RU2333195C1 - Method for obtaining palladium acetate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention concerns platinum-group metal salt synthesis, particularly of palladium salts, namely palladium (II) acetate applied as catalyst or for obtaining basic salt for production of other palladium salts. The method for obtaining palladium acetate involves dissolution of metal palladium in concentrated nitric acid, filtration and evaporation of palladium nitrate solution and reaction with acetic acid, where after evaporation but prior to palladium (II) nitrate crystallisation the palladium nitrate solution is processed by distilled water in the volume of (2-5) l per 1 kg of palladium in the initial nitrate solution, then by acetic acid diluted with water, with acid concentration of (30-70)% and volume of (1.5-2.5) l of acetic acid per 1 kg of palladium in the initial nitrate solution, the resulting solution being matured for at least 8 hours at (15-40)°C.

EFFECT: streamlined method for obtaining palladium (II) acetate and its synthesis in monophase condition without admixture of insoluble polymeric palladium (II) acetate and palladium (II) nitritoacetate.

2 cl, 1 tbl, 1 ex

Description

The invention relates to the field of chemistry of platinum metals, in particular the synthesis of palladium compounds, namely the synthesis of palladium acetate used as a catalyst, for example, to obtain vinyl acetate or a starting salt to obtain other salts of palladium, for example, to obtain palladium acetylacetonate.

A known method of producing palladium (II) acetate by dissolving palladium oxide in acetic acid. Palladium oxide is obtained from palladium hydroxide precipitated from palladium chloride solution with sodium hydroxide (Korean Patent No. KR 8904783, 1989). The disadvantage of this method is the incomplete dissolution of palladium oxide in acetic acid, which requires an additional filtering operation. In this case, palladium hydroxide obtained by precipitation with alkali requires a special isolation method.

A known method of producing palladium acetate by dissolving palladium black in a mixture of glacial acetic acid and concentrated nitric acid in an inert atmosphere (Japanese Patent No. JP 61047440, 1986). The disadvantage of this method is the need for the presence of excess palladium black throughout the process, which requires crystallization of the solution from black before crystallizing the product. The absence of excess palladium black leads to the formation of an oxidizing medium in the solution (due to the presence of nitric acid or nitrogen oxygen compounds), which contributes to the formation of polymeric palladium (II) polymer insoluble in acetic acid and organic solvents [Pd (СН ₃ СОО) ₂ ] _n .

A known method of producing palladium (II) acetate by reacting one stripped off nitric acid solution of palladium with acetic acid at room temperature, filtering the precipitate formed and heating it in a mixture of acetic acid and ethyl acetate, and then heating in acetic acid (Russian Patent No. 2288214). The disadvantage of this method is the staged process for the production of palladium (II) acetate. An intermediate stage of the process is the isolation of palladium (II) nitritoacetate [Pd ₃ (СН ₃ СОО) ₅ NO ₂ ], upon the release of which the presence of nitric acid is inevitable, which contributes to the dissolution of palladium (II) nitritoacetate. The process of converting palladium (II) nitritoacetate to palladium (II) acetate [Pd ₃ (СН ₃ СОО) ₆ ] is characterized by a duration and requires a high temperature. Under such conditions, the formation of nitrogen oxides, which have oxidizing ability and are catalysts for the conversion of soluble palladium (II) acetate [Pd ₃ (CH ₃ COO) ₆ ] to insoluble palladium (II) acetate [Pd (CH ₃ COO) ₂ ] _n . To suppress the oxidizing ability of nitrogen oxides, ethyl acetate is introduced into the solution, the drawback of which is the interaction with water to form ethyl alcohol, which is able to reduce palladium (II) acetate to metallic palladium.

A known method of producing palladium (II) acetate by reacting hydrated palladium (II) oxide with acetic acid. Hydrated palladium (II) oxide is obtained by hydrolysis of a nitric acid solution of palladium nitrate with an aqueous solution of NaOH and repeated decantation of the precipitate formed (US Patent No. 3318891, 1967). This method is adopted as a prototype.

The disadvantage of this method is the incomplete dissolution of hydrated palladium (II) oxide in acetic acid and the stages of the whole process, which complicates the implementation. Moreover, the hydrated palladium (II) oxide used is contaminated with alkali, which cannot be completely removed by repeated decantation. The presence of sodium acetate in an acetic acid solution of palladium acetate leads to the formation of anionic complexes of the type [Pd (CH ₃ COO) ₄ ] ^2- and [Pd ₂ (CH ₃ COO) ₆ ] ^2- , which, in an aqueous solution of acetic acid, are able to recover when heated to metal.

The technical result to which the invention is directed is to simplify the process of producing palladium (II) acetate and to obtain it in a monophasic state [Pd ₃ (СН ₃ СОО) ₆ ] without impurities of polymer palladium (II) acetate catena-poly- [Pd ( CH ₃ COO) ₂ ] _n and palladium (II) nitritoacetate [Pd ₃ (CH ₃ COO) ₅ NO ₂ ].

The desired technical result is achieved in that the palladium nitrate solution after evaporation, before crystallization of the palladium (II) nitrate salt begins, is treated with distilled water and then diluted with water (30-70%) acetic acid at a temperature of (15-40) ° С with a flow rate ( 2-5) l of distilled water per 1 l of prepared nitric acid solution and (1.5-2.5) l of acetic acid per 1 kg of palladium in solution.

The essence of the method is that the synthesis of palladium (II) acetate is carried out by replacing the nitrate group in the complex palladium nitrate with acetate. Since nitric acid is formed during the reaction, water is introduced into the solution to suppress nitration. Moreover, water is also necessary to suppress nitrosation. Since the initial nitric acid solution of palladium was obtained by dissolving metallic palladium in nitric acid, dissolved nitrogen oxides, which contribute to nitrosation, are present in such a solution. The process without the presence of water is characterized by the formation of nitrosated palladium acetate - palladium nitritoacetate [Pd ₃ (CH ₃ COO) ₅ NO ₂ ].

In the course of the studies, it was found that for the process of obtaining palladium (II) acetate from a dilute nitric acid solution of palladium by replacing the complex-bound nitrate group with acetate by the introduction of acetic acid, the optimal conditions are:

- the temperature of dilution of the nitric acid solution of palladium with distilled water is not more than 40 ° C;

- flow rate of distilled water per 1 liter of the initial prepared nitric acid solution (2-5) l;

- dilution with water of acetic acid to its mass content (30-70%);

- the temperature of the interaction of diluted acetic acid with a nitric acid solution of palladium (15-40) ° C;

- consumption of glacial acetic acid per 1 kg of palladium in a nitric acid solution (1.5-2.5) l;

- the duration of the crystallization process of palladium (II) acetate with stirring the reaction solution for at least 8 hours

An increase in the dilution temperature of one stripped off nitric acid solution of more than 40 ° С leads to partial hydrolysis of complex palladium nitrate, which, ultimately, leads to the appearance of an impurity of palladium hydroxide.

The consumption of added water of less than 2 liters per 1 liter of the prepared palladium nitrate solution leads to the appearance of nitration and nitrosation reactions in the solution, which ultimately leads to the appearance of impurities of polymer palladium (II) acetate or palladium (II) nitroacetate. An increase in the flow rate of added distilled water of more than 5 liters per 1 liter of the prepared palladium nitrate solution increases the amount of the reaction solution, which requires a larger reactor volume, as well as an increase in the solubility of the product.

An increase in dilution with water of glacial acetic acid to its mass content of less than 30% leads to a decrease in its reactivity, which ultimately leads to a decrease in the yield of the product. A decrease in dilution of glacial acetic acid with water to its mass content of more than 70% can lead to nitrosation processes, which ultimately leads to the isolation of the palladium nitritoacetate complex or its contamination of the main product.

An increase in the temperature of introducing dilute acetic acid into a palladium nitrate solution of more than 40 ° C leads to nitrosation or nitration, which causes the appearance of an impurity of the nitrite acetate or polymer acetate complex of palladium.

The consumption of added acetic acid of less than 1.5 liters per 1 kg of palladium in a nitric acid solution leads to its lack and incomplete replacement of all palladium nitrate. An increase in the consumption of added acetic acid over 2.5 L per 1 kg of palladium in a nitric acid solution leads to an increase in the amount of solution and dissolution of the product in it.

Reducing the duration of the substitution process less than 8 hours leads to incomplete crystallization of the product.

An increase in the temperature of the interaction of water and acetic acid with a palladium nitrate solution of more than 40 ° С leads to the manifestation of nitration and nitrosation reactions in the solution, which ultimately leads to the appearance of an impurity of polymer palladium (II) acetate or palladium (II) nitritoacetate. A decrease in temperature below 15 ° C slows down the exchange interaction, which increases the duration of the process.

Examples of the method

As a starting product for experiments No. 1-28 (table 1) for the production of palladium (II) acetate, a solution of palladium nitrate was prepared by dissolving metallic palladium in nitric acid and evaporating it. The palladium content in the solution is 500 g / l, free nitric acid - 200 g / l.

Example 1

To a certain volume of the prepared palladium nitrate solution, the calculated volume of distilled water was added, and then the solution was diluted with acetic acid water and mixed. The precipitate of palladium (II) acetate was recovered by filtration, washed with distilled water, unloaded onto a baking sheet and dried at 40 ° C for 24 hours. The precipitate was weighed, analyzed for palladium content and the phase composition was determined. The mother liquor was sent for regeneration. The experimental data are shown in table 1.

As can be seen from the above examples, the use of the proposed method allows to obtain palladium (II) acetate in a monophasic state and to eliminate the appearance of an impurity of insoluble polymer palladium (II) acetate and palladium (II) nitritoacetate compounds.

Claims (2)

1. A method of producing palladium acetate, comprising dissolving palladium metal in concentrated nitric acid, evaporating the resulting solution and reacting with acetic acid, characterized in that the palladium nitrate solution after evaporation, before crystallization of the palladium (II) nitrate salt begins, is treated with distilled water in volume in (2-5) l per 1 kg of palladium in the initial nitric acid solution, then diluted with water with acetic acid (30-70%) with a flow rate (1.5-2.5) l of acetic acid per 1 kg of palladium in the initial nitric acid th solution and the resulting solution was allowed to stand for at least 8 hours at a temperature (15-40) ° C. 2. The method according to claim 1, characterized in that the evaporation of the nitric acid solution of palladium is carried out to a palladium content of 500 g / l and a free nitric acid of 200 g / l.