Claims:1. An improved process for the synthesis of alkali metal naphthionate of Formula I, wherein M represents an alkali metal selected from sodium (Na) and potassium (K); the process including converting 1-nitronaphthalene to 1-amino-naphthalene; and in-situ conversion of 1-amino-naphthalene to alkali metal naphthionate; wherein the process comprises the steps of:
a) converting 1-nitronaphthalene to 1-amino-naphthalene by hydrogenation;
b) sulphonation of 1-amino-naphthalene;
c) thermal rearrangement of sulphonated naphthylamine; and
d) alkali salt formation resulting in alkali metal naphthionate of Formula I;
characterized in that the 1-aminonaphthalene is not isolated from the reaction mass and is used as such for sulphonation.

Formula I
2. The process as claimed in claim 1, wherein the hydrogenation reaction for the conversion of 1-nitronaphthalene to 1-aminonaphthalene is carried out in the presence of transition metal catalyst at a pressure in the range of 5-30 kg/cm2 and temperature in the range of 50 to 130 oC in a high boiling solvent.
3. The process as claimed in claim 2, wherein the transition metal catalyst is Raney Nickel.
4. The process as claimed in claim 2, wherein the high boiling solvent is selected from chlorobenzene, dichlorobenzene (m-dichlorobenzene, p-dichlorobenzene), 1,2,3-trichlorobenzene, 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, hexachlorobenzene, 1-chloro-3-nitrobenzene, 1-bromo-4-chlorobenzene and mixtures thereof.
5. The process as claimed in claim 1, wherein sulphonation is carried out with 1.1 equivalent of 98% sulphuric acid at 70-185 ?C.
6. The process as claimed in claim 1, wherein sulphonated mass is neutralized with alkali metal carbonate or alkali metal hydroxide to obtain alkali metal salt of napthionate.
7. The process as claimed in claim 6, wherein alkali metal carbonate is selected from sodium carbonate and potassium carbonate and alkali metal hydroxide is selected from sodium hydroxide and potassium hydroxide.
8. The process as claimed in claim 1, wherein thermal rearrangement of sulphonated naphthylamine to naphthionic acid occurs at a temperature in the range of 70 to 185 ?C.
9. The process as claimed in claims 1 to 8, wherein sulfonation and salt formation result in selectivity in the range of 98-99% and yield of 1-aminonaphthalene to alkali metal naphthionate in the range of 85-88%.
, Description:FIELD OF THE INVENTION
[0001] The present invention relates to organic synthesis. Specifically, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the process is safer, non-hazardous, environmental friendly, cost effective, has improved time cycle, better selectivity and high yield.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Alkali metal naphthionates such as sodium naphthionate and potassium naphthionate, are derivatives of naphthalene with both amine and sulphonic acid functional groups. Sodium naphthionate, also known as sodium 4-aminonaphthalene-1-sulfonate or Sodium 4-amino-1-naphthalenesulfonate, is the sodium salt of naphthionic acid and exists as white or gray white flake crystals. Alkali metal naphthionates are widely used to prepare food color, acid direct dye, edible red pigment and are also used as an antidote for nitrite and iodine poisoning. Sodium naphthionate is also employed as analytical reagent for organic synthesis and is an intermediate for producing various dyes.
[0004] The production of alkali metal naphthionate, particularly sodium naphthionate is usually carried out on an industrial scale by reducing 1-nitronaphthalene with iron in dilute hydrochloric acid (Bechamp reduction) or catalytically with hydrogen in the presence of nickel catalysts (e.g. Raney nickel) or by reacting 1-Naphthol with ammonia and ammonium bisulfite (Bucherer reaction) as described in Kirk-Othmer, Volume 4, 1st edition, pages 258 to 260. The yield obtained using iron reduction is about 90% of theory whereas the catalytic hydrogenation using nickel catalysts gives yield of over 90%, upto even 96.4% (as described in US Patent No. 2105321, J. Chem. Soc. Japan, 54, 371 to 373 (1951) and CA 48,1979d). The hydrogenated mass, thus obtained is used for the preparation of sodium naphthionate by sulphonation reaction.
[0005] Reduction of nitronaphthalenes is also described, at elevated temperature and pressure in the presence of noble metal catalysts, which can optionally be applied to supports (see, for example, DE-OSen 2456308 and 2519838). However, the hydrogenations of nitro compounds described in the aforementioned German published applications require special conditions which have some disadvantages for an industrial process. Thus, the hydrogenation according to DE-OS 2456308 is carried out with the addition of special diluents in which the nitro compound to be hydrogenated is soluble and the hydrogenation product consisting essentially of amino compound and water is practically insoluble. The process described in DE-OS 2519838 takes place in the trickle phase over fixed catalysts. A disadvantage of the process of DE-OS 24 56 308 is the addition of special diluents, the high dilution of the reactants with the resulting low throughputs, and the technically complex recovery. In the process of DE-OS2519838, the trickle phase is of little advantage, since high dilution is also carried out, which means that only low throughputs are possible, which is also at the expense of the economics of the process. In addition, deposits are to be expected on the fixed bed contact, which can lead to high pressure losses in the system, possibly even to blockages.
[0006] In the British Patent 227,481 (1924) a catalytic hydrogenation of nitro naphthalene to alpha naphthylamine is disclosed. In this process the reaction is carried out at 50 to 60 ?C under a pressure of a fraction of an atmosphere to 4 to 5 atmospheres in the presence of a nickel catalyst, wherein the nitro-compound is mixed with a large amount of water. A quantity of water equal to 2 to 5 times the weight of the nitro naphthalene is specified.
[0007] Chinese patent document CN 101434550B (application No. 200810174591.9) discloses a method for preparing 1-naphthylamine from 1-nitronaphthalene, wherein 1-nitronaphthalene, ethanol and a supported nickel catalyst are added into a reaction kettle, hydrogenation reaction is performed for 3-8 hours, and solid-liquid separation is performed after the reaction is completed. The mixture is then extracted several times with toluene. The combined organic phases are over dried sodium sulfate.
[0008] CN104016890B describes a method wherein solid-phase continuous reaction is used for the preparation of 1- amino -4 sodium naphthalene sulfonate. CN106243001A describe the gas phase SO3 sulfonation method for synthesis of naphthalidine-4-sodium sulfonate.
[0009] DE3531922A1 discloses a process wherein a mixture of 96.0% sulfuric acid and ammonium sulfate are used at 25 °C, and cooled 1-aminonaphthalene in solid form is reacted. The reaction mixture is then heated to 130 °C in 30 minutes and at this temperature up to stirring continued within 16 h at the end of the reaction. After that the reaction mixture is cooled to 50 ° C, diluted with water and neutralized with sodium hydroxide solution.
[0010] From commercial point of view, several processes related to catalytic hydrogenation and reduction of iron- hydrochloric acid of 1-nitro naphthalene are known. All the known processes involve the isolation of amino naphthalene before performing sulphonation and salt formation to obtain alkali metal naphthionate.
[0011] Thus there is an urgent need to develop a rapid and facile process for the synthesis of alkali metal naphthionates which can overcome deficiencies associated with the known arts. Need is also felt for a process for the preparation of alkali metal naphthionate, which is environmental friendly, is less hazardous, more safe and involves low production cost, while retaining high conversion rate and better selectivity.

OBJECTS OF THE INVENTION
[0012] An object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate, which can overcome deficiencies associated with the known arts.
[0013] Another object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate, which is economically viable and safe.
[0014] Another object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate which restricts large time cycle, has less chemical hazards and less number of operations.
[0015] Another object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate which minimizes or eliminate undesirable side reaction during sulphonation and salt formation of 1-amino naphthalene.
[0016] Another object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate, wherein the reaction mass comprising 1-amino naphthalene need not be isolated and can be directly utilized for sulphonation, followed by thermal rearrangement and alkali metal salt formation.
[0017] Another object of the present invention is to provide an improved process for the synthesis of alkali metal naphthionate, which results in high quantitative isolated yield.
[0018] The other objects and preferred embodiments and advantages of the present invention will become more apparent from the following description of the present invention when read in conjunction with the accompanying examples and figures, which are not intended to limit scope of the present invention in any manner.

SUMMARY OF THE INVENTION
[0019] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0020] The present invention relates to an improved process for the synthesis of alkali metal naphthionate. Specifically, the present invention relates to an improved process for the synthesis of alkali metal naphthionate of Formula I.
[0021] In one aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate of Formula I, wherein M represents an alkali metal selected from sodium (Na) and potassium (K); the process including converting 1-nitronaphthalene to 1-amino-naphthalene; and in-situ conversion of 1-amino-naphthalene to alkali metal naphthionate; wherein the process comprises the steps of:
a) converting 1-nitronaphthalene to 1-amino-naphthalene by hydrogenation;
b) sulphonation of 1-amino-naphthalene;
c) thermal rearrangement of sulphonated naphthylamine; and
d) alkali salt formation resulting in alkali metal naphthionate of Formula I;
characterized in that the 1-amino-naphthalene is not isolated from the reaction mass and is used as such for next step of sulphonation.

Formula I
[0022] In another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the process results in decrease in the overall time cycle and high productivity.
[0023] In yet another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the process is safe and results in less formation of degradation product at high temperature.
[0024] In yet another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, which is economically viable and safe.
[0025] In another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate which restricts large time cycle, has less chemical hazards and less number of operations.
[0026] In another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate which minimizes or eliminates undesirable side reaction during sulphonation and salt formation.
[0027] In another aspect, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, which results in high quantitative isolated yield.
[0028] Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention.

DETAILED DESCRIPTION
[0029] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0030] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0031] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0032] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0033] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0034] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0035] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0036] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
[0037] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0038] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0039] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0040] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0041] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0042] The present invention relates to an improved process for the synthesis of alkali metal naphthionate. Specifically, the present invention relates to an improved process for the synthesis of alkali metal naphthionate of Formula I.
[0043] In one embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate of Formula I, wherein M represents an alkali metal selected from sodium (Na) and potassium (K); the process including converting 1-nitronaphthalene to 1-amino-naphthalene; and in-situ conversion of 1-amino-naphthalene to alkali metal naphthionate; wherein the process comprises the steps of:
a) converting 1-nitronaphthalene to 1-amino-naphthalene by hydrogenation;
b) sulphonation of 1-amino-naphthalene;
c) thermal rearrangement of sulphonated naphthylamine; and
d) alkali salt formation resulting in alkali metal naphthionate of Formula I;
characterized in that the aminonaphthalene is not isolated from the reaction mass and is used as such for sulphonation.

Formula I
[0044] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the reduction of 1-nitro naphthalene to 1-aminonaphthalene is carried out by hydrogenation reaction in the presence of transition metal catalyst at a pressure in the range of 5-30 kg/cm2 and temperature in the range of 50-130 oC, in high boiling solvent.
[0045] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the transition metal catalyst for hydrogenation can be selected from Pd based catalyst, Pt based catalyst, Raney Nickel and the like. In a preferred embodiment, the transition metal catalyst is Raney Nickel.
[0046] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the high boiling solvent is a halogenated aromatic hydrocarbon selected from but not limited to chlorobenzene, dichlorobenzene (m-dichlorobenzene, p-dichlorobenzene), 1,2,3-trichlorobenzene, 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, hexachlorobenzene, 1-chloro-3-nitrobenzene, 1-bromo-4-chlorobenzene and mixtures thereof. Preferably the high boiling solvent is dichlorobenzene.
[0047] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein 1-aminonaphthalene is prepared in-situ, not isolated from the reaction mass and is used as such for next step of sulphonation.
[0048] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein sulphonation of 1-aminonaphthalene is carried out with sulphuric acid at high temperature.
[0049] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein sulphonation is carried out with 98% sulphuric acid at 70-185 ?C. The sulphonation step can be carried out using 1.1 equivalent of sulphuric acid with respect to 1-aminonaphthalene.
[0050] In still another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein sulphonated mass, is neutralized with alkali metal carbonate or alkali metal hydroxide to obtain alkali metal salt of naphthionate.
[0051] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein alkali metal carbonate can be selected from sodium carbonate and potassium carbonate.
[0052] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein alkali metal hydroxide can be selected from sodium hydroxide and potassium hydroxide.
[0053] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein thermal rearrangement of naphthylamine sulphate to naphthionic acid occurs at a temperature in the range of 70 to 185 oC.
[0054] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein in-situ sulfonation and salt formation occurs in the high boiling solvent resulting in selectivity in the range of 98-99% and yield of 1-aminonaphthalene to alkali metal naphthionate is in the range of 85-88%.
[0055] In yet another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the process results in decrease in the overall time cycle and high productivity. The process of the present invention can result in decrease in overall time from 60 hours to 48 hours, i.e., about 20-25%; with productivity higher by 15-20% than previously known processes. Furthermore, the process of the present invention results in minimum residues e.g., oligomers and polymers of amino naphthalene are formed only about 2-3%. The isolated alkali metal naphthionate, is of better quality, with improvement in colour, as measured by gardner scale, due to lesser exposure to heat as distillation is avoided. Sodium naphthionate prepared by the known processes results in sodium naphthionate with yellow ting, with gardner scale value of 1.3 whereas Sodium naphthionate prepared by the process of the present invention is off white in colour with gardner scale value of 1.0.
[0056] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein the process is safe and results in less formation of degradation product at high temperature. The observed degradation product is amino-naphthalene which is observed in the range of only 2-3%.
[0057] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, wherein thermal rearrangement of sulfonated mass occurs selectively with quantitative formation of alkali metal salt of naphthionate. The thermal rearrangement according to the embodiments of the present invention is selective leading to the rearrangement of naphthalene-amino sulphate to alkali metal 4-aminonaphthalene-1-sulfonate. Thermal rearrangement occurs selectivity at position-4 with only minor rearrangement observed at position-2.
[0058] In one embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, which is economically viable and safe.
[0059] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate which restricts large time cycle, has less chemical hazards and less number of operations.
[0060] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate which minimizes or eliminates undesirable side reaction during sulphonation and salt formation of 1-amino naphthalene.
[0061] In another embodiment, the present invention relates to an improved process for the synthesis of alkali metal naphthionate, which results in high quantitative isolated yield.
[0062] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
[0063] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
[0064] Example 1: Hydrogenation of Nitronaphthalene
[0065] 1000g (5.78 moles) of Nitro-Naphthalene was dissolved in 1300g of di-chlorobenzene and added into 5L S.S. Autoclave. To the solution, was added 15g Raney Nickel and autoclaved was closed, followed by heating the autoclave up to 130 °C under 30kg/cm2 of Hydrogen pressure for 6 hours. After 6 hours when the hydrogen pressure absorption had ceased, the reaction mass was cooled to 30 °C and remaining pressure was released. Reaction mass was then taken out from Autoclave and filtered. Filtrate was a mixture of 1-aminonaphthalene, along with dichlorobenzene and water. Water is separated from the organic layer and 1-aminonaphthalene along with the solvent (2081g) is separated and used as such for next reaction.
[0066] Example 2: Preparation of Sodium Naphthionate
[0067] 2081 g of 1-aminonaphthalene solution containing 785 g (5.49 moles) of 1-aminonaphthalene of 1-aminonaphthalene (obtained in Example 1, without further isolation) is taken in S.S. reactor, and diluted with 2183 g di-chlorobenzene. To the solution was added 598 g (6.09 mole) of sulphuric acid and the solution was heated upto 185 ?C for 5 hours. The reaction mass was then cooled followed by the addition of sodium carbonate solution (1496 g Sodium Carbonate solution prepared by adding 997 g water and 499 g Na2CO3 powder). After completion of addition, additional 872 g of water was added and the reaction mass was heated up to 85 ?C, for 2h. After the completion of the reaction, bottom organic mass was separated from the aqueous layer. The resulting reaction mass was filtered to remove undissolved material and cooled to 25 ?C and again filtered to obtain pure 1558 of sodium naphthionate. The product was characterized by diazotization titration and found to be 74% pure.
[0068] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.