Mepiquat chloride

Abstract: Mepiquat chloride is formed from the reaction between N-methylpiperidine and chloromethane in an anhydrous liquid solvent in the absence of sodium hydroxide. Mepiquat chloride precipitates as a solid of high purity and is recovered under a substantially moisture-free atmosphere. The solid mepiquat chloride can be sealed into a water soluble pouch or into a water soluble encapsulated solid form (e.g., granule, pellet, or briquette) for convenient handling. The pouch contains powdered mepiquat chloride or the encapsulated solid is merely introduced directly into a spray tank or reservoir for application with low human exposure and no containers in contact with the mepiquat chloride that require disposal. Mepiquat chloride is used as a component of a system for growing a number of commodity plants including cotton. The first component is a plant growth regulator applied to at least one of: (a) a furrow for cotton plant seeds, (b) to a cotton plant bearing the first true leaves, (c) to a cotton plant at pinhead square, and (d) to a cotton plant at early bloom. The plant growth regulating agents produce higher plant masses with high levels of boll retention. At mid-bloom, mepiquat chloride is applied to retard vegetative growth in favor of fruit (boll) production.

Description: The invention relates to the manufacture of mepiquat chloride. Mepiquat chloride (N,N-dimethylpiperidinium chloride) is used annually as the active ingredient for controlling excessive vegetative growth on millions of acres of cotton, potatoes, sweet potatoes, peanuts, grapes, corn, wheat, citrus, tomatoes, and onions. The desired growth stunting effects are particularly desired when the crop is grown in fertile soil or after weather conditions that favor plant growth rather than fruit production. Mepiquat chloride has traditionally been made in a basic aqueous solution (maintained with NaOH) by adding two methyl groups to the ring nitrogen atom in piperidine by contacting an aqueous solution containing piperidine with chloromethane in a molar ratio of about 2:1 chloromethane to piperidine at a pressure of about 0.65 - 0.69 MPa (95-100 psi). This dimethylation process yields about 50-60% mepiquat chloride in aqueous solution. A wash is used to remove the NaCl byproduct of the reaction to a level of about 1 wt% NaCl. Thereafter, a dye is added as a safety measure to warn users and antimicrobial agents are added to protect the product during storage. The aqueous solution is then packaged in containers and distributed. Like all containers of pesticides (a regulatory term referring to insecticides, plant growth regulators, herbicides, etc.), empty containers for mepiquat chloride must be rinsed three times and disposed of with care. Such handling is a part of the normal routine for growers today. It would be desirable, however, if mepiquat chloride could be presented in a form and package that would reduce the time for and expense of container handling and disposal without adversely affecting the performance of the mepiquat chloride. Cotton is a representative plant for describing the uses and effects of mepiquat chloride. Mepiquat chloride has the effect on cotton plants of stunting vegetative growth thereby forcing the plant to redirect its energies into fruit (cotton boll) production. With appropriate application of mepiquat chloride to plants that are beginning to exhibit excessive vegetative growth, cotton plant yields can be maintained or increased without harm to the plant. Cotton plants have a predictable life cycle and growth period. Cotton plants emerge 7-10 days after the seeds are planted in a furrow. The cotton plant exhibits growth of a root system and the extension of plant height through stem and branch growth in a pattern referred to as "vegetative growth." " Cotton plants that have directed the majority of the available plant energy to vegetative growth are referred to as "rank" cotton and produce little or no cotton bolls. Cotton that exhibits signs of going rank are readily visible by abnormal plant height relative to the boll loads. Mepiquat chloride is used to stop cotton from going rank by modifying the cotton plant's growth characteristics. The branches off the main stem generally always extend from alternating sides of the stem. Each branch site is called a "node" with 5-7 nodes being formed above the cotyledon leaves before the first fruit bearing branch with true leaves is formed. Node counting starts at the bottom of the plant and extends up the main stem. The "internode length" is the distance between branch sites with a new node being formed roughly every three days. For purposes of measurement and comparison, the number of nodes and internode length above node 8 is generally used to eliminate interplant fruiting node variations because fruit bearing branches will necessarily have been formed by node 8. Fruiting sites in cotton are referred to as "squares." Each fruit bearing branch will form three fruiting sites ("squares") with approximately six days between square formations on each branch. New squares and the beginning of reproductive growth in cotton plants are referred to as "pinhead" squares due to their barely visible size. After about three days, the square has grown to about the size of a match head and is a period in the plant cycle referred to as a "match head square." The match head square continues to grow to about the size of an average adult fingernail before blooming ("early bloom"). Three days later, a boll has formed beneath the bloom. Roughly thirty days after early bloom, the product boll is fully mature and ready for harvest. Overall, about 80% of the total cotton yield is set within the first 3 weeks of early bloom and 95% of the total yield is set within 5 weeks of early bloom. Generally, mepiquat chloride is applied to cotton plants in one of two ways as a plant growth stunting agent. The method used until about 1987 was a single application of 600-1200ml/hectare (8-16 ounces per acre) of a 4.2 wt% solution at early bloom. This type of single treatments did control plant height although it was noticed that plant yields were occasionally reduced particularly if the plant was stressed during or after the application. Since 1987, the trend has been to apply mepiquat chloride in a series of applications each having a lower dose than the single dose application. The first treatment occurs at match head square with a second treatment 7-14 days thereafter. Both treatments are made at a rate within the range from about 0-300ml of 4.2 wt% solution per hectare (0-4 ounces/acre) with the specific application rate depending on whether the cotton plant was exhibiting signs of being stressed (no application), moderate growth (about 60ml/hectare or 2 ounces of solution per acre), or vigorous growth (about 120ml/hectare or 4 ounces of solution per acre). Thereafter, two additional treatments at 7-14 day intervals may be used with application rates extending up to about 600ml (8 ounces) of 4.2 wt% mepiquat chloride solution with the specific application rate dependent on the amount of vegetative growth in the field. Stunted plant growth can have the effect of increasing yields and boll retention but at the expense of the plant's ability to generate new growth. Such an effect can have broader ramifications, however, because the plant growing abilities hindered by mepiquat chloride are the same abilities that permit the plant's immune system to fight off diseases and to recover from insect damage to the plant tissues. It would be desirable if the use of mepiquat chloride could be integrated into a system of treatment that would increase plant tissue mass in the roots, stems, and leaves to provide higher levels of nutrient transfer while, at the same time, restricting vegetative growth to enhance fruit production. DE-A-2207575 discloses a method of preparing plant growth regulators related to mepiquat chloride by reacting a piperidine with an alkyl halide in an inert solvent. It is an object of the invention to provide a method of making mepiquat chloride by a process that results in a solid form of mepiquat chloride in high yield and purity. In accordance with the invention, the process of making mepiquat chloride comprises: contacting chloromethane with N-methylpiperidine in anhydrous acetone in the absence of NaOH for a time sufficient to precipitate solid mepiquat chloride; separating said solid mepiquat chloride from said acetone; and recovering said solid mepiquat chloride whereby said mepiquat chloride exhibits a purity of at least 98 wt%. By the present invention, the manufacture of mepiquat chloride provides a solid product in high yield with a high purity and a level of efficacy that surpasses mepiquat chloride made by the previous aqueous dimethylation process. The solid form permits the active ingredient to be formed into packaged forms that present a significantly reduced risk of contact through handling and fewer or no containers which require special handling procedures for disposal. Mepiquat chloride produced in accordance with the invention may be used as a part of a system for growing cotton that provides a strong plant physiology and nutrient gathering network so that boll production and retention are maximised. Mepiquat chloride may be produced according to the invention in a batch process by (a) contacting N-methylpiperidine with chloromethane in anhydrous acetone for the N-methylpiperidine and chloromethane at a temperature within the range from about 0-200° C for a time sufficient to produce at least 90% of the N-methylpiperidine to solid mepiquat chloride (N,N-dimethylpiperidinium chloride), (b) separating the mepiquat chloride from the anhydrous acetone, and (c) recovering solid mepiquat chldride having a purity of at least 99 wt%. The recovered solvent can be reused for a later batch thereby increasing the economic operation of the process. N-methylpiperidine is a restricted chemical available in purity levels of greater than 98 % but which is substantially more expensive (about 400%) per unit weight than piperidine. In the present process, however, N-methylpiperidine can be readily methylated in anhydrous solvent in yields of greater than 90% to produce a solid precipitate product (100% retained on fast filter paper) having a degree of purity in excess of 99% without the formation of sodium chloride byproducts. More advantageously, use of an anhydrous solvent according to the invention permits recovery of a solid mepiquat chloride powder that exhibits a higher level of efficacy per unit weight of mepiquat chloride than the aqueous product commercially available to date. Such improved efficacy indicates that mepiquat chloride from the present invention will produce more consistent control over vegetative growth at the same application rates as mepiquat chloride made by the conventional aqueous dimethylation process using NaOH to maintain a basic solution pH. Solid mepiquat chloride powder according to the invention exhibits a white to light yellow color. Increased activity means that less active ingredient can be used to attain the same level of plant growth control or the same application rates will give more consistent control. Chloromethane is a gas and can be contacted with the liquid phase by any of the conventional gas/liquid contact methods that is effective to transfer material in the gas into the liquid. The simplest and preferred method for the present invention is a tube extending below the surface of the liquid phase through which the chloromethane is passed. The tube exhibits a length sufficient to permit chloromethane to dissolve in the anhydrous solvent as a bubble of gas rises through the liquid. An array of distribution tubes and nozzles may be used, however, if desired. The introduction rate of the chloromethane is desirably controlled to provide a reactor pressure of about 0.58 MPa (70 psig) or less solely for economic reasons. Use of low reactor pressures reduces the cost of the reactor vessel. Higher reactor pressures from higher rates of chloromethane introduction may be used if the cost of the vessel is not a limiting factor. It should be noted, however, that the methylation of N-methylpiperidine is an exothermic reaction and dependent on the introduction rate of the chloromethane. Bench top reactors will not generally need a cooling system if the heat can naturally dissipate through the reactor walls. When scaled up to larger reactor volumes, however, some form of cooling jacket or coils should be used whether on the outside of the reactor vessel or disposed within the reactor. The cooling rate and efficiency of the cooling system will be chosen by a chemical engineer exercising no more than the ordinary level of skill for one in this art as a part of an integrated process design at a given chloromethane feed rate. The reactants and mepiquat chloride product of the present invention are quite stable against thermal degradation. Thus, the reaction temperature is functionally limited at the lower end of the operable range by the desired rate of reaction. Generally temperatures of greater than about 0° C are needed for economic reaction rates. The highest practical temperature is limited by a combination of the vaporization temperature of the acetone used as the solvent and the pressure rating of the reaction vessel. A temperature of about 70° C or less is preferred with a temperature within the range from about 40°-50° C being most preferred to provide for some operational temperature variation during control over the process. Because the mepiquat chloride product is insoluble in the acetone solvent, the product solid can be separated from the anhydrous solvent with most conventional equipment. Examples of suitable separation equipment include, inter alia, centrifuges, cylindrical filters (e.g., a Neutsche) equipped with appropriate filtration material, and plate and frame filters. The filtering apparatus is desirably made of a corrosion resistant material such as stainless steel. A recovered acetone wash during the separation process will assist in recovery of any unreacted N-methylpiperidine. The product can be similarly dried with any of the conventional solids drying equipment. A vacuum drier made of stainless steel or glass lined carbon steel are particularly preferred. Because mepiquat chloride powder is highly hygroscopic, contact with moisture or moisture laden atmospheres should be avoided to prevent caking or dissolution of the product. All separation, drying, forming, and packaging steps should be conducted under an inert atmosphere with a relative humidity that is as low as possible. Preferably, all handling steps where the solid mepiquat chloride product might be exposed to atmospheric or other moisture are conducted under a blanket of nitrogen although, e.g., any of the noble gases or carbon dioxide can also be used. The recovered solid mepiquat chloride powder can be sealed in bulk, dissolved in water, packaged into disposable or recyclable containers, and sold in exactly the same manner as previously available from the aqueous methylation process. The solid form of mepiquat chloride resulting from the present invention provides the opportunity to package and use mepiquat chloride in a manner that poses less risk of accidental contact with less disposable materials than has previously been possible. Example 1 Mepiquat chloride is made in a small batch process by loading 4 liters of acetone into a reactor. One thousand grams of N-methylpiperidine is added to the solvent and sealed into a reactor. A total of 510 g of chloromethane (10% molar excess) is then introduced below the surface of the liquid in the reactor with a dip tube over a period of 2-6 hours. The introduction rate is controlled so that a pressure of 0,48 MPa (70 psi) is not exceeded to stay within the pressure rating of the reactor vessel. The reaction was allowed to continue overnight so that the entire cycle took about 24 hour. Over 95% of the N-methylpiperidine was converted to mepiquat chloride which precipitated on the bottom of the reactor. The solid mepiquat chloride was separated from the acetone solvent (which was recovered for reuse) by filtration. An acetone wash was used to remove any adsorbed impurities. The solid mepiquat chloride was dried with vacuum filtration and exhibited a purity of over 99.5 %. The proportions used in this example presented a molar ratio of chloromethane to N-methylpiperidine that was 1.1:1. In commercial operations where solvent recovery will return any unreacted chloromethane to the next batch, this ratio should be considered a minimum for maximum conversion with a molar ratio of chloromethane to N-methylpiperidine being at least 1:1, preferably within the range from about 1.05:1 to about 1.5:1. Example 2 Solid mepiquat chloride dissolved in water to make a 4.2 wt% solution was compared to a 4.2 wt% aqueous solution sold under the trademark PIX®. PIX® is believed to be made by the conventional aqueous process of dimethylating piperidine under basic conditions maintained with NaOH. The comparison tests were performed on a statistically significant number of cotton plants under controlled growing conditions. Active ingredient (AI) was applied to the cotton plant foliage at match head square with rates corresponding to 12.5g/hectare and 25g/hectare (5g/acre and 10g/acre) respectively. This period in the life cycle of the cotton was chosen to identify any difference in effects with the cotton in a period of vigorous growth. The designation SP represents a mepiquat chloride solution made from a soluble powder of mepiquat chloride as produced according to the invention. The results are reported in Table 1. Measurement 12.5g AI/hectare 5g AI/acre (25g AI/hectare) 10g AI/acre SP PIX® SP PIX® Plant height (in cm, 14 days after treatment) 76 82 76 78 Improvement (%) 7.3 2.6 Change in plant height (in cm, 14 days after treatment) 8 14.7 9.6 10.8 Improvement (%) 45.6 11.1 Average internode length above node 8 (cm) 3.9 4.6 3.9 4.2 Improvement (%) 15.2 0.7 Plant height above node 8 (cm) 36.7 44.3 39 38 Improvement ( %) 17.2 -2.6 From the results in Table 1, mepiquat chloride solutions made from the water soluble powders produced by the anhydrous process of the invention control plant height above node 8 better than the commercially available product believed to be made by the aqueous methylation process.

Claims: A process for making mepiquat chloride comprising: contacting chloromethane with N-methylpiperidine in anhydrous acetone in the absence of NaOH for a time sufficient to precipitate solid mepiquat chloride; separating said solid mepiquat chloride from said acetone; and recovering said solid mepiquat chloride whereby said mepiquat chloride exhibits a purity of at least 98 wt%. A process as in Claim 1, wherein the contacting step comprises: contacting chloromethane with N-methylpiperidine in a molar ratio of chloromethane to N-methylpiperidine at least 1:1. A process as in Claim 1, wherein the recovering step comprises: recovering mepiquat chloride solids having a purity of at least 99 wt%. A process as in Claim 1, wherein the recovering step comprises: recovering mepiquat chloride solids having a purity of at least 99.5 wt%. The process of Claim 1, wherein the separating step and the recovering step are each conducted under an atmosphere substantially free of moisture.

Inventors: ATKINS RHETT R, BRISTOL DAVID WILLIAM, CLARK RICHARD U, FRISBEE ALBERT ROGER, HICKEY JOSEPH A, LOVELL JAMES S, THIGPEN JAMES C, TYNDALL JOHN RAYMOND, ATKINS, RHETT R., BRISTOL, DAVID WILLIAM, CLARK, RICHARD U., FRISBEE, ALBERT ROGER, HICKEY, JOSEPH A., LOVELL, JAMES S., THIGPEN, JAMES C., TYNDALL, JOHN RAYMOND
Applicants: MICRO FLO CO, MICRO-FLO COMPANY
Application year: 1993
Main classification: C07D211
IPC codes: A01N43, A01G7, C07D295