Process for the catalytic production of methionine analogues

Abstract

The invention relates to a process for the preparation of 2-hydroxy-4-methylthiobutyric acid (HMTBA) or 2-hydroxy-4-methylselenobutyric acid (HMSeBA) by catalytic conversion of 2-hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile, respectively, characterized in that the conversion is carried out in the presence of water and at least one weak acid and a catalyst comprising at least one of aluminium oxide, titanium dioxide and zirconium oxide.

Description

Technical Field

[0001] This invention relates to an improved method for producing 2-hydroxy-4-methylthiobutyric acid, methionine analogues or their selenium counterparts, and 2-hydroxy-4-methylselenobutyric acid from 2-hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile, respectively. Background Technology

[0002] 2-Hydroxy-4-methylthiobutyric acid (HMTBA) is a hydroxy analog of methionine, and its salts, chelates, especially metal chelates (Zn, Ca, Mn, Mg, Cu, Na, etc.), and esters, such as isopropyl ester and tert-butyl ester of HMTBA, are widely used in animal nutrition. Selenium derivatives of this acid, these salts, these chelates, and these esters are also important components in animal nutrition.

[0003] The preparation of 2-hydroxy-4-methylthiobutyric acid can be carried out by different methods involving various synthetic intermediates, particularly 2-hydroxy-4-methylthiobutyronitrile (HMTBN) and 2-hydroxy-4-methylthiobutyramide (HMTBM).

[0004] Document US2001 / 0001105A1 describes a continuous method for synthesizing 2-hydroxy-4-methylthiobutyric acid (HMTBA) from 2-hydroxy-4-methylthiobutyronitrile (HMTBN). According to this method, in the first step, HMTBN is hydrolyzed to 2-hydroxy-4-methylthiobutyramide (HMTBM) in the presence of an aqueous solution of an inorganic acid (such as sulfuric acid), and then in the second step, HMTBM is hydrolyzed to HMTBA. This method has the disadvantage of using large amounts of sulfuric acid, which is often used in excess relative to HMTBN, resulting in the formation of numerous byproducts, such as ammonium bisulfate, which must be separated and are difficult to recycle. The method also requires long residence times ranging from several hours.

[0005] According to document WO2004 / 089863A1, a method for producing the ammonium salt of HMTBA from its nitrile precursor (HMTBN) is known. According to this method, HMTBN in aqueous solution is converted to the ammonium salt of HMTBA in a single step in the presence of a titanium-based catalyst. This synthesis also results in the formation of methionine and HMTBM, and the reported yields of the HMTBA ammonium salt are in the range of 1%. These figures are insufficient to envision the industrial-scale application of this method. Summary of the Invention

[0006] This invention provides an alternative to existing methods that eliminates the need for sulfuric acid and combines hydration and hydrolysis stages in a single catalytic phase, resulting in unusually high yields of HMTBA or its selenium counterparts.

[0007] According to the present invention, hydroxynitrile intermediates (HMTBN or its selenium equivalent) can be converted to 2-hydroxy-4-methylthiobutyric acid (or to seleno-hydroxy-methionine) in a single step in the presence of at least one catalyst and a weak acid. The accessibility and performance of this conversion enable the industrial production of its conversion into methionine hydroxy analogs. This invention represents a true advancement compared to known synthetic methods and developed improvements (which can improve upon conventional industrial methods but offer limited benefits). Significant yields are achieved in a very short time, and the method avoids the consumption of sulfuric acid and the formation of byproducts or synthetic intermediates.

[0008] The present invention provides a preparation method for preparing hydroxy analogs of methionine or selenohydroxy analogs of methionine by catalytic conversion of 2-hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile, respectively, wherein the conversion is carried out in the presence of water and at least one weak acid and a catalyst comprising at least one of alumina, titanium dioxide and zirconium oxide.

[0009] According to the present invention, after converting the ammonium salt of hydroxy acid according to conventional technology, hydroxy nitrile compounds are directly converted into hydroxy acids without resorting to a re-separation step, thereby obtaining considerable economic benefits.

[0010] Before disclosing the invention in more detail, certain terms used herein are defined.

[0011] The term hydroxy acid is used interchangeably with 2-hydroxy-4-methylthiobutyric acid or 2-hydroxy-4-methylselenobutyric acid, whether considered together or separately. Similarly, the term hydroxy-nitrile refers to 2-hydroxy-4-methylthiobutyronitrile and 2-hydroxy-4-methylselenobutyronitrile, whether considered together or separately, and the term hydroxy-amide refers to 2-hydroxy-4-methylthiobutyramide or 2-hydroxy-4-methylselenobutyramide, whether considered together or separately.

[0012] According to the present invention, a weak acid is any organic or inorganic acid, or any compound or mixture thereof, that has a pKa constant of at least 1 and at most 10 at 25°C. Examples of weak organic acids include carboxylic acids and polyacids, which may or may not have one or more functional groups, such as those selected from OH and C=O, like acetic acid and formic acid. Examples of weak inorganic acids include phosphoric acid, dihydrogen phosphate, hydrofluoric acid (HF), hypochlorous acid (HOCl), boric acid (H3BO3), sulfurous acid (H2SO3), and hydrocyanic acid (HCN).

[0013] The term catalyst is generally used to refer to the active phase of a catalyst, but this does not exclude the fact that catalysts can be doped and / or supported.

[0014] Alumina, titanium dioxide, and zirconium oxide refer to all polymorphs (if any) of alumina (Al₂O₃), titanium dioxide (TiO₂), and zirconium dioxide (ZrO₂), respectively, which are well known to those skilled in the art. The catalyst may also be a combination of two or three of alumina, titanium dioxide, and zirconium oxide. It may also include any other entity that enhances its catalytic function.

[0015] The features, applications, and advantages of the invention will now be disclosed in more detail. It should be understood that these features may be considered independently of each other or in combination, however the combination may be.

[0016] The weak acid is preferably an organic acid having one or more carboxyl groups or an inorganic acid with a pKa of at least 1 at 25°C, preferably at most 10, and more preferably at most 7. In practice, its boiling point is less than or equal to 170°C, preferably less than or equal to 150°C, or even less than or equal to 120°C, to facilitate separation from the reaction medium, typically by distillation. Such acids that can be used according to the invention are particularly selected from formic acid, acetic acid, propionic acid, straight-chain or branched butyric acid, valeric acid, carbonic acid, glycolic acid, thioacetic acid, cyanoacetic acid, lactic acid, pyruvate, oxalic acid, methionine or its selenium equivalent, or hydroxy analogs of methionine or its selenium equivalent. These acids can be used alone or in mixtures. According to one variant, they are selected from formic acid, acetic acid, propionic acid, straight-chain or branched butyric acid, valeric acid, carbonic acid, glycolic acid, thioacetic acid, cyanoacetic acid, lactic acid, pyruvate, and oxalic acid. Preferably, the acid used is formic acid, acetic acid, and / or propionic acid. According to another variant of the invention, the weak acid is an inorganic acid, such as phosphoric acid or dihydrogen phosphate, used alone or in mixtures.

[0017] The weak acid is added in a molar ratio of weak acid to hydroxynitrile of 0.001 to 50, or even 0.001 to 30, or even 0.001 to 10, or even 0.001 to 1. In practice, the molar concentration of the weak acid in the reaction medium varies between 0.05M and 10M, preferably 0.1M to 2M, and even more preferably between 0.2M and 1M.

[0018] According to the invention, the catalyst is selected from alumina, titanium dioxide, and zirconium oxide; the compound constitutes at least the active phase of the catalyst and optionally forms the support. Therefore, if the catalyst is not entirely composed of one or more of the aforementioned oxides, it may contain any other compounds that do not affect or even enhance the catalyst performance. In variations of the invention, the catalyst is composed of one of the aforementioned oxides.

[0019] The catalyst can be doped and / or supported. It can be doped with any element or compound conventionally used and known to those skilled in the art. As an example, catalyst doping can be carried out by one or more compounds selected from: sulfates (SO4), phosphates (PO4), tungstates (WO3), borates (B2O3), and compounds corresponding to the formula H... n XM 12 O 40 and H n X2M 18 O 62 One of the heteropoly acids, where n is preferably an integer not exceeding 10, X represents Si, Ge, P or As, and M represents Mo or W, for example, the formula H6P2Mo. 18 O 62 Phosphomolybdic acid, and any other dopant compounds that provide acidity to the catalyst. The following compounds are included: PO4, SO4, and H6P2Mo. 18 O 62 This is preferred. If the catalyst is not composed of alumina, titanium dioxide and / or zirconium oxide, it may also be supported by any other compound commonly used and known to those skilled in the art, particularly silica and aluminosilicates.

[0020] According to the present invention, all of the above-mentioned solid catalysts may be in powder form, or preferably in bead, extrusion, tablet, trefoil or any other form that allows them to be used in fixed bed or other types of continuous reactors, or in batch mode in open or pressurized reactors.

[0021] The catalyst advantageously has at least 10m 2 The specific surface area is approximately 50 m² / g. Below this limit, the catalyst performance declines rapidly, particularly the selectivity for hydroxy acids, which in turn leads to a decrease in the selectivity for hydroxy amides and a reduction in the conversion of hydroxy nitriles. This observation applies to selenium equivalents. Advantageously, a specific surface area of ​​at least 50 m² / g is preferred. 2 / g. In the context of this invention, the upper limit of the specific surface area is not critical; the specific surface area is imposed by a commercially available active phase. The specific surface area values ​​shown herein were determined by the most common method, namely nitrogen physical adsorption, and calculated by the BET method.

[0022] In a preferred embodiment of the method of the present invention, the catalyst is present at a mass concentration of 0.1% to 200%, preferably 0.5% to 100%, and more preferably 1% to 50% relative to the mass of HMTBN.

[0023] According to the invention, various devices are conceivable for batch or continuous reactions: doped or undoped solid catalysts can be fixed in the reactor in the form of particles or extrusions or any other form, or loaded on metal foams. Reactors associated with this type of catalyst are preferably tubular or multi-tubular fixed beds operating in trickle or overflow, isothermal or adiabatic modes, or preferably catalyst-coated exchange reactors.

[0024] The conversion of HMTBN within the scope of this invention is advantageously carried out at temperatures ranging from 20°C to 200°C, preferably from 50°C to 180°C, and more preferably from 80°C to 170°C. It has been observed that during the reaction period, ranging from approximately 10 minutes to 3 hours, the reaction slows significantly at temperatures below 20°C, and starting from 180°C, selectivity for methionine and dinitrile, as well as methionine peptides, increases with increasing temperature, while selectivity for 2-hydroxy-4-methylthiobutyric acid is unfavorable. Selectivity for the hydroxy acids is highest in the range of 100°C to 180°C.

[0025] In the context of this invention, the contact time between the reaction mixture containing water, hydroxynitriles and acid and the catalyst is in the range of 30 seconds to 1 hour, preferably 1 minute to 30 minutes, and even more preferably 2 minutes to 20 minutes.

[0026] Hydroxynitriles are typically found in aqueous solutions. This may be in preparation for the implementation of this method. The weak acid used in the reaction can be added to the aqueous solution of the hydroxynitrile before entering the catalytic reactor, or it can be added via a mixer.

[0027] The concentration of hydroxynitriles affects the performance of the method, especially when the concentration is too high. Therefore, according to a variant of the invention, the hydroxynitriles are in the form of an aqueous solution with a concentration in the range of 0.01 M to 10 M, preferably 0.05 M to 1 M. It has been noted that above 1 M, if the conversion to hydroxynitriles remains high, the selectivity for hydroxy acids decreases, while the selectivity for hydroxyamides, dinitriles, and even peptides increases, respectively.

[0028] This invention also relates to the continuous implementation of the method of the invention. According to this variant, the method is carried out at a pressure in the range of 1 to 20 bar, preferably 2 to 10 bar. Thus, the invention provides an apparatus comprising a tank for a hydroxynitrile solution and the addition of a weak acid therein. The resulting hydroxy acid solution is pumped into a reactor containing a catalyst and heated at a temperature of 80-180°C by a sleeve or oven. The reaction medium is drawn into a gas / liquid separator, from which the gas is removed and the liquid is treated to recover the hydroxy acid. The solution is then evaporated to separate excess water and the weak acid, which may or may not form an azeotrope, and these compounds are subsequently advantageously recycled in the method. The phase containing the hydroxy acid can then be stripped to remove all or part of the ammonia constituting the ammonium salt of the hydroxy acid. Other electrodialysis steps or other techniques known to those skilled in the art are conceivable to completely recover the hydroxy acid (2-hydroxy-4-methylthiobutyric acid or the corresponding selenic acid) in acid form and to completely recycle the ammonia formed during the hydrolysis of the HMBTM intermediate in the catalytic step. Advantageously, the recovered ammonia can be recycled upstream of hydroxy acid production processes, such as in the synthesis of HCN. Attached Figure Description

[0029] The present invention and its advantages over the prior art are illustrated in the following embodiments, which support the following figures:

[0030] [ Figure 1 The diagram shows the conversion rate of HMTBN, selectivity for HMTBA, selectivity for methionine, and selectivity for HMTBM of the reaction according to the method of the present invention as a function of time, under the conditions described in Example 1.

[0031] [ Figure 2 The diagram shows the conversion rate of HMTBN, selectivity for HMTBA, selectivity for methionine, and selectivity for HMTBM of the reaction according to the method of the present invention as a function of time under the conditions described in Example 2. Detailed Implementation

[0032] In the following experimental sections:

[0033] Examples 1-6 illustrate various variations of the method of the present invention;

[0034] Examples 7 and 8 illustrate techniques for doping catalysts to obtain doped catalysts that can be used in the methods of the present invention, according to variations of the subject matter of, for example, Example 6.

[0035] Example 9 illustrates the steps for separating hydroxy acid salts into hydroxy acids; and

[0036] Examples 10 to 15 illustrate methods other than those described in this invention, for comparison.

[0037] Example 1: Preparation of HMTBA in the presence of titanium dioxide and acetic acid according to the present invention. The following figure illustrates the hydrolysis reaction of HMTBN and its conditions.

[0038]

[0039] In a 1-liter screw-cap flask, 14.0 g of HMTBN, 2000 ml of H2O, and 60 mg of acetic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.05 ml / min (contact time 24 min) into a solution heated to 120 °C containing 60 g of TiO2 (anatase type, 150 mg / L). 2 In a tubular reactor ( / g, Norpro, ST 61120).

[0040] HPLC was performed after the reaction. The yield of HMTBA was 88%.

[0041] Example 2: Preparation of HMTBA in the presence of titanium dioxide and acetic acid according to the present invention. The following figure illustrates the hydrolysis reaction of HMTBN and its conditions.

[0042]

[0043] In a 1-liter screw-cap flask, 13.1 g of HMTBN, 990 ml of H₂O, and 10 ml of acetic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a solution heated to 160°C containing 4 g of TiO₂ (anatase type, 150 ml). 2 The HMTBA salt was converted to HMTBA by ammonia stripping in a tubular reactor ( / g, Norpro, ST 61120). The process was carried out according to the technique described in Example 9.

[0044] HPLC was performed after the reaction: the conversion of HMTBN, selectivity for HMTBA, selectivity for methionine, and selectivity for HMTBM are shown as a function of time. Figure 1 middle.

[0045] The yield of HMTBA was 95%, and the yield of methionine was 5%.

[0046] Example 3: Preparation of HMTBA in the presence of titanium dioxide and acetic acid according to the present invention. The following figure illustrates the hydrolysis reaction of HMTBN and its conditions.

[0047]

[0048] In a 1-liter screw-cap flask, 13.1 g of HMTBN, 800 ml of H₂O, and 200 ml of acetic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a tubular reactor heated to 160°C. The reactor contained 4 g of TiO₂ (anatase type, 150 ml). 2 / g, Norpro, ST 61120). According to the technique described in Example 9, the obtained HMTBA salt is converted to HMTBA by ammonia stripping.

[0049] HPLC was performed after the reaction: the conversion of HMTBN, selectivity for HMTBA, selectivity for methionine, and selectivity for HMTBM are shown as a function of time. Figure 2 middle.

[0050] The yield of HMTBA was 89%, and the yield of methionine was 11%.

[0051] Example 4: Preparation of HMTBA in the presence of titanium dioxide and formic acid according to the present invention. The following figure illustrates the hydrolysis reaction of HMTBN and its conditions.

[0052]

[0053] In a 1-liter screw-cap flask, 13.1 g of HMTBN, 990 ml of H₂O, and 10 ml of formic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a tubular reactor heated to 160°C. The reactor contained 4 g of TiO₂ (anatase type, 150 ml). 2 / g, Norpro, ST 61120).

[0054] HPLC was performed after 2 hours of reaction.

[0055] According to the technique described in Example 9, the obtained HMTBA salt is converted into HMTBA by stripping ammonia.

[0056] The yield of HMTBA was 90%, and the yield of methionine was 10%.

[0057] Example 5: Preparation of HMTBA in the presence of sulfate-doped alumina and acetic acid according to the present invention.

[0058] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0059]

[0060] In a 1-liter screw-cap flask, 13.1 g of HMTBN, 800 ml of H₂O, and 200 ml of acetic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a tubular reactor heated to 160°C. The reactor contained 4 g of Al₂O₃ (γ, 300m 2 / g, IFPEN, 33006GFSA401, alumina doped with 10% by weight sulfate functional groups).

[0061] HPLC was performed after 2 hours of reaction.

[0062] According to the technique shown in Example 9, the obtained HMTBA salt is converted into HMTBA by ammonia stripping.

[0063] The yield of HMTBA was 96%, and the yield of methionine was 4%.

[0064] Example 6: Preparation of HMTBA in the presence of zirconium oxide and acetic acid according to the present invention

[0065] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0066]

[0067] In a 1-liter screw-cap flask, 13.1 g of HMTBN, 800 ml of H₂O, and 200 ml of acetic acid were introduced. The solution was stirred with a nitrogen stream at room temperature and then injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a tubular reactor heated to 160°C. The reactor contained 6 g of ZrO₂ (monoclinic, 100 ml). 2 / g, Norpro, ST 16075).

[0068] HPLC was performed after 2 hours of reaction.

[0069] According to the technique described in Example 9, the obtained HMTBA salt is converted into HMTBA by stripping ammonia.

[0070] The yield of HMTBA was 74%, and the yield of methionine was 16%.

[0071] Example 7: Preparation of TiO2 doped with 10% by weight sulfate (SO4) using sulfuric acid

[0072] Add 20g of TiO2 (anatase type, 150ml) to a 1-liter flask. 2 / g, Norpro, ST 61120) powder and 500ml water and 2.04g sulfuric acid. The solution was stirred at room temperature for 2 hours, and then the water was evaporated. The resulting powder was then dried at 200°C for 3 hours and then calcined in air at 700°C for 2 hours. Elemental analysis was performed to measure sulfur, and the amount of sulfur was observed to be 3.4% by mass of the catalyst, corresponding to 10% by mass of sulfate.

[0073] Example 8: Preparation of TiO2 doped with ammonium sulfate and containing 10% by weight sulfate (SO4)

[0074] Add 20g of powdered TiO2 (anatase type, 150ml) to a 1-liter flask. 2 / g, Norpro, ST 61120) and 500ml water and 2.78g ammonium sulfate. The solution was stirred at room temperature for 2 hours, and then the water was evaporated. The resulting powder was then dried at 200°C for 3 hours and then calcined in air at 700°C for 2 hours. Elemental analysis was performed to measure sulfur, and the amount of sulfur was observed to be 3.2% by mass of the catalyst, corresponding to 9.8% by mass of sulfate.

[0075] Example 9: Conversion of HMTBA ammonium salt to HMTBA

[0076] The ammonium salt solution of HMTBA obtained according to the present invention was concentrated in organic matter to an organic matter content of 87% by weight. The temperature of the medium varied from 100 to 130°C (atmospheric pressure). After this concentration step, the conversion to HMTBA was 21% (mol). Then, a steam stripping stage was carried out. Stripping water was introduced in liquid form. The organic matter content was kept constant at 87% by weight. The temperature was stabilized between 115 and 121°C. The stripping rate was 3.8 to 4.3 ml / min. After 200 minutes under these conditions, a conversion to HMTBA of 47% was obtained. A further stripping step was carried out to obtain HMTBA in a yield of approximately 100%.

[0077] Example 10: Preparation of HMTBA in the presence of acetic acid (not part of this invention)

[0078] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0079]

[0080] In a 20 ml screw-cap bottle, add 0.131 g of HMTBN, 8 ml of H2O, and 2 ml of acetic acid. Stir the solution at 160 °C for 10 minutes.

[0081] Analysis of the solution by HPLC revealed no reaction.

[0082] Example 11: Preparation of HMTBA in the presence of formic acid, which does not constitute part of this invention.

[0083] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0084]

[0085] In a 20 ml screw-cap flask, add 0.131 g of HMTBN, 9 ml of H2O, and 1 ml of acetic acid. Stir the solution at 160 °C for 10 minutes.

[0086] Analysis of the solution by HPLC revealed no reaction.

[0087] Example 12: Preparation of HMTBA in the presence of titanium dioxide according to existing technology

[0088] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0089]

[0090] In a 1-liter screw-cap flask, 13.1 g of HMTBN and 1000 ml of H2O were introduced. The solution was stirred with a nitrogen stream at room temperature and injected at a flow rate of 0.1 ml / min (contact time 10 minutes) into a container heated to 160°C and containing 4 g of TiO2 (anatase type, 150 ml). 2 In a tubular reactor ( / g, Norpro, ST 61120).

[0091] After the reaction, HPLC was performed, and the yield of HMTBA was 1% and the yield of methionine was 15%.

[0092] Example 13: Preparation of HMTBA in the presence of γ-phase alumina according to existing technology

[0093] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0094]

[0095] Add 0.4g of γ-Al₂O₃ (300ml) to a 10ml screw-cap bottle. 2 Add 0.1 g HMTBN (97%) and 1 ml water. Heat the solution at 90 °C for 60 minutes, then filter the solution and analyze it by proton NMR.

[0096] No HMTBN conversion was observed.

[0097] Example 14: Preparation of HMTBA in the presence of γ-phase alumina according to existing technology

[0098] The figure below illustrates the hydrolysis reaction of HMTBN and the conditions under which it proceeds.

[0099]

[0100] Add 0.4g of γ-Al₂O₃ (300ml) to a 20ml screw-cap bottle. 2 Add 1.1 g HMTBN (97%) and 10 ml water. Heat the solution at 90 °C for 18 hours, then filter the solution and analyze it by proton NMR.

[0101] The yield of HMTBM was observed to be 30%, and the yield of HMTBA was 6%.

[0102] Example 15: Preparation of HMTBA in the presence of anatase titanium dioxide according to the prior art. The following figure illustrates the hydrolysis reaction of HMTBN and its conditions.

[0103]

[0104] In a 10 ml screw-cap flask, add 1 g TiO2 (anatase type), then add 1.1 g HMTBN (97%) and 1 ml water. Heat the solution at 90 °C for 96 hours, then filter the solution and analyze it by proton NMR.

[0105] No traces of HMTBM or HMTBA were observed.

[0106] Comparison of the results of Examples 1 to 6 according to the present invention with the results obtained by the method without a catalyst (Examples 10, 11) or without a weak acid (Examples 12 to 15) demonstrates that the production performance of hydroxy acids is significantly improved in the method of the present invention, which is unexpected.

Claims

1. A method for preparing 2-hydroxy-4-methylthiobutyric acid (HMTBA) or 2-hydroxy-4-methylselenobutyric acid (HMSeBA) by catalytic conversion of 2-hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile, respectively, characterized in that... The conversion is carried out in the presence of water and at least one weak acid, and a catalyst comprising at least one of alumina, titanium dioxide, and zirconium oxide. The transformation is performed in a single step. The weak acid is selected from formic acid, acetic acid, propionic acid, straight-chain or branched butyric acid, valeric acid, carbonic acid, phosphoric acid, dihydrogen phosphate, glycolic acid, thioacetic acid, cyanoacetic acid, lactic acid, pyruvic acid, and oxalic acid.

2. The method according to claim 1, characterized in that... The weak acid is selected from acetic acid, formic acid, and propionic acid.

3. The method according to claim 1 or 2, characterized in that... The molar ratio of the weak acid to 2-hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile is in the range of 0.001 to 50.

4. The method according to claim 3, characterized in that... The weak acid has a molar equivalent relative to the hydroxynitrile of at least 1 molar equivalent.

5. The method according to claim 1 or 2, characterized in that... The mass concentration of the catalyst is from 0.1% to 200% of the mass of HMTBN.

6. The method according to claim 5, characterized in that... The mass concentration of the catalyst is 0.5% to 100% of the mass of HMTBN.

7. The method according to claim 1 or 2, characterized in that... The mass concentration of the catalyst is 1% to 50% of the mass of HMTBN.

8. The method according to claim 1 or 2, characterized in that... 2-Hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile is available in aqueous solution form with a concentration ranging from 0.01 M to 10 M.

9. The method according to claim 8, characterized in that... 2-Hydroxy-4-methylthiobutyronitrile or 2-hydroxy-4-methylselenobutyronitrile is available in aqueous solution form with a concentration ranging from 0.05 M to 1 M.

10. The method according to claim 1 or 2, characterized in that... The catalyst has a BET specific surface area of ​​at least 10 m². 2 / g.

11. The method according to claim 10, characterized in that... The catalyst has a BET specific surface area of ​​at least 50 m². 2 / g.

12. The method according to claim 1 or 2, characterized in that... The catalyst is doped with one or more compounds selected from the following: sulfates, phosphates, borates, tungstates, and compounds conforming to the formula H. n XM 12 O 40 and H n X2M 18 O 62 One of the heteropoly acids, where n is an integer not exceeding 10, X represents Si, Ge, P or As, and M represents Mo or W.

13. The method according to claim 12, characterized in that... The catalyst is doped with the formula H6P2Mo. 18 O 62 Phosphomolybdic acid.

14. The method according to claim 1 or 2, characterized in that The conversion is carried out at temperatures ranging from 20°C to 200°C.

15. The method according to claim 14, characterized in that... The conversion is carried out at temperatures ranging from 50°C to 180°C.

16. The method according to claim 14, characterized in that... The conversion is carried out at temperatures ranging from 80°C to 170°C.

17. The method according to claim 1 or 2, characterized in that... The method is performed continuously.

18. The method according to claim 1 or 2, characterized in that... The method is carried out continuously and the conversion is performed at a temperature ranging from 50°C to 180°C.

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