RU2127250C1 - Process for preparing 2-metal ethyl hexanoates - Google Patents

Abstract

FIELD: electrochemical synthesis of organic compounds, more particularly manufacture of polymeric materials as stabilizers and modifying additives. SUBSTANCE: 2-metal ethylhecanoates are prepared by anodic dissolution of corresponding metals in organic solvent in the presence of 2-ethylhexanic acid and conducting additive. Electrolysis is carried out in anion-exchange electrolyzer solvent being methanol and additive being 2- ethylhexanic acid ammonium salt. Process is conducted by periodically adding 2-ethylhexanic acid as the latter in being consumed. Use of conducting additive having anion with anion of the desired product makes it possible to prepare 2-lead and bismuth ethylhexanoates with high yield and high purity. EFFECT: more efficient preparation process. 4 cl, 6 ex

Description

 The invention relates to the field of electrochemical synthesis of organic compounds, in particular 2-ethylene hexanoates of metals, which, among other salts of aliphatic acids, are widely used in the manufacture of polymeric materials. They can serve as stabilizers and modifying additives, often allowing you to change the rheological properties of polymeric materials. Many 2-ethylhexanoates soluble in non-polar organic solvents are used as additives for dyes, varnishes, lubricants, catalysts for organic reactions, and fuel additives. At the same time, in recent years, a completely new field of application of salts of aliphatic acids has been intensively developed, associated with their use as starting materials for applying complex oxide films by the decomposition of organic metal compounds (MOD). It turned out that precisely 2-ethylhexanoates of metals are the most convenient precursors for the preparation of complex oxides by this method. The use of 2-ethylhexanoates as starting materials in microelectronics presents significantly different, very high requirements for the purity of these substances.

 Alkali metal 2-ethylhexanoates are obtained by saponification of acids. At the same time, as a rule, two main methods are used to obtain salts of less active metals. The first is called the double decomposition method and includes two stages: first, a soluble alkali metal or ammonium salt is obtained, and then this salt is reacted with a salt of a heavier metal. In this case, a water-insoluble salt of a heavy metal precipitates (AS Shaikh, GM Vest J. Amer Ceram. Soc. V. 69, N 9, 682 (1986). In another, even more common method, usually used to obtain derivatives Group II metals, acids are reacted with metal oxides or hydroxides.After an intense exothermic reaction, usually carried out in an autoclave, is completed, a cake is obtained, which is then ground (US 2899232, EP 0086362). features for obtaining soluble in organic sol organic acid salts, it is limited.The method of double decomposition, in addition to the use of rather expensive soluble salts, is also associated with the use of very complex equipment, the final products are contaminated with reaction by-products that must be removed before using the salts.Methylation methods, which are cheaper, are not suitable to obtain the majority of derivatives of polyvalent elements (in practice, they can only be used to obtain derivatives of metals of group II).

 A direct method is also known for the preparation of salts of 2-ethylhexanoic acid soluble in organic solvents (US 2584041). This method involves the interaction of powders of lead, cobalt, manganese, iron, copper, zinc and nickel, as well as some other metals with aliphatic acids when heated and vigorously stirred in the presence of a substantial amount of water and oxygen. The solvents used are usually high boiling nonpolar organic solvents which are not miscible with water, most often white spirit. After completion of the reaction, water is distilled off from the reaction mixture, the solutions are filtered from possible residues of unreacted metal. Salts, as a rule, do not emit, the final products are solutions of salts in white spirit. Such solutions usually contain a large excess of acid (up to 25% by weight). In most cases, however, these reactions proceed slowly, with large induction periods, and are associated with the need to introduce a very large amount of water and a very large oxygen consumption. Subsequently, this method was modified using catalysts - ammonium salts (EP 0512342 A2) or alkali metals (EP 0094760) allowed to reduce the acid content in the final product, as well as the amount of water and oxygen required for the reaction, and to increase the efficiency of metal dissolution processes. However, the solutions in this case contain impurities of either an ammonium cation (and often the presence of ammonium salts causes a decrease in the catalytic activity of such solutions used as catalysts in dimerization processes in organic synthesis) or alkali metal cations, which excludes their use in microelectronics.

The closest in technical essence to the present invention is the electrochemical method of producing 2-ethylhexanoates, which allows, if necessary, to carry out a continuous process for the production of salts, and at the same time allows to obtain high-purity and high-quality products (N. Kumar, DG Tuck, and KD Watson Can. J. Chem, V. 65, 740 (1987). 2-Ethyl hexanoates Mn, Fe, Ni, Co, and Cu were prepared by anodically dissolving the corresponding metals as a metal foil in a conventional electrochemical cell with Pt as a cathode in acetonitrile or ace it in the presence of 2-ethylhexanoic acid, using as a conductive additive Et ₄ NClO _4. After the electrolysis selection 2-ethylhexanoate usually performed by removing the solvent in vacuo.

 However, this method is not applicable for the production of 2-ethylhexanoates of metals that are reduced at the cathode under electrolysis conditions, for example, in the synthesis of p-metals 2-ethylhexanoates of groups III-IV of the Periodic Table of the Elements, in particular lead and bismuth. So, during electrolysis in a cell similar to that described in [6], the dissolution of lead and bismuth anodes really intensively occurs. However, cations of lead and bismuth, moving to the cathode, are discharged with the release of the corresponding metals on the cathode. Thus, salt does not accumulate in solutions. In addition, the use of acetonitrile and acetone as solvents in this method greatly reduces the choice of an electrically conductive additive and makes it necessary to use tetraethylammonium perchlorate for this purpose, which pollutes the target products with chlorine.

 The aim of the invention is to develop an electrochemical method for producing 2-ethylhexanoates of metals that are reduced at the cathode, and to increase the purity of the target products.

 This goal is achieved in that the anodic dissolution of the corresponding metals in an organic solvent in the presence of 2-ethylhexanoic acid and an electrically conductive additive is carried out in an electrolyzer with an anion exchange membrane, methanol is used as a solvent, and the ammonium salt of 2-ethylhexanoic acid is used as an electrically conductive additive, and the process is carried out with the periodic addition of 2-ethylhexanoic acid as it is consumed.

 The essence of the method is as follows. A solution of ammonium 2-ethylhexanoate in methanol and 2-ethylhexanoic acid are placed in an electrolyzer with an anion exchange membrane. The anion-exchange membrane prevents metal ions formed during the anodic dissolution and recovery of the metal ions generated by the anodic dissolution, and the passage of electric current in the electrolyte is carried out by 2-ethylhexanoic acid anions passing from the catholyte through the anion-exchange membrane in an amount equivalent to the dissolved metal, which leads to the accumulation of salt in the anolyte. Anions of 2-ethylhexanoic acid removed from catholyte must be replenished by introducing portions of 2-ethylhexanoic acid into the catholyte. The portioned addition of 2-ethylhexanoic acid to the catholyte is due to the fact that upon a single addition, a sharp decrease in the conductivity of the solution occurs and the electrolysis ceases. The use of an anion exchange membrane for the implementation of electrochemical synthesis processes in alcohol solutions is not described.

 The use of an electrically conductive additive having an anion of the same name as the anion of the target product determines the absence of contamination of the target product with extraneous anions.

In the preparation of lead and bismuth salts, the concentration of 2-ethylhexanoic acid has a very large influence on the course of electrolysis. If the acid concentration in the anolyte is less than 5% by volume during the preparation of the lead salt, the precipitate of lead alkoxocarboxylate Pb (CH ₃ O) (C ₇ H ₁₅ COO) precipitates from the solution during electrolysis. When carrying out electrolysis with an acid concentration above 5 volume% at a temperature of 50-55 ^o C in the reaction volume, sufficiently high salt concentrations are achieved. In the synthesis of bismuth 2-ethylhexanoate, a lack of acid in the solution leads to atomization of the anode, and its surface is covered with a loose layer of sponge. The optimal concentration of acid in the anolyte is 5-10 volume%. When this concentration is converted, the anode becomes covered with a whitish-yellow coating, which leads to the attenuation of the electrochemical process.

 The invention is illustrated by the following examples.

 Example 1

To obtain lead 2-ethylhexanoate, an electrochemical reactor (electrolyzer) is used, which is a glass cylindrical vessel with a jacket for temperature control, a lid and a tap for the cathode chamber. The cathode chamber is a fluoroplastic cylinder with a union nut, the bottom of which is the MA-40 ion-exchange membrane. On the lid of the electrolyzer are taps for a thermometer, reflux condenser and anode. The anode is a lead plate with an area of 3 cm ² , the cathode is a graphite rod with an area of 3 cm ² . The volume of the anode space is 100 ml, and the volume of the cathode space is 30 ml.

100 ml of a methanol solution containing 0.5 g of ammonium 2-ethylhexanoate and 5 ml of 2-ethylhexanoic acid (5% by volume) are placed in the anode chamber of the electrolyzer. 30 ml of a methanol solution containing about 0.5 g of ammonium 2-ethylhexanoate and 3 ml of 2-ethylhexanoic acid are placed in a cathode chamber. The electrolysis is carried out at a temperature of 55 ^o C and a current strength of 0.070 A for 6 hours, 5 ml of 2-ethylhexanoic acid was added to the catholyte every 3 hours. After electrolysis is complete, the solution is cooled to room temperature (20-22 ^° C), the precipitate formed is filtered off, recrystallized from methanol and dried in a vacuum oven at a residual pressure of 1-5 mm Hg. and a temperature of 50-60 ^o C for 7-8 hours. 2.9 g of a colorless glassy liquid Pb (C ₇ H ₁₅ COO) _{2 are} obtained; the yield of the substance was 75.1%.

Found: Pb 41.81 C 38.94 H 6.10
Calculated for Pb (C ₇ H ₁₅ COO0 ₂ ): Pb 41.98 C 38.90 H 6.08
The filtrate and catholyte can be used for the next synthesis.

Example 2
Under the conditions described in example 1, an electrolysis of a solution containing 7.5 ml of 2-ethylhexanoic acid is carried out. After isolation, similar to that described in example 1, receive 3.3 g of 2-ethylhexanoate lead; the yield on the substance is 85.5%.

Example 3
Under the conditions described in example 1, electrolysis of a solution containing 10 ml of 2-ethylhexanoic acid is carried out. After isolation, carried out analogously to that described in example 1, 3.1 g of lead 2-ethylhexanoate are obtained; the yield of the substance is 80.3%.

Example 4
The synthesis is carried out in the electrolyzer described in Example 1 at 60 ^° C. 100 ml of a methanol solution are placed in the anode chamber. Containing 10 ml of 2-ethylhexanoic acid and about 1.6 g of ammonium 2-ethylhexanoate. The anode is made by casting bismuth in the form of a plate with an immersion surface area of 10 cm ² . 30 ml of a methanol solution containing about 0.5 g of ammonium 2-ethylhexanoate and 3 ml of 2-ethylhexanoic acid are placed in a cathode chamber with a graphite cathode. The process is carried out at a current strength of 0.100 A for 20 hours, adding every 3 hours 2 ml of 2-ethylhexanoic acid to the cathode space.

After electrolysis, the anolyte is filtered, the mother liquor is cooled to a temperature of 0-2 ^o C, the crystals are separated on a vacuum filter, washed with methanol and dried in a vacuum oven at a residual pressure of 1-5 mm Hg and a temperature of 50-60 ^o C for 7-8 hours. Obtain about 14.3 g of a colorless glassy liquid Bi (C ₇ H ₁₅ COO) ₃ .

Found: Bi 32.63 C 45.20 H 7.20
Calculated for Bi (C ₇ H ₁₅ COO) ₃ : Bi 32.69 C 45.10 H 7.19
The yield on the substance is 89.9%
The mother liquor after filtration and washing (about 83 g) and catholyte can be used for the next synthesis.

Example 5
Under the conditions described in example 4, an electrolysis of a solution containing 7.5 ml of 2-ethylhexanoic acid is carried out. After isolation, similar to that described in example 4, receive 14.8 g of bismuth 2-ethylhexanoate. The yield on the substance is 93.1%.

Example 6
Under the conditions described in example 4, electrolysis of a solution containing 5 ml of 2-ethylhexanoic acid is carried out. After isolation, similar to that described in example 4, receive 14.2 g of bismuth 2-ethylhexanoate; the yield of the substance is 89.3%.

 Thus, the proposed method allows to obtain 2-ethylhexanoates of lead, bismuth with a high yield and a high degree of purity, due to the absence of extraneous ions.

References
1. AS Shaikh, GM Vest J. Amer. Ceram. Soc. v. 69, No. 9, 682 (1986).

 2. Pat. U.S. 2,899,232; European patent 0,086,362.

 3. Pat. U.S. 2,584,041.

 4. European patent 0,512,346 A2.

 5. European patent 0,094,760.

 6. N. Kumar, D.G. Tuck, and K.D. Watson, Can, J. Chem. v. 65, 740 (1987) is a prototype.

Claims (3)

 1. The method of producing 2-ethylhexanoates of metals by electrochemical dissolution of the anodes from the corresponding metals in an organic solvent in the presence of 2-ethylhexanoic acid and an electrically conductive additive, followed by isolation of the target product from the electrolyte, characterized in that the electrolysis is carried out in an electrolyzer with an anion exchange membrane as a solvent use methanol, and as an electrically conductive additive - ammonium salt of 2-ethylhexanoic acid and the process is carried out with the periodic addition of 2- tilgeksanovoy acid as it is consumed.  2. The method according to claim 1, characterized in that the metals used are lead, bismuth.  3. The method according to claim 1, characterized in that the concentration of 2-ethylhexanoic acid in the initial solution is 5 to 10 volume%.