%, 3%, and 4% shades of the azo disperse dye, respectively. The dyed polyester fabrics obtained after dyeing with 2%, 3%, and 4% shades of the azo disperse dye were tested for wash fastness, and perspiration fastness. The dyed polyester fabrics 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;
• an azo disperse dye that provides a yellowish-red hue;
• a simple, efficient, and economical process for the preparation of an azo disperse dye;
• an azo disperse dye having improved dyeing and printing properties; and
• an azo disperse dye that imparts good to excellent wash fastness, and perspiration fastness to the dyed synthetic fabrics.
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.