Synthesis method of bis (oxalato) palladium (II) acid ammonium

Abstract

Bis (oxalate) palladium (II) acid ammonium is a water-soluble Pd (II) complex, the molecular formula is (NH4) 2 [Pd (C2O4) 2], and the bis (oxalate) palladium (II) acid ammonium generally contains two crystal waters, does not contain chlorine elements, can provide [Pd (C2O4) 2] 2-ligand anions, is a catalytic precursor with excellent performance, and has important application prospects. The invention discloses a novel synthesis method of bis (oxalate) palladium (II) acid ammonium, and belongs to the field of precious metal chemical catalysis. The specific technical route is as follows: palladium chloride is taken as a raw material, water is taken as a solvent, and the preparation method comprises the following three steps of reaction: firstly dissolving palladium chloride in ammonia water to form a [Pd (NH3) 4] Cl2 solution, then reacting with H2C2O4 / (NH4) 2C2O4 to generate a water-insoluble intermediate cis-[Pd (NH3) 2 (C2O4)], and finally quantitatively reacting cis-[Pd (NH3) 2 (C2O4)] with H2C2O4 to obtain a target product (NH4) 2 [Pd (C2O4) 2]. 2H2O, and the yield is greater than 95%. The method is mild in reaction condition, simple to operate, high in yield and high in product purity, the chlorine content can be reduced to 100 ppm or below, and batch production is easy to realize.

Description

Technical Field

[0001] This invention relates to a method for synthesizing ammonium bis(oxalate)palladium(II)ate, belonging to the field of rare and precious metal chemical catalysis. Background Technology

[0002] Ammonium bis(oxalato)palladium(II) is a water-soluble Pd(II) complex with the molecular formula (NH4)2[Pd(C2O4)2]. It typically contains two molecules of water of crystallization and is internationally known as ammonium bis(oxalato)palladium(II). It is one of the few water-soluble palladium compounds that does not contain chlorine. Its structural formula is:

[0003]

[0004] As is well known, in many important applications of palladium catalysts (e.g., automotive exhaust purification, VOCs emission treatment in industrial processes, and deep benzene desulfurization in petrochemicals), chloride ions, even in trace amounts, have a very detrimental effect on catalytic reactions. Therefore, it is essential to strictly control the introduction of chlorine, especially from the palladium catalyst itself. Using water-soluble palladium compounds that do not contain chlorine as catalytic precursors, replacing traditional palladium chloride, chloropalladium acid, and chloropalladium salts, is an important means of effectively controlling the chlorine content in palladium catalysts. Furthermore, the mainstream industrial technique for preparing palladium-supported catalysts is aqueous chemical impregnation, which requires the selected catalytic precursor to have sufficient water solubility.

[0005] (NH4)2[Pd(C2O4)2] contains no chlorine and no other elements harmful to catalytic reactions (such as K, Na, P, S, etc.). It has high water solubility (approximately 330 g / L at room temperature, equivalent to 100 g Pd / L), and a 10% aqueous solution has a pH of approximately 4-5. It can provide negatively charged [Pd(C2O4)2]. 2- Ammonium bis(oxalate)palladium(II)ate is an anionic compound that is easily anchored by a support. Furthermore, it undergoes a self-redox reaction at relatively low temperatures (≈200℃), decomposing into metallic palladium, ammonia, CO2, and water; the gaseous products are relatively environmentally friendly. Based on these characteristics, ammonium bis(oxalate)palladium(II)ate is an ideal catalytic precursor with significant application prospects in the preparation of supported palladium catalysts. However, existing publicly available synthesis techniques for ammonium bis(oxalate)palladium(II)ate suffer from low yields and low product purity, particularly high residual chloride ion content (approximately 0.1–0.5%), which fails to meet the technical requirements of industrial applications.

[0006] Currently, the main methods for synthesizing (NH4)2[Pd(C2O4)2] disclosed in existing literature include:

[0007] [1] Yu Jianmin (ed.). Handbook of Synthesis of Noble Metal Compounds and Complexes. Beijing: Chemical Industry Press, 2009, 105.

[0008] The literature describes a synthetic method involving the addition of oxalic acid to (NH3)2PdCl4. The chemical reactions involved are as follows:

[0009] 【2】Anti K. Prodjosantoso. Preparation and characterization of chlorine-free palladium catalysts. ICICs, 2013.

[0010] The literature mentions that Ammonium bisoxalatopalladium(II) [(NH4)2Pd(ox)2·2H2O] was prepared by dissolving (NH4)2PdCl6 in a hot 2 M (NH4)2(ox) solution. The solution was then evaporated until about 10 mL remained. The resulting fine yellow needles were then collected by filtration and washing successively with cold water, alcohol, and acetone. The crystals were air-dried.

[0011] 【3】Qing-Song Ye, Zai-Fu Pan, Ming-Jin Xie, Jia-Lin Chen, Wei-PingLiu. Crystal structure of diammonium bis(oxalato)palladium(II) dihydrate,(NH4)2[Pd(C2O4)2] 2H2O. Z. Kristallogr. NCS 2010, 225, 423-424.

[0012] Method described in the literature: To a solution of palladium(II) chloride (0.89g,5.0mmol) in dilute hydrochloric acid (2M, 6mL), ammonium oxalate (1.86g,15.0mmol) in 10mL of distilled water was added. The resulting solution wasstirred for 1h at 60°C, and then the pH was adjusted to 5.5 by adding dilutesodium hydroxide solution. After cooling to room temperature, a yellow prodctprecipitated from the solution. The product was filtrated, washed with ice-cold water, and dried under vacuum at 70°C. A solution of mmol was prepared, and the resulting solution was stirred at 60°C for 1 hour. Then, dilute sodium hydroxide solution was added to adjust the pH to 5.5. After cooling to room temperature, yellow crystals precipitated. These crystals were washed with cold water and dried under vacuum at 70°C.

[0013] The method reported in reference [1] did not provide the reaction conditions and the yield of the synthesis. From the chemical reactions involved, the selected starting materials potassium chloropalladate, oxalic acid, and the products (NH4)2[Pd(C2O4)2] and HCl are all soluble in water. Among them, the water solubility of hydrochloric acid at 20°C is 721 g / L. Oxalic acid is a moderately strong organic acid. After neutralization with a base, it generates oxalate ions, which then have the ability to coordinate and replace chloride ions to coordinate with Pd(II). Therefore, the reaction cannot be complete. Thus, it is technically difficult to separate the water-soluble product (NH4)2[Pd(C2O4)2] from the unreacted starting materials potassium chloropalladate, oxalic acid, and hydrochloric acid solution, which are all soluble in water, especially the difficulty in controlling the residual chloride ions.

[0014] The method reported in reference [2] uses Pd (which is sparingly soluble in water) Using compound (NH4)2PdCl6 as the starting material, Pd(NH4)2PdCl6 was first reacted with a portion of ammonium oxalate. The chloride ion is reduced to Pd(II) to give the intermediate (NH4)2PdCl4, where the oxalate ion replaces the chloride ion ligand to give the product. The chemical reactions involved are:

[0015]

[0016] The problem is that the reaction products (NH4)2[Pd(C2O4)2] and NH4Cl have a water solubility of 372 g / L at 25°C, which is close to the room temperature solubility of (NH4)2[Pd(C2O4)2] (330 g / L). Separating them by utilizing the difference in solubility makes it difficult to improve the yield or ensure the purity of the products. In particular, controlling the residual chloride ion content is difficult and the synthesis cost is high. Therefore, whether this method has industrial application value is questionable.

[0017] Reference [3] describes a synthetic method reported by the inventors, which involves using palladium chloride as a starting material, dissolving it in a mixture of hydrochloric acid and oxalic acid, adjusting the pH of the solution to 5.5 with NaOH, and then cooling to precipitate the target product. The chemical reactions involved are as follows:

[0018]

[0019] When hydrochloric acid and ammonium oxalate are added in excess of 20% and 50%, respectively, the product sodium chloride has a water solubility of 360 g / L at 25°C, which is not much different from the solubility of (NH4)2[Pd(C2O4)2]. Similarly, using the difference in solubility between these substances and the product to separate the product makes it difficult to improve the yield or ensure product purity, especially since controlling chloride ion residue is extremely difficult. Therefore, this method has shortcomings in industrial applications.

[0020] Chinese patent CN114773181A discloses a method for preparing hydrated dioxalatopalladium(II) acid H2[Pd(C2O4)2], comprising the following steps: dissolving palladium powder in aqua regia and removing nitrates to obtain a palladium chloride H2PdCl4 solution, then converting the palladium chloride to tetrahydroxypalladium acid Na2[Pd(OH)4] with sodium hydroxide; reacting sodium tetrahydroxypalladium with oxalic acid to obtain a hydrated dioxalatopalladium acid precipitate, which is then filtered, washed, and dried to obtain hydrated dioxalatopalladium(II) acid with a purity ≥99.95%. Those skilled in the art know that adding sodium hydroxide to a palladium chloride solution, even in large excess, only forms a PdO / Pd(OH)2 precipitate, not the so-called Na2[Pd(OH)4]. [Reference: Tan Qinglin, Que Zhenhuan, eds. Platinum Group Metals - Properties, Metallurgy, Materials, Applications. Beijing: Metallurgical Industry Press, 1990, 43-111]. For Pt( In terms of OH, it belongs to the hard acid family. -Palladium (Pt(OH)6) is a hard base. According to the soft-hard acid-base theory in chemistry, K2[Pt(OH)6] is stable. Its preparation method can be found in the reference: Yu Jianmin (ed.). *Handbook of Synthesis of Noble Metal Compounds and Complexes*. Beijing: Chemical Industry Press, 2009, 189. Pt(II), however, is a soft base. When it reacts with KOH, it only yields PtO / Pt(OH)2. Similarly, Pd(II) is a soft base. When it reacts with KOH, it only yields PdO / Pd(OH)2 and not Na2[Pd(OH)4]. Anyone with knowledge of noble metal chemistry knows this property of palladium(II). In fact, the existence of Na2[Pd(OH)4] has not been reported domestically or internationally. Meanwhile, the reference [Yu Jianmin (ed.). *Handbook of Synthesis of Noble Metal Compounds and Complexes*. Beijing: Chemical Industry Press, 2009, 104] reports that H2[Pd(C2O4)2] is a pale yellow needle-like crystal that turns black upon exposure to light and heat, and is soluble in water, exhibiting strong acidity. CN114773181A states in its technical background that "hydrated bis(oxalato)palladium(II) is soluble in water." However, the patent repeatedly describes in its invention content and embodiments that "hydrated bis(oxalato)palladium(II) precipitates from the water-soluble system of the reaction, is collected by filtration, repeatedly washed with deionized water, and dried, with a yield greater than 95%." Since hydrated bis(oxalato)palladium(II) is highly water-soluble, it would not precipitate from an aqueous solution, and the yield after repeated washing with deionized water would not be very high. Therefore, it is reasonable to believe that the technology in CN114773181A clearly violates existing chemical common sense, and its feasibility needs further verification.

[0021] Our research team used (NH4)2[Pd(C2O4)2] as a raw material and followed the synthetic method reported in the literature [1. ChemCatChem, 2024, 16, e202301015, 2. Yu Jianmin (ed.). Handbook of Synthesis of Noble Metal Compounds and Complexes. Beijing: Chemical Industry Press, 2009, 104]. Through the following reaction route, we obtained an aqueous solution of H2[Pd(C2O4)2]. After concentrating it under reduced pressure to near dryness, it quickly turned black and decomposed into metallic palladium. This further confirmed that H2[Pd(C2O4)2] has high water solubility and can only exist in solution, and is not very stable in the solid state.

[0022]

[0023] cis-[Pd(NH3)2(C2O4)] is a known compound that is sparingly soluble in water (approximately 1.2 g / L at room temperature). It lacks clear industrial applications, therefore, research reports on it are scarce both domestically and internationally, with only the following three publicly available publications:

[0024] [1] Yu Jianmin (ed.). Handbook of Synthesis of Noble Metal Compounds and Complexes. Beijing: Chemical Industry Press, 2009, 112.

[0025] The synthetic method described in the literature is as follows: 17.5 g of K₂C₂O₄H₂O is dissolved in 80 mL of aqueous solution and mixed with cis-[Pd(NH₃)₂Cl₂] which is turbid in 20 mL of water. The mixture is stirred or heated, and the resulting pale yellow precipitate is filtered. The precipitate is washed with water, alcohol, and ether, respectively, and then dried in air. The chemical reactions involved are:

[0026]

[0027] 【2】Wenzheng Xia, Zaifu Pan, Jialin Chen, Qingsong Ye and Weiping Liu. A facile synthesis and thermal stability of cis-[Pd(NH3)2(C2O4)]. Asian JChem, 2011, 23 (2), 785-787.

[0028] Synthesis of cis-[Pd(NH3)2(C2O4)]: The powder of PdCl2 (2.00 g, 11.28mmol) was slowly added to a solution of (NH4)2C2O4·H2O (4.80 g, 33.80 mmol) in120 mL of water at 60-70 ºC. After stirring for 10 min, the pH of the mixture was adjusted to 7 by adding NaOH solution drop by drop and the precipitatedimmediately. The mixture was cooled to room temperature and the yellowproduct was collected by filtration, washed with cold water and then dried in a vacuum oven at 60 ºC. The yield was about 76 % (PdCl2 (2.00 g, 11.28 mmol) powder was slowly added to 120 mL at 60-70 ºC (NH4)2C2O4·H2O (4.80 g, 33.80 In an aqueous solution (mmol), after stirring for 10 minutes, NaOH solution was added dropwise to adjust the pH to 7. A precipitate immediately formed. The mixture was cooled to room temperature, filtered to collect the yellow product, washed with cold water, and dried under vacuum at 60°C. (Yield approximately 76%). The chemical reactions involved are:

[0029]

[0030] [3] Chinese Patent CN 101362781 B: Synthesis method of tetraamminepalladium(II) oxalate

[0031] Palladium chloride (PdCl2) reacts with ammonium oxalate to produce cis-diaminepalladium(II)oxalate. 3.2 g (22.5 mmol) of (NH4)2C2O4·H2O was dissolved in 100 mL of water and heated to 50–60 °C. While stirring, 2.0 g (11.3 mmol) of solid PdCl2 was added in portions. The PdCl2 dissolved rapidly, and a pale yellow precipitate formed. The reaction was continued for 1 h, then cooled to room temperature, filtered, washed with a small amount of water, and dried under vacuum at 65 °C for 4 h to obtain 2.48 g of Pd(NH3)2C2O4. The chemical reactions involved are as follows:

[0032]

[0033] The methods described above [1]-[3] all use water-insoluble trans-[Pd(NH3)2Cl2] or PdCl2 as raw materials, involving a solid-liquid reaction to generate a water-insoluble cis-[Pd(NH3)2(C2O4)] precipitate. As is well known, this reaction is often incomplete, and the generated cis-[Pd(NH3)2(C2O4)] precipitate inevitably encapsulates trans-[Pd(NH3)2Cl2] or PdCl2, resulting in low product purity, especially a high chloride ion content. Method [1] did not report the specific yield and product purity; Method [2] was the inventor's team's preliminary work, with a yield of only 75%, and we found that the product contained about 0.5% unreacted PdCl2, with a chloride ion content as high as 0.2%, which could not meet the technical requirements of the downstream product (NH4)2[Pd(C2O4)2]; Method [3] was also the inventor's team's preliminary work, and although the yield could reach more than 96%, there was still the problem of unreacted PdCl2 raw material that was insoluble in water being wrapped in the product, and the chloride ion content was as high as 0.3% as measured.

[0034] The research and development team of this invention patent referred to the hydration-precipitation method for platinum-based drug synthesis [Justin J. Wilson and Stephen J. Lippard. Synthetic methods for the preparation of platinum anticancer complexes. Chem Rev, 2013 dx.doi.org / 10.1021 / cr4004314.] and followed the process as follows:

[0035]

[0036] High-purity cis-[Pd(NH3)2(C2O4)] can be prepared, and the chlorine content can be reduced to 250ppm. However, the process uses relatively expensive cis-[Pd(NH3)2Cl2] and silver nitrate as raw materials, resulting in high preparation costs. In addition, a small amount of silver will be introduced into the product, which does not give it a competitive advantage.

[0037] In summary, the currently disclosed methods for synthesizing (NH4)2[Pd(C2O4)2] and the preparation processes for cis-[Pd(NH3)2(C2O4)] generally suffer from low yields, low product purity, and, in particular, the inability to effectively control chloride ion content, making them unsuitable for industrial applications.

[0038] Therefore, there is an urgent need to develop an efficient batch synthesis method for (NH4)2[Pd(C2O4)2] to improve yield, control chlorine content (≤250ppm), reduce production costs, and realize the industrial application of the product. Summary of the Invention

[0039] The technical problem to be solved by this invention is:

[0040] To address the shortcomings of existing technologies for the synthesis of ammonium bis(oxalate)palladium(II)ate, such as low yield, low product purity, and especially the difficulty in controlling chloride ion content, this paper improves the synthesis method through repeated research and experiments based on previous studies. This method significantly increases the yield and product purity, reduces costs, and is suitable for mass industrial production.

[0041] This invention provides a novel synthetic method for ammonium bis(oxalate)palladium(II)ate, including a route and conditions, and comprising the following steps:

[0042] Using palladium chloride as a raw material and water as a solvent, the product is prepared through a three-step reaction. First, palladium chloride is dissolved in ammonia water to form a [Pd(NH3)4]Cl2 solution. Second, the [Pd(NH3)4]Cl2 solution reacts with H2C2O4 / (NH4)2C2O4 to generate the water-insoluble intermediate cis-[Pd(NH3)2(C2O4)]. Third, cis-[Pd(NH3)2(C2O4)] reacts quantitatively with H2C2O4 to obtain the target product (NH4)2[Pd(C2O4)2]. This invention overcomes the shortcomings of existing synthetic methods, significantly improves yield and product purity, and particularly overcomes the technical challenge of controlling chloride ions in the product.

[0043]

[0044] The chemical reactions involved are:

[0045]

[0046] Furthermore, in this technical route, the palladium compound PdCl2, which has the lowest production cost, is used as the starting material. At the same time, the entire synthesis process does not use chemical reagents containing other components that are harmful to the catalyst (such as other halogens, K, Na, P, S, etc.).

[0047] Furthermore, in this technical approach, a slightly excessive amount of ammonia is used to dissolve PdCl2, so that PdCl2 is almost entirely converted into water-soluble [Pd(NH3)4]Cl2.

[0048] Furthermore, in this technical route, the molar ratio of [Pd(NH3)4]Cl2 to H2C2O4 is 1:1 to ensure that one oxalic acid molecule can quantitatively neutralize the two amino ligands in the [Pd(NH3)4]Cl2 molecule. Simultaneously, (NH4)2C2O4 is added to increase the concentration of oxalate in the reaction solution, which is beneficial for the oxalate to replace the two amino ligands and form cis-[Pd(NH3)2(C2O4)]. Experiments have shown that a molar ratio of H2C2O4 to (NH4)2C2O4 of 1:1 to 1.2 yields the best results. Since cis-[Pd(NH3)2(C2O4)] is poorly soluble in water, it will precipitate from the reaction solution and be collected by filtration. Both the unreacted (NH4)2C2O4 and the generated NH4Cl are soluble in water and can be separated by thorough washing with water, ensuring that the chloride ion content in the final product (NH4)2[Pd(C2O4)2]•2H2O is less than 100ppm.

[0049] Furthermore, in this technical route, the molar ratio of cis-[Pd(NH3)2(C2O4)] to H2C2O4 is 1:1. The inventors have discovered that cis-[Pd(NH3)2(C2O4)] can undergo a quantitative reaction with H2C2O4; that is, 1 mol of cis-[Pd(NH3)2(C2O4)] can completely dissolve in a hot aqueous solution containing 1 mol of H2C2O4, forming a clear red (NH4)2[Pd(C2O4)2] pure solution. This solution is freeze-dried or concentrated to dryness under reduced pressure at 50°C to obtain a powdery, earthy-yellow (NH4)2[Pd(C2O4)2]•2H2O product.

[0050] Furthermore, the reaction temperatures in the second and third steps are maintained at 45–60 °C to accelerate the reaction. Since oxalic acid has reducing properties and will reduce palladium(II) compounds at higher temperatures, the reaction temperature should not be too high. Experimental optimization has shown that the optimal temperature range is 45–60 °C.

[0051] Furthermore, the second step reaction needs to take 5-6 hours to ensure complete reaction and improve yield.

[0052] The synthesis method of this invention involves three chemical reactions: a solid-liquid reaction to generate a liquid-liquid reaction, a liquid-liquid reaction to generate a solid-liquid reaction, and a solid-liquid reaction to generate a single substance solution. This method overcomes the shortcomings of existing technologies and significantly improves the yield (over 95%) and purity of ammonium bis(oxalate)palladium(II)ate synthesis. In particular, the chloride ions, which are harmful to the catalytic reaction, can be controlled below 100 ppm, thereby greatly reducing costs and making it easier to achieve mass industrial production. Attached Figure Description

[0053] Figure 1Thermogravimetric analysis curve of ammonium bis(oxalate)palladium(II)ate (sample number: Pd-X5) prepared by the method of the present invention in argon atmosphere.

[0054] Figure 2 UV spectrum of the aqueous solution of ammonium bis(oxalate)palladium(II) acid prepared by the method of the present invention (C=1.17mmol / L).

[0055] Figure 3 Infrared spectrum (KBr pellet) of ammonium bis(oxalate)palladium(II)ate prepared by the method of this invention.

[0056] Figure 4 : DMSO of the ammonium bis(oxalate)palladium(II) acid prepared by the method of this invention. Detailed Implementation

[0057] Example 1: Preparation of intermediate cis-[Pd(NH3)2(C2O4)]

[0058] 100 g (0.565 mol) of PdCl2 was suspended in 220 mL of distilled water. 180 mL of concentrated ammonia solution with a content of 25-28% (about 5% excess) was slowly added. The mixture was stirred at 60 °C until almost all of the palladium chloride was dissolved. The solution was filtered to remove a small amount of insoluble residue, and a pale yellow solution was obtained. The solution was concentrated to dryness under reduced pressure at 60 °C to remove excess ammonia solution. The solution was then dissolved in 500 mL of distilled water to obtain a pure [Pd(NH3)4]Cl2 solution.

[0059] 72 g of H₂C₂O₄·2H₂O (0.565 mol) and 80 g of (NH₄)₂C₂O₄·H₂O (0.565 mol) were weighed and dissolved in 500 mL of hot distilled water at 60 °C. The above [Pd(NH₃)₄]Cl₂ solution was added dropwise under stirring, resulting in a pale yellow precipitate. The reaction was continued at 60 °C for 5 hours with stirring. After cooling to room temperature, the precipitate was collected by filtration, washed twice with distilled water and ethanol respectively, and dried at 60 °C for 4 hours to obtain 124 g of cis-[Pd(NH₃)₂(C₂O₄)], with a yield of 96%. The Pd content was determined to be 46.4% by hydrogen reduction-gravimetric method, consistent with the theoretical calculation of 46.6%. The chlorine content was determined to be 155 ppm by ion chromatography.

[0060] Example 2: Preparation of intermediate cis-[Pd(NH3)2(C2O4)]

[0061] 100 g (0.565 mol) of PdCl2 was suspended in 220 mL of distilled water. 180 mL of concentrated ammonia solution with a content of 25-28% (about 5% excess) was slowly added. The mixture was stirred at 60 °C until almost all of the palladium chloride was dissolved. The solution was filtered to remove the small amount of insoluble residue, and a pale yellow solution was obtained. The solution was concentrated to dryness under reduced pressure at 60 °C to remove the excess ammonia solution. Then it was dissolved in 500 mL of distilled water to obtain the [Pd(NH3)4]Cl2 solution.

[0062] 72 g of H₂C₂O₄·2H₂O (0.565 mol) and 96 g of (NH₄)₂C₂O₄·H₂O (0.678 mol) were weighed and dissolved in 600 mL of hot distilled water at 60 °C. The above [Pd(NH₃)₄]Cl₂ solution was added dropwise under stirring, resulting in a pale yellow precipitate. The reaction was continued at 60 °C for 6 hours with stirring. After cooling to room temperature, the precipitate was collected by filtration, washed twice with distilled water and ethanol respectively, and dried at 60 °C for 4 hours to obtain 127 g of cis-[Pd(NH₃)₂(C₂O₄)], with a yield of 97%. The Pd content was determined to be 46.2% by hydrogen reduction-gravimetric method, consistent with the theoretical calculation of 46.6%. The chlorine content was determined to be 144 ppm by ion chromatography.

[0063] Example 3: Synthesis of (NH4)2[Pd(C2O4)2]•2H2O

[0064] Weigh 66.2 g (0.525 mol) of H₂C₂O₄·2H₂O and dissolve it in 350 mL of distilled water at 55 °C. Add 120 g (0.525 mol) of cis-[Pd(NH₃)₂(C₂O₄)] in portions, stirring continuously until almost all of cis-[Pd(NH₃)₂(C₂O₄)] is dissolved. Filter to remove any insoluble residue, yielding a brownish-red solution. Concentrate to dryness under reduced pressure at 55 °C, and then further dry under vacuum at 55 °C to obtain 184 g of the yellowish-brown product (NH₄)₂[Pd(C₂O₄)₂]•2H₂O, with a yield of 99%. The sample was sent for palladium and chlorine content determination. Results: Pd 29.8% (consistent with the theoretical calculation of 30.0%), Cl - Content: 97 ppm.

[0065] Example 4: Synthesis of (NH4)2[Pd(C2O4)2]•2H2O

[0066] Weigh 66.2 g (0.525 mol) of H₂C₂O₄·2H₂O and dissolve it in 350 mL of distilled water at 50 °C. Add 120 g (0.525 mol) of cis-[Pd(NH₃)₂(C₂O₄)] in portions, stirring continuously until almost all of cis-[Pd(NH₃)₂(C₂O₄)] is dissolved. Filter to remove any insoluble residue, yielding a brownish-red solution. Freeze-dry to obtain 187 g of the yellowish-brown product (NH₄)₂[Pd(C₂O₄)₂]•2H₂O, with a yield close to 100%. The sample was sent for palladium and chlorine content determination and structural analysis. Results: Pd 29.6% (consistent with the theoretical calculation of 30.0%), Cl - Content: 88 ppm.

[0067] The structural test results and characterization of the ammonium bis(oxalate)palladium(II)ate of this invention:

[0068] (1) Pd content analysis (hydrogen reduction-gravimetric method): theoretical value (%): 30.0%; measured value (%): 29.6%. The measured value and the theoretical value are consistent.

[0069] (2 Thermogravimetric analysis TG-DTA (in an inert atmosphere, such as...) Figure 1 As shown): In argon gas, at T=102℃, the endothermic peak shows a weight loss of 9.06%, which is equivalent to the loss of 2 water molecules of crystallization, basically consistent with the theoretical weight loss rate (10.1%); at T>223℃, endothermic decomposition occurs, with a residual amount of 29.1%, equivalent to the content of metallic palladium, basically consistent with the theoretical value (30.0%) (Note: The relative error of thermogravimetric analysis is relatively large).

[0070] (2) Visible-ultraviolet spectrum UV-Vis (H2O, such as Figure 2 As shown): λmax = 380 nm, ε = 1.11 × 10⁻⁶ 2 l / mol cm -1 , belonging to the dd transition of Pd(Ⅱ).

[0071] (3) Infrared spectrum IR (cm) -1 , KBr, such as Figure 4 shown): 3528, 3464 [vs, ν(OH), H2O)], 3246[w, ν(NH), NH4 + )], 1702 [vs,ν as (COO - )], 1410 [(s,ν as (COO - )], 1320, 1256 [vs, γ(COO - )+δ(NH4+ )], 903, 825 [γ(NH4) + ) + δ(COO - )], 569 [m, ν(Pd-O)], 483 [m, five-membered chelate ring oscillation].

[0072] (4) Carbon nuclear magnetic resonance spectrum ( 13 C NMR, 400MHz, DMSO, such as Figure 3 As shown), chemical shift (ppm): the multiplet at 39 ppm is attributed to the solvent DMSO, and a resonance peak at 167 ppm is attributed to the carbon on the carboxyl group.

[0073] Elemental analysis, UV-Vis, IR spectroscopy, and carbon spectroscopy results indicate that the sample is consistent with the structure of (NH4)2[Pd(C2O4)2]•2H2O.

[0074] In summary, the embodiments of the present invention provide a new method for synthesizing ammonium bis(oxalate)palladium(II)ate, which has the advantages of simple operation, high conversion rate, high product purity and low cost, and is suitable for mass industrial production.

[0075] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing ammonium bis(oxalate)palladium(II)ate, characterized in that, This method uses palladium chloride as a raw material and water as a solvent to prepare the product through a three-step reaction. The three-step reaction is as follows: First, palladium chloride is dissolved in ammonia water to form a [Pd(NH3)4]Cl2 solution; Second, [Pd(NH3)4]Cl2 reacts with H2C2O4 / (NH4)2C2O4 to generate a water-insoluble intermediate cis-[Pd(NH3)2(C2O4)]; Third, cis-[Pd(NH3)2(C2O4)] reacts quantitatively with H2C2O4 to obtain (NH4)2[Pd(C2O4)2]·2H2O, and the reaction formula is as follows: 。 2. The synthesis method according to claim 1, characterized in that, In the second step reaction, the molar ratio of H2C2O4 to (NH4)2C2O4 is 1:1 to 1.2, and the molar ratio of H2C2O4 to [Pd(NH3)4]Cl2 is 1:

1.

3. The synthesis method according to claim 1, characterized in that, The molar ratio of cis-[Pd(NH3)2(C2O4)] to H2C2O4 in the third step reaction is 1:

1.

4. The synthesis method according to claim 1, characterized in that, The second step reaction is carried out at a temperature of 45-60℃ for 5-6 hours.

5. The synthesis method according to claim 1, characterized in that, The temperature of the third step reaction is 45~60℃.

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