HK1241354B - Process for the fabrication of 2-(n-3,4- dimethylpyrazol)succinic acid - Google Patents

Description

The invention relates to a process for the preparation of 2-(N-3,4-dimethylpyrazol) succinic acid (a mixture of isomers of 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid and 2-(2,3-dimethyl-1H-pyrazol-1-yl) succinic acid, preferably in a ratio of about 80:20, also referred to as DMPBS), or one of the individual compounds, as well as an aqueous solution of DMPBS.

To provide plants in agriculture with the nitrogen they need, fertilizers containing ammonium compounds are often used.

Ammonium compounds are microbially converted to nitrate relatively quickly in the soil (nitrification). However, nitrate can be leached from the soil. The leached portion is no longer available for plant nutrition, which is why rapid nitrification is undesirable. In order to better utilize the fertilizer, nitrification inhibitors are therefore added to the fertilizer. A well-known group of nitrification inhibitors are pyrazole compounds.

A problem in using pyrazole compounds as nitrification inhibitors is their high volatility. When storing fertilizer preparations containing pyrazole compounds, there is thus a continuous loss of active ingredient due to evaporation. Therefore, the pyrazole compounds must be formulated in a non-volatile form by appropriate measures.

In EP-B-1 120 388, phosphoric acid addition salts of 3,4-dimethylpyrazole and 4-chloro-3-methylpyrazole are described for use as nitrification inhibitors. By using the salt form, volatility can be significantly reduced.

Patent WO 96/24566 relates to the use of non-volatile pyrazole derivatives with hydrophilic groups as nitrification inhibitors. For example, 2-(N-3-methylpyrazol)butyric acid is proposed as a nitrification inhibitor. Ammonium-containing nitrates, sulfates or phosphates are mentioned as suitable mineral fertilizers. The toxicity of this nitrification inhibitor complicates its use, especially at higher application concentrations.

The WO 2011/032904 and WO 2013/11384 describe, among other things, DMPBS as nitrification inhibitors. Grandberg, I. I.; Kost, A. N.: "Pyrazoles. III. Addition of α,β-unsaturated compounds to pyrazoles" discloses a method for the preparation of (3,5-dimethylpyrazolyl) succinic acid.

Nitrification inhibitors suitable for KAS fertilizers are not yet known, which is why KAS fertilizers have been used so far without nitrification inhibitors.

The objective of the present invention is to provide an effective nitrification inhibitor for KAS, which exhibits low volatility during storage and application in the soil. Furthermore, an improved method for the production of 2-(N-3,4-dimethylpyrazol) succinic acid is to be provided.

The invention is solved by a process for the preparation of 2-(N-3,4-dimethylpyrazol) succinic acid, comprising the reaction of 3,4-dimethylpyrazole with maleic acid and/or maleic anhydride in the absence of organic solvents or diluents, followed by crystallization from the resulting reaction product in the absence of organic solvents or diluents.

The invention also relates to an aqueous solution of 2-(N-3,4-dimethylpyrazol) succinic acid with a pH value greater than 7.

2-(N-3,4-Dimethylpyrazol)butyric acid is preferably a mixture of isomers of 2-(3,4-dimethyl-1H-pyrazol-1-yl)butyric acid and 2-(2,3-dimethyl-1H-pyrazol-1-yl)butyric acid, preferably in a molar ratio of 5:95 to 95:5, particularly preferably 50:50 to 95:5, especially 70:30 to 90:10.

It may be present in the acid form or completely or partially neutralized, or in the form of a salt, for example as an alkali salt such as a potassium salt. The term "2-(N-3,4-dimethylpyrazol)butyric acid" used according to the invention also includes partially or fully neutralized or salt forms.

It has been found according to the invention that the combination of 2-(N-3,4-dimethylpyrazol) succinic acid with calcium ammonium nitrate mineral fertilizers results in an effective nitrification inhibitor, which exhibits reduced volatility or a reduced loss during storage and also after application to the soil.

Furthermore, 2-(N-3,4-dimethylpyrazol)succinic acid was found to be a particularly effective nitrification inhibitor with low volatility and low toxicity.

The preparation of 2-(N-3,4-dimethylpyrazol) succinic acid is carried out by reacting 3,4-dimethylpyrazole with maleic acid or maleic anhydride. This reaction is typically performed in an acidic environment. For the preparation of 3,4-dimethylpyrazole, reference may be made to Noyce et al., Jour. of Org. Chem. 20, 1955, pages 1681 to 1682. Furthermore, reference may be made to EP-A-0 474 037, DE-A-3 840 342, and EP-A-0 467 707, as well as to EP-B-1 120 388.

For the cleaning of 3,4-dimethylpyrazole, reference can be made to DE-A-10 2009 060 150.

Conveniently, the reaction is carried out at temperatures ranging from 0 to 150°C, preferably from 50 to 120°C, particularly from 70 to 105°C, under normal pressure and in the absence of an organic solvent.

Maleic anhydride can be dissolved in water and converted into maleic acid. Then, an aqueous solution of 3,4-dimethylpyrazole can be added. The conversion can take place, for example, at temperatures around 100°C, such as between 70°C and 105°C. Since 3,4-dimethylpyrazole tautomerizes under the reaction conditions typically used for the reaction, or because substitution at the nitrogen atom eliminates the 3,5-tautomerism of the pyrazole ring, it is generally not possible to avoid obtaining a mixture of isomers of the resulting substituted succinic acid, which are structural isomers.

The preparation of 2-(N-3,4-dimethylpyrazol) succinic acid is carried out by reacting 3,4-dimethylpyrazole with maleic acid, maleic anhydride, or mixtures of maleic acid and maleic anhydride in the absence of organic solvents or diluents, followed by crystallization from the resulting reaction product in the absence of organic solvents or diluents. If the reaction product is not in solution after the reaction, it is dissolved in an inorganic solvent before crystallization.

It has been found according to the invention that the product is obtained in high yield and purity when organic solvent or diluent agents are not used during production and crystallization.

The presence of small amounts of organic solvents or diluents during the reaction or crystallization can be tolerated. According to the invention, up to 10 weight-%, preferably up to 5 weight-%, and particularly preferably up to 2.5 weight-% of organic solvents or diluents can be tolerated, based on the non-organic solvents or diluents used in the process. Particularly preferably, the use of organic solvents or diluents during the reaction and crystallization is completely avoided. This makes the process especially environmentally friendly.

Water is preferably used as the solvent, and crystallization occurs from the (dissolved) aqueous reaction product.

In this process, aqueous solutions or pastes of 3,4-dimethylpyrazole and/or maleic acid and/or maleic anhydride can be used. Particularly preferred are both 3,4-dimethylpyrazole and maleic acid (anhydride) as aqueous solutions or pastes. Individual substances can also be used as solid materials. For example, 3,4-DMP can also be used as a solid.

Crystallization preferably occurs by cooling the aqueous reaction product. Seed crystals can be used simultaneously to initiate crystallization.

The implementation and crystallization can be carried out continuously or discontinuously. One or more reactors or crystallizers can be used. For example, a cascade of reactors and/or crystallizers can be employed. Batch-wise conversion as well as semi-continuous or continuous conversion and crystallization are possible.

The 2-(N-3,4-dimethylpyrazol) succinic acid obtained after crystallization preferably has a purity of at least 99.7%, particularly preferably at least 99.9%. This purity is preferably already achieved after the first crystallization.

Through the inventive production method, a high yield and high purity can be achieved with minimal effort. In particular, the use of expensive and potentially environmentally and health-hazardous organic solvents and diluents is not necessary. Also, separation or exchange of solvents is not required.

By using the reaction product of 3,4-dimethylpyrazole with maleic acid, the volatility of 3,4-dimethylpyrazole can be significantly reduced.

The application of 2-(N-3,4-dimethylpyrazol)butyric acid as a nitrification inhibitor for KAS fertilizers is carried out according to generally established methods: it can, for example, be applied in solid form together with KAS fertilizers as a powder or granulate directly onto the soil. It can also be added to liquid KAS fertilizers, for example in dissolved form, for nitrogen stabilization, or applied together with them in dissolved form. It is also possible to apply DMPBS and KAS fertilizers separately but in close succession.

It has proven particularly effective to use mixtures of 2-(N-3,4-dimethylpyrazol)butyric acid with a KAS mineral fertilizer, for example, a fertilizer mixture containing: A. A calcium ammonium nitrate mineral fertilizer, which, in addition to ammonium nitrate, calcium carbonate and/or magnesium carbonate and optionally water, may contain up to 15% by weight of other ingredients, based on the calcium ammonium nitrate mineral fertilizer without water, B. 100 to 10,000 ppm by weight, based on component A without water, of 2-(N-3,4-dimethylpyrazol)butyric acid.

Such fertilizer mixtures preferably contain 100 to 10,000 weight-ppm of nitrification inhibitor, based on the mineral fertilizer, particularly 0.01 to 1 weight-%, especially 0.03 to 0.5 weight-%, in particular 0.05 to 0.2 weight-%.

The water content in component A and in the fertilizer mixture is preferably at most 1.0 wt.%, particularly preferably at most 0.5 wt.%, especially at most 0.3 wt.%, and is thus negligible in the mass balance. Components A and B preferably constitute at least 90 wt.%, particularly preferably at least 95 wt.% of the fertilizer mixture.

The mineral fertilizer can contain, in addition to ammonium nitrate, calcium carbonate or magnesium carbonate or a mixture of calcium carbonate with magnesium carbonate.

Here and in the following text, quantity specifications, particularly those of the nitrification inhibitor, preferably refer to the solid mineral fertilizer A, even if water is additionally present, for example in liquid formulations.

Fertilizer mixtures may also contain small amounts of water, for example 0.1 to 0.5 weight percent, based on the fertilizer mixture including water. High amounts of water in the fertilizer mixture should be avoided.

Mixtures of fertilizers have proven especially effective due to their good long-term action. These mixtures are produced according to the following method: granules of mineral fertilizers, preferably calcium ammonium nitrate mineral fertilizers, are impregnated or coated with 2-(N-3,4-dimethylpyrazol)butyric acid by spraying them with a solution of a nitrification inhibitor and then drying them again. This method is, for example, known from DE-A-41 28 828, which is fully referenced here. The additional sealing of the impregnated granules with paraffin wax proposed there is generally unnecessary because of the significantly lower volatility of the nitrification inhibitor according to the invention.

The 2-(N-3,4-dimethylpyrazol) succinic acid can also be added during the production of the mineral fertilizer, for example in the mash.

If necessary, a treatment of the mineral fertilizer with polysaccharides can also be carried out, as described in WO 98/05607/EP-B-0 971 526.

Nitrification inhibitors are usually applied to the soil in amounts ranging from 100 g/ha to 10 kg/ha.

The application in liquid fertilizer formulations can, for example, be carried out by fertigation with or without excess water, as described in DE-C-102 30 593.

The 2-(N-3,4-dimethylpyrazol) succinic acid, which can be simply produced from inexpensive starting materials, is particularly characterized by its ability to effectively inhibit the nitrification of ammoniacal nitrogen in the soil over a long period of time.

In addition, this compound has favorable toxicological properties, a low vapor pressure, and is well adsorbed in soil. As a result, 2-(N-3,4-dimethylpyrazol)butyric acid is neither released to the atmosphere to any significant extent by sublimation nor easily leached away by water. This leads to economic benefits, such as high efficiency due to the long-lasting effect of the nitrification inhibitor, and ecological benefits, such as reduced pollution of air (climate gas-reducing), surface waters, and groundwater. In soil, 2-(N-3,4-dimethylpyrazol)butyric acid diffuses similarly fast as nitrate or ammonium and can therefore act optimally. In its most general form, the invention allows the use of any suitable mineral fertilizers. These are fertilizers containing ammonium or urea. Examples of such ammonium-containing fertilizers are NPK fertilizers, calcium ammonium nitrate, ammonium sulfate nitrate, ammonium sulfate, or ammonium phosphate.

The following quantity specifications refer to the mineral fertilizer, preferably without water.

A combination of 2-(N-3,4-dimethylpyrazol)butyric acid with calcium ammonium nitrate mineral fertilizer is particularly preferred. This fertilizer contains ammonium nitrate and calcium carbonate and/or magnesium carbonate as main components, and water depending on the moisture content. According to the invention, the calcium ammonium nitrate mineral fertilizer may contain additional ingredients up to 15% by weight, preferably up to 10% by weight, particularly preferably up to 5% by weight, based on the calcium ammonium nitrate mineral fertilizer without water. Additional ingredients may include, for example, trace elements, other minerals, flow agents, binders, etc.

The nitrogen content in component A (without water) is preferably 20 wt.%, preferably at least 22 wt.%, particularly preferably 25 to 29 wt.%, especially 26 to 28 wt.%. Calcium ammonium nitrate usually contains 26 to 27 wt.% nitrogen, for example, 13.5 wt.% quickly available nitrate nitrogen and 13.5 wt.% slowly available ammonium nitrogen.

The calcium content in component A (without water), when using calcium carbonate and ammonium nitrate as ingredients, is preferably 6 to 15 wt.%, particularly preferably 7 to 13 wt.%, especially 7 to 11 wt.%. A typical calcium content is about 10 wt.%.

When using magnesium instead of calcium in the carbonate, a corresponding amount of Mg may be preferentially present.

According to a preferred embodiment, component A can contain 0.5 to 7 wt.%, preferably 1 to 5 wt.%, particularly preferably 3 to 5 wt.%, based on component A without water, MgO and/or Mg-salt such as magnesium carbonate, when calcium carbonate and ammonium nitrate are used as ingredients. Typically, MgO or MgCO3 is used here.

Furthermore, component A can, according to an embodiment of the invention, contain boron as an element and/or in the form of boron compounds, based on component A without water, in an amount of 0.1 to 1 weight percent, preferably 0.1 to 0.5 weight percent, particularly 0.15 to 0.3 weight percent.

For a description of ammonium nitrate, for example, reference can be made to the definition in the EU Fertilizers Regulation 2003/2003.

Potassium ammonium sulfate is a white to gray solid substance that is usually odorless. The pH of a 10% aqueous solution typically ranges above 4.5. The melting point is generally between 160 and 170 °C, depending on the moisture content. The specific density is usually between 0.93 and 1.4 kg/l. The salt is hygroscopic and absorbs atmospheric humidity.

Calcium ammonium nitrate usually has a moisture content of 0.1 to 0.5 weight percent, preferably 0.1 to 0.2 weight percent, especially about 0.15 weight percent. By applying an aqueous solution of 2-(N-3,4-dimethylpyrazol) succinic acid to the calcium ammonium nitrate mineral fertilizer, this moisture content can more than double. Therefore, it may be necessary to dry the treated calcium ammonium nitrate mineral fertilizer after applying or incorporating the nitrification inhibitor.

It is preferable to use 2-(N-3,4-dimethylpyrazol) succinic acid as an aqueous solution with a pH greater than 7, particularly preferably greater than 10, especially greater than 12. Due to the basic pH value, the nitrification inhibitor is stabilized on the fertilizer mixture. The pH can, for example, be adjusted by adding a base, particularly an alkali hydroxide such as NaOH or KOH.

Furthermore, it has been found according to the invention that an aqueous solution of 2-(N-3,4-dimethylpyrazol) succinic acid is more stable at a pH higher than 7, particularly preferably higher than 10, especially higher than 12, so that highly concentrated aqueous solutions can be produced. The content of 2-(N-3,4-dimethylpyrazol) succinic acid, based on the aqueous solution, can preferably be from 20 to 40 wt.%, particularly preferably from 25 to 35 wt.%, especially from 27.5 to 32.5 wt.%.

It was further found according to the invention that by adding one or more phosphates or polyphosphates to the aqueous solution, the water content of the aqueous solution can be reduced and the stability of the aqueous solution of the nitrification inhibitor can be improved again. Therefore, the aqueous solution preferably contains 0.5 to 20 wt.%, particularly preferably 1 to 10 wt.%, especially 1.5 to 7 wt.%, based on the aqueous solution, of one or more phosphates or polyphosphates.

For example, phosphates such as Na2HPO4, Na3PO4, K2HPO4, K3PO4, ammonium dihydrogen phosphate, or calcium ammonium phosphate may be considered.

The invention also relates to the aqueous solutions of 2-(N-3,4-dimethylpyrazol) succinic acid described above with a pH value greater than 7, as well as the preferred solutions containing the specified amount of nitrification inhibitor, and particularly preferred phosphates or polyphosphates.

The invention will be explained in more detail through the following examples:

Examples A. Manufacturing Examples Example 1 (Reference)

9.6 g of 3,4-dimethylpyrazole (0.1 mol) and 9.8 g of maleic anhydride (0.1 mol) were heated to 100 °C in 50 ml of 50% acetic acid. After 16 hours, the solution was evaporated to dryness. When the residue was dissolved in diethyl ether, the product (2-(N-3,4-dimethylpyrazol) succinic acid) crystallized out pure and was filtered off: white crystals with a yield of 92%. In the NMR spectrum, several methyl signals are visible, which is consistent with the suppression of the 3,5-tautomerism by substitution on nitrogen.

Example 2: Production on a 200 kg scale

For the experiments, maleic anhydride from CVM with a purity of over 99.5% and an 80% aqueous solution of 3,4-dimethylpyrazole (3,4-DMP) from BASF SE were used. According to the NMR spectrum, the 3,4-DMP solution contained approximately 2% of unspecified impurities.

The experiments were initially carried out in a 20 L reactor, which was replaced by a 25 L reactor in further experiments.

In the first experiment, 41,608 mol of maleic anhydride were introduced and dissolved in 11 liters of distilled water. The temperature increased by 10 °C during this process. Subsequently, 41,608 mol of 80% aqueous solution of 3,4-dimethylpyrazole were added, causing the temperature to rise by another 12 °C. After completion of the addition, the reaction mixture was heated to an internal temperature of 100 °C. Once this temperature had been reached, the reaction mixture was stirred for 24 hours at 100 °C and then allowed to cool. After the reaction mixture had cooled down to 90 °C, a sample was taken for NMR spectroscopic reaction monitoring, and the reaction mixture was subsequently inoculated with 1 g of product (crystals of 2-(N-3,4-dimethylpyrazol)butyric acid). At this temperature, no crystallization had yet occurred.The admitted crystals no longer dissolved. Upon further cooling, crystallization started slowly at about 85 °C. Crystallization of the main portion of the product began just below 80 °C upon heating. The reaction mixture was cooled overnight with stirring to allow complete crystallization. The precipitated solid was filtered under vacuum using a suction flask and membrane pump through three 8 L G3 glass funnel filters, washed with a total of 8 liters of distilled water, and subsequently dried under vacuum at a bath temperature of 60 °C. The resulting dry product was placed into a container, thoroughly mixed, and a sample was analyzed by NMR spectroscopy. In subsequent experiments, instead of distilled water, an equivalent amount of the combined filtrate was used as the reaction medium.The excess amount of the combined filtrate was disposed of.

NMR spectroscopic reaction control after 24 hours showed a relatively constant conversion of approximately 92% with a relatively constant ratio of isomers P1/P2 (2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid / 2-(2,3-dimethyl-1H-pyrazol-1-yl) succinic acid) around 3.3. At the beginning of the series of experiments, the ratio was slightly higher. However, this was also expected, since using the filtrate instead of distilled water as the reaction medium led to a larger amount of P2 (the P1/P2 ratio in the filtrates is approximately 1.0) being introduced into the subsequent experiments.

The composition of the reaction mixture after 24 hours of reaction time already reached constant values after just a few trials. Similarly, the composition of the isolated products from each individual experiment differs only slightly from one another.

The obtained solid substances, with an average yield of 90.22%, had a purity of 99.9% and an average ratio of isomers of 4.0 (2-(3,4-dimethyl-1H-pyrazol-1-yl)butanedioic acid to 2-(2,3-dimethyl-1H-pyrazol-1-yl)butanedioic acid). Contaminations of 3,4-DMP, maleic acid, and racemic malic acid were not detectable or only present in traces (< 0.1%) in the 1H-NMR spectra.

Example 3

As a carrier fertilizer, calcium ammonium nitrate with 27% N and 10% Ca was used. 2 g of 2-(N-3,4-dimethylpyrazol)butyric acid and 46 g of KOH were dissolved in 133 g of water. 20 kg of the carrier fertilizer in the form of granules were slowly sprayed with 85 g of the pyrazole compound formulation in a drum.

Example 4

Example 3 was repeated, using 111 g of water and 22 g of diammonium phosphate instead of 133 g of water.

Comparison example

Analog example 3 used 3,4-dimethylpyrazolophosphat (DMPP) instead of 2-(N-3,4-dimethylpyrazol)butyric acid.

B. Application examples Example 1 Investigation of Storage Stability

The calcareous ammonium nitrate (CAN) mineral fertilizer, supplemented with 2-(N-3,4-dimethylpyrazol)butyric acid (DMPBS) or DMPP, as described in Example 3 or Comparative Example, was examined regarding its storage stability in a rapid test. The nitrification-inhibited mineral fertilizers were stored for 40 days at 30 °C, 40 to 50% relative humidity, and approximately 1.2 m/s air velocity in a ventilated incubation cabinet. The nitrification inhibitor concentration on the mineral fertilizer was determined before, during, and after storage at two different depths of the pile, and the loss of nitrification inhibitor was calculated. Approximately 10 to 30 g of treated mineral fertilizer were stored. The initial DMPP concentration was 1.028 g/kg fertilizer, while that of 2-(N-3,4-dimethylpyrazol)butyric acid was 1.244 g/kg fertilizer.

Samples were taken from a superficial area of the fertilizer pile (0 to 5 cm depth of sampling or > 5 cm depth of sampling) after 20 and 40 days.

The results are shown in the following Table 1, where DMPBS stands for 2-(N-3,4-Dimethylpyrazol) succinic acid. Tabelle 1

Lagerstabilität von DMPP und DMPBS auf KAS
	Analysenwert [g/kg]
DMPP auf KAS
Startwert	1,028
d20, 0 - 5 cm	0,86
d20, > - 5 cm	0,91
d40, 0 - 5 cm	0,45
d40, > - 5 cm	0,68

Tabelle 1

DMPBS auf KAS
Startwert	1,244
d20, 0 - 5 cm	1,15
d20, > - 5 cm	1,18
d40, 0 - 5 cm	1,21
d40, > - 5 cm	1,26

Tabelle 1

d = Tag 0 - 5 cm Tiefe der Probenahme

It is clear from the table that the loss for 2-(N-3,4-dimethylpyrazol)succinic acid is significantly lower than that of DMPP when stored for 20 to 40 days.

This demonstrates the advantages of the inventive fertilizer.

Example 2 Proof of the biological (nitrification-inhibiting) effect of 2-(N-3,4-dimethylpyrazol) succinic acid

The biological effectiveness of 2-(N-3,4-dimethylpyrazol) succinic acid was tested in several field trials under different environmental conditions.

The usual procedures applied in agricultural experimentation were used for the setup, sampling, harvesting, and evaluation of the field trials.

The analysis of plant and soil samples was conducted according to standard methods. The remaining production measures, such as plant protection, conformed to good agricultural practices and were carried out uniformly.

A biologically effective nitrification inhibitor is preferably characterized by having higher levels of ammonium nitrogen in the soil compared to the control (here, non-additized KAS carrier fertilizer) within a period of up to 4 weeks and longer after application. As a result of these conditions, the yield is increased and the nitrate content in the plants is reduced.

The active ingredient was applied to solid KAS fertilizer at a rate of 0.73% based on the reduced nitrogen. The active ingredient shows a strong nitrification-inhibiting effect in the soil after application of the fertilizers. In the example listed in Table 2, KAS (calcium ammonium nitrate) + DMPBS still contains significant amounts of reduced nitrogen after 14 days as well as after 28 days, compared to untreated products. Without a nitrification inhibitor, all the reduced nitrogen is nitrified and converted into nitrate-N by the latest after 28 days. Tabelle 2:

KAS	100	9,1	0,0
KAS + DMPBS	100	79,3	61,9

Example 3 Reduction of greenhouse gas emissions (N2O)

In addition to protecting the hydrosphere, a major challenge for agriculture is the extensive prevention of the release of climate-relevant gases resulting from the agricultural use of soils. (Note: The phrase "möglichsweitgehende" was translated as "as extensive as possible" to maintain the original meaning. However, if you'd like a more natural English phrasing, it could be reworded as:) **"In addition to protecting the hydrosphere, a major challenge for agriculture is the extensive prevention of the release of climate-relevant gases resulting from the agricultural use of soils."**

The compilation of measurements of nitrous oxide (N2O), an extremely potent greenhouse gas (about 300 times stronger than CO2), both during the growing season of winter wheat after fertilization and until the end of winter, showed a 28% reduction when using KAS+DMPBS according to Example 3, compared to conventional KAS (Table 3). Tabelle 3:

Ohne Düngung	KAS	KAS + DMPBS
1149	2690	1953
43%	100%	72%

Example 4 Effect on Yield and Quality of Agricultural and Horticultural Crops Yields

In addition to possible effects on the conservation of soil, water, and air, the effect on yield and quality is particularly important for farmers. The compilation of weighted yields from different crops shows a consistently better yield performance of fertilizers with DMPBS compared to the use of the respective conventional fertilizers (Table 4) as shown in Example 3. Practically no differences were found between agricultural crops and vegetable crops or between different climatic regions and various soils. The reasons for the increased yields are, on the one hand, reduced losses due to leaching and gaseous losses through denitrification, and on the other hand, partial ammonium nutrition of plants, which has a beneficial effect on plant metabolism compared to the usual nitrate nutrition with conventional fertilizers. Tabelle 4:

Kartoffel	Hannover/D	KAS	464	609	31
Kartoffel	Jütland/DK	KAS	390	405	32
Kartoffel	Picardie/F	KAS	642	667	4
Kartoffel	Orgiano/I	KAS	531	582	9
Kartoffel	Galicien/E	KAS	644	728	13
Sellerie*	Pfalz/D	KAS	563	595	5
Sellerie*	Pfalz/D	KAS	756	781	3
Chinakohl**	Pfalz/D	KAS	757	842	11
Chinakohl**	Pfalz/D	KAS	817	930	13

Tabelle 4:

*Gewicht/100 Pfl. ** Gewicht pro Kopf, g

Claims (8)

1. Process for preparing 2-(N-3,4-dimethylpyrazole)succinic acid by reaction of 3,4-dimethylpyrazole with maleic acid and/or maleic anhydride in the absence of organic solvents or diluents, and subsequent crystallization from the reaction product obtained in the absence of organic solvents or diluents.
2. Process according to Claim 1, characterized in that the reaction takes place in water as solvent and the crystallization takes place from the aqueous reaction product.
3. Process according to Claim 1 or 2, characterized in that aqueous solutions or pastes of 3,4-dimethylpyrazole and/or maleic acid and/or maleic anhydride are reacted.
4. Process according to any of Claims 1 to 3, characterized in that the crystallization takes place by cooling of the aqueous reaction product, optionally with accompanying use of seed crystals.
5. Process according to any of Claims 1 to 4, characterized in that the 2-(N-3,4-dimethylpyrazole)succinic acid obtained after the crystallization has a purity of at least 99.7%, preferably of at least 99.9%.
6. Aqueous solution of 2-(N-3,4-dimethylpyrazole)succinic acid having a pH of greater than 7.
7. Aqueous solution according to Claim 6, characterized in that the fraction of 2-(N-3,4-dimethylpyrazole)succinic acid, based on the aqueous solution, is 20 to 40 wt%, preferably 25 to 35 wt%, more preferably 27.5 to 32.5 wt%.
8. Aqueous solution according to Claim 6 or 7, characterized in that the aqueous solution contains 0.5 to 20 wt%, preferably 1 to 10 wt%, more particularly 1.5 to 7 wt%, based on the aqueous solution, of one or more phosphates or polyphosphates.