Synthesis of N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) using solid acid catalysts

Abstract

A method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide from a mixture of 2,4-dinitroaniline, 4-nitrobenzoyl chloride, and a solid acid catalyst in an organic solvent, wherein the solid acid catalyst is not soluble in the organic solvent and is an acidic clay, an ion exchange resin, a beta zeolite, a sulfonated tetrafluoroethylene-based fluoropolymer copolymer, or a mixture thereof.

Description

[Technical field]

[0001] The present invention relates to an improved process for the preparation of N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) from 2,4-dinitroaniline (2,4-DNA) and 4-nitrobenzoyl chloride (4-NBC). [Background technology]

[0002] Related Art The description in Russian Patent No. 2283307(C1) discloses a method for the synthesis of 5(6)-amino-2-(4'-aminophenyl)benzimidazole from N-(2,4-dinitrophenyl)-4-nitrobenzamide. The method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide involves an acylation reaction between 2,4-dinitroaniline and 4-nitrobenzoyl chloride in the presence of ferric chloride as a catalyst in a solvent medium selected from chlorobenzene, paraxylene, or a mixture of xylene, toluene, or ethylbenzene, which is said to form 2,4',4-trinitrobenzanilide, which is the same as N-(2,4-dinitrophenyl)-4-nitrobenzamide. The reaction is carried out at an elevated temperature, and when it is essentially complete, the solution is cooled, resulting in the precipitation of TNBA from the solvent medium. The TNBA is then washed with fresh solvent medium, followed by washing with water, to yield the desired TNBA. Other publications such as Russian Patent No. 2394810 (C2) and Russian Patent No. 2547262 (C3) disclose similar methods for producing TNBA in the presence of iron chloride catalyst.

[0003] The ferric chloride (iron) catalyst has been found to be problematic in that it is soluble in the solvent medium, meaning that both the solvent system and the precipitated TNBA produced by this method contain the catalyst as an undesirable impurity that must be further removed. Specifically, the preferred method of removing the catalyst from TNBA, such as the method disclosed in Russian Patent No. 2283307 (C1), is to first isolate TNBA from the solvent system and then further wash the TNBA with a large amount of water to remove the catalyst. Furthermore, if the TNBA produced by the above prior art method is subsequently used in other catalytic reactions, any residual ferric chloride (iron) present in the TNBA may destroy any downstream catalysts and / or impart color to the final product. Furthermore, the ferric chloride catalyst used in the above prior art method cannot be recycled and reused, and its use represents a significant disposal problem and increases the operating costs of the manufacturing process.

[0004] What is needed is a process that avoids all of the problems associated with using catalysts that are soluble in organic solvent systems, while also allowing flexibility in process design to either precipitate TNBA from the solvent system or use TNBA dissolved in the solvent system for further processing. Summary of the Invention [Means for solving the problem]

[0005] The present invention also relates to a method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA), a monomer useful in the production of advanced polymers.

[0006] In some embodiments, the present invention provides a) forming a first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent; b) reacting the first mixture in the presence of a solid acid catalyst that is not soluble in the organic solvent at a temperature of at least 90° C. to form a second mixture comprising N-(2,4-dinitrophenyl)-4-nitrobenzamide and the organic solvent, wherein the solid acid catalyst is an acidic clay, an ion exchange resin, a beta zeolite, a sulfonated tetrafluoroethylene-based fluoropolymer copolymer, or a mixture thereof; c) cooling the second mixture to precipitate N-(2,4-dinitrophenyl)-4-nitrobenzamide as a solid; and d) removing solid N-(2,4-dinitrophenyl)-4-nitrobenzamide from the second mixture. [Brief description of the drawings]

[0007] [Figure 1] A continuous process for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) is described. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention relates to a method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide from a mixture of 2,4-dinitroaniline, 4-nitrobenzoyl chloride, and a solid acid catalyst in an organic solvent, where the solid acid catalyst is not soluble in the organic solvent. This is an improvement over methods that utilize catalysts such as iron chloride (FeCl3), which are soluble in organic solvents; when such soluble catalysts are used, they can contaminate the final reaction product and are difficult to remove from the reaction medium. Soluble catalysts such as iron chloride (FeCl3) are traditionally used because they are inexpensive and such homogeneous catalysis of the Lewis acid type is known to be useful in this reaction.

[0009] Solid acid catalysts that are suitable for the desired reaction and that are insoluble in the organic solvent used for the reaction include acidic clays, ion exchange resins, beta zeolites, sulfonated tetrafluoroethylene-based fluoropolymer copolymers, and mixtures of these catalysts. It was surprising to the inventors that heterogeneous catalysis using a Bronsted type catalyst is effective for this reaction.

[0010] The process for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) from a mixture of 2,4-dinitroaniline (2,4-DNA), 4-nitrobenzoyl chloride (4-NBC), and a solid acid catalyst in an organic solvent can be accomplished by either a batch, semi-batch or stepwise process, or a continuous process. For example, a fixed bed or packed bed catalytic reactor (essentially a vessel with immobilized catalyst packed into it) that does not require any agitation is utilized. A mixture of 2,4-DNA and 4-NBC in a solvent can be reacted in the presence of a catalyst to form TNBA in a continuous process. Alternatively, 2,4-DNA and 4-NBC can be reacted in a solvent to form TNBA in the presence of a catalyst using equipment such as a mechanically stirred autoclave, a gas-agitated reactor such as a continuous stirred tank reactor (CSTR) or a slurry bubble column reactor (SBCR) in a batch, semi-batch, or continuous slurry process.

[0011] The claimed reaction is carried out in a solvent, preferably under an inert atmosphere. Suitable organic solvents are aromatic solvents in which 2,4-DNA, 4-NBC, and the desired product TNBA are soluble at temperatures above 60° C. Preferably, the boiling point of the solvent at atmospheric pressure is above 100° C., more preferably above 120° C., and most preferably above 140° C. Furthermore, it is preferred that the solvent can be dried azeotropically.

[0012] In some embodiments, suitable organic solvents include xylene, toluene, chlorobenzene, o-dichlorobenzene, and trichlorobenzene, or mixtures thereof, with preferred organic solvents being chlorobenzene and o-dichlorobenzene, or mixtures thereof, in some embodiments, the preferred organic solvent is chlorobenzene.

[0013] For a sufficient yield of the reaction, the 2,4-DNA should be dry, which means that the 2,4-DNA preferably contains less than 500 ppm water by weight, more preferably contains less than 200 ppm water by weight. Similarly, the 4-NBC should also be dry, preferably contains less than 500 ppm water by weight, more preferably contains less than 200 ppm water by weight.

[0014] Furthermore, impurities in the components can reduce yields and affect the purity of the resulting product mixture. Therefore, it is desirable that both 2,4-DNA and 4-NBC have a purity of at least 90%, preferably 95%, and more preferably greater than 99%. Specifically, it is preferred that 4-NBC is substantially free of organic impurities and contains less than 0.5 weight percent of 4-nitrobenzoic acid (4-NBA).

[0015] The mixture further includes a solid acid catalyst that is not soluble in the organic solvent. By "not soluble in the organic solvent" it is meant that there is no difference between the elemental analysis of the reaction mixture containing the catalyst and the same reaction mixture without the catalyst, or any such difference is within the experimental error of the instrument. Specifically, there is no difference between the elemental analysis of (1) a mixture containing 2,4-dinitroaniline, 4-nitrobenzoyl chloride, and the solid acid catalyst in an organic solvent and (2) a mixture containing only 2,4-dinitroaniline, 4-nitrobenzoyl chloride, and the organic solvent, or any such difference is within the experimental error of the instrument.

[0016] A catalyst is a material that shifts the transition state of a reaction to a lower activation energy, thereby increasing the rate of the reaction. By "solid acid catalyst" is meant a catalyst that has protons or coordinatively unsaturated cationic centers on their surface that have the required thermal stability to withstand the reaction conditions and are not substantially dissolved in the reaction medium under the reaction conditions. Solid acid catalysts can be unsupported or supported on at least one catalyst support.

[0017] Solid acid catalysts that are suitable for the desired reaction and that are insoluble in the organic solvent used for the reaction include acidic clays, ion exchange resins, beta zeolites, sulfonated tetrafluoroethylene-based fluoropolymer copolymers, and mixtures of these catalysts.

[0018] In some embodiments, the preferred solid acid catalyst is a natural acid clay mineral. Natural acid clay minerals include kaolinite, bentonite, attapulgite, and montmorillonite. Montmorillonite is a preferred acid clay.

[0019] Suitable ion exchange resins are crosslinked copolymer particles (e.g., beads) that have been chemically treated to attach or form functional groups to provide capacity for ion exchange. In one embodiment, the ion exchange resin comprises an aromatic polymer, further comprising a crosslinked copolymer of styrene or substituted styrene with a crosslinker such as divinylbenzene. Moreover, such ion exchange resins with sulfonic acid functional groups have been found to be particularly active and selective. U.S. Pat. Nos. 2,366,007 and 2,500,149 describe the preparation of such cation exchange resins based on sulfonated styrene-divinylbenzene copolymers.

[0020] Suitable sulfonated tetrafluoroethylene-based fluoropolymer copolymers include those such as Nafion® NR50.

[0021] In an embodiment, the solid acid catalyst is a supported acid catalyst. The support of the solid acid catalyst can be any solid material that is inert under the reaction conditions, such as, but not limited to, oxides such as silica, alumina, titania, sulfated titania, and compounds thereof and combinations thereof; barium sulfate; calcium carbonate; zirconia; carbon, particularly acid-washed carbon; and combinations thereof. Acid-washed carbon is carbon that has been washed with an acid, such as nitric acid, sulfuric acid, or acetic acid, to remove impurities. The support can be in the form of a powder, granules, pellets, and the like. The supported acid catalyst can be prepared by depositing the acid catalyst on the support by any number of methods, such as spraying, soaking, or physical mixing, followed by drying, calcination, and, if necessary, activation by methods such as reduction or oxidation. The loading of the at least one acid catalyst on the at least one support ranges from 0.1 to 20 weight percent based on the combined weight of the at least one acid catalyst and the at least one support. Certain acid catalysts work better at low loadings, such as 0.1-5%, while other acid catalysts are more likely to be useful at higher loadings, such as 10-20%. In embodiments, the acid catalyst is an unsupported catalyst, 100% acid catalyst, with no support, such as high purity beta zeolite and ion exchange resin.

[0022] Both supported and unsupported solid acid catalysts can be in any physical form typical of the materials, including but not limited to powder form having particle sizes of 0.01-150 μm. For fixed bed reactors, the catalysts are generally in the form of tablets, extrudates, spheres, and / or high functional particles with a uniform size of 0.5-10 mm.

[0023] A typical method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide is a) forming a first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent; b) reacting the first mixture in the presence of a solid acid catalyst that is not soluble in the organic solvent at a temperature of at least 90° C. to form a second mixture comprising N-(2,4-dinitrophenyl)-4-nitrobenzamide and the organic solvent, wherein the solid acid catalyst is an acidic clay, an ion exchange resin, a beta zeolite, a sulfonated tetrafluoroethylene-based fluoropolymer copolymer, or a mixture thereof; c) cooling the second mixture to precipitate N-(2,4-dinitrophenyl)-4-nitrobenzamide as a solid; and d) removing solid N-(2,4-dinitrophenyl)-4-nitrobenzamide from the second mixture.

[0024] In a continuous process, it may be advantageous to carry out the mixing step a) and the reacting step b) in separate vessels, such as a stirred reactor for mixing and a fixed-bed or packed-bed catalytic reactor for reacting the components. However, steps a) and b) can conceivably be carried out in a single vessel, either in a continuous process or in a batch, semi-batch, or semi-continuous process, if necessary. For example, the combination of steps a) and b) can be achieved in a batch process by forming a first mixture of 2,4-DNA, 4-NBC, and solid acid catalyst in an organic solvent and reacting this mixture, optionally with stirring, to form a second mixture containing TNBA, solid acid catalyst, and organic solvent as well as any unreacted 2,4-DNA and 4-NBC.

[0025] Preferably both steps a) and b), or the combined steps a) and b), are carried out in an inert atmosphere, such as under a nitrogen atmosphere. Preferably some type of agitation is present in steps a) and b), either by mechanical stirring or the like, or by static mixers, or even by fluid dynamics, such as turbulence created in pumping the mixture through a packed column or a slurry reactor.

[0026] Ideally, equimolar amounts of 2,4-DNA and 4-NBC are required for the reaction, but typically a molar excess of 4-NBC is added to compensate for common impurities. 4-NBC is almost always contaminated with a certain amount of the corresponding acid PNBA. In some preferred embodiments, the molar ratio of 4-NBC to 2,4-DNA is 1.05 to 1.07. Furthermore, in some preferred embodiments, the first mixture is formed by mixing at least 50 grams of 2,4-DNA per liter of solvent, and in some embodiments, it is even more preferred to mix 200 grams or more of 2,4-DNA per liter of solvent.

[0027] When steps a) and b) are carried out in a single vessel, possibly using an unsupported catalyst, the catalyst is present in the first mixture in an amount that is generally at least 5 weight percent of the amount of 2,4-DNA present in the first mixture. Preferably, the catalyst is present in the first mixture in an amount of at least 20 weight percent of the amount of 2,4-DNA present in the first mixture, more preferably at least 30 weight percent of the amount of 2,4-DNA present in the first mixture.

[0028] Various proactive measures can be taken to avoid moisture in the individual reactants and / or in the first mixture. For example, individual components such as 2,4-DNA can be pre-dried (e.g., under vacuum; 85-100 °C in a vacuum oven using a small nitrogen bleed). In some process variants such as batch, semi-batch or stepwise reactions, the combination of unsupported catalyst and 2,4-DNA can be dried together in the solvent by sparging with nitrogen and simultaneously heating the mixture in a reactor under reflux conditions. However, when these mixtures are heated under reflux conditions, it is desirable to cool the system to below 120 °C before the introduction of (4-NBC). Alternatively, a mixture of 2,4-DNA, 4-NBC, and organic solvent can be formed and subsequently, or simultaneously, the undesired amount of water in the mixture can be removed by heating or by certain other known techniques prior to the catalysis. This dried mixture can then be contacted with a solid acid catalyst for the catalysis to take place.

[0029] The catalytic reaction of the first mixture forms a second mixture comprising at least N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) in an organic solvent. It is advantageous to react the components at a temperature of at least about 90°C. In some embodiments, it is advantageous to react the components at a temperature of at least about 100°C. In some embodiments, the reaction temperature may range from about 90°C to about 135°C. In some embodiments, the reaction temperature may range from about 100°C to about 135°C. In some embodiments, the reaction temperature may range from about 100°C to about 125°C. In some embodiments, the temperature may be gradually increased from one level to another and held for a certain period of time, and this process may be continued several times until a final temperature is reached and held for a certain period of time. For example, in a batch reaction, the holding time may range from 0.5 to 10 hours, preferably 0.5 to 7.5 hours, more preferably 0.5 to 5 hours. Preferably, the by-product hydrochloric acid gas produced from the reaction is purged from the reaction using an inert gas (typically nitrogen gas) to seal the reaction. Agitation is desirable during the hold time, especially in batch reactions, and is continued until the reaction is complete or a sufficient amount of TNBA has been formed. The extent of the reaction can be determined by the disappearance of 2,4-DNA, the limiting reactant, as determined by analyzing a small aliquot from the reaction mixture using thin layer chromatography (TLC) or high performance liquid chromatography (HPLC).

[0030] When an unsupported solid acid catalyst is used for the reaction and is part of the TNBA product mixture along with the solvent, the solid acid catalyst can be removed by filtration, preferably by hot filtration. For example, TNBA has very high solubility in the solvent chlorobenzene at high temperatures and very low solubility at low temperatures. For this reason, it is advantageous to remove the solid acid catalyst at high temperatures to avoid removing any of the desired TNBA. The mixture of TNBA and the solvent can then be cooled to crystallize and precipitate the solid TNBA, which can then be separated from the solvent. Typically, this separation is performed by filtration. Preferably, the filtration is performed using a Rosenmund filter, a Nutsche filter, a filter press, or a rotary drum filter. Finally, the solid TNBA is washed and dried in a vacuum oven. Specifically, the solid TNBA can be washed with an alcohol, such as methanol, or otherwise treated to remove residual organic solvent. Similarly, if necessary, the TNBA can be washed with a weak aqueous base, such as sodium hydroxide, to remove any acidic by-products of the reaction, such as hydrochloric acid. EXAMPLES

[0031] As used in the following examples, percent conversion (%) and percent yield are

number

[0032] Comparative Example E and Examples 1 to 4: Comparative Example A and Examples 1 to 4 illustrate a batch process for manufacturing N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA). 15 grams (0.082 moles) of 2,4-dinitroaniline (2,4-DNA), 17.2 grams (0.092 moles) of 4-nitrobenzoyl chloride (4-NBC), 5.0 grams of catalyst, and 200 ml of chlorobenzene, which had been dried overnight in a vacuum furnace at 100 °C under a small continuous bleed of nitrogen, were placed into a 500 ml four-neck reaction flask equipped with a thermocouple, mechanical stirrer, nitrogen inlet, and condenser. The reaction mixture was heated to 120 °C and stirred for the desired reaction time. After the reaction was carried out for the operating times listed in the following table, it was cooled to room temperature overnight. Then, 100 ml of dimethylformamide was added into the reactor, heated to 80 °C, and stirred for 1 hour. The reaction mixture was filtered at high temperature using a 0.2 μ frit filter, and the solution was analyzed by HPLC. The conversion rate of 2,4-DNA and the yield of N-(2,4-dinitrophenyl)-4-nitrobenzamide (TNBA) for different types of solid acid catalysts and operating times are shown in the following table.

[0033]

Table 1

[0034] The calculation of the reaction rate in these examples shows that the reaction rate is the lowest in the absence of a catalyst, and the relative reaction rates are as follows: without catalyst (7.8 h-1) < CP-814E beta zeolite (8.3 h-1) < Dowex® Marathon® CH+ (10 h-1) < Nafion® NR50 (10.7 h-1) < montmorillonite clay (16.6 h-1).

[0035] Example 5 This example describes a step-wise process for preparing N-(2,4-dinitrophenyl)-4-nitrobenzamide) (TNBA). 30 grams (0.164 moles) of 2,4-dinitroaniline (2,4-DNA) and 200 ml of chlorobenzene were placed in a 1000 ml 4-neck reaction flask equipped with a thermometer, magnetic stir bar, nitrogen inlet and a Dean-Stark trap. The mixture was stirred for 5 minutes under nitrogen atmosphere. The mixture was heated to reflux and 7 ml of chlorobenzene condensate was collected to help remove any residual moisture. 10 grams of solid montmorillonite (K-10) catalyst was added after the 7 ml of chlorobenzene condensate was collected.

[0036] The solution temperature was cooled to 120°C and 32.1 grams (0.168 moles) of 4-nitrobenzoyl chloride (4-NBC) was added using a powder funnel. Once the addition of 4-NBC was complete, the reaction mixture was heated to reflux and stirred for 5 hours. After cooling to room temperature overnight, a light brown solid precipitated from the solution. The solid was collected by filtration. The collected solid was washed in a beaker with 200 ml of methanol, filtered, and washed with 500 ml of water adjusted to pH 7.0 with 0.1 N NaOH. The solid was collected and dried overnight in a vacuum oven at 100°C. The reaction yielded 51.56 grams of N-(2,4-dinitrophenyl)-4-nitrobenzamide) (TNBA) (94.7% yield based on 2,4-DNA). The TNBA weight was corrected for the weight of montmorillonite as it is not removed in this procedure.

[0037] Examples 6 to 8 15 grams (0.082 moles) of 2,4-dinitroaniline (2,4-DNA), dried overnight in a vacuum oven at 100° C. under a small continuous bleed of nitrogen, the designated amount of catalyst listed in Table 2, and 100 ml of 1,2-dichlorobenzene were placed in a 500-mL, four-necked reaction flask fitted with a thermocouple, mechanical stirrer, an addition funnel with nitrogen inlet, and a condenser. The reaction mixture was heated to 120° C., and 17.2 grams (0.092 moles) of 4-nitrobenzoyl chloride (4-NBC) dissolved in 100 ml of 1,2-dichlorobenzene was added continuously from the addition funnel in 30 minutes under constant stirring. The reaction mixture was maintained at 120° C. and stirred for the desired reaction time. After the reaction was carried out for the run time listed in the table below, it was cooled to room temperature overnight. Then, 100 ml of dimethylformamide was added into the reactor, heated to 80° C., and stirred for 1 hour. The reaction mixture was filtered hot using a 0.2μ frit filter and the solution was analyzed by HPLC. The conversion of 2,4-DNA and yield of N-(2,4-dinitrophenyl)-4-nitrobenzamide) (TNBA) for different types of solid acid catalyst, amount of catalyst, and run time are shown in the table below.

[0038] [Table 2]

[0039] Comparative example B Comparative Example B illustrates the prior art use of an iron chloride catalyst, which is soluble in a solvent. The batch procedure of Examples 1-4 was used, using FeCl3 as the catalyst. Specifically, 68 mg of FeCl3 catalyst was added and the reaction was run for 2.5 hours. A 97.8% yield of TNBA was obtained for 99.6% conversion of 2,4-DNA (the limiting reactant), which is comparable to the inventive examples. However, an additional step was required to remove the FeCl3 catalyst from the final product.

[0040] Typically, a process such as the following is required to remove iron chloride from the final product: After complete conversion of the 2,4 DNA, the TNBA wetcake is separated from the mother liquor. The wetcake is first washed four times with methanol (approximately 1.4 x wt. of wetcake in each wash), followed by one wash with ammonium hydroxide water with 0.25 wt% ammonia (approximately 2.5 x wt. of wetcake), and finally two washes with deionized water (2 x wt. of wetcake in each wash).

[0041] Example 9 This example describes one continuous method for producing N-(2,4-dinitrophenyl)-4-nitrobenzamide) (TNBA) as shown in FIG. 1. The process utilizes a mixing vessel 1 and a fixed bed catalytic reactor 2 containing a solid acid catalyst. The reactants 2,4-DNA and 4-NBC and the solvent chlorobenzene are introduced into the mixing vessel 1 via inlet point 3 where they are mixed. The mixing vessel 1 is inerted using nitrogen which is introduced through inlet point 8 and purged from the vessel through outlet point 9. The mixture of 2,4-DNA and 4-NBC in chlorobenzene is transported to the catalytic reactor 2 via pump 4. The catalytic reactor is fitted with a multi-point thermocouple 10 to maintain and control the temperature of the catalyst bed. The desired TNBA produced in an organic solvent in the fixed bed reactor exits the process via outlet 7. A portion of the outlet stream from the fixed bed reactor is recycled to the process via pump 5. The catalytic reactor 2 is fed with nitrogen via inlet point 6. This allows nitrogen to be fed via the recycle line to the recycle stream, which can be fed directly to the catalytic reactor if desired. Next, an embodiment of the present invention will be described. 1. a) forming a first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent; b) reacting the first mixture in the presence of a solid acid catalyst that is not soluble in the organic solvent at a temperature of at least 90° C. to form a second mixture comprising N-(2,4-dinitrophenyl)-4-nitrobenzamide and the organic solvent, wherein the solid acid catalyst is an acidic clay, an ion exchange resin, a beta zeolite, a sulfonated tetrafluoroethylene-based fluoropolymer copolymer, or a mixture thereof; c) cooling the second mixture to precipitate the N-(2,4-dinitrophenyl)-4-nitrobenzamide as a solid; and d) removing said solid N-(2,4-dinitrophenyl)-4-nitrobenzamide from said second mixture. 2. The method according to claim 1, wherein the first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent formed in a) contains the solid acid catalyst. 3. The method of claim 2, wherein the first mixture containing the solid acid catalyst is formed by premixing the 2,4-dinitroaniline, an organic solvent, and a solid acid catalyst, and then adding 4-nitrobenzoyl chloride. 4. The method of claim 1, wherein the solid acid catalyst is part of a continuous fixed bed reactor. 5. The method according to claim 2 or 3, wherein step b) comprises stirring the first mixture. 6. The method of claim 2 or 3, wherein after step b) but before step c), the solid acid catalyst is removed from the second mixture. 7. The method of claim 6, wherein the solid acid catalyst is removed by filtration. 8. The method according to any one of claims 1 to 3, wherein the acidic clay is a montmorillonite clay. 9. The method according to any one of 1 to 3 above, wherein the ion exchange resin is an ion exchange resin having a sulfonic acid functional group. 10. The method according to any one of 1 to 3 above, wherein at least step b) is carried out under an inert atmosphere. 11. The method of any one of 1 to 3 above, wherein prior to step a), the 2,4-dinitroaniline is combined with an organic solvent and water is removed from the combination. 12. The method according to any one of 1 to 3 above, wherein the organic solvent is chlorobenzene. 13. The method according to any one of 1 to 3 above, wherein the solid N-(2,4-dinitrophenyl)-4-nitrobenzamide is removed by filtration in step d). 14. The method according to any one of 1 to 3 above, wherein step a) is carried out at a temperature of about 100°C to about 135°C.

Claims

1. a) forming a first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent; b) reacting the first mixture in the presence of a solid acid catalyst that is not soluble in the organic solvent at a temperature of at least 90° C. to form a second mixture comprising N-(2,4-dinitrophenyl)-4-nitrobenzamide and the organic solvent, wherein the solid acid catalyst is an acidic clay, an ion exchange resin, a beta zeolite, a sulfonated tetrafluoroethylene-based fluoropolymer copolymer, or a mixture thereof; c) cooling the second mixture to precipitate the N-(2,4-dinitrophenyl)-4-nitrobenzamide as a solid; and d) removing said solid N-(2,4-dinitrophenyl)-4-nitrobenzamide from said second mixture.

2. 2. The method of claim 1, wherein the first mixture comprising 2,4-dinitroaniline and 4-nitrobenzoyl chloride in an organic solvent formed in a) contains the solid acid catalyst.

3. 3. The method of claim 2, wherein the first mixture containing the solid acid catalyst is formed by premixing the 2,4-dinitroaniline, an organic solvent, and a solid acid catalyst, and then adding 4-nitrobenzoyl chloride.

4. The method according to any one of claims 1 to 3, wherein the acidic clay is a montmorillonite clay.

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