JPH021082B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining iodine by oxidizing ammonium iodide. Iodine is widely used as an intermediate in organic synthesis, catalysts, medicines, health drugs, fungicides, household feed additives, organic compound stabilizers, dyes, photoengraving, agricultural chemicals, rare metal scouring, and analytical reagents. It is a useful compound. Brine water, which generally comes out with natural gas,
Obtained from chili saltpeter. Industrially, many methods are used to oxidize iodine anions contained in salt water using an aqueous solution of copper sulfate () and iron sulfate (). Since this method is usually carried out under strong acidic conditions, salts of strong acids and strong alkalis such as sodium sulfate are produced as by-products, which poses problems in their treatment. Methods for obtaining iodine from ammonium iodide include a method using electrolysis (U.S. Pat. No. 3,975,439) and a method using a cupric compound (Japanese Patent Application Laid-open No. 50122-1989).
method by oxygen oxidation (Japanese Patent Application Laid-open No. 53-73489)
(No. Publication), etc. In the method using electrolysis (U.S. Pat. No. 3,975,439), the reaction is carried out in a dilute solution and a diaphragm is required, making the equipment large-scale and consuming a large amount of electricity, making it difficult for industrial use. This cannot be said to be an advantageous method. In the method using a cupric compound (JP-A-53-50122), since the reaction is stoichiometric, the cupric compound does not act as a catalyst and is disadvantageous for producing a large amount of iodine. In the method using oxygen oxidation (Japanese Unexamined Patent Publication No. 53-73489), ammonium iodide is oxidized with oxygen in an ammonia aqueous solution using a copper compound as a catalyst to obtain iodine. In this method, the iodine production reaction is carried out under ammoniacal alkaline conditions, so the rate of iodine production is extremely slow, and as ammonia is produced along with the production of iodine, it is expected that the reaction will become even slower. . Furthermore, under ammoniacal alkaline conditions, explosive nitrogen iodide is likely to be produced, as is clear from the Chemistry Encyclopedia (Kyoritsu Shuppan, Vol. 9, p. 447), and this cannot be said to be industrially advantageous. The present inventors had been considering a method of obtaining iodine by oxidizing ammonium iodide, but by combining a weak acid of a copper compound, ammonium iodide could be oxidized in the presence of molecular oxygen. The inventors have discovered that iodine can be obtained in high yield without by-products such as nitrogen iodide, and have arrived at the present invention. That is, the present invention is based on the above findings, and when ammonium iodide is oxidized with oxygen or air to obtain molecular iodine, the oxidation reaction is performed using at least one selected from the group consisting of copper compounds and This is a method for producing iodine in an aqueous medium containing a weak acid. In particular, the present invention uses a weak acid to obtain a sufficient rate of iodine production, and then extracts the generated iodine or consumes it in an appropriate reaction to remove the iodine from the system. By thermally decomposing the ammonium salt of a weak acid, recovering the weak acid, and reusing it in the iodine production reaction,
This provides a highly efficient method of obtaining iodine. Using the reaction of the present invention using a copper compound and ammonium dihydrogen phosphate as an example, it is estimated that iodine is produced by the following reaction mechanism. Cu ⁺ +NH ₄ ICuI+NH ₄ ⁺ Cu ²⁺ +2NH ₄ ICuI ₂ +2NH ₄ ⁺ 2CuI+1/2O ₂ +2NH ₄ I+H ₂ O →2CuI ₂ +2NH ₄ OH 2CuI ₂ →2CuI+I ₂ 2NH ₄ OH+2NH ₄ H ₂ PO ₄ →2(NH ₄ ) ₂ HPO ₄ +2H ₂ O Therefore, the copper compound used as a catalyst is considered to be simply a source of copper ions, and the type of anion side of the copper compound has no relation to the nature of the reaction, and there are no special restrictions. It is thought that there is no. There are no particular limitations on the copper compound, and most copper compounds are used, but examples include cuprous iodide, cuprous chloride, cuprous oxide, cuprous bromide, cuprous cyanide, copper sulfate, and cuprous chloride. di-copper,
Preferable examples include cupric hydroxide, cupric oxide, cupric bromide, cupric phosphate, copper nitrate, copper carbonate, and copper acetate.
The amount of the copper compound used is not particularly limited, but in practice it is preferably 3 x 10 ^-4 to 0.3 mol per 100 g of water. Furthermore, the copper compound may or may not be dissolved in the aqueous medium. The amount of ammonium iodide used is not particularly limited, but the higher the concentration in the aqueous medium, the faster the rate of iodine production tends to be. Practically preferred is 10 to 200 g per 100 g of water. As for the oxygen used, not only oxygen gas but also air can be used to achieve the purpose of this method.
The oxygen pressure or partial pressure is not particularly limited, but the higher the pressure, the faster the iodine production rate tends to be.
In practical terms, it is preferably 0.2 to 10 atm. The higher the temperature, the faster the oxidation reaction, but if the temperature is too high, the ammonium salt of the weak acid will decompose, increasing the ammonia concentration in the system and slowing down the oxidation. Usually, preferably between room temperature and 100°C. The weak acid is used to react with ammonia produced by the iodine production reaction, keep the pH in the system low, accelerate the oxidation reaction rate, and prevent the production of nitrogen iodide. Further, it is preferable to thermally decompose the ammonium salt of the weak acid produced as necessary, recover the weak acid, and reuse it in the iodine generation reaction. The weak acid used may be one that releases ammonia when the ammonium salt is heated.
Preferred examples include inorganic acids such as phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, boric acid, arsenic acid, chromic acid, telluric acid, and silicic acid, and organic acids such as acetic acid and propionic acid. Phosphoric acid, ammonium dihydrogen phosphate, and organic acids. Further, in the case of ammonium dihydrogen phosphate, when the ammonium salt thereof, ammonium monohydrogen phosphate, is heated, ammonia is quantitatively released in a short period of time and returns to ammonium dihydrogen phosphate, which is particularly preferred. In order to recover the weak acid in the present invention, the generated iodine is removed from the system by extraction with ether or a suitable iodine consumption reaction, and then the aqueous medium containing the generated ammonium salt of the weak acid is heated. good. The weak acid recovered here can be used again as a raw material for the iodine production reaction, and there is no particular need to add new acid. The higher the decomposition temperature of the ammonium salt of a weak acid, the better the decomposition rate and decomposition rate, and is preferably 100 to 210°C. The main aqueous medium used in the present invention is water alone, but substances that do not substantially react with iodine in this system, such as benzene and chlorobenzene, can be used in combination with water. The hydrogen ion concentration of the aqueous medium is not limited as it varies depending on the acid used and conditions, but the higher the hydrogen ion concentration, the faster the iodine production rate tends to be. The method of the present invention is an extremely advantageous industrial method for producing iodine that produces iodine at a high rate, has a good yield, can recover and reuse weak acids, does not produce by-products such as nitrogen iodide, and does not generate industrial waste. I can say it. In addition, the method of the present invention can also be applied to a method for obtaining useful iodide without purifying and isolating iodine, if the iodination reaction is performed simultaneously with the generation of iodine. Furthermore, since ammonia is generated when the weak acid is recovered, it is possible to recover this ammonia and use it for other purposes if necessary. The present invention will be explained in more detail with reference to Examples below. In the following examples, the oxidation reaction is performed using a weak acid.
When using ammonium dihydrogen phosphate, the yield of iodine was determined from equation (2), assuming that the following equation (1) was followed. 1/2O ₂ +2NH ₄ I+2NH ₄ H ₂ PO ₄ Cu ⁺ or Cu ²⁺ ――――――――――→ I ₂ +2(NH ₄ ) ₂ HPO ₄ +H ₂ O (1) Iodine yield (%) = Number of moles of iodine generated/Number of moles of weak acid charged x 1/
2×100(2) Also, assuming that the thermal decomposition of a weak acid follows equation (3) when ammonium dihydrogen phosphate is used as the weak acid,
The recovery rate of weak acid was determined from equation (4). (NH ₄ ) ₂ HPO ₄ →NH ₄ H ₂ PO ₄ +NH ₃ (3) Recovery rate (%) = Number of moles of ammonia generated / Number of moles of ammonium salt of weak acid generated x 100 (4) Also, other weak acids Even when using , calculations were performed using equations (2) and (4). Example 1 (1) Generation of iodine 300 g (2.07 mol) of ammonium iodide and 5 g of copper iodide were placed in a 500 ml pressure-resistant glass autoclave.
(0.0263mol), ammonium dihydrogen phosphate 100g
(0.870mol), 200ml of pure water, oxygen pressure 2~
The reaction was carried out under stirring under conditions of 5 Kg/cm ² (gauge pressure) and a temperature of 50°C. When the pressure was reduced from 5 Kg/cm ² to 2 Kg/cm ² , oxygen was supplied again to 5 Kg/cm ² . After 7 hours, the amount of iodine generated was determined using a 0.1N sodium thiosulfate aqueous solution and found to be 77.3.
g (0.305 mol). Yield of iodine is 70%
It was hot. (2) Recovery of weak acid After adding 600 ml of pure water to the iodine aqueous solution obtained in (1), iodine was extracted three times with diethyl ether from 1, and almost all of the generated iodine could be recovered. Furthermore, a trace amount of iodine remaining in the aqueous solution was cyclically removed with sodium thiosulfate to obtain an aqueous solution containing no molecular iodine. This aqueous solution is 1
The ammonia is charged into a SUS316 autoclave, heated and stirred at 170 to 210℃ under a nitrogen atmosphere, and ammonia is released along with water vapor from a nozzle installed at the top of the autoclave. Approximately 600 c.c. of ammonia water is produced in 2 hours through a cooling pipe. Obtained. The generated ammonia was determined using a 1N sulfuric acid aqueous solution.
It was 10.4g (0.612mol). The ammonia recovery rate was 100%. (3) Add 88g of ammonium iodide to the aqueous solution obtained in reoxidation (2).
(0.607 mol) and using a pressure-resistant glass autoclave, oxygen was added at 2 to 5 Kg/cm ² (gauge pressure).
When the oxidation reaction was carried out again under pressure and temperature of 50°C, iodine was obtained with a yield of 50% in 4 hours. Examples 2 to 4 Reactions were carried out in the same manner as in Example 1 using the compositions shown in Table 1. The results obtained are shown in Table 1. Comparative Examples 1-2 When the oxidation reaction was carried out in the same manner as in Example 1 (1) with the composition shown in Table 1 without using a weak acid, the amount of iodine was less than or equal to the amount of the catalyst used. It did not occur. At the start of the reaction, the system was neutral, but as iodine was produced, it became alkaline. In Comparative Example 2, nitrogen iodide was produced, and when dried, it exploded upon a slight impact.

[Table] Examples 5 to 8 A reaction was carried out in the same manner as in Example 1 using the compositions shown in Table 2. The results obtained are shown in Table 2. Examples 9 to 13 Using the compositions shown in Table 2, reactions were carried out in the same manner as in Example 1 (1). The results obtained are shown in Table 2.

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Claims (1)

[Claims] 1. When ammonium iodide is oxidized with oxygen or air to obtain molecular iodine, the oxidation reaction is carried out in an aqueous medium containing at least one member selected from the group consisting of copper compounds and a weak acid. A method for producing iodine characterized by the following. 2. The manufacturing method according to claim 1, wherein the weak acid is one selected from the group consisting of phosphoric acid, ammonium dihydrogen phosphate, and organic acids. 3. The manufacturing method according to claim 1, wherein the oxidation reaction is carried out at a temperature of 100°C or lower. 4. The manufacturing method according to claim 1, wherein the weak acid is at least partially obtained by thermally decomposing an ammonium salt of a weak acid generated in an oxidation reaction. 5 Thermal decomposition of the ammonium salt of a weak acid is
The manufacturing method according to claim 4, characterized in that the manufacturing method is carried out at 100 to 210°C.