Process for the preparation of N-(2-nitrophenyl)phosphoric acid triamide

Abstract

Process for the preparation of N-(2-nitrophenyl)phosphoric triamide (2-NPT) by reaction of 2-nitroaniline and phosphorus pentachloride to an iminophosphoric trichloride (I), subsequent hydrolysis of the iminophosphoric trichloride (I) without its prior isolation or purification with a hydrolyzing agent to the phosphoric amide dichloride (II), and subsequent ammonolysis of the phosphoric acid amide dichloride (II) without its prior isolation or purification to 2-NPT, characterized by that the 2-nitroaniline is dosed into a suspension of phosphorus pentachloride in an inert solvent via a dip tube within 0.5 to 5 h at a temperature between 40 and 60 °C and then heated to boiling. and the addition of the hydrolyzing agent to the iminophosphoric acid trichloride (I) a) at a temperature of 70 to 100 °C for a period of less than one hour or b) at a temperature of 45 to 60 °C over a period of up to 5 h or simultaneously, within a period of up to 5 h, approximately equimolar amounts of the solution of iminophosphoric acid trichloride (I) and the hydrolyzing agent are dosed into a separate reactor, wherein the temperature of the iminophosphoric acid trichloride solution and the reactor temperature are 50-100 °C.

Description

[0001] The invention relates to a technically simple process for the production of N-(2-nitrophenyl)phosphoric triamide (2-NPT) starting from 2-nitroaniline and phosphorus pentachloride. The process is characterized in that, in a first step, a phosphoric amide dichloride is produced, which is then reacted with ammonia to give the final product. The reaction conditions are selected such that the 2-NPT is obtained with a low impurity content and in high yield. Furthermore, the resulting product is particularly fine-crystalline and lump-free, which facilitates further processing. State of the art

[0002] Urea is a naturally occurring biogenic metabolic product that is broken down into ammonia and carbon dioxide by the enzyme urease. This reaction is exceptionally rapid and efficient, and is therefore responsible for nitrogen losses when urea-based fertilizers are applied. These losses can be particularly high under certain climatic conditions if the soil lacks sufficient sorption capacity to bind the released ammonia in the form of ammonium ions. As a result, agriculture loses considerable amounts of nitrogen annually, contributing to environmental pollution and simultaneously increasing the demand for fertilizers.

[0003] The use of urease inhibitors is an effective way to significantly slow down the enzymatic urea hydrolysis, which under normal conditions proceeds extremely rapidly, thus enabling the use of urea and urea-containing fertilizers for light soil sites without loss.

[0004] A number of different compounds are described in the literature as urea absorption inhibitors (see S. Kiss, M. Simihäian, Improving Efficiency of Urea Fertilizers by Inhibition of Soil Uresse Activity, Kluwer Academic Publishers (2002)).

[0005] With the discovery of phosphoric acid ester diamides (DD 1 22 177 A3), compounds were found that represent highly effective urease inhibitors. A number of derivatives of phosphoric acid triamide, including the parent compound (see, e.g., US 4 540 428 A, US 4 676 822 A, US 4 517 004 A, EP 0 119 487 A1), are similarly effective. To date, only N-(n-butyl)thiophosphoric acid triamide (active ingredient: NBTPT) (IMC AGRICO Corp., product name Agrotain®) and mixtures of NBTPT and analogous N-(n-propyl)thiophosphoric acid triamide (BASF SE, product name Limus®) have been commercialized.

[0006] Particularly effective urease inhibitors are phosphoric triamides or thiophosphoric triamides, in which two of the three amide groups are unsubstituted (EP 0 119 487 A1; WO 00 / 058 317 A1; WO 2001 / 087 898 A2; WO 2006 / 010 389 A1). A highly effective inhibitor that exhibits significant activity even at very low application rates is N-(2-nitrophenyl)phosphoric triamide (2-NPT) [WO 2006 / 010 389 A1].

[0007] The synthesis of 2-NPT usually starts with phosphoryl chloride (POCl3) or phosphorus pentachloride (PCl5) and 2-nitroaniline. First, an N-(2-nitrophenyl)phosphoramide dichloride is prepared from these in an inert solvent, which is then reacted with ammonia to give the final product, yielding not only the desired 2-NPT but also ammonium chloride (WO 2006 / 010 389 A1).

[0008] The resulting 2-NPT is contaminated with varying proportions of different by-products, depending on the reaction conditions. Some of these by-products can only be removed from the final product with considerable effort. Minimizing the content of such by-products is therefore of significant importance for the quality of the synthesis process.

[0009] Since all chlorine atoms of phosphorus chloride (POCl3 or PCl5) are not part of 2-NPT but are lost as byproducts (hydrogen chloride or ammonium chloride), synthesis starting from phosphoryl chloride (POCl3) would be more economical from a material perspective. However, to achieve acceptable yields of 2-NPT with this route, unfavorable reaction conditions are necessary, such as an excess of POCl3, large amounts of solvent, and the use of a catalyst. Even then, the 2-NPT produced in this way is contaminated by a large proportion of sparingly soluble byproducts. Because significantly fewer of these byproducts are formed in the synthesis starting from phosphorus pentachloride, this route is preferable.

[0010] DE 10 2004 035 742 A1 relates to N-phenylphosphoric triamides, processes for their production, compositions containing them, and the use of these N-phenylphosphoric triamides or compositions containing them as agents for regulating or inhibiting enzymatic (urease-catalyzed) urea hydrolysis (also in combination with agents for limiting nitrification) to prevent nitrogen losses during the application of urea-based fertilizers, as well as for reducing ammonia levels in animal housing by largely eliminating urea hydrolysis, and as an additive to feed-grade urea in animal nutrition, especially for ruminants. The invention of DE 10 2004 035 742 A1 further relates to fertilizer compositions containing N-phenylphosphoric triamides and a urea-based fertilizer. Subject matter of the invention

[0011] The present invention was therefore based on the objective of finding a process for the synthesis of N-(2-nitrophenyl)phosphoric triamide (2-NPT) starting from 2-nitroaniline and PCl5 that is technically simple and provides 2-NPT in high yield with a low proportion of byproducts. Furthermore, the formation of clumps during ammonolysis should be avoided, and the product should be obtained in a fine-crystalline form without significant aggregation. Description of the invention

[0012] This problem was solved according to the invention by the method described below. Advantageous and / or preferred embodiments of the invention are the subject of the dependent claims.

[0013] To minimize the content of minor compounds during synthesis starting from PCl5, various investigations were conducted. Some of the observed correlations will be briefly explained below.

[0014] During the synthesis, the reaction of phosphorus pentachloride with 2-nitroaniline initially yields iminophosphoric trichloride (I), which is partially hydrolyzed with a hydrolyzing agent such as water or organic carboxylic acids to form phosphoramide dichloride (II). This dichloride is then ammonolyzed with ammonia to give 2-NPT. A small amount of doubly nitrophenyl-substituted byproduct (III) is also formed during the preparation of intermediate (II). This byproduct reacts further with ammonia to form N,N'-bis(2-nitrophenyl)phosphoramide (bisproduct). Because this bisproduct is difficult to separate from 2-NPT due to its solubility properties, it remains as the main impurity in the final product.

[0015] The reaction of phosphoric acid pentachloride and 2-nitroanline, followed by hydrolysis, releases significant quantities of gas, totaling 3 moles of hydrogen chloride per mole of phosphoric acid pentachloride. Rapid reaction can cause the reaction mixture to foam, potentially carrying solvents into the gas scrubber. Furthermore, rapid reaction requires a very large gas scrubber to remove the substantial amounts of HCl gas from the exhaust stream. Therefore, it would be advantageous to allow the reaction of phosphoric acid pentachloride and 2-nitroanline, as well as the subsequent hydrolysis, to proceed slowly, enabling controlled removal of the significant volume of exhaust gas.

[0016] While the reaction of phosphoric acid pentachloride and 2-nitroaniline can be easily slowed down by low temperatures or slow dosing of the nitroaniline, slowing the hydrolysis leads to the formation of byproducts. It was surprisingly found that when iminophosphoric acid trichloride (I) and the phosphoridoid dichloride (II) formed during its hydrolysis are present simultaneously, a reaction occurs between the two components to form the doubly nitrophenyl-substituted byproduct (III), and the bisproduct content in the 2-NPT formed after ammonolysis increases sharply. Longer dosing times therefore lead to correspondingly higher bisproduct contents (see Example 2d). Separate solutions of (I) or (II), on the other hand, are stable for several hours even at high temperatures.

[0017] To suppress the reaction between (I) and (II), a rapid addition of the hydrolysant to the iminophosphoric acid trichloride (I) is desirable to shorten the time that components (I) and (II) exist in parallel. However, as mentioned, this is disadvantageous due to the considerable gas volumes and the associated problems in gas scrubbing. Another way to suppress the reaction between (I) and (II) and the associated bisproduct formation is to reduce the reaction temperature. However, this causes the iminophosphoric acid trichloride to dimerize, and the dimer, which is sparingly soluble in toluene, reacts very slowly with the hydrolysant and, moreover, leads to increased bisproduct formation via side reactions (see Example 2f).

[0018] The ammonolysis of phosphoamide dichloride(II) can be carried out with hydrated ammonia or with anhydrous ammonia. Since, when reacting with hydrated ammonia, phosphoamide dichloride(II) can react not only with ammonia but also with water, the reaction with anhydrous ammonia is preferable, specifically by adding the phosphoamide dichloride(II) solution to liquefied ammonia. Introducing ammonia gas into the phosphoamide dichloride(II) solution leads to side reactions and a reduced 2-NPT yield.

[0019] Furthermore, during ammonolysis, deposits frequently form on the reactor walls, agitator, and internal components, consisting of 2-NPT and ammonium chloride, which precipitate immediately during the reaction. In unfavorable cases, these deposits can reach considerable proportions and severely impede the subsequent removal of the reaction mixture from the reactor. Moreover, product quality, such as purity and particle size distribution, is negatively affected. In addition, these deposits reduce the efficiency of heat transfer from the reaction chamber to the cooling jacket, leading to impaired reaction control and increased energy consumption for cooling the highly exothermic ammonolysis step. Therefore, such deposits must be strictly avoided through appropriate reaction control.

[0020] The process according to the invention for the preparation of N-(2-nitrophenyl)phosphoric triamide (2-NPT) is characterized in that, in a first step, phosphorus pentachloride and 2-nitroaniline are reacted in an inert solvent to form an iminophosphoric trichloride (I). This step is hereinafter referred to as phosphorylation. Subsequently, the solution of iminophosphoric trichloride (I) is partially hydrolyzed with a hydrolyzing agent to form a phosphoric amide dichloride (II) without prior work-up or isolation. This step is hereinafter referred to as hydrolysis.

[0021] The process according to the invention is further characterized in that, without further work-up or isolation of the phosphoric acid amide dichloride (II), the solution obtained is reacted with ammonia in a further step to give 2-NPT and the byproduct ammonium chloride. This step is hereinafter referred to as ammonolysis. The reaction conditions are selected such that the 2-NPT is formed from 2-NPT and ammonium chloride in high yield and with a low impurity content, and without caking or lumping during ammonolysis. Furthermore, the 2-NPT has a specific particle size that is advantageous for further processing of the product.

[0022] An inert solvent is defined as a solvent that does not negatively affect yield and product quality. Suitable solvents have a boiling point between 50 and 150 °C at standard pressure. Solvents with a boiling point between 80 and 120 °C at standard pressure are particularly suitable. Examples of inert solvents include aliphatic and aromatic hydrocarbons, as well as halogenated hydrocarbons such as heptane, cyclohexane, toluene, xylene, chloroform, and chlorobenzene. Due to its suitable boiling point, good solubility, and easy and inexpensive availability, the use of toluene has proven advantageous.

[0023] The amount of solvent is not critical and is chosen to ensure good stirrability of the reaction mixture. An optimal amount of solvent is between 500 and 1000 ml per mole of 2-nitroaniline, but this is not the limit.

[0024] The ratio of the reactants 2-nitroaniline and phosphorus pentachloride is approximately equimolar, where approximately equimolar is defined as a molar ratio in the range of 1:0.95 to 1:1.1. To achieve maximum yield and minimize unwanted byproducts, an amount of 1.005 to 1.03 mol of phosphorus pentachloride per mol of 2-nitroaniline is particularly suitable.

[0025] The reaction between 2-nitroaniline and phosphorus pentachloride begins upon heating in the temperature range between 40 and 50 °C. When both reactants are added together, a considerable amount of hydrogen chloride is produced within a short time. To prevent foaming of the reaction mixture and the entrainment of solvent into the gas scrubbing system, the process according to the invention is characterized in that the 2-nitroaniline is not added together with the phosphorus pentachloride, but rather added to it. Surprisingly, it has been found that the initial excess of phosphorus pentachloride significantly reduces undesirable byproducts such as N,N'-bis(2-nitrophenyl)phosphoric triamide (bisproduct) and prevents the formation of other impurities.In the preferred embodiment of the process according to the invention, the phosphorus pentachloride is placed in the reactor in a partial quantity of toluene, heated to 40–60 °C with stirring, and the 2-nitroaniline is added in such a way that the evolution of HCl remains controllable. For this purpose, the 2-nitroaniline is dissolved in toluene in a separate container at 40–60 °C and pumped into the reactor. To prevent clogging of the metering tube by the formation of 2-nitroaniline hydrochloride, the process according to the invention is further characterized in that the 2-nitroaniline solution is pumped directly into the suspension of phosphorus pentachloride in toluene via a dip tube within 0.5 to 5 hours.

[0026] The addition of 2-nitroaniline can of course also be done as a solid via a suitable solid dosing device or in the form of a 2-nitroaniline melt.

[0027] After the addition of 2-nitroaniline, the reaction mixture is heated to boiling to complete the reaction and held at boiling temperature for 30 minutes. As the reaction progresses, the initial suspension transforms into a clear solution of iminophosphoric acid trichloride (I).

[0028] For the subsequent partial hydrolysis of iminophosphoric acid trichloride (I), an approximately equimolar amount of hydrolyzing agent is also used. The use of 1 mol of hydrolyzing agent per mol of 2-nitroaniline is advantageous.

[0029] Water or organic carboxylic acids are used as hydrolyzing agents. Examples of organic carboxylic acids are formic acid, acetic acid, and oxalic acid. Since the use of water can lead to minor side reactions and the formation of oily or tar-like byproducts, the use of formic acid has proven advantageous.

[0030] When formic acid is used as a hydrolysis agent, carbon monoxide is also produced in addition to hydrogen chloride, thus exacerbating the exhaust gas problem described at the beginning.

[0031] Surprisingly, it has been shown that by lowering the reaction temperature to less than 60 °C, but not below 45 °C, the dosing time of the hydrolyzing agent can be significantly extended, thereby reducing the gas release rate, and the bisproduct content in the 2-NPT increases only slightly. Lowering the temperature reduces the reaction rate between (I) and (II) to such an extent that only a small amount of compound (III), and thus bisproduct, is formed. Maintaining a lower limit of 45 °C simultaneously prevents undesired dimerization of iminophosphoric acid trichloride (I).

[0032] In a further embodiment of the process according to the invention, a solution of iminophosphoric acid trichloride (I) and the hydrolyzing agent are simultaneously dosed into a separate reaction vessel. Surprisingly, it has been found that when both reactants are dosed simultaneously into a separate vessel, the formation of the doubly nitrophenyl-substituted compound (III) is suppressed and no further side reactions occur, provided that approximately equimolar amounts of iminophosphoric acid trichloride (I) and hydrolyzing agent arrive in the reaction vessel at all times and immediately react further to form phosphoramide dichloride.

[0033] To avoid dimerization of the iminophosphoric acid trichloride (I), both the solution of the iminophosphoric acid trichloride (I) and the reactor are heated to 50 to 100 °C, without being limited to this period.

[0034] The measures described above allow dosing times to be extended so that the exhaust gases can be safely discharged. For example, dosing times of up to 5 hours are possible without being limited to this period.

[0035] The hydrogen chloride produced as a byproduct in the first two synthesis steps (phosphorylation and hydrolysis) is collected and neutralized in a scrubbing column with an aqueous alkali. Ammonia, sodium hydroxide, or potassium hydroxide, for example, are suitable as cost-effective neutralizing agents. Since a certain excess of ammonia is used for the ammonolysis in the second step, it is advantageous to also perform the gas scrubbing using ammonia solution and to use the excess ammonia present at the end of the synthesis to prepare the ammoniacal absorber solution. Alternatively, water can also be used for gas scrubbing.

[0036] In the preferred embodiment of the process, the toluene solution of phosphoamide dichloride obtained by the hydrolysis step is reacted with ammonia without further work-up. The reaction with ammonia takes place in a temperature range of -50 to 50 °C. The reaction of the toluene solution of phosphoamide dichloride can be carried out by adding it to liquid ammonia, a solution of liquid ammonia in toluene or another solvent, or by adding it to an aqueous ammonia solution. It is also possible to introduce ammonia gas into the toluene solution of phosphoamide dichloride. Another variant is the atomization of the toluene solution of phosphoamide dichloride, or of the crude phosphoamide dichloride remaining after distillation of the solvent, with ammonia.

[0037] Due to the high yield of 2-NPT combined with low impurity formation, the toluene solution of the phosphoric acid amide dichloride is dosed to liquid ammonia in the process according to the invention.

[0038] Four moles of ammonia are required to react one mole of phosphoamide dichloride(II). To ensure complete reaction, using a certain excess of ammonia is advisable and even advantageous, as the good solubility of ammonium chloride in ammonia counteracts the formation of ammonium chloride deposits. The excess ammonia can then be used at the end of the reaction to prepare an ammoniacal absorber solution for gas scrubbing during the production of phosphoamide dichloride(II).

[0039] In principle, the exothermic ammonolysis of phosphoric acid amide dichloride (II) can be carried out at reactor internal temperatures from -50 to 50 °C. However, as described above, the formation of deposits consisting of 2-NPT and ammonium chloride is observed.

[0040] Surprisingly, it has been shown that as the reactor internal temperature decreases, the degree of solid deposits also decreases, and that at a reaction mixture temperature of up to 10 °C, almost no deposits form.

[0041] In a preferred embodiment of the process, the dosing rate of the toluene solution of phosphoric acid amide dichloride (II) and the temperature of the cooling medium are therefore selected such that the exothermicity of the reaction prevents the reactor internal temperature from exceeding 10 °C. The dosing can be carried out either at a constant rate or temperature-controlled.

[0042] When only ammonia is present, the liquid level in the reactor is initially very low. Since the stirrer is then not submerged, or only partially submerged, optimal mixing cannot be achieved, and reaction mixture is splashed onto the reactor wall or internal components, which promotes the formation of deposits. Therefore, in a further preferred embodiment of the process, toluene is also added to the ammonolysis reactor alongside ammonia to ensure good mixing and avoid splashing of the reaction mixture from the outset.

[0043] Instead of adding more toluene, the amount of ammonia can alternatively be increased. Since ammonium chloride is readily soluble in ammonia, this can also effectively remove any deposits from a previous batch in the reactor.

[0044] Since, when the toluene solution of phosphoamide dichloride (II) is added dropwise to the ammonia at the opening of the metering tube, an undesirable reaction with ammonia in the gas phase results in the formation of solids consisting of 2-NPT and ammonium chloride, in a further preferred embodiment of the process the toluene solution of phosphoamide dichloride (II) is metered directly into the ammonia or the ammonia / toluene mixture via a dip tube.

[0045] Angled blade and anchor impellers are particularly suitable as stirrers. Of course, other impellers are also suitable if they ensure efficient mixing and heat dissipation. The impeller is operated at a speed in the range of 100 to 1500 rpm. -1The process is operated at low speeds. Since effective mixing cannot be guaranteed at low speeds and excessively high speeds promote splashing of the reaction mixture and thus the formation of deposits, the process according to the invention is operated at speeds in the range of 400 to 600 rpm. -1 worked, but without being limited to that.

[0046] After dosing is complete, the product is warmed to room temperature. Warming can be passive or active, using a heating element. The duration of warming does not affect product quality. Any remaining excess ammonia will dissipate within 15 to 30 minutes after warming.

[0047] The precipitated solid is then separated from the mother liquor. This separation can be achieved by filtration, for example, using a stirred-tank filter dryer or a centrifuge. If the ammonium chloride-containing raw product is to be used further, it is then dried. A largely ammonium chloride-free product with a maximum chloride content of 5% can be obtained by washing the raw product with water. At least as much water is used as is required to produce a saturated ammonium chloride solution. The optimal amount is 2.5 to 3.5 liters of water per kilogram of final product, although this is not the only acceptable range. To improve washing efficiency, the water volume can be divided into two or more washes.

[0048] After washing, the product is dried at temperatures up to 100 °C, and the drying process can be accelerated using a vacuum.

[0049] The organic and aqueous phases remaining after washing are separated. The toluene used can be easily recycled by distilling the organic phase. Since toluene mainly contains residues of 2-nitroaniline, it can also be reused without prior distillation after appropriate adjustment of the amount of phosphorus pentachloride.

[0050] When using the process according to the invention, the 2-NPT is obtained free of lumps. To regulate or inhibit urease-catalyzed urea hydrolysis, the 2-NPT obtained in this way can be easily incorporated into liquid drug formulations based on vegetable oils or rapeseed methyl esters. Examples

[0051] The following examples illustrate the invention without limiting it. Example 1 - Phosphorylation: Synthesis of a toluene N-(2-nitrophenyl)iminophosphoric acid trichloride solution

[0052] In a reactor, 0.51 mol of phosphorus pentachloride is suspended in 200 ml of toluene and heated to 50 °C with stirring. In a stirred tank, 0.5 mol of 2-nitroaniline is dissolved in 150 ml of toluene at 50 °C, and the toluene 2-nitroaniline solution is pumped into the toluene phosphorus pentachloride suspension via a dip tube over a period of 30 minutes. The mixture is then heated to boiling and held at this temperature for 30 minutes. Example 2 - Hydrolysis: Synthesis of a toluene N-(2-nitrophenyl)phosphoric acid amide dichloride solution. Example 2a: Rapid dosing of formic acid (0.5 h) at 80 °C

[0053] The toluene solution of 0.5 mol N-(2-nitrophenyl)iminophosphoric acid trichloride obtained according to Example 1 is cooled to 80 °C and 0.5 mol formic acid is added dropwise over 30 min with vigorous stirring. The mixture is then stirred for 5 min at 80 °C and cooled to room temperature. Example 2b: slow dosing of formic acid (3 h) at 50 °C

[0054] The toluene solution of 0.5 mol N-(2-nitrophenyl)iminophosphoric acid trichloride obtained according to Example 1 is cooled to 50 °C and 0.5 mol formic acid is added dropwise over 3 h with vigorous stirring. The mixture is then stirred for 15 min at 50 °C and cooled to room temperature. Example 2c: Simultaneous slow dosing of formic acid and iminophosphoric acid trichloride solution (3 h) into a separate reactor at 80 °C

[0055] The toluene solution of 0.5 mol N-(2-nitrophenyl)iminophosphoric trichloride obtained according to Example 1 is heated to 80 °C. This dichloride solution is added to a stirred reactor in parallel with formic acid. The dosing rate of both components is controlled so that aquimolar amounts of the reactants enter the reactor at all times, and the total dosing time is 3 h. The reaction temperature in the reactor is maintained at 80 °C. After the addition is complete, the mixture is stirred for 5 min at 80 °C and then cooled to room temperature. Example 2d: slow dosing of formic acid (3 h) at 80 °C (comparative experiment)

[0056] The experiment is carried out analogously to Example 2b at a temperature of 80 °C. Example 2e: slow dosing of formic acid (5 h) at 80 °C (comparative experiment)

[0057] The experiment is carried out analogously to Example 2b at a temperature of 80 °C. Example 2f: Rapid dosing of formic acid (0.5 h) at 25 °C (comparative experiment)

[0058] The toluene solution of 0.5 mol N-(2-nitrophenyl)iminophosphate trichloride obtained according to Example 1 is cooled to 25 °C, causing the precipitation of dimeric iminophosphate trichloride. With vigorous stirring, 0.5 mol of formic acid is added dropwise over 0.5 h. The mixture is then stirred for 30 min at 80 °C to monomerize the dimeric iminophosphate trichloride and complete the reaction, and the resulting reaction mixture is cooled to room temperature. Example 3 - Ammonolysis: Synthesis of N-(2-Nitrophenyl)phosphoric triamide (2-NPT)

[0059] The solution of N-(2-nitrophenyl)phosphoramide dichloride obtained according to Example 2 is reacted with ammonia. For this purpose, 3.5 mol of ammonia are first placed in a pressure reactor with an inclined-blade stirrer, and 150 ml of toluene are pumped in. The reaction continues for 500 min. -1The toluene solution of N-(2-nitrophenyl)phosphoamide dichloride is pumped into the ammonia / toluene mixture via a dip tube using the stirrer. The flow rate of the dichloride solution and the cooling jacket temperature are selected so that the temperature inside the reaction chamber does not exceed 10 °C (example: flow rate: 10 ml / min, cooling jacket temperature: 0 °C). After the addition is complete, the reaction mixture is heated to 20 °C within 60 min, and the reactor pressure is reduced to ambient pressure within 15 min. The ammonium chloride-containing crude product is centrifuged and washed twice with 200 ml and 100 ml of water, respectively, to remove the ammonium chloride. The washed final product is dried at 10 mbar and 60 °C. 2-NPT is obtained in a gross yield of 90% (2-NPT content 95%). Example 4 - Synthesis of N-(2-Nitrophenyl)phosphoric triamide (2-NPT) - Variant of the ammonolysis process:

[0060] The solution of N-(2-nitrophenyl)phosphoric amide dichloride obtained according to Example 2 is reacted with ammonia. For this purpose, 150 ml of toluene is first placed in a pressure reactor with an inclined blade / anchor stirrer, heated to 0 °C, and the toluene phase is saturated with ammonia by passing a stream of ammonia gas (50 l / h) through it for 10 minutes.

[0061] Subsequently, with intensive stirring, the toluene solution of N-(2-nitrophenyl)phosphoramide dichloride is pumped into the pre-mixed ammonia / toluene solution via a dip tube. During the dosing of the dichloride, more gaseous ammonia is introduced into the reactor.

[0062] The flow rate of the dichloride solution and the cooling jacket temperature are selected so that the temperature inside the reaction chamber does not exceed 10 °C. The flow rate of ammonia is dimensioned so that there is always an excess of ammonia in the reactor.

[0063] After the addition of the N-(2-nitrophenyl)phosphoric acid amide dichloride solution is complete, ammonia is passed through the reactor for 10 minutes to complete the reaction.

[0064] The ammonia dosage is then stopped and the product is warmed to 20 °C. The processing of the ammonium chloride-containing crude product is carried out analogously to Example 3. 2-NPT is obtained as a particularly fine-crystalline yellow product in a gross yield of 90% (2-NPT content 90%). Example 5 - Synthesis of N-(2-Nitrophenyl)phosphoric triamide (2-NPT) - Variant of the ammonolysis process:

[0065] The solution of N-(2-nitrophenyl)phosphoramide dichloride obtained according to Example 2 is reacted with ammonia. First, 150 ml of toluene is placed in a pressure reactor equipped with an inclined-blade / anchor stirrer and brought to 0 °C. The reactor is then purged with ammonia and pressurized to 0.5 bar overpressure.

[0066] Now, with intensive stirring, the toluene solution of N-(2-nitrophenyl)phosphoramide dichloride is pumped into the pre-mixed ammonia / toluene solution via a dip tube. During the addition of the dichloride, the amount of gaseous ammonia is continuously adjusted to maintain a constant overall pressure.

[0067] The volume flow rate of the dichloride solution and the cooling jacket temperature are selected so that the temperature inside the reaction chamber does not exceed 10 °C.

[0068] After the addition of the N-(2-nitrophenyl)phosphoric acid amide dichloride solution is complete, the reaction is stirred for 20 minutes at 0.5 bar overpressure to complete.

[0069] The ammonia dosing is then stopped, the reactor is depressurized, and heated to 20 °C. The work-up of the ammonium chloride-containing crude product is carried out analogously to Example 3. 2-NPT is obtained as a particularly fine-crystalline yellow product in a gross yield of 90% (2-NPT content 90%). Example 6

[0070] Bisproduct content in the 2-NPT obtained after ammonolysis as a function of the dosing time of formic acid and the reaction temperature during the production of N-(2-nitrophenyl)phosphoric amide dichloride (see Example 2) Experiment No. dosage Dosage time T Bisproduct content in 2-NPT 2a Formic acid is added to dissolve the trichloride (II). 0,5 h 80 °C 1,8 % 2b Formic acid is added to dissolve the trichloride (II). 3 h 50 °C 2,8 % 2c Formic acid and iminophosphoric acid trichloride solution (II) are simultaneously dosed into a separate reactor. 3 h 80 °C 1,8 % 2d Formic acid is added in a measured dose to dissolve the trichloride (comparative experiment). 3 h 80 °C 6,7 % 2e Formic acid is added in a measured dose to dissolve the trichloride (comparative experiment). 5 h 80 °C 9,9 % 2f Formic acid is added in a measured dose to dissolve the trichloride (comparative experiment). 0,5 h 25 °C 9,2 %

Claims

[1] Process for the preparation of N-(2-nitrophenyl)phosphoric triamide (2-NPT) by reaction of 2-nitroaniline and phosphorus pentachloride to an iminophosphoric trichloride (I), subsequent hydrolysis of the iminophosphoric trichloride (I) without prior isolation or purification with a hydrolyzing agent to give phosphoric amide dichloride (II), and subsequent ammonolysis of the phosphoric acid amide dichloride (II) without its prior isolation or purification to 2-NPT, characterized by , that the 2-nitroaniline is dosed into a suspension of phosphorus pentachloride in an inert solvent via a dip tube within 0.5 to 5 h at a temperature between 40 and 60 °C and then heated to boiling. and the addition of the hydrolyzing agent to the iminophosphoric acid trichloride (I) a) at a temperature of 70 to 100 °C for a period of less than one hour or b) at a temperature of 45 to 60 °C over a period of up to 5 h or simultaneously, within a period of up to 5 h, approximately equimolar amounts of the solution of iminophosphoric acid trichloride (I) and the hydrolyzing agent are dosed into a separate reactor, wherein the temperature of the iminophosphoric acid trichloride solution and the reactor temperature are 50-100 °C. [2] Method according to claim 1, characterized by that toluene is used as an inert solvent. [3] Method according to one of claims 1 or 2, characterized by that 0.95 to 1.1 mol of phosphorus pentachloride are used per mole of 2-nitroaniline. [4] Method according to one of claims 1 or 2, characterized by that 1.005 to 1.03 mol of phosphorus pentachloride are used per mole of 2-nitroaniline [5] Method according to any one of claims 1 to 4, characterized bythat water or an organic carboxylic acid is used as the hydrolyzing agent in an amount of 0.95 to 1.05 mol per mol of 2-nitroaniline. [6] Method according to claim 5, characterized by that the organic carboxylic acid is formic acid. [7] Method according to any one of claims 1 to 6 characterized by , that the solution of phosphoric acid amide dichloride (II) is reacted with ammonia at -50 to 50 °C without further work-up, whereby 4 to 8 mol of ammonia are used to react 1 mol of phosphoric acid amide dichloride (II). [8] Method according to any one of claims 1 to 7, characterized by , that the solution of phosphoric acid amide dichloride (II) is dosed directly into liquid ammonia or into an ammonia / toluene mixture via a dip tube, wherein the dosing rate of the solution and the cooling power are selected so that the reactor internal temperature does not exceed 10 °C. [9] Method according to any one of claims 1 to 7, characterized by , that a toluene solution of phosphoric acid amide dichloride (II) is dosed into a reactor at normal pressure while simultaneously dosing ammonia gas. [10] Method according to any one of claims 1 to 7, characterized by , that a toluene solution of phosphoric acid amide dichloride (II) is pumped into a reactor which is pressurized with ammonia gas at an overpressure of 0 to 2.5 bar and ammonia is added to the reactor during the addition of the dichloride. [11] Method according to claims 9 or 10 characterized by , that toluene is introduced into the reactor prior to the dosing of the phosphoric acid amide dichloride (II). [12] Method according to any one of claims 9 to 11 characterized by that ammonia is introduced into the reaction mixture or passed over the liquid. [13] Method according to any one of claims 9 to 12, characterized by, that the ammonia flow is adjusted so that 4 to 8 mol of ammonia are dosed per unit time mole of phosphoric acid amide dichloride (II). [14] Method according to any one of claims 9 and 11 to 13 characterized by that the reactor internal temperature is in the range of 0 to 50 °C, particularly preferably between 10 and 20 °C. [15] Method according to any one of claims 1 to 14, characterized by that the ammonia is present wholly or partially bound in compounds that readily release ammonia under the reaction conditions. [16] Method according to any one of claims 1 to 15, characterized by that the ammonia is wholly or partly bound in associations with ammonium salts, particularly preferably in the form of the associations NH4Cŀ3 NH3 or NH4Cŀ6 NH3.