Description:
FIELD OF THE INVENTION:
The present invention relates to a process for the preparation of anhydrous Acrolein. More particularly, the present invention provides a process for the preparation of Glufosinate or salts of Glufosinate or isomers thereof.

BACKGROUND OF THE INVENTION:
Glufosinate is a non-selective herbicide, belonging to the group of organophosphorous herbicides, which is widely used around the world. It is generally used in the form of an ammonium salt for unwanted vegetation control and to control growth of weeds and grasses. Glufosinate contains an asymmetric carbon atom, and its biological activity is seen in racemic mixture (of L-glufosinate and D-glufosinate) and L-glufosinate enantiomer. The ammonium salt of these compounds (both L-glufosinate enantiomer and racemic mixture) is particularly important. The ammonium salts of glufosinate and L-glufosinate are preferably formulated as aqueous solutions. Ammonium glufosinate [Ammonium 2-amino-4-(hydroxymethylphosphinyl)butanoate] is a highly effective and non-selective herbicide widely used in genetically modified and glufosinate-tolerant crops.

Acrolein is an important raw material used for preparation of Aldehyde intermediate in the production of Glufosinate Ammonium, which contains ~ 3.5% moisture. The presence of water in Acrolein decomposes the Aldehyde (an intermediate of Glufosinate ammonium), which results in loss of yield of the final product: Glufosinate Ammonium.

US2767216A relates to a process for drying of aqueous acrolein. The ‘261 patent presses upon the need to reduce the moisture content from Acrolein. It discloses that the ability to use acrolein in many fields is often dependent upon the absence therein of any substantial amount of water.

US 9115067B1 relates to a process for the continuous production of acrolein via the catalytic oxidation of propylene. IN 211751 relates to an alternate process for producing Glufosinate ammonium, by allowing the number of ester precursors to be reduced and being suitable for preparing Glufosinate and related compounds.

The processes provided in the prior arts are laborious and involves the use of freshly distilled acrolein. None of the available arts provide a cost-effective process to reduce the moisture content in Acrolein to address the problem existing in the art.

Another challenge in the art was to develop a cost-effective process. There is a worldwide drive to reduce the cost of pesticides applied on the field so as not to increase the cost of food. This can be done by reducing overall cost for production. Such objective can also be met by reducing the overall productions steps, as reduced numbers of steps shall save energy, manpower and loss of active ingredients in transfer/isolation of product and so on.

Thus, there exists a need in the art to develop a process for producing Glufosinate in a more efficient and cost-effective manner. In particular, an efficient and cost-effective process having improved selectivity, improved overall yield, and improved catalyst life.

Therefore, the process of the present invention overcomes all the above stated limitations, solves one or more aforementioned problems, and provides a simple, economic and environment-friendly process for preparing Glufosinate, or salts or isomers thereof.

OBJECTIVE OF THE INVENTION:
Accordingly, it is a primary objective of the present invention to provide a low cost and an efficient process for preparing anhydrous Acrolein.
Another objective of the present invention is to provide an industrially viable, cost effective and a simple process for reducing the moisture content of Acrolein by using acetic anhydride in the presence of a catalyst.

It is yet another objective of the present invention to provide a process for the preparation of Glufosinate, or salts of Glufosinate or isomers thereof.

SUMMARY OF INVENTION:
According to an aspect of the present invention, there is provided a process for preparation of anhydrous Acrolein.

According to another aspect of the present invention, there is provided a process for reducing the moisture content of Acrolein by using acetic anhydride in the presence of a catalyst.

According to yet another aspect of the present invention, there is provided a process for preparation of Glufosinate, or salts of Glufosinate or isomers thereof by using anhydrous Acrolein.

According to an aspect of the present invention, there is provided a process for improving the yield of Glufosinate, or salts of Glufosinate or isomers thereof.

According to another aspect of the present invention, there is provided a process for reducing the moisture content of Acrolein by using acetic anhydride in the presence of catalyst, and use of such acrolein for yield improvement in a process for preparation of Glufosinate Ammonium.

DETAILED DESCRIPTION OF THE INVENTION:
Acrolein is an important raw material used for preparation of aldehyde intermediate in the production of Glufosinate Ammonium, which contains ~ 3.5% moisture. The presence of water in acrolein decomposes the aldehyde (an intermediate of Glufosinate ammonium), which results in loss of yield of the final product: Glufosinate Ammonium.

Removal of substantially all water from acrolein is rendered difficult by the fact that acrolein and water form an azeotropic mixture under ordinary distillation conditions. The use of solvents in processes directed to the treatment of acrolein is often rendered difficult because of the reactivity of acrolein with many of these materials under the conditions at which they are employed therein. Although processes enabling the dehydration of acrolein are available, such processes often entail the use of operative steps the nature or complexity of which render them impractical or too costly in many of the industrial uses wherein acrolein is employed in a relatively dry state.

The present inventors have developed a novel process for producing Glufosinate in a more efficient and cost-effective manner by reducing or, as far as possible, eliminating the moisture content of acrolein. The present invention provides an efficient and cost-effective process having improved selectivity and overall yield.

In an embodiment, the present invention also provides a process involving the use of acetic anhydride in the presence of catalyst to produce anhydrous acrolein, which is further used in the manufacturing process of agrochemically active ingredient, Glufosinate.

The process of the present invention may involve in-situ production of acetic acid by the reaction of Acetic anhydride with water in the presence of a catalyst to form Acetic acid which is further used in the process.

Those skilled in art will be aware that the invention described herein is subject to variations and modifications other than those specifically described. It is to be understood that the invention described herein includes all such variations and modifications. The invention also includes all such steps, features, compositions and processes referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more said steps or features.

For convenience, before further description of the present invention, certain terms employed in the specification, examples are described here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art. The terms used throughout this specification are defined as follows, unless otherwise limited in specific instances.

The terms used herein are defined as follows.

It must be noted that, as used in this specification, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. The terms “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances.

As used herein, the terms “comprising”, “including”, “having”, “containing”, “involving”, and the like are to be understood to be open-ended i.e., to mean including but not limited to.

It must be noted that the term “anhydrous” means “without water”.

As used herein, the terms “about” or “approximately” are inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±10 or ±5 of the stated value.

The use of any and all examples, or exemplary language (e.g., “such as”), is intended merely to better illustrate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure as used herein.

While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure is not limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.

As used herein, the term “herbicide” encompasses both herbicides as well as plant growth regulators, in so far as this does not otherwise emerge from the context.

As used herein the term “composition” is used interchangeably with the term “formulation”.

The term “liquid formulation” unless stated otherwise, includes all aqueous based liquid formulations such as soluble liquid, emulsion in water, microemulsion, emulsifiable concentrate, suspension concentrates, and so on.

The term “room temperature” unless stated otherwise, essentially means temperature in a range from about 20°C to about 45°C.

As used herein, the term “glufosinate” comprises glufosinate acid, L-glufosinate, D-glufosinate, or isomers thereof. The terms may be used interchangeably. The term “L-glufosinate” is used interchangeably with the term “glufosinate P”. The terms “L-glufosinate acid” and “Glufosinate P acid” are used interchangeably.

According to yet another embodiment, the glufosinate is selected from the group comprising racemic glufosinate, L-glufosinate, D-glufosinate, a racemic mixture of L-glufosinate and D-glufosinate, isomers, or combinations thereof.

According to an embodiment, the glufosinate comprises a racemic mixture of L-glufosinate and D-glufosinate.

According to an embodiment, the glufosinate comprises L-glufosinate.

According to an embodiment, the glufosinate comprises a racemic mixture of D-enantiomer (about 50%) and L-enantiomer (about 50%).

In an embodiment, the glufosinate comprises a racemic mixture of D-glufosinate (about 50%) and L-glufosinate (about 50%).

According to an embodiment, the glufosinate comprises a weight ratio of L-isomer to D-isomer in a range from about 1:99 to about 99:1.

In an embodiment, the glufosinate comprises a weight ratio of L-glufosinate to D-glufosinate in a range from about 1:99 to about 99:1.

According to an embodiment, the glufosinate is selected from the group comprising racemic glufosinate, L-glufosinate, D-glufosinate, a racemic mixture of L-glufosinate and D-glufosinate, isomers, or combinations thereof, wherein a weight ratio of L-isomer to D-isomer is in a range from about 1:99 to about 99:1.

In an embodiment, the glufosinate is selected from the group comprising racemic glufosinate, L-glufosinate, D-glufosinate, a racemic mixture of L-glufosinate and D-glufosinate, isomers, or combinations thereof, wherein a weight ratio of L-glufosinate to D-glufosinate is in a range from about 1:99 to about 99:1.

It has been found by the present inventors that the yield of glufosinate can be surprisingly improved by reducing the moisture content of acrolein used in the process for preparing the glufosinate.

Therefore, in an aspect, the present invention provides a process for preparing glufosinate, wherein the process proceeds via acrolein having a reduced moisture content.

In an embodiment, the present invention provides a process for preparing glufosinate, wherein the process proceeds via anhydrous acrolein.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 3.5%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 3.0%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 2.5%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 2.0%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 1.5%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 1.0%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.5%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.4%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.3%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.2%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.1%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of less than 0.05%.

In an embodiment, the anhydrous acrolein means acrolein having a moisture content of about 0%.

The process used for preparing such anhydrous acrolein is not particularly limiting.

In an embodiment, anhydrous acrolein may be prepared as per processes that are known in the art.

For example, one such process known for preparing anhydrous acrolein may be utilized which is disclosed and exemplified in US3860495A. its entirety.

In an embodiment, the anhydrous acrolein may be prepared by a process that is preferred according to an embodiment of the present invention described hereinbelow.

In an embodiment, the present invention provides a process for producing anhydrous acrolein comprising steps of:
1. Preparing a pre-mix of acetic anhydride and a catalyst;
2. Charging the pre-mix of acetic anhydride and a catalyst to Acrolein; and
3. Optionally, maintaining the reaction mass for 3-4 hrs after complete charging to obtain anhydrous acrolein.

In another embodiment, the ratio of acetic anhydride to catalyst in pre-mix is 10 ppm to 15000 ppm.

In yet another embodiment, the catalyst used in step (3) is selected from organic acids, inorganic acids, benzene sulfonic acid, Amberlyst catalyst, Zncl2 (Zinc chloride), Alcl3 (Aluminium chloride).

In a further embodiment, the catalyst used in step (3) is selected from sulfuric acid, phosphoric acid, p-toluenesulfonic acid, sulfonic acid, hydrochloric acid, organic sulfonic acid, Sodium bisulfate, or Napthalene sulfonic acid.

According to an embodiment, the process includes in-situ generation of acetic acid by the reaction of Acetic anhydride with water in the presence of a catalyst to form Acetic acid which is further used in the process.

According to another embodiment, approximately 16% w/w acetic acid is generated in-situ, because of which, lesser amount of Acetic acid is required to be added for further reaction.

In a further embodiment, step (2) involves charging a mixture of acetic anhydride and catalyst to the Acrolein and maintaining the reaction mass till the moisture content of acrolein is below 0.5% and Acetic anhydride is nil in the GC profile.

According to an embodiment, the moisture content of Acrolein is reduced from ~3.5 % to 0.

According to another embodiment, the moisture content of Acrolein is reduced from ~3.5 % to <0.1%.

In a further embodiment, the moisture content of Acrolein is reduced from ~3.5 % to <0.2%.

According to an embodiment, the moisture content of Acrolein is reduced from ~3.5 % to <0.3%.

According to another embodiment, the moisture content of Acrolein is reduced from ~3.5 % to <0.4%.

According to yet another embodiment, the moisture content of Acrolein is reduced from ~3.5 % to <0.5%.

According to an embodiment, the reduction in moisture of Acrolein is in the range of 90% - 100%.

According to another embodiment, the reduction in moisture of Acrolein is in the range of 95% - 100%.

According to yet another embodiment, the reduction in moisture of Acrolein is in the range of 98% - 100%.

In the embodiments described hereinafter, the term acrolein having a reduced moisture content is intended to include, but not being limited to, anhydrous acrolein.

Thus, in an aspect, the present invention provides a process for preparing glufosinate, wherein the process proceeds via acrolein having a reduced moisture content.

In an embodiment, the acrolein having a reduced moisture content is used to prepare aldehyde, which is converted to glufosinate.

In an embodiment, the acrolein having a reduced moisture content is reacted with diethyl dimethyl phosphite to prepare aldehyde, which is converted to glufosinate.

Thus, in this embodiment, the present invention provides a process for preparing glufosinate, wherein the process comprises (i) reacting acrolein having a reduced moisture content diethyl dimethyl phosphite to prepare aldehyde; and (b) converting the aldehyde to glufosinate.

In an embodiment, the diethyl dimethyl phosphite used herein may be used as available commercially, or may be obtained using processes that are known in the art, or may be prepared by a process that is preferred according to an embodiment of the present invention described hereinbelow.

According to an embodiment, the diethyl dimethyl phosphite may be prepared by a process comprising:
(i) Preparing diethylchloro phosphite (DECP) from phosphorous trichloride (PCL3) and triethyl phosphite (TEP); and
(ii) Preparing diethyl methyl phosphite (DEMP) from diethylchloro phosphite (DECP) and grignard reagent (MMC).

Thus, in this embodiment, there is also provided a process for the preparation of Glufosinate, or salts of Glufosinate or isomers thereof, said process comprising:
1. Preparing diethylchloro phosphite (DECP) from phosphorous trichloride (PCL3) and triethyl phosphite (TEP);
2. Preparing diethyl methyl phosphite (DEMP) from diethylchloro phosphite (DECP) and grignard reagent (MMC);
3. Preparing aldehyde using acrolein having a reduced moisture content and DEMP (Diethyl methyl phosphite);
4. Converting aldehyde to Glufosinate.

According to an embodiment, there is provided a process for preparing ammonium salt of glufosinate, or isomers thereof, said process comprising:
1. Preparing diethylchloro phosphite (DECP) from phosphorous trichloride (PCL3) and Triethyl phosphite (TEP);
2. Preparing diethyl methyl phosphite (DEMP) from diethylchloro phosphite (DECP) and grignard reagent (MMC);
3. Preparing aldehyde using anhydrous Acrolein and DEMP (Diethyl methyl phosphite);
4. Converting Aldehyde to Glufosinate.

In an embodiment, the glufosinate is L-glufosinate.

According to an embodiment, step 1) is carried out at a temperature range from about 10°C to about 50°C, to form diethylchloro phosphite (DECP).

According to another embodiment, step 2) is carried out at a temperature range from about 10 °C to about 60°C, to form diethylmethyl phosphite (DEMP).

According to yet another embodiment, the process involves charging the mixture of acetic anhydride and catalyst to Acrolein and maintaining the reaction mass for 3 – 4 hrs after complete charging to obtain anhydrous Acrolein.

According to an embodiment, step 3) is carried out at a temperature range from about 20°C to about 70°C, to form aldehyde adduct.

According to another embodiment, step 3) is carried out at a temperature range from about 30°C to about 40°C, to form aldehyde adduct.

In another embodiment, the glufosinate product obtained by the present invention may be directly used to prepare a herbicidal composition.

Thus, the present invention also provides a process for preparing a herbicidal composition comprising glufosinate, wherein the process comprises preparing glufosinate via acrolein having a reduced moisture content, and adding at least one agrochemically acceptable excipient to said glufosinate to obtain a herbicidal composition.

In an embodiment, the present invention also provides a herbicidal composition comprising glufosinate, wherein the glufosinate is prepared via acrolein having a reduced moisture content; and at least one agrochemically acceptable excipient.

In an embodiment, the glufosinate or a composition comprising the glufosinate prepared according to the present invention may be used to control at least one weed in a crop.

In an embodiment, Glufosinate or a composition comprising glufosinate prepared by the process of the present disclosure maybe used to target weeds such as Allium cepa, Ananas comosus, Arachis hypogaea, Asparagus officinalis, Avena sativa, Beta vulgaris spec altissima, Beta vulgaris spec rapa, Brassica napus var. napus, Brassica napus var. napobrassica, Brassica rapa var. silvestris, Brassica oleracea, Brassica nigra, Camellia sinensis, Carthamus tinctorius, Carya illinoinensis, Citrus limon, Citrus sinensis, Coffea arabica (Coffea canephora, Coffea liberica), Cucumis sativus, Cynodon dactylon, Daucus carota, Elaeis guineensis, Frag aria vesca, Glycine max, Gossypium hirsutum, (Gossypium arboreum, Gossy-pium herbaceum, Gossypium vitifolium), Helianthus annuus, Hevea brasiliensis, Hordeum vul-gare, Humulus lupulus, Ipomoea batatas, Juglans regia, Lens culinaris, Linum usitatissimum, Lycopersicon lycopersicum, Malus spec., Manihot esculenta, Medicago sativa, Musa spec., Ni-cotiana tabacum (N.rustica), Olea europaea, Oryza sativa, Phaseoius iunatus, Phaseoius vul garis, Picea abies, Pinus spec., Pistacia vera, Pisum sativum, Prunus avium, Prunus persica, Pyrus communis, Prunus armeniaca, Prunus cerasus, Prunus dulcis and prunus domestica, Ribes sylvestre, Ricinus communis, Saccharum officinarum, Secale cereale, Sinapis alba, So-lanum tuberosum, Sorghum bicolor (s. vulgare), Theobroma cacao, Trifolium pratense, Triticum aestivum, Triticale, Triticum durum, Vicia faba, Vitis vinifera, Zea mays.

In another embodiment, Glufosinate prepared by the process of the present disclosure maybe used to target weeds among the crops such as rice, wheat, barley, rye, oat, sorghum, cotton, soybean, peanut, buckwheat, beet, rapeseed, sunflower, durum wheat, fall wheat, field corn, winter barley, cotton, fall barley, fallow, spring wheat, triticale, winter wheat, sugar cane, tobacco, etc.; vegetables; solanaceous vegetables such as eggplant, tomato, pimento, popper, potato, etc., cucurbit vegetables such as cucumber, pumpkin, zucchini, water melon, melon, squash, etc., cruciferous vegetables such as radish, white turnip, horseradish, kohlrabi, Chinese cabbage, cabbage, leaf mustard, broccoli, cauliflower, etc., asteraceous vegetables such as burdock, crown daisy, artichoke, lettuce, etc., liliaceous vegetables such as green onion, onion, garlic, and asparagus, ammiaceous vegetables such as carrot, parsley, celery, parsnip, etc., chenopodiaceous vegetables such as spinach, Swiss chard, etc., lamiaceous vegetables such as Perilla frutescens, mint, basil, etc. strawberry, sweet potato, Dioscorea japonica, colocasia, etc., flowers, foliage plants, turf grasses, fruits: pome fruits such apple, pear, quince, etc. stone fleshy fruits such as peach, plum, nectarine, Prunus mume, cherry fruit, apricot, prune, etc., citrus fruits such as orange, lemon, rime, grapefruit, etc., nuts such as chestnuts, walnuts, hazelnuts, almond, pistachio, cashew nuts, macadamia nuts, etc. berries such as blueberry, cranberry, blackberry, raspberry, etc., grape, kaki fruit, olive, plum, banana, coffee, date palm, coconuts, etc., trees otter than fruit trees; tea, mulberry, flowering plant, trees such as ash, birch, dogwood, Eucalyptus, Ginkgo biloba, lilac, maple, Quercus, poplar, Judas tree, liquidambar formosana, plane tree, zelkova. Japanese arborvitae, fir wood, hemlock, juniper, Pinus, Picea, and Taxus cuspidate, etc.

In yet another embodiment, the present invention provides a method of controlling weeds using Glufosinate or its salts or isomers thereof or a composition comprising the same.

An embodiment of the present invention provides a kit of parts comprising the composition prepared by the process of the present invention. Such kits may comprise, in addition to the present composition, one or more additional active and/or inactive ingredients and a user manual for using said composition.

The present invention achieves at least one of the following advantages:
1. Reduction in Acrolein moisture.
2. Improved yield of glufosinate.
3. In-situ generation of acetic acid because of which lesser amount of acetic acid is required to be added.
4. Lesser amount of ingredients required as compared to the conventional processes.
5. Simple, efficient and cost-effective process can be carried out in lesser amount of time.

In view of the above, it will be seen that the several advantages of the disclosure are achieved, and other advantageous results are attained. Although the present disclosure has been disclosed in full, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the disclosure. The embodiments may be combined together for better understanding of the disclosure, without departing from the scope of the disclosure.

In another embodiment, alternative or multiple embodiments of the disclosure disclosed herein are not to be construed as limitations. Each embodiment can be referred to and claimed individually or in any combination with other embodiments of the disclosure. One or more embodiments of the disclosure can be combined together to exhibit the teaching of the invention, without departing from the scope of the disclosure.

The following examples are presented to provide what is believed to be the most useful and readily understood description of procedures and conceptual aspects of this invention. The examples provided below are merely illustrative of the invention and are not intended to limit the same to disclosed embodiments. Variations and changes obvious to one skilled in the art are intended to be within the scope and nature of the invention.

EXAMPLES:
A. An exemplary process for demoisturization of Acrolein:
A solution of 415 gm of Acetic Anhydride and 0.86 to 0.9 gm of Methane sulfonic acid (MSA) was prepared and added to 2159 gm of Acrolein, taken in a clean and dry 5 litre glass kettle. After charging the mixture of Acetic anhydride + MSA to the reactor, the reaction mass was maintained for 3.0 – 3.5 hrs till the moisture content of acrolein was below 0.5% and Acetic anhydride was nil in the GC profile. After moisture reduction, Acetic acid was charged to the above reaction mass. The above prepared premix was used for further reaction i.e., Aldehyde preparation.

B. Preparation of Aldehyde using Demoisturized Acrolein and Diethylmethyl phosphite (DEMP):
2575 gm of demoisturized Acrolein was taken in a reactor under Nitrogen blanketing and cooled to 10°C. 1570 gm of Acetic acid was charged in this mass and mixed well for 10 mins. A Premix of Acrolein & Acetic acid was prepared. Aldehyde was taken as a heal (Heal is the product of this reaction, which is taken in reactor for better mixing of reactant) in reactor and the reaction mass was cooled upto 10°C. Subsequently, dropwise addition of 4581 gm DEMP and 4145 gm premix of Acrolein & Acetic acid was carried out, while, maintaining temperature below 32 – 33°C for 6 -7 hrs. After addition of DEMP and Premix, the reaction was carried out at 32 – 35°C for 2.0 hrs to produce 8726 gm Aldehyde adduct. The GC analysis of the DEMP was 0.5%, and HPLC w/w was around 120% - 122% (w/w with 2-4DNP complex form). The Yield obtained was 94 – 96%.

As is evident from above, the present invention results in higher yield as compared to the conventional process at each stage of the process.

Reagent screening and Comparative Study:
Various reagents and methods were tested alone and in various combinations before arriving at the present process to reduce the moisture content of Acrolein. The present disclosure provides the rationale behind the selection of the specific reagents and the process parameters used in the process:

Moisture Content of Acrolein: ~3.52%,
Acetic Anhydride + Cat.
H2SO4 NA 0.1 – 0.2 % 1. Moisture reduction upto nil.
2. In presence of H2SO4 , moisture reduces within 1.5 – 2.0 hrs.
Acetic Anhydride + Cat.
H3PO4 NA 0.5 – 0.4 % Moisture reduction upto nil.

Acetic Anhydride + Cat.
NaHSO4 NA 0.4 – 0.3 % Moisture reduction upto nil.

Acetic Anhydride + Cat.PTSA
(para-toluene sulphonic acid) 118.5% 0.4 – 0.3 % 1. Moisture reduction upto nil.
2. Yield was around 92 – 93%.
Acetic Anhydride +
Cat.N2SA (Naphthalene
sulphonic acid) 119% 0.4 – 0.3 % 1. Moisture reduction upto nil.
2. Yield was around 92 – 93%.
Acetic Anhydride + Cat.MSA
(Methane sulphonic acid) 119 - 121% 0.4 – 0.3 % 1. Moisture reduction upto nil.
2. Yield was around 94 – 95%.

Acetic Anhydride + Cat.MSA
+ Heal (treated Acrolein mass) 119 - 121% 0.3 – 0.25 % Moisture reduction upto nil.

Table 2
The above table shows the efficiency of the premix of acetic anhydride and catalyst in reducing the moisture content of Acrolein to a great extent. As is evident from the above table, the premix of acetic anhydride and catalyst showed no degradation of active ingredient, thus improvising the yield of final product.

It was further found that when acetic anhydride alone was used in the process, only 50% moisture reduction was observed, however, when acetic anhydride was used in the presence of catalyst such as Methane sulphonic acid, Naphthalene sulphonic acid, para-toluene sulphonic acid etc., 95-100% reduction in moisture content was observed and a yield of around 90-95% was obtained.

Table 3: Different combinations of Catalyst with Acetic Anhydride: Another study was carried out to test the combinations of Acetic anhydride with various catalysts.

Acrolein
(in gm) Reagent qty
(in gm) Catalyst (cat) Catalyst in PPM Maintaining Temperature Maintaining Time % moisture Acrolein GC (% area) Acetic acid (% area) AC2O GC (% area)

100 AC2O 10 - - 33 – 34°C 6.0 hrs 2.68% 91.64 1.34 6.55
100 AC2O 22 - - 48°C 4.0 hrs 2.76% 92.72 0.68 4.85
50 Acetyl chloride
+ Sod. Acetate 7 + 8 - - 30 -33°C 3.5 hr 1.10% 90.1 2.46 2.355
50 Acetyl chloride
+
Pyridine 7 + 8 - - 30 -33°C 1.0 hr 0.58% 94.2 0.32 2.8
100 AC2O 20 H2SO4 500 30 – 31°C 1.0 hr 0.35% 87.41 7.26 Nil
50 AC2O 11 H3PO4 3000 27 - 28°C 6.5 hr 0.31% 87.53 8.71 0.26
50 AC2O 11 H3PO4 6000 27 – 28°C 2.5 hr 0.34% 88.2 8.622 0.246
67.5 AC2O 13 PTSA 500 30 – 32°C 4.0 hr 0.32% 91.76 8.05 0.043
67.5 AC2O 13 PTSA + Heal 500 30 – 32°C 2.0 hr 0.31% 90.97 6.98 0.05
67.5 AC2O 13 N2SA 500 30 – 32°C 4.5 hr 0.35% 89.72 8.06 nil
67.5 AC2O 13 N2SA + Heal* 500 30 – 32°C 3.0 hr 0.31% 89.79 7.3 0.03
67.5 AC2O 13 MSA 300 30 – 32°C 2.5 hr 0.36% 89.18 8.2 nil
67.5 AC2O 13 MSA 500 10 – 37°C 2.5 hr 0.39% 89.37 7.85 0.012
67.5 AC2O 13 MSA 1000 35 – 48°C 40 min 0.28% 89.63 7.41 nil
67.5 AC2O 13 MSA* 500 30 - 35°C 2.0 hr 0.32% 89.39 7.94 0.017
*MSA: Methane Sulfonic acid *Heal: Output / product which is used for better mixing the reactant *AC2O: Acetic anhydride

It is evident from above table that acetic anhydride in the presence of catalyst provides enhanced results. The presence of catalyst has a synergistic action on the activity of acetic anhydride and significant reduction in moisture content of acrolein is obtained in less time. As shown in the above table, the maintaining time is less, when a combination of acetic anhydride and catalyst is used. Hence, the process of the present invention is efficient, cost effective and requires less maintenance.

Acetic anhydride in presence of catalytic amount of acids like H2SO4, H3PO4, N2SA, PTSA, NaHSO4 and MSA, not only reduces the moisture content of acrolein in less time, but also results in in-situ generation of acetic acid, as a result of which lesser amount of acetic acid is required to be added to carry out the process. Hence, the selection of specific reagents and process parameters in the present invention play a crucial role in achieving the desired technical effect.

C. Role of acrolein moisture content in increasing the yield of Glufosinate:
The acrolein moisture content was reduced by reduction with Acetic anhydride and MSA. Acrolein conventionally contained 3.5% moisture which contribute 4 to 5% yield loss in GF acid.

Aldehyde was prepared by reaction of DEMP with Acrolein premix solution. Taken aldehyde in Reactor as a Heal and cooled to 15 -20°C. Meanwhile to prepare mixture of Acrolein and Acetic acid at 10°C and stir for 15 min which had moisture around 1.8 to 1.9% by KF. This Premix and DEMP both were simultaneously added in reactor with maintaining temp 28 -33°C in 2-3 hrs. During addition exotherm observed which maintained by outer ice water cooling. Maintain the reaction at 28 -33°C for 2.0 hrs. Withdraw sample for GC analysis for DEMP confirmation and HPLC w/w for aldehyde Confirmation. (DEMP < 0.5%, HPLC >= 118 – 122).

Acrolein Moisture reduction by Acetic anhydride and MSA catalyst.
1. Acrolein taken in Dry and clean reactor which was moisture free.
2. Meanwhile prepared the solution of Acetic anhydride and MSA. (MSA was 400 to 500 ppm of total acrolein quantity.)
3. Charged the above mixture (Acetic anhydride + MSA) to the Acrolein.
4. Maintained the reaction mass for 2.5 hrs. after complete charging.
5. Ensure the % m/c by KF or Acetic anhydride %GC in acrolein. (%m/c should be less than 0.4% and Acetic anhydride should be nil. If not then maintain further to complete.)
6. After moisture reduction charged Acetic acid to above reaction mass.
7. Taken the above prepared premix for further Aldehyde Preparation.

Comparison of present invention and conventional process is provided in below table for better demonstration of the advantages of present invention and is not intended to limit the scope of invention in any way.

SOP DEMP Acrolein Acetic acid A. Anh. MSA HCL 1st hydrolysis GF acid HPLC w/w GFacid Yield %
Current process 143 61 63 0 0 1140 1762 8.90% 86.64%
Modified Process 143 67.5 49 14 0.026 1140 1786 9.40% 92.75%
143 67.5 49 14 0.021 1140 1738 9.80% 94.10%
143 67.5 47 14 0.021 1140 1761 9.70% 94.70%

It was thus found that the yield of glufosinate was surprisingly enhanced due to the use of acrolein having a reduced moisture content.

, Claims:

1. A process for preparing glufosinate, wherein the process proceeds via acrolein having a reduced moisture content.

2. The process as claimed in claim 1, wherein the process proceeds via anhydrous acrolein.

3. The process as claimed in claim 1 or claim 2, wherein acrolein has a moisture content of less than 3.5%.

4. The process as claimed in any one of the preceding claims, wherein anhydrous acrolein is prepared by a process comprising steps of:
(a) Preparing a pre-mix of acetic anhydride and a catalyst;
(b) Charging the pre-mix of acetic anhydride and a catalyst to Acrolein; and
(c) Optionally, maintaining the reaction mass for 3-4 hrs after complete charging to obtain anhydrous acrolein.

5. The process as claimed in claim 4, wherein the catalyst used in step (a) is selected from sulfuric acid, phosphoric acid, p-toluenesulfonic acid, sulfonic acid, hydrochloric acid, organic sulfonic acid, Sodium bisulfate, or Napthalene sulfonic acid.

6. The process as claimed in claim 1, wherein the acrolein having a reduced moisture content is reacted with diethyl dimethyl phosphite to prepare aldehyde, which is converted to glufosinate.

7. The process as claimed in claim 6, wherein the diethyl dimethyl phosphite is prepared by a process comprising:
(a) Preparing diethylchloro phosphite (DECP) from phosphorous trichloride (PCL3) and triethyl phosphite (TEP); and
(b) Preparing diethyl methyl phosphite (DEMP) from diethylchloro phosphite (DECP) and grignard reagent (MMC).

8. A process for the preparation of Glufosinate, or salts of Glufosinate or isomers thereof, said process comprising:
(a) Preparing diethylchloro phosphite (DECP) from phosphorous trichloride (PCL3) and triethyl phosphite (TEP);
(b) Preparing diethyl methyl phosphite (DEMP) from diethylchloro phosphite (DECP) and grignard reagent (MMC);
(c) Preparing aldehyde using acrolein having a reduced moisture content and DEMP (Diethyl methyl phosphite); and
(d) Converting aldehyde to Glufosinate.

9. The process as claimed in claim 1 or claim 8, wherein the glufosinate is L-glufosinate.

10. A process for preparing a herbicidal composition comprising glufosinate, wherein the process comprises preparing glufosinate via acrolein having a reduced moisture content, and adding at least one agrochemically acceptable excipient to said glufosinate to obtain a herbicidal composition.

11. A herbicidal composition comprising glufosinate, wherein the glufosinate is prepared via acrolein having a reduced moisture content; and at least one agrochemically acceptable excipient.

12. A method of controlling weeds using Glufosinate or its salts or isomers thereof prepared according to a process as claimed in claim 1 or 8.

13. A method of controlling weeds using a composition claimed in claim 11.

14. The process as claimed in claim 1 or claim 8, wherein the yield of glufosinate is enhanced by at least 5%.