Synthesis of ammonium trisoxalatomanganate

Abstract

The present application relates to the technical field of trivalent manganese, and provides a synthesis method of ammonium triscitrate manganese (III). The present application obtains a reaction solution by mixing manganese oxalate, manganese dioxide and an aqueous solution of ammonium oxalate and carrying out a centralization reaction; the pH value of the reaction solution is adjusted to 4.9-5.1 by using an aqueous solution of oxalic acid under the conditions of avoiding light and 5-15 DEG C, and then the reaction solution is left to stand and stratified to obtain an upper clear liquid; the upper clear liquid is mixed with ethanol and subjected to crystallization treatment to obtain solid ammonium triscitrate manganese (III). The present application uses a centralization reaction for the first time, and only manganese (III) is obtained by using manganese (IV) to oxidize manganese (II), the raw material manganese dioxide of manganese (IV) and the raw material manganese oxalate of manganese (II) are both difficult to dissolve in water, and ammonium triscitrate manganese (III) is easy to dissolve in water, so that the purity of the product is improved, and the product contains a very small amount of manganese (II). The synthesis method of the present application is simple and practical, has a high conversion rate, and the obtained product has a high purity.

Description

Technical Field

[0001] The present invention relates to the technical field of trivalent manganese, in particular to a method for synthesizing ammonium trioxalatomanganate (III). Background Art

[0002] Manganese (III) can act as both an oxidant and a reducing agent, and has the chemical property of easily undergoing single electron transfer reactions. It has received increasing attention in the fields of pharmaceuticals and chemicals, degradation of organic pollutants, and microbiology.

[0003] In the prior art, manganese (III) mainly exists in the form of ammonium trioxalatomanganate (III) or potassium trioxalatomanganate (III). The method for preparing ammonium trioxalatomanganate (III) or potassium trioxalatomanganate (III) is generally to oxidize oxalic acid with potassium permanganate under weak alkaline conditions. However, the product prepared by this process contains oxidized manganese (VII), manganese (V), and manganese (III), and is not pure manganese (III). At the same time, the proportion of manganese (III) is low, resulting in low product purity and low conversion rate. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a method for synthesizing ammonium trioxalato manganate (III). The method for synthesizing ammonium trioxalato manganate (III) provided by the present invention is simple and practical, has a high conversion rate, and the obtained ammonium trioxalato manganate (III) has high purity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for synthesizing ammonium trioxalatomanganate (III), comprising the following steps:

[0007] (1) mixing manganese oxalate, manganese dioxide and an aqueous ammonium oxalate solution to perform a neutralization reaction to obtain a reaction solution;

[0008] (2) in a dark environment at 5-15° C., adjusting the pH of the reaction solution to 4.9-5.1 with an oxalic acid aqueous solution, and then allowing the reaction solution to stand for stratification to obtain a supernatant;

[0009] (3) The supernatant is mixed with ethanol and crystallized to obtain solid ammonium trioxalatomanganate (III).

[0010] Preferably, the mixture of manganese oxalate, manganese dioxide and ammonium oxalate aqueous solution comprises:

[0011] washing the manganese oxalate and manganese dioxide with water and performing solid-liquid separation to obtain a mixture of manganese oxalate and manganese dioxide;

[0012] The mixture of manganese oxalate and manganese dioxide is mixed with an ammonium oxalate aqueous solution at 5-15° C. in a dark environment; the temperature of the water washing is 5-10° C.

[0013] Preferably, the molar ratio of manganese oxalate, manganese dioxide and ammonium oxalate is 1:1:3-4.

[0014] Preferably, the concentration of the ammonium oxalate aqueous solution is 0.3 to 1.5 mol / L, and the concentration of the oxalic acid aqueous solution is 2 to 4 mol / L.

[0015] Preferably, the temperature of the centralization reaction is 5 to 15° C., and the time is 10 to 50 min; the centralization reaction is carried out in a light-proof environment.

[0016] Preferably, in step (2), the pH value of the reaction solution is adjusted using an oxalic acid aqueous solution by dropwise adding the oxalic acid aqueous solution into the reaction solution at a rate of 0.01 to 0.0125 times the volume of the ammonium oxalate solution per minute.

[0017] Preferably, after the crystallization treatment in step (3), the method further comprises sequentially crushing, washing, filtering and drying the obtained crystalline solid product to obtain solid ammonium trioxalatomanganate (III).

[0018] Preferably, the standing time is 2 to 3 hours; and the volume ratio of the supernatant to ethanol is 1:1 to 2.

[0019] The present invention provides a method for synthesizing ammonium trioxalatomanganate (III), comprising the following steps: (1) mixing manganese oxalate, manganese dioxide, and an aqueous ammonium oxalate solution for a neutralization reaction to obtain a reaction solution; (2) adjusting the pH value of the reaction solution to 4.9 to 5.1 using an aqueous oxalic acid solution at 5 to 15° C. in the dark, and then allowing the solution to stand for stratification to obtain a supernatant; (3) mixing the supernatant with ethanol for crystallization to obtain solid ammonium trioxalatomanganate (III). The present invention adopts a neutralization reaction for the first time, utilizing manganese (IV) to oxidize manganese (II) to obtain only manganese (III). Manganese dioxide, a raw material for manganese (IV), and manganese oxalate, a raw material for manganese (II), are both insoluble in water, while ammonium trioxalatomanganate (III) is readily soluble in water, thereby improving the purity of the product and ensuring that the product contains a very small amount of manganese (II). The method for synthesizing ammonium trioxalatomanganate (III) provided by the present invention is simple and practical, has a high conversion rate, and the obtained ammonium trioxalatomanganate (III) is of high purity. According to the data in the examples, the purity of the ammonium trioxalatomanganate (III) provided by the present invention is as high as 95.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention provides a flow chart of the synthesis method of ammonium trioxalatomanganate (III). DETAILED DESCRIPTION

[0021] The present invention provides a method for synthesizing ammonium trioxalatomanganate (III), comprising the following steps:

[0022] (1) mixing manganese oxalate, manganese dioxide and an aqueous ammonium oxalate solution to perform a neutralization reaction to obtain a reaction solution;

[0023] (2) in a dark environment at 5-15° C., adjusting the pH of the reaction solution to 4.9-5.1 with an oxalic acid aqueous solution, and then allowing the reaction solution to stand for stratification to obtain a supernatant;

[0024] (3) The supernatant is mixed with ethanol and crystallized to obtain solid ammonium trioxalatomanganate (III).

[0025] In the present invention, unless otherwise specified, all substances are commercially available products well known to those skilled in the art.

[0026] The present invention mixes manganese oxalate, manganese dioxide and an aqueous solution of ammonium oxalate for a neutralization reaction to obtain a reaction solution. In the present invention, the mixing of the aqueous solution of manganese oxalate, manganese dioxide and ammonium oxalate preferably includes: washing the manganese oxalate and manganese dioxide with water and then performing solid-liquid separation to obtain a mixture of manganese oxalate and manganese dioxide; mixing the mixture of manganese oxalate and manganese dioxide with an aqueous solution of ammonium oxalate under conditions of light protection and 5 to 15°C; the water is preferably deionized water; the washing is preferably a shaking wash; the number of washes is preferably 1; the solid-liquid separation method is preferably to carefully absorb the supernatant with a syringe; the temperature of the water washing is preferably 5 to 10°C; after obtaining the mixture of manganese oxalate and manganese dioxide, it is preferably to immediately add an ammonium oxalate solution. The reason why the present invention controls the immediate addition of the ammonium oxalate solution after obtaining the mixture of manganese oxalate and manganese dioxide is that a small amount of unstable Mn(III) begins to slowly generate during the uniform mixing of manganese oxalate and manganese dioxide, and a large amount of C2O4 is generated by adding oxalate. 2- The invention adds low-temperature water to wash manganese oxalate and manganese dioxide, removes impurity ions in manganese oxalate and manganese dioxide, and allows the two to be fully mixed, which is conducive to the neutralization reaction.

[0027] In the present invention, the molar ratio of manganese oxalate, manganese dioxide and ammonium oxalate is preferably 1:1:3-4, more preferably 1:1:3.5-3.75; the concentration of the aqueous ammonium oxalate solution is preferably 0.3-1.5 mol / L, more preferably 0.5-0.75 mol / L; the temperature of the neutralization reaction is preferably 5-15°C, more preferably 8-12°C, and the time is preferably 10-50 min, more preferably 10-25 min; the neutralization reaction is preferably carried out in a light-proof environment; the reaction equipment of the neutralization reaction preferably provides a low-temperature function, and in a specific embodiment of the present invention, a low-temperature test chamber is preferably used. The present invention controls the amount of ammonium oxalate added to ensure that there is a sufficient amount of free C2O4 in the system. 2-It can quickly react with the free Mn generated continuously in the system 3+ Combined, Mn 3+ The product exists stably in the solution in the form of trioxalato manganese (III) ions. Since manganese (IV) and manganese (III) are affected by light and heat and will destroy oxalic acid, trioxalato manganese (III) ammonium is more stable in a light-proof and low-temperature environment. Therefore, the present invention conducts the reaction at a low temperature and light-proof environment to improve the product yield.

[0028] In the present invention, the reaction equation of the centralization reaction is as follows:

[0029] 5(NH4)2C2O4+MnC2O4+MnO2+2H2O=2(NH4)3[Mn(C2O4)3]+4NH3·H2O.

[0030] The present invention proposes the above reaction for the first time, utilizes manganese (IV) to oxidize manganese (II) to obtain manganese (III), and utilizes the characteristics that both manganese dioxide, a raw material of manganese (IV), and manganese oxalate, a raw material of manganese (II), are insoluble in water, while ammonium trioxalatomanganate (III) is easily soluble in water. Therefore, the prepared product contains only a very small amount of manganese (II), specifically containing ammonium trioxalatomanganate (III), manganese (II) oxalate, and manganese monoxide, of which the content of ammonium trioxalatomanganate (III) accounts for more than 94%.

[0031] After obtaining the reaction solution, the present invention uses an oxalic acid aqueous solution to adjust the pH value of the reaction solution to 4.9-5.1 under the conditions of avoiding light and 5-15°C, and then performs static stratification to obtain a supernatant. In the present invention, the concentration of the oxalic acid aqueous solution is preferably 2-4 mol / L; in the step (2), the oxalic acid aqueous solution is preferably used to adjust the pH value of the reaction solution by dropwise adding the oxalic acid aqueous solution to the reaction solution, and the rate of the dropwise addition is preferably 0.01-0.0125 times the volume of the ammonium oxalate solution per minute; the dropwise addition of the oxalic acid aqueous solution is preferably carried out under stirring; in a specific embodiment of the present invention, after the pH value of the reaction solution is adjusted to 4.9-5.1, the addition of the oxalic acid aqueous solution is stopped, and after continuing to stir for 5 minutes, the pH is 4.9-5.1 and there is basically no change, and the subsequent static stratification step can be carried out; the static stratification time is preferably 2-3 hours; after the static stratification, the supernatant is preferably obtained by aspirating the supernatant with a pipette. The present invention adjusts the pH of the reaction solution with oxalic acid to ensure the stability of trivalent manganese in the reaction solution. If the reaction solution is too acidic, the trivalent manganese is easily decomposed. If the reaction solution is too alkaline, the trivalent manganese is converted to tetravalent manganese. The reaction equation for this process is NH3·H2O+H2C2O4=(NH4)2C2O4+H2O. The present invention allows trace amounts of unreacted manganese oxalate and manganese dioxide to precipitate by standing, thereby improving the purity of the final product.

[0032] After obtaining the supernatant, the present invention mixes the supernatant with ethanol for crystallization to obtain solid ammonium trioxalatomanganate (III). In the present invention, the volume ratio of the supernatant to ethanol is preferably 1:1-2; the crystallization treatment time is preferably 0.5-1h, and the temperature is preferably 5-10°C; after the crystallization treatment, the obtained crystalline solid product is preferably crushed, washed, filtered, and dried in sequence to obtain solid ammonium trioxalatomanganate (III); the present invention has no special requirements for the crushing method, and methods well known to those skilled in the art can be used; the particle size of the crushed crystalline solid product is preferably 16-36 mesh; the washing solvent is preferably ethanol; the mass ratio of the crushed crystalline solid product to ethanol is preferably 1g:1-2.5mL; the number of washing times is preferably 3; the filtration is preferably vacuum filtration; the drying is preferably drying the wet solid ammonium trioxalatomanganate (III) in a nitrogen-filled, 7-15°C vacuum dryer; the vacuum dryer is preferably placed in a low-temperature box at 7-15°C. The prepared ammonium trioxalatomanganate (III) crystals are stored in a light-proof, low-temperature and oxygen-free environment.

[0033] To further illustrate the present invention, the synthesis method of ammonium trioxalatomanganate (III) provided by the present invention is described in detail below with reference to the following examples, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Figure 1 The invention provides a flow chart of a method for synthesizing ammonium trioxalatomanganate (III). According to the method, manganese oxalate and manganese dioxide solids are fully mixed, washed and separated, an ammonium oxalate aqueous solution is added to the obtained mixture of manganese oxalate and manganese dioxide, the mixture is mixed and stirred in a dark and low temperature environment, an oxalic acid aqueous solution is added dropwise to adjust the pH, a supernatant is separated to which ethanol is added, crystals are precipitated, the crystals are washed, and vacuum filtration is performed to finally obtain ammonium trioxalatomanganate (III).

[0035] Example 1

[0036] (1) In a 50 mL centrifuge tube, add 1.4295 g of manganese oxalate, 0.8693 g of manganese dioxide, and 25 mL of 10°C deionized cold water, shake thoroughly and wash for 1 min. Centrifuge to obtain a mixed precipitate of 2.2875 g of manganese oxalate and manganese dioxide.

[0037] (2) In a light-proof, 10°C low-temperature test chamber, 2.2875 g of manganese oxalate and manganese dioxide were mixed and precipitated into a 200 mL beaker, and 50 mL of 0.7 mol / L ammonium oxalate aqueous solution was added. The mixture was stirred for 10 min to obtain a dark red reaction solution. The pH detector head was inserted into the reaction solution, and the observation window was covered with black mesh to achieve light-proof effect.

[0038] (3) In a dark place and at 10°C, add 2 mol / L oxalic acid aqueous solution to the reaction solution at a rate of 0.1 mL / min using a peristaltic pump. Observe the change in the pH meter reading. The reading decreases continuously until it reaches pH = 5. Stop adding oxalic acid aqueous solution. Stir for 5 minutes until the pH value is substantially unchanged.

[0039] (4) The dark blood-red reaction solution after pH adjustment was allowed to settle in a dark place for 3 hours, and then 52.1 mL of a blood-red transparent supernatant was separated. The supernatant was carefully pipetted into a beaker, and 60 mL of pure ethanol was added to the supernatant to precipitate 9.7673 g of a crystalline solid product. The crystallization temperature was 10°C and the crystallization time was 0.5 h.

[0040] (5) In a dark place, 9.7673 g of the precipitated crystalline solid product was taken, and the crystalline solid product was crushed with a glass rod to a particle size of 20 to 25 mesh. 20 mL of ethanol was then added to fully wash and remove the oxalic acid and ammonium oxalate present in the crystalline solid product. The washing was repeated three times, and the mixture was filtered under reduced pressure to obtain 6.2235 g of wet solid ammonium trioxalato manganate (III). The wet solid ammonium trioxalato manganate (III) was placed in a nitrogen-filled, 10°C reduced pressure dryer for drying, wherein the reduced pressure dryer was placed in a 10°C low temperature box to obtain 5.6326 g of solid ammonium trioxalato manganate (III).

[0041] Example 2

[0042] (1) Add 1.5 g of manganese oxalate, 0.9 g of manganese dioxide, and 25 mL of 7°C cold water to a 50 mL centrifuge tube, shake thoroughly for 1 min, and centrifuge to obtain a mixed precipitate of 2.3891 g of manganese oxalate and manganese dioxide.

[0043] (2) In a light-proof, 7°C low-temperature test chamber, 2.3891 g of manganese oxalate and manganese dioxide were mixed and precipitated into a 200 mL beaker, and 50 mL of 0.75 mol / L ammonium oxalate aqueous solution was added. The mixture was stirred for 10 min to obtain a dark red reaction solution. The pH detector head was inserted into the reaction solution, and the observation window was covered with black mesh to achieve light-proof effect.

[0044] (3) In a dark, low-temperature test chamber at 7°C, add 2 mol / L oxalic acid aqueous solution to the reaction solution at a rate of 0.1 mL / min using a peristaltic pump. Observe the change in the pH meter reading. The reading decreases continuously until it reaches pH = 5. Stop adding oxalic acid aqueous solution. Stir for 5 minutes until the pH value is substantially unchanged.

[0045] (4) The dark blood-red reaction solution after pH adjustment was allowed to settle in a dark place for 1 hour, and then 52.9 mL of blood-red transparent supernatant was separated. The supernatant was carefully pipetted into a beaker, and 60 mL of pure ethanol was added to the supernatant to precipitate 11.0136 g of crystalline solid product. The crystallization temperature was 7°C and the crystallization time was 0.5 h.

[0046] (5) In a dark place, 11.0136 g of the precipitated crystalline solid product was taken, and the crystalline solid product was crushed with a glass rod to a particle size of 20 to 25 mesh. 20 mL of ethanol was then added to thoroughly wash and remove the oxalic acid and ammonium oxalate present in the crystalline solid product. The washing was repeated three times, and the mixture was filtered under reduced pressure to obtain 6.7194 g of wet solid ammonium trioxalato manganate (III). The wet solid ammonium trioxalato manganate (III) was placed in a nitrogen-filled, 7°C reduced pressure dryer for drying, wherein the reduced pressure dryer was placed in a 7°C low temperature box to obtain 6.0814 g of solid ammonium trioxalato manganate (III).

[0047] Testing of product purity and conversion rate

[0048] (1) Determination of conversion rate

[0049] The obtained solid (NH4)3[Mn(C2O4)3] weighs C1 (C1 is not more than 1g), which is then added to 20mL of 1mol / L H2SO4 solution C2 (the solution is placed in a beaker, and C2 contains the weight of the beaker). The following reaction occurs under irradiation with a 250W ultraviolet high-pressure mercury lamp:

[0050] 2(NH4)3[Mn(C2O4)3]=2MnC2O4+3(NH4)2C2O4+2CO2↑

[0051] After the reaction is completed, weigh the weight of the reaction solution C3 (C3 includes the weight of the beaker), C1+C2-C3 is the mass of CO2 generated, and the mass of pure (NH4)3[Mn(C2O4)3] in the solid product can be calculated according to the reaction equation.

[0052] According to the above test method, the purity of the solid ammonium trioxalato manganate (III) obtained in Example 1 was 95.6%; the purity of the solid ammonium trioxalato manganate (III) obtained in Example 2 was 94.36%.

[0053] (2) Determination of conversion rate

[0054] After the reaction is completed, the only insoluble precipitate left is manganese oxalate, which can be directly recovered. The mixed solution of ethanol and water produced during crystallization and washing contains water, ethanol, oxalic acid, and ammonium oxalate, which can be recovered by fractional distillation. The overall reaction equation for the preparation of ammonium trioxalatomanganate (III) is as follows:

[0055] 3(NH4)2C2O4+MnC2O4+MnO2+2H2C2O4=2(NH4)3[Mn(C2O4)3]+2H2O

[0056] According to the overall reaction equation, theoretically, the amount of substance n1 obtained from ammonium oxalatomanganate (III) is twice the amount of MnO2 added. Then, the conversion rate can be obtained by the following calculation formula:

[0057] Conversion rate % = mass of solid ammonium manganate (III) trioxalate C1 * purity / (molecular weight of ammonium manganate (III) trioxalate * 2n1) * 100%

[0058] According to the above test method, the product conversion rate of the solid ammonium trioxalato manganate (III) obtained in Example 1 was 72.19%; the product conversion rate of the solid ammonium trioxalato manganate (III) obtained in Example 2 was 74.30%.

[0059] It can be seen from this that the synthesis method provided by the present invention has a high product conversion rate and the obtained ammonium trioxalatomanganate (III) has high purity.

[0060] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing ammonium trioxalatomanganate (III), characterized in that: The following steps are involved: (1) mixing manganese oxalate, manganese dioxide and an aqueous ammonium oxalate solution to perform a neutralization reaction to obtain a reaction solution; (2) in a dark environment at 5-15° C., adjusting the pH of the reaction solution to 4.9-5.1 with an oxalic acid aqueous solution, and then allowing the reaction solution to stand for stratification to obtain a supernatant; (3) The supernatant is mixed with ethanol and crystallized to obtain solid ammonium trioxalatomanganate (III).

2. The synthesis method according to claim 1, wherein The mixture of manganese oxalate, manganese dioxide and ammonium oxalate aqueous solution comprises: washing the manganese oxalate and manganese dioxide with water and performing solid-liquid separation to obtain a mixture of manganese oxalate and manganese dioxide; The mixture of manganese oxalate and manganese dioxide is mixed with an ammonium oxalate aqueous solution at 5-15° C. in a dark environment; the temperature of the water washing is 5-10° C.

3. The synthesis method according to claim 1 or 2, characterized in that The molar ratio of manganese oxalate, manganese dioxide and ammonium oxalate is 1:1:3-4.

4. The synthesis method according to claim 1, characterized in that The concentration of the ammonium oxalate aqueous solution is 0.3-1.5 mol / L, and the concentration of the oxalic acid aqueous solution is 2-4 mol / L.

5. The synthesis method according to claim 1, characterized in that The temperature of the centralization reaction is 5 to 15° C., and the time is 10 to 50 minutes; the centralization reaction is carried out in a light-proof environment.

6. The synthesis method according to claim 1 or 4, characterized in that In the step (2), the pH value of the reaction solution is adjusted using an oxalic acid aqueous solution by dropwise adding the oxalic acid aqueous solution into the reaction solution at a rate of 0.01 to 0.0125 times the volume of the ammonium oxalate solution per minute.

7. The synthesis method according to claim 1, characterized in that After the crystallization treatment in step (3), the method further comprises sequentially crushing, washing, filtering and drying the obtained crystalline solid product to obtain solid ammonium trioxalatomanganate (III).

8. The synthesis method according to claim 1, characterized in that The standing time is 2 to 3 hours; the volume ratio of the supernatant to ethanol is 1:1 to 2.

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