Claims:We Claim:
1. A process comprises reducing an amount of N-Nitroso pendimethalin from untreated reaction mass, wherein said process comprises contacting the reaction mass with a mineral acid in presence of a solvent and a catalyst to obtain treated mass.
2. The process as claimed in claim 1, wherein said untreated reaction mass comprises a mixture of N-Nitroso pendimethalin and pendimethalin, and wherein said product mass comprises N-Nitroso pendimethalin in an amount ranging from 30000 ppm to 150000 ppm.
3. The process as claimed in claim 1, wherein N-Nitroso pendimethalin is reduced in an amount ranging from 0.1 ppm to 100 ppm.
4. The process as claimed in claim 1 wherein treated mass comprises N-Nitroso pendimethalin in an amount ranging from 0.1 ppm to 100 ppm.
5. The process as claimed in claim 1 wherein said catalyst comprises methyl triphenyl phosphonium bromide, ethyl triphenyl phosphonium bromide, propyl triphenyl phosphonium bromide, n-butyl triphenyl phosphonium bromide, tetrabutyl ammonium bromide, isopropyl triphenyl phosphonium bromide, n-pentyl triphenyl phosphonium bromide.
6. The process as claimed in claim 1, wherein reaction is carried out at temperature in the range from 65°C to 85°C.
7. The process as claimed in claim 1, wherein said mineral acid comprises hydrochloric acid, hydrobromic acid, sulphuric acid or nitric acid.
8. The process as claimed in claim 1, wherein said solvent comprises acetone, diethyl ketone, diisobutyl ketone, diisopropylketone, methyl isobutyl ketone, methyl isopropyl ketone, acetone or diethyl ketone.
9. The process as claimed in claim 1, wherein said acid is hydrochloric acid and said solvent is acetone used in a weight ratio ranges from 90:10 to 97:3.
10. The process as claimed in claim 1, wherein the catalyst is in an amount ranging from 0.01% to 2% by weight of the mass.

Dated this 24th day of March 2022

Dr. Sanchita Ganguli
IN/PA Reg No: 625
Of S. MAJUMDAR & CO.
(Applicant’s Agent)
, Description:TECHNICAL FIELD
[0001] The present disclosure relates to a process for reducing n-nitroso impurity from dinitroaniline herbicide. More particularly the present invention relates to a process for reducing N-Nitroso pendimethalin from a product mass that is cost effective, less time consuming and affords improved yield of pendimethalin.
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] Pendimethalin is an herbicide of the dinitro-aniline class used in pre-emergence and post-emergence applications to control annual grasses and certain broadleaf weeds. It inhibits cell division and cell elongation. Currently, it is one of the most widely used and accepted pre-emergent herbicides in the urban residential environment. With increase in demand, there has been a sharp rise in the production of Pendimethalin over the years. Numerous methods were adopted by the scientists and researchers for the synthesis of Pendimethalin with high yield and purity. However, one of the main challenges is generation of effluents during the process of synthesis. Larger the number of reaction steps and requirement of purity of pendimethalin more is the waste generated. Direct discharge of such untreated effluent containing impurities and other side-products is not suitable, since it gives rise to various environmental concerns, such as the pollution of surface and groundwater resources. Accordingly, need is felt for the treatment of effluents generated during the production of Pendimethalin.
[0004] The process of manufacturing dinitroanilines for example pendimethalin produces by-products of N-nitroso compounds, particularly N-Nitroso pendimethalin. Several methods have been proposed so far to reduce impurity of N-Nitroso pendimethalin from the product mass. In practice, the amount of N-Nitroso pendimethalin reduces to the extent of 0.1% by the conventional methods i.e. the product mass still contains N-Nitroso pendimethalin in an amount higher than 1000 ppm. As a person skilled in the art would readily appreciate that Environmental Protection Agencies world over has placed stringent limit over the allowable concentration of N-Nitroso pendimethalin that may be present in the Pendimethalin or Pendimethalin based products.
[0005] Consequently, rigorous research has been done so far to further reduce the amount/concentration of N-Nitroso pendimethalin that may be present in the product mass. One of the methods is to subject the product mass containing N-Nitroso pendimethalin to an elevated temperature one or more times to decompose the N-Nitroso pendimethalin, as disclosed in US5922915A, contents whereof is incorporated herein by way of reference. This patent disclose a method of reducing the concentration of an N-nitroso-containing compound in a composition comprising a desired dinitroaniline herbicide and the N-nitroso derivative of the dinitroaniline herbicide, comprising heating the composition to a temperature wherein the N-nitroso derivative of the dinitroaniline herbicide decomposes, but at a temperature less than or near the decomposition temperature of the desired dinitroaniline herbicide, particularly the temperature is from about 100°C. to about 260° C and maintaining the temperature for an effective amount of time. In this process the product mass having N-Nitroso compound was subjected twice to the elevated temperature which leads to significant loss of pendimethalin. Further, this process is time consuming and beneficial for increasing the yield of the desired product.
[0006] There is therefore a long felt need in the art to develop a new process for reducing an amount of N-Nitroso pendimethalin from a product mass that is cost effective and less time consuming while affording improved yield of pendimethalin. The present disclosure satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.
[0007] 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.
OBJECTS OF THE INVENTION
[0008] It is an object of the present disclosure to provide a process for reducing an amount of N-Nitroso pendimethalin from a product mass that overcomes one or more limitations associated with the conventional methods.
[0009] It is an object of the present disclosure to provide a process for reducing an amount of N-Nitroso pendimethalin from a product mass that is cost effective.
[0010] It is an object of the present disclosure to provide a process for reducing an amount of N-Nitroso pendimethalin from a product mass that can be implemented at an industrial scale.
[0011] It is an object of the present disclosure to provide a process for reducing an amount of N-Nitroso pendimethalin from a product mass that is economical.
[0012] It is an object of the present disclosure to provide a process for for reducing an amount of N-Nitroso pendimethalin from a product mass that does not lead to significant loss of pendimethalin.

SUMMARY OF INVENTION
[0013] In an aspect the present invention provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass containing pendimethalin.
[0014] In another aspect the present invention provides an environment friendly process for reducing N-Nitroso pendimethalin impurity produced during manufacturing of pendimethalin.
[0015] In another aspect the present invention provides a simple, industrially viable, reproduceable, environment friendly and cost-effective process for producing pendimethalin with reduced amount of N-Nitroso pendimethalin.
[0016] In another aspect the present invention provides a process for producing pendimethalin which will reduce the quantity of N-nitroso-pendimethalin to the desired level preferably less than 50ppm on a commercial scale.
[0017] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. 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 invention as defined by the appended claims.
[0019] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0020] 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.
[0021] 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.”
[0022] 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.
[0023] 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.
[0024] 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.
[0025] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, 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 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.
[0026] 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.
[0027] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0028] 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.
[0029] 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.
[0030] The present disclosure relates to an improved process for reducing an amount of N-Nitroso pendimethalin from a product mass.
[0031] Generally, the process of manufacturing dinitroanilines produces by-products of N-nitroso compounds. Typically, N-Nitroso pendimethalin formed as an impurity during manufacturing of desired pendimethalin product. An aspect of the present disclosure provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass.
[0032] The present invention relates to a simple commercial process for reducing N-Nitroso pendimethalin impurity content during the manufacturing of pendimethalin. The method comprising the steps of: (a) contacting the product mass containing pendimethalin with a mineral acid in presence of a catalyst and organic solvent at a temperature ranging from 50°C to 90°C to obtain a crude product mass, (b) separating, washing the organic fraction and (d) removing the solvent to obtain treated product mass having reduced amount of N-Nitroso pendimethalin.
[0033] In an embodiment, the product mass comprises N-Nitroso pendimethalin and pendimethalin. In an embodiment, the product mass has N-Nitroso pendimethalin in an amount ranging from 30000 ppm to 150000 ppm. In an embodiment, the treated product mass has N-Nitroso pendimethalin in an amount ranging from 0.1 ppm to 100 ppm. In preferred embodiment, N-Nitroso pendimethalin impurity is reduced to below 50 ppm.
[0034] A typical process for production of Pendimethalin includes - hydrogenation of 4-Nitro-o-Xylene using hydrogen gas in presence of a catalyst under high pressure to generate N-alkylated xylene, which is subsequently purified, and subjected to nitration using a nitrating mixture of nitric acid and sulphuric acid in presence of a chlorinated solvent to produce a product mass containing pendimethalin. This nitrated mass is subjected further to chemical denitrososation (CDN) to produce crude pendimethalin mass. In CDN stage the nitro mass is reacted with mixture of ketone & mineral acid to reduce the nitroso content desirable for next step. Further thermal denitrososation (TDN) is performed. In this stage crude pendimethalin mass is treated with sodium bicarbonate and water and further thermal denitrososation is done twice at elevated temperature to reduce the nitroso content to desired level. This process is time consuming and also lead to loss of pendimenthalin.
[0035] Following this process, the Nitroso impurity in the reaction mass reduces from 15-17% to <0.5% generally ~0.05 to 0.1%. The reaction mass is washed with water and sodium bicarbonate followed by solvent recovery, TDN-1 (to reduce nitroso from ~1000 ppm to 100 ppm), TDN-2 (to reduce the nitroso to less than 100ppm). During this process yield loss of about 4% (2% in each TDN1 & TDN2 stage) is observed on commercial stage which makes the process not suitable and not economically viable at large scale.
[0036] Typically, the untreated product mass includes N-Nitroso pendimethalin in an amount ranging from 3% to 15% (i.e. 30000 ppm to 150000 ppm). The present invention describes an inexpensive and simple process for reducing the concentration of N-nitroso pendimethalin impurity generated during manufacture of pendimethalin. The present invention thus provides a process which reduces the cost and implementability and improves the yield. Advantageously the present process is simple, safe, environmentally friendly as well as sustainable.
[0037] Accordingly, in an aspect the present invention provides a simple commercial process for reducing an amount of N-Nitroso pendimethalin from a product mass, the method comprising the steps of: (a) contacting the product mass with a mineral acid in presence of a catalyst and organic solvent at a temperature ranging from 60°C to 85°C to obtain a crude product mass, (b) separating an organic fraction from the crude product mass; (c) removing the solvent from the organic fraction to obtain a product mass having reduced content of N-Nitroso pendimethalin.
[0038] In an embodiment, the product mass comprises N-Nitroso pendimethalin and pendimethalin. In an embodiment, the product mass has N-Nitroso pendimethalin in an amount ranging from 30000 ppm to 150000 ppm. In an embodiment, according to the present method N-Nitroso pendimethalin impurity in the treated product mass is reduced to an amount ranging from 0.1 ppm to 100 ppm preferably less than 50ppm.
[0039] In an embodiment the catalyst is a phase transfer catalyst.
[0040] In an embodiment the catalyst is selected from methyl triphenyl phosphonium bromide, ethyl triphenyl phosphonium bromide, propyl triphenyl phosphonium bromide, n-butyl triphenyl phosphonium bromide, tetrabutyl ammonium bromide, isopropyl triphenyl phosphonium bromide, n-pentyl triphenyl phosphonium bromide and the like.
[0041] In preferred embodiment the catalyst is selected from Ethyl Triphenyl phosphonium bromide, Tetrabutyl ammonium bromide, Aliquat® 330 and the like.
[0042] In an embodiment, the catalyst is used in an amount ranging from 0.01% to 5% by weight of the product mass, preferably 0.05% to 2% by weight.
[0043] In an embodiment, the mineral acid is selected from hydrochloric acid, sulphuric acid, nitric acid, hydrobromic acid and the like.
[0044] In an embodiment, the solvent is selected from acetone, diethyl ketone, diisobutyl ketone, diisopropylketone, methyl isobutyl ketone, methyl isopropyl ketone, acetone, diethyl ketone and the like.
[0045] In an embodiment, the mineral acid is hydrochloric acid having concentration of 30% v/v. In an embodiment, the solvent is acetone. In an embodiment, weight ratio of 30% hydrochloric acid to acetone ranges from 90:10 to 97:3.
[0046] Typically the step of contacting the product mass with the mineral acid comprises: (a) mixing the product mass with an organic solvent to obtain a first mixture; (b) heating the first mixture at a temperature ranging from 60°C to 85°C; (c) effecting addition of the catalyst in the heated first mixture; (d) mixing the mineral acid with solvent to obtain a second mixture; (e) effecting addition of said second mixture to said heated first mixture under stirring condition while maintaining temperature within the range of 60°C to 85°C to obtain a reaction mass; and (f) stirring the reaction mass maintaining it at temperature ranging from 60°C to 85°C to obtain the crude product mass.
[0047] In an embodiment, the step of effecting the addition of said second mixture to said heated first mixture comprises effecting addition of said second mixture to said heated first mixture over a time period ranging from 10 minutes to 50 minutes under stirring condition while maintaining temperature of said second mixture within the range of 60°C to 85°C to obtain a reaction mass.
[0048] In an embodiment, the present process further comprises separating the organic layer from the reaction mixture and recovering the solvent and washing the reaction mass after completion of reaction.
[0049] In an embodiment, the step of washing the reaction mass with any or a combination of the alkaline solution and water which comprises washing the organic fraction with the alkaline solution and washing the organic fraction with water.
[0050] In an embodiment, the solvent is removed/recovered from the organic fraction by distillation. Typically, an emulsion is formed after completion of reaction, advantageously it is observed that according to present process formation of emulsion is reduced, thus yield loss is also reduced/minimized.
[0051] Typically, after completion of reaction, the reaction mass is separated, and organic layer is washed with water and sodium bicarbonate solution. The organic mass is analysed for Nitroso impurity which is <50 ppm. The solvent is recovered to get molten Pendimethalin and the bottom mass is further analysed for Nitroso impurity which is <50 ppm.
[0052] The present invention thus provides a process for treating the effluent containing N-nitroso impurity which can be reduced to less than 50 ppm, preferably less than 1ppm.

[0053] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. 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.
[0054] EXAMPLES
[0055] EXAMPLE – 1
[0056] 750 gm of untreated effluent mass (having about 1000 ppm of N-Nitroso Pendimethalin) was added in a reactor. Catalyst was added to the mixture in an amount of about 1 gm. A mixture of conc. HCL (30%) and acetone (weight ratio of 96:4) was taken in an addition funnel and was added to the reaction mass over a period of 30 minutes. The reaction mixture was then stirred and heated to 70-80°C. The reaction mass was then allowed to be cooked at the same temperature and after completion of the reaction, the reaction mass was separated in a separating funnel and kept stagnant for 30 min. The organic layer was separated, and mass was washed with water and sodium bicarbonate solution to obtain treated effluent (N-Nitroso Pendimethalin content- less than 50 ppm).

[0057] EXAMPLES – 2 to 11
[0058] The process as described in Example 1 was repeated with different amounts of the catalyst. After 10 hr of cooking the sample of reaction mass was evaluated. After the completion of reaction, the organic mass is subjected to washing and after that EDC is recovered from mass. The reaction mass gets concentrated, so nitroso also gets concentrates.
[0059] Results are provided in Table 1 below:
Table 1: Reaction Parameters and amount of N-Nitroso Pendimethalin
EXAMPLE Process parameters Amount of N-Nitroso
(ppm) % Emulsion of total Mass
Catalyst Loading RPM & stirrer After 10 hr cooking (Reaction) After workup and EDC recovery After reaction
Ex. 2 1% 400/1 PBT 19 58 0%
Ex. 3 0.6% 400/1 PBT 28 58 0.6%
Ex. 4 0.15% 400/1 PBT 22 42 0.8%
Ex. 5 0.1% 400/1 PBT 7 17 1.1%
Ex. 6 0.1% 400/1 PBT 9 27 1.7%
Ex. 7 0.05% 400/1 PBT 21 52 2.6%
Ex. 8 0.05% 250/1 PBT 6 9 3.2%
Ex. 9 0.10% 250/1 PBT 12 28 1.4%
Ex. 10 0.10% 250/1 PBT 15 21 2.1%
Ex. 11 0.10% 250/1 PBT 10 55 2.1%
• PBT- Pitch blade turbine

It is evident from above table that the present process is advantageous in reducing amount of N-Nitroso pendimethalin from a product mass. It can be seen from the above data that lesser the emulsion means less yield loss and vice a versa.
INDUSTRIAL APPLICABILITY
[0060] The process of the present invention is simple and fast, economically viable at industrial scale, sustainable and meets disposal guidelines & norms. Thus, present invention is encompassing a feature that involves technical advance as compared to the existing knowledge or having economic significance or both and that makes the invention not obvious to a person skilled in the art.
The advantages of the present process are provided as follows.

ADVANTAGES OF THE PRESENT INVENTION
[0061] The present disclosure provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass that overcomes one or more limitations associated with the conventional methods.
[0062] The present disclosure provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass that is cost effective.
[0063] The present disclosure provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass that can be implemented at an industrial scale.
[0064] The present disclosure provides a process for reducing an amount of N-Nitroso pendimethalin from a product mass that is economical.
[0065] The present disclosure provides a process for for reducing an amount of N-Nitroso pendimethalin from a product mass that does not lead to significant loss of pendimethalin.