DESC:FIELD OF THE INVENTION
The present invention relates to optical brightening agents and process for preparing the same.

BACKGROUND OF THE INVENTION
Optical brightening agents have been extensively used to impart higher degree of whiteness to paper, paperboard, woven and non-woven fabrics. The anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilben-2,2’-disulphonic acid are especially important optical brightening agents for the paper and textile industry. The anilino-substituent may additionally contain sulphonic acid groups, which impart higher water solubility to these agents owing to its hydrophilicity. The tetrasulpho- and hexasulpho- optical brightening agents derived from 4,4’-diaminostilben-2,2’-disulphonic acid, therefore have higher solubility in water. The disulpho- optical brightening agents derived from 4,4’-diaminostilben-2,2’-disulphonic acid, that is with aniline-substituent without any sulphonic acid group, however, have higher affinity for cellulose fibres and are therefore most preferred in the wet-end applications.

The paper and paperboard industry demands aqueous formulations of the optical brightening agents in the form of suspensions or clear solutions in water for the obvious advantages during handling, transport, storage and metering. Particularly preferred are the clear concentrated aqueous solutions of the optical brightening agents, which are stable for prolonged period of at least a few months at temperatures ranging from 4-40°C. The formulations in the form of a clear liquid also reduce the time required to dissolve the otherwise solid form of the optical brightening agents.

Thus, there exists a challenge to develop storage stable aqueous formulations, especially clear solutions of the anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilben-2,2’-disulphonic acid without any sulphonic acid group on the anilino-substituent, which are most preferred in the paper and paperboard industry but have substantially less solubility in water by virtue of their structure.

Still another problem that exists and is unavoidable in the case of all the optical brightening agents based on bistriazinyl derivatives of 4,4’-diaminostilben-2,2’-disulphonic acid is the presence of inorganic salts, sodium chloride being the most common, as a result of the manufacturing process. This problem stems from the fact that these optical brightening agents are manufactured using cyanuric chloride and inevitably generate a minimum of six moles of sodium chloride for every mole of the optical brightening agent produced. Furthermore, the synthesis processes use water as the solvent, resulting in appreciable solubility of salts such as sodium chloride in the reaction medium, which are therefore difficult to remove. These residual salts tend to destabilise the aqueous solutions of the optical brightening agents and call for expensive and tedious processing steps such as membrane filtration.

It has been a practice in the industry to add solubilising additives such as urea, caprolactum, ethylene glycol in amounts as high as ~30% of the formulation, with the content of the optical brightening agent at ~20-35%, to achieve the desired solubility and storage stability. These solubilising additives neither contribute to the performance of the optical brightening agent as such nor have any affinity towards cellulose. At the end of the paper manufacturing process therefore, these solubilising additives are released into the effluent.

US 3012971discloses whitening compositions in the form of concentrated aqueous solutions of 4,4’-bis-[2-phenylamino-4-diethanolamino-1,3,5-triazyl(6)]-diaminostilbene-2,2’-disulphonic acid, or an alkali metal salt thereof together with alkanolamines. The patent mentions that, “the proportion by weight of the alkylolamine agents to whitening agent may vary widely, say from 0.5:1 to 3.0:1”. This ratio translates into significantly large excess of the alkanolamines in terms of moles per mole of the whitening agent.

US 4717502 discloses aqueous optical brightener compositions of disulpho-, tetrasulpho- as well as hexasulpho- optical brighteners based on bistriazinyl derivatives of 4,4’-diaminostilben-2,2’-disulphonic acid with the following general formula:

in which,
R1 and R2 are hydrogen or –SO3M;
R3 is hydrogen, C2-3- hydroxyalkyl, C1-4-alkyl, -CH2CH2CN or –CH2CH2CONH2;
R4 is hydrogen, C1-4-alkyl, C2-3-hydroxyalkyl, hydroxyl-ethoxy-ethyl, N,N-Bis-(C1-3-alkyl)-amino-C2-6-alkyl or benzyl; or R3 and R4 together with the neighbouring nitrogen atom signify a morpholine, pyrrolidine, piperidine or N-methylpiperazine ring; and

M is hydrogen or a colourless cation; provided that one of R3 and R4 is hydrogen, with polyethylene glycol with an average molecular weight in the range of 1000 to 3000. The disclosure suggests10-500 parts by weight of polyethylene glycol per 100 parts of the brightening agent and that at least 20% of the composition is water. The disclosure also suggests the use of mono- and triethanolamine salts of the brightening agents by way of the examples cited. The optical brightener compositions disclosed in both these disclosures are thus unacceptable in current context from the point of view of economics and more particularly the eco-friendliness of the application process.

US 2004/0074021 attempts to solve the problem by providing a mixture of two or more bis(triazinylamino)stilbene derivatives. However, the brightening agents are used in the form of mixed sodium/triethanolammonium salt. Furthermore, it also recommends the use of additive, which is employed at a concentration of 0.2 to 3.0% by weight of the solution. Preferred additives are tertiary alkanolamines, triisopropanolamine being especially preferred.

WO 2005/028749 discloses optical brightener compositions comprising an alkanolamine and a bis(triazinylamino)stilbene derivative of the following general formula:

wherein, X is hydrogen, an alkali metal ion, an ammonium ion or hydroxyalkyl ammonium radical derived from the said alkanolamine and R7, R8, R9 and R10 are independently of the others –OR11, -NR11R12 or a group of formula
, , or ,
wherein, R11 and R12 are each independently of the other hydrogen, alkylhydroxyalkyl, alkoxyalkyl, carboxyalkyl, dicarboxyalkyl, H2N-CO-alkyl or alkylthio.

Preferred alkanolamines are 2-amino-2-methyl-1-propanol, 1-amino-2-propanol or a mixture of 2-amino-2-methyl-1-propanol and 2-(N-methylamino)-2-methyl-1-propanol. The examples cited in this disclosure indicate that at least 17% molar excess of the alkanolamine per mole of the brightening agent is needed for acceptable stability of the resulting formulation.

US 8221588 discloses storage stable solutions of certain anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilbene-2,2’-disulphonic acid, wherein, at least 25% of the [M+] ions associated with the sulphonate groups have been replaced by (CH3)2NH+CH2CH2OH ions. The general structure of the optical brightener is as follows:

in which, R is hydrogen or a methyl radical, R1 is hydrogen, an alkyl radical with 1 to 4 carbon atoms, a ?-hydroxyalkyl radical containing 2 to 4 carbon atoms, a 13-alkoxyalkyl radical containing 3 or 4 carbon atoms or CH2CH2CONH2; R2 is hydrogen or a methyl radical; M+ is Li+, Na+, or K+ and n is less than or equal to 1.5. It is however evident from the examples 1 and 6 in this disclosure, that only ~50-55% of the dimethylaminoethanol employed during the synthesis is retained in the final formulation.

US 2010/0294447 discloses storage stable solutions of anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilbene-2,2’-disulphonic acid, which are substituted at the triazine rings with diethanolamine, wherein, at least 25% of the [M+] ions associated with the sulphonate groups have been replaced by (CH3)2NH+CH2CH2OH ions. The general structure of the optical brightener is as follows:

in which, R is hydrogen or a methyl radical; M+ is Li+, Na+, or K+, and n is less than or equal to 1.5, and of 0.05 to 5% by weight of an organic acid selected from citric acid, glyoxylic acid, acetic acid or formic acid. Similar to the above mentioned disclosure, only ~38-40% of the dimethylaminoethanol employed during the synthesis is retained in the final formulation. Furthermore, the process for the production of these solutions employs carboxylic acids (e.g., citric acid) in almost equimolar quantities with respect to the dimethylaminoethanol used.

WO 2013/018012 discloses stable aqueous solutions of anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilbene-2,2’-disulphonic acid in the form of a tertiaryalkanolammonium salts. 2-(dimethylamino)ethanol is mentioned as the preferred tertiary alkanolamine for this purpose. However, the concentration of the optical brighteners reported in the examples is relatively low (~20%) moreover, ~50% molar excess of the alkanolamine is required to get a stable solution.

WO 2014/009479 discloses stable aqueous solutions of the hydrates of tertiary alkanolamine salts of anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilbene-2,2’-disulphonic acid. Once again, only ~50-65% of the tertiary alkanolamine used during the synthesis of these solutions is retained in the final product.

Unfortunately, although most of the abovementioned methods offer a solution for the problem of effluent generation during the end application, there is, nevertheless, generation of such effluents during the manufacturing of the optical brightening formulations. The effluent generation is thus shifted one step earlier in the supply chain.

There is therefore a need to provide an improved optical brightener which gives stable aqueous solutions of anilino-substituted bistriazinyl derivatives of 4,4’-diaminostilbene-2,2’-disulphonic acids which are easy to manufacture and cause minimum harm to the environment by way of lesser effluent generation during manufacturing and application.

SUMMARY OF THE INVENTION
The present invention relates to optical brighteners of Formula I having the structure

Formula I
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ is the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and

n is 0, 1 or 2

Another aspect of the present invention relates to a process for preparing compound of Formula I by mixing compound of Formula II and an amine of Formula III.

Formula II

Formula III

DESCRIPTION OF THE INVENTION
An embodiment of the present invention discloses compounds of Formula I for optically brightening an article, compound of Formula I has the following structure:

Formula I
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ is the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and
n is 0, 1 or 2

In an embodiment of the present invention, the preferred substituents of compound of Formula I are:
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are – CH3;
p is 0.25;
q is 2; and
n is 0

In another embodiment of the present invention, the preferred substituents of compound of Formula I are:
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are–CH2CH3;
p is 0.25;
q is 2; and
n is 0

In an embodiment of the present invention, the preferred substituents of compound of Formula I are:
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are–CH2CH3;
p is 0.8;
q is 4; and
n is 1

In an embodiment of the present invention, the preferred substituents of compound of Formula I are:
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.4;
q is 6; and
n is 2

In an embodiment of the present invention, the preferred substituents of compound of Formula I are:
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH3;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.66;
q is 6; and
n is 2

The present invention also discloses a stable aqueous solution for optically brightening an article. The aqueous solution comprises compound of Formula I having the structure

Formula I
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ is the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and

n is 0, 1 or 2

The aqueous solution is present in a concentrated form. The concentration of the compound of Formula I in the formulation may be in the range of 10% to 60%.

The aqueous solution of compound of Formula I optionally comprises of additives such as carriers, antifreeze, defoamers, solubilizing agents, preservatives, complexing agents, inorganic or organic salts.

The aqueous solutions of the compounds encompassed by the present invention are stable on prolonged storage for at least one year over a wide range of temperature with minimal or no extra solubilising agent.

An embodiment of the present invention relates to a process for preparing compounds of Formula I. The process comprises of mixing compound of Formula II with an amine of Formula III not exceeding the stoichiometric requirement and adjusting the pH to 8.5-9.5 with any inorganic or organic base, such as NaOH, KOH, LiOH, mono- di- or tri-alkyl amine or mono-, di- or tri-alkanolamine. The process further comprises of mixing of compound of Formula II with an amine of Formula III in the presence of water and adjusting the pH to 8.5-9.5 with a suitable inorganic or organic base.

Formula II

Formula III
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;
R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ is the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and

n is 0, 1 or 2

Compound of Formula I as prepared by this process is obtained in an aqueous solution form.

Another embodiment of the present invention relates to preparing stable aqueous solution comprising compound of Formula I by mixing compound of Formula II with an aqueous solution of amine of Formula III and a suitable inorganic or organic base.

Preferably, the amine of Formula III is 3- aminopropionamide or derivatives thereof.

The amines used in the invention can be prepared by reaction of acrylamide with a suitable primary or secondary amine as well as ammonia in water. The desired amine products can be employed as such or after the isolation of the unreacted starting amine and excess water.

In a preferred embodiment, compound of Formula I is obtained by directly adding compound of Formula II in the form of a dry powder or a wet cake to the solution containing the amine of Formula III and finally adjusting the pH of the resulting solution to 8.5 to 9.5 with the help of a base. The base used for adjusting the pH may be any inorganic or organic base, such as NaOH, KOH, LiOH, mono- di- or tri-alkyl amine or mono-, di- or tri-alkanolamine.

In an embodiment of the present invention, compound of Formula I is prepared by mixing compound of Formula II and Formula III not exceeding the stoichiometric amount. They can also be prepared by a treatment of the lithium, sodium or potassium salt of the optical brightening agent of a general formula IV,

Formula IV
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+, etc.

with a mineral acid such as hydrochloric acid, sulphuric acid or any mono-, di-, tri-carboxylic acid or by a sequential treatment of compound of Formula II with a cation-exchange resin followed by amine of the present invention, not exceeding the stoichiometric amount. The pH of the resulting solution is adjusted to 8.5 to 9.5 with the help of any inorganic or organic base.

Surprisingly, it has been found that the use of amines of the present invention in the process leads to the formation of an exceptionally stable solution of optical brightening agents of Formula I.

The present invention also discloses a method of optically brightening an article. The method comprises of adding compound of Formula I to the article. Preferably, aqueous solution of compound of Formula I is added to the article to make it optically brightened. The suitable articles for optical brightening are paper, paperboards, woven and non-woven textiles, etc.

Any conventionally known process can be incorporated for optical brightening of an article with compound of Formula I.

The optical brighteners of compound of Formula I are used for optically brightening or whitening articles such as woven and non-woven fabrics, paper, paperboards and the like.

In an embodiment, a packaging containing aqueous solution of compound of Formula I is disclosed.

The optical brighteners of the present invention can be easily manufactured, safely handled and conveniently used. The stable aqueous solution of the optical brighteners obtained as per the present invention, causes minimum harm to the environment during manufacturing as large excess of solubilizing agents are not incorporated in the process. Still, more preferably, extra solubilizing agents are not used in the solution of optical brighteners.

The aqueous solution of optical brighteners of the present invention is highly stable over a wide range of temperature for a prolonged duration and therefore remains in usable condition during storage and transportation.

Examples
The examples illustrate the present invention but are not limiting thereof.
Example 1
30g demineralised water, 10.8g 52% aqueous solution of 3-(dimethylamino)propanamide and 60g wet cake containing 22g of the compound of Formula V.

Formula V
were mixed in a 250 mL beaker. The resultant amber coloured solution was clarified through a hyflo bed to get 96g clear solution of compound A with an extinction value of 137.5. The solution was found to be stable to storage at 25°C and 4°C for at least 120 days. No crystal formation or turbidity was observed in the solution during the storage.

Compound A

Example 2
200g demineralised water, 161g 65% aqueous solution of 3-(diethylamino)propanamide and 1200g wet cake containing 442g of the compound of Formula V were mixed together and agitated for 10min. 28g of 35% aqueous sodium hydroxide solution was added and the agitation was continued for a further 10min. The agitation was then stopped and the phases were allowed to separate for 30min. The lower amber coloured oily layer was separated and clarified through a hyflo bed to get 1515g clear solution of compound B with an extinction value of 233. The solution thus obtained was found to be stable to storage at 25°C and 4°C for at least 120 days. No crystal formation or turbidity was observed in the solution during the storage.

Compound B
Example 3-6
The clear solution obtained in Example 2 was diluted with demineralised water as per the details given in Table 1.
Table 1
Example Solution from Example2 (g) Water (g) Weight of final liquid (g) Extinction value
Example 3 200 244 444 102
Example 4 200 205 405 114
Example 5 200 140 340 137
Example 6 200 33 233 201

All the four solutions were found to be stable to storage at 25°C and 4°C for at least 120 days. No crystal formation or turbidity was observed in the solution during the storage.

The sample obtained in Example 6 was subjected to five freeze-thaw cycles. For this, the sample was frozen at -5°C and then allowed to attain ambient temperature (~25°C). These cycles were repeated five times. It was observed that the freezing was reversible and every time the sample turned to a clear solution after attaining the ambient temperature.

Example 7:
26.14g dry powder containing 23g compound of formula VI and 0.62g sodium chloride

Formula VI
was dispersed in 50g demineralised water at ambient temperature (25°C). 1.6g 50% sulphuric acid was added followed by 3.6g 65% aqueous solution of 3-(diethylamino)propanamide under stirring. The weight of the solution was made up to 100g by addition of demineralised water. The solution thus obtained was clarified through hyflo bed to get 100g clear solution of compound C with an extinction value of 125.

Compound C
The percentage of total inorganic salts in the final solution was thus >1.8. The solution was found to be stable to storage at 25°C and 4°C for at least 120 days in spite of appreciable content of inorganic salts. No crystal formation or turbidity was observed in the solution during the storage.

Example 8:
20g dry powder containing 16g compound of formula VII and 0.42g sodium chloride

Formula VII
was dispersed in 50g demineralised water at ambient temperature (25°C). 2.75g 50% sulphuric acid was added followed by 6.2g 65% aqueous solution of 3-(diethylamino)propanamide under stirring. The weight of the solution was made up to 100g by addition of demineralised water. The solution thus obtained was clarified through hyflo bed to get 100g clear solution of compound D with an extinction value of 80.

Compound D
The percentage of total inorganic salts in the final solution was thus >2.4. The solution was found to be stable to storage at 25°C and 4°C for at least 120 days in spite of appreciable content of inorganic salts. No crystal formation or turbidity was observed in the solution during the storage.

Example 9:
100g wet cake containing 44.5g compound of formula VIII and 5.56g sodium chloride

Formula VIII
was dispersed in 150g demineralised water at ambient temperature (25°C). 6.7g 50% sulphuric acid was added followed by 15.3g 65% aqueous solution of 3-(diethylamino)propanamide under stirring. The weight of the solution was made up to 320g by addition of demineralised water. The solution thus obtained was clarified through hyflo bed to get 312g clear solution of compound E with an extinction value of 69.7.

Compound E
The percentage of total inorganic salts in the final solution was thus >4.8. The solution was found to be stable to storage at 25°C and 4°C for at least 120 days in spite of appreciable content of inorganic salts. No crystal formation or turbidity was observed in the solution during the storage.

INVESTIGATIONS
1. Application of the product of Example 5 in paper pulp.
Pulp suspension having 1% by weight of dry fibre with 80% short fibre and 20% long fibre was bought from a vendor and utilized for determining the whitening efficiency of the product from Example 5. The pulp was beaten to a SchopperRiegler wetness of 35°SR, 20% by weight of precipitated calcium carbonate (PCC) was mixed well into the pulp and the slurry was divided into seven parts. The optical brightener solution from Example 5 was added to six of the pulp suspensions obtained above in varying dosages and stirred for 10min. One part was left without the addition of the optical brightening agent for reference. Paper sheets were made by drawing each of the pulp slurry through a wire mesh. Paper sheets thus obtained were pressed and dried in an oven at 108°C for 2hours. Whiteness of the dried paper sheets were measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 2:
Table 2
Sr. # Dosage of the Optical brightener solution from Example 5 CIE Whiteness Delta
1 0% 74.67 -
2 0.10% 96.23 + 21.56
3 0.20% 107.26 + 32.59
4 0.40% 119.44 + 44.77
5 0.60% 124.48 + 49.81
6 0.80% 127.69 + 53.02
7 1.00% 130.49 + 55.82

The results from table 2 clearly demonstrate the effectiveness of the optical brightener solution. The degree of whiteness in the absence of optical brightener was 74.67 and addition of optical brightener led to a high increase in the degree of whiteness.

2. Application of the product of Example 7 in paper pulp.
Pulp suspension having 1% by weight of dry fibre with 80% short fibre and 20% long fibre was used for determining the whitening efficiency of the product from Example 7.The pulp was beaten to a SchopperRiegler wetness of 35°SR, 20% by weight of precipitated calcium carbonate (PCC) was mixed well into the pulp and the slurry was divided into seven parts. The optical brightener solution from Example 7 was added to six of the pulp suspensions obtained above in varying dosages and stirred for 10 min. One part was left without the addition of the optical brightening agent for reference. Paper sheets were made by drawing each of the pulp slurry through a wire mesh. Paper sheets thus obtained were pressed and dried in an oven at 108°C for 2 hours. Whiteness of the dried paper sheets were measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 3:
Table 3
Sr. # Dosage of the Optical brightener solution from Example 7 CIE Whiteness Delta
1 0% 74.97 -
2 0.10% 88.46 + 13.49
3 0.20% 96.8 + 21.83
4 0.40% 104.27 + 29.3
5 0.60% 108.88 + 33.91
6 0.80% 111.06 + 36.09
7 1.00% 113.9 + 38.93

The results from table 3 clearly demonstrate the effectiveness of the optical brightener solution.

3. Application of the product of Example 8 in paper pulp.
Pulp suspension having 1% by weight of dry fibre with 80% short fibre and 20% long fibre was used for determining the whitening efficiency of the product from Example 8. The pulp was beaten to a SchopperRiegler wetness of 35°SR, 20% by weight of precipitated calcium carbonate (PCC) was mixed well into the pulp and the slurry was divided into seven parts. The optical brightener solution from Example 8 was added to six of the pulp suspensions obtained above in varying dosages and stirred for 10 min. One part was left without the addition of the optical brightening agent for reference. Paper sheets were made by drawing each of the pulp slurry through a wire mesh. Paper sheets thus obtained were pressed and dried in an oven at 108°C for 2 hours. Whiteness of the dried paper sheets were measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 4:
Table 4
Sr. # Dosage of the Optical brightener solution from Example 8 CIE Whiteness Delta
1 0% 75.57 -
2 0.10% 78.23 + 2.66
3 0.20% 80.14 + 4.57
4 0.40% 82.67 + 7.1
5 0.60% 84.45 + 8.88
6 0.80% 86.08 + 10.51
7 1.00% 87.65 + 12.08

The results from table 4 clearly demonstrate the effectiveness of the optical brightener solution.
4. Application of the product of Example 5 in a size press.
Oxidised Starch solution of 5% solids on dry basis was prepared in distilled water. The prepared solution was divided in to 5 parts. The product from Example 5 was added to six of starch solutions obtained above in varying dosages and one part was left as is for reference. These starch solutions were stirred continuously for 10 min while maintaining the temperature at 75°C. Each of the above 5 starch solutions was applied on base paper strips of known CIE whiteness using zero number laboratory bar coater. After the application, the strips were air dried for 1 hour and the whiteness was measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 5:

Table 5
Sr. # Dosage of the product from Example 5 (gpL) CIE Whiteness Delta
1 0 68.88 -
2 1.5 79.55 + 10.67
3 3.5 85.71 + 16.83
4 5.5 88.56 + 19.68
5 7.5 89.72 + 20.84

The results from table 5 clearly demonstrate the effectiveness of the optical brightener solution.

5. Application of the product of Example 7 in a size press.
Oxidised Starch solution of 5% solids on dry basis was prepared in distilled water. The prepared solution was divided in to 5 parts. The product from Example 7 was added to six of starch solutions obtained above in varying dosages and one part was left as is for reference. These starch solutions were stirred continuously for 10 min while maintaining the temperature at 75°C. Each of the above 5 starch solutions was applied on base paper strips of known CIE whiteness using zero number laboratory bar coater. After the application, the strips were air dried for 1hour and the whiteness was measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 6:
Table 6
Sr. # Dosage of the product from Example 7 (gpL) CIE Whiteness Delta
1 0 68.88 -
2 1.5 81.12 + 12.24
3 3.5 90.24 + 21.36
4 5.5 94.99 + 26.11
5 7.5 95.35 + 26.47

The results from table 6 clearly demonstrate the effectiveness of the optical brightener solution.

6. Application of product of Example 8 in a size press.
Oxidised Starch solution of 5% solids on dry basis was prepared in distilled water. The prepared solution was divided in to 5 parts. The product from Example 8was added to six of starch solutions obtained above in varying dosages and one part was left as is for reference. These starch solutions were stirred continuously for 10 min while maintaining the temperature at 75°C. Each of the above 5 starch solutions was applied on base paper strips of known CIE whiteness using zero number laboratory bar coater. After the application, the strips were air dried for 1hour and the whiteness was measured using Data Colour Elerpho Brightness tester. The results are summarised in the following table 7:
Table 7
Sr. # Dosage of the product from Example 8 (gpL) CIE Whiteness Delta
1 0 68.88 -
2 1.5 78.48 + 9.6
3 3.5 86.92 + 18.04
4 5.5 92.5 + 23.62
5 7.5 95.76 + 26.88

The results from table 7 clearly demonstrate the effectiveness of the optical brightener solution.

7. Application of product of Example 5 in paper coating.
The coating composition was prepared by mixing 70 parts of Ground Calcium Carbonate, 30 parts of Ultra Gloss 90, 11.5 parts of Binder (Sternol Latex), 0.75 parts of Lubricant (LB – 50), 0.18 parts CMC (FIN FIX) and 0.12 parts of NaOH in demineralised water so as to get a solid content of 70%. The composition was divided in to 5 parts. The product from Example 5 was added to six of the compositions obtained above in varying dosages and one part was left as is for reference. The composition was stirred for 10min before applying on base paper strips of known CIE whiteness using zero number laboratory bar coater (Coat weight of 10gsm). After the application, the strips were air dried for 1 hour and the whiteness was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table 8:
Table 8
Sr. # Dosage of the product from Example 5 (gpL) CIE Whiteness Delta
1 0 67.74 -
2 1.5 87.89 + 20.15
3 3.5 93.86 + 26.12
4 5.5 97.13 + 29.39
5 7.5 100.88 + 33.14

The results from table 8 clearly demonstrate the effectiveness of the optical brightener solution.

8. Application of product of Example 7 in paper coating.
The coating composition was prepared by mixing 70 parts of Ground Calcium Carbonate, 30 parts of Ultra Gloss 90, 11.5 parts of Binder (Sternol Latex), 0.75 parts of Lubricant (LB – 50), 0.18 parts CMC (FIN FIX) and 0.12 parts of NaOH in demineralised water so as to get a solid content of 70%. The composition was divided in to 5 parts. The product from Example 7 was added to six of the compositions obtained above in varying dosages and one part was left as is (for reference). The composition was stirred for 10 min before applying on base paper strips of known CIE whiteness using zero number laboratory bar coater (Coat weight of 10gsm). After the application, the strips are air dried for 1 hour and the whiteness was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table 9:
Table 9
Sr. # Dosage of the product from Example 7 (gpL) CIE Whiteness Delta
1 0 67.74 -
2 1.5 88.27 + 20.53
3 3.5 96.58 + 28.84
4 5.5 101.53 + 33.79
5 7.5 102.78 + 35.04

The results from table 9 clearly demonstrate the effectiveness of the optical brightener solution.

9. Application of the product of Example 8 in paper coating.
The coating composition was prepared by mixing 70 parts of Ground Calcium Carbonate, 30 parts of Ultra Gloss 90, 11.5 parts of Binder (Sternol Latex), 0.75 parts of Lubricant (LB – 50), 0.18 parts CMC (FIN FIX) and 0.12 parts of NaOH in demineralised water so as to get a solid content of 70%. The composition was divided in to 5 parts. The product from Example 8 was added to six of the compositions obtained above in varying dosages and one part was left as is for reference. The composition was stirred for 10 min before applying on base paper strips of known CIE whiteness using zero number laboratory bar coater (Coat weight of 10gsm). After the application, the strips were air dried for 1 hour and the whiteness was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table 10:
Table 10
Sr. # Dosage of the product from Example 8 (gpL) CIE Whiteness Delta
1 0 67.74 -
2 1.5 84.12 + 16.38
3 3.5 94.76 + 27.02
4 5.5 102.08 + 34.34
5 7.5 107.96 + 40.22

The results from table 10 clearly demonstrate the effectiveness of the optical brightener solution.

10. Application of the product of Example 5 in textile (Exhaust Method):
4 pieces of a white 100% cotton bleached fabric weighing 5 ± 0.05g each were used for the exhaust application. Three pieces were immersed in solutions obtained by dissolving varying quantities of the product obtained in Example 5 in 100mL distilled water at 85-90°C for 45 min. One piece was immersed in distilled water without the optical brightening agent for reference. After 45 min, the pieces were taken out and washed with distilled water and air dried at 25-30°C. Whiteness of the fabric was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table:

Table 11
Sr # Loading of the product from Example 5(%) CIE Whiteness
Delta
1 0 78.22 --
2 0.2 140.84 +62.62
3 0.4 146.52 +68.3
4 0.6 148.19 +69.97

The results from table 11 clearly demonstrate the effectiveness of the optical brightener solution.

11. Application of the product of Example 7 in textile (Exhaust Method):
4 pieces of a white100% cotton bleached fabric weighing 5 ± 0.05g each were used for the exhaust application. Three pieces were immersed in solutions obtained by dissolving varying quantities of the product obtained in the Example 7 in 100mL distilled water at 45°C for 45 min. One piece was immersed in distilled water without the optical brightening agent for reference. After 45 min, the pieces were taken out and washed with distilled water and air dried at 25-30°C. Whiteness of the fabric was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table:
Table 12
Sr # Loading of the product from Example 7(%) CIE Whiteness
Delta
1 0 76.9 --
2 0.2 88.13 +11.23
3 0.4 94.84 +17.94
4 0.6 97.5 +20.60

The results from table 12 clearly demonstrate the effectiveness of the optical brightener solution.

12. Application of the product of Example 8 in textile (Exhaust Method):
4 pieces of a white 100% cotton bleached fabric weighing 5 ± 0.05g each were used for the exhaust application. Three pieces were immersed in solutions obtained by dissolving varying quantities of the product obtained in the Example 8 in 100mL distilled water at 30°C for 45 min. One piece was immersed in distilled water without the optical brightening agent for reference. After 45 min, the pieces were taken out and air dried at 25-30°C. Whiteness of the fabric was measured using Data Colour Elerpho Brightness Tester. The results are summarised in the following table:
Table 13
Sr # Loading of the product from Example 8 (%) CIE Whiteness
Delta
1 0 77.20 -
2 0.2 144.14 +66.94
3 0.4 148.36 +71.16
4 0.6 153.04 +75.84

The results from table 13 clearly demonstrate the effectiveness of the optical brightener solution.
,CLAIMS:We Claim:
1. A compound of Formula I for optically brightening an article

Formula I
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;

R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ is the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and

n is 0, 1 or 2

2. The compound as claimed in claim 1, wherein
R and R’ each are H;
R1, R2, R’1 and R’2each are –CH2CH2OH;
M is Na;
R3 and R4 each are –CH3;
p is 0.25;
q is 2; and
n is 0

3. The compound as claimed in claim 1, wherein
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.25;
q is 2; and
n is 0

4. The compound as claimed in claim 1, wherein
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.8;
q is 4; and
n is 1

5. The compound as claimed in claim 1, wherein
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH2OH;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.4;
q is 6; and
n is 2

6. The compound as claimed in claim 1, wherein
R and R’ each are H;
R1, R2, R’1 and R’2 each are –CH2CH3;
M is Na;
R3 and R4 each are –CH2CH3;
p is 0.66;
q is 6; and
n is 2
7. A process for preparing compound of Formula I, the process comprising mixing compound of Formula II and compound of Formula III to obtain compound of Formula I.

Formula II

Formula III
wherein,
R and R’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl;

R1 and R1’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2, -CH2CH2CN, -CH2CH2COO-, -CH2COO-;

R2 and R2’ independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2COO-, CH(COO-)CH2COO-, CH(COO-)CH2CH2COO-, CH2CH2SO3-;
R3 and R4 independent of each other are hydrogen, C1-C4 straight chain or branched alkyl, C1-C4 straight chain or branched hydroxyalkyl, -CH2CH2CONH2;

M+ represents Li+, Na+, K+ or a quaternary ammonium ion derived from mono-, di- or trialkanolamine, or a mixture thereof, with ‘p’ less than or equal to 0.8 and ‘q’ being the number of functional groups in the optical brightener molecule, that are capable of forming a quaternary ammonium salt; and

n is 0, 1 or 2

8. The process as claimed in claim 7 comprising adjusting pH of the mixture with a base.

9. The process as claimed in claim 8, wherein the base is selected from NaOH, KOH, LiOH, mono- di- or tri-alkyl amine or mono-, di- or tri-alkanolamine.

10. The process as claimed in claim 7 comprising mixing compound of Formula II and compound of Formula III in the presence of water.

11. A stable aqueous solution for optically brightening an article, the aqueous solution comprising compound of Formula I as claimed in claim 1.

12. The stable aqueous solution as claimed in claim 11, wherein the solution is present in a concentrated form.

13. The stable aqueous solution as claimed in claim 11, wherein compound of Formula I is present at a concentration ranging from 10% to 60%.

14. The stable aqueous solution as claimed in claim 11 optionally comprising additives such as carriers, antifreeze, defoamers, solubilizing agents, preservatives, complexing agents, inorganic or organic salts.

15. A method of optically brightening an article comprising adding compound of Formula I to the article.

16. The method as claimed in claim 15 comprising adding an aqueous solution of compound of Formula I to the article.

17. An optically brightened article obtained by the method as claimed in claim 15.

18. The article as claimed in claim 15, wherein the article paper, paperboards, woven and non-woven textiles.

19. A packaging containing aqueous solution of compound of Formula I as claimed in claim 1.
Dated this 10th day of March, 2015
FOR DEEPAK NITRITE LIMITED
By their Agent

(GIRISH VIJAYANAND SHETH) (IN/PA 1022)
KRISHNA & SAURASTRI ASSOCIATES