JPS5973406A - Preparation of iodine - Google Patents

Abstract

PURPOSE:To prepare high-quality molecular iodine from ammonium iodide in high yield, by oxidizing ammonium iodide in an aqueous medium containing a V compound and a weak acid. CONSTITUTION:Ammonium iodide is oxidized with oxygen or air by using any of almost all V compounds as a catalyst in an aqueous medium containing the V compound and a weak acid such as phosphoric acid, ammonium dehydrogenphosphate, etc., to give molecular iodine. A weak acid obtained by hydrolyzing an ammonium salt of weak acid such as ammonium phosphate formed by the oxidation for the preparation of iodine is partially used as the weak acid. Iodine is obtained from ammonium iodide in high yield economically without preparing by-products such as nitrogen iodide, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for oxidizing ammonium iodide to obtain iodine.

Iodine is widely used as an intermediate in organic synthesis, catalysts, medicines, health drugs, disinfectants, livestock feed additives, organic compound stabilizers, dyes, photoengraving, agricultural chemicals, rare metal scouring, and analytical reagents. It is a useful compound. Industrially, iodine anions contained in brine are treated with copper sulfate (IF) and iron sulfate (I[
) Many methods are used to oxidize with an aqueous solution.

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 electrolysis (German Patent No. 4436,111);
Examples include a method using a cupric compound (JP-A-53-50122), a method using oxygen oxidation (JP-A-53-73489), and the like.

In the method using electric nitrogen (German Patent No. 4436,111), the reaction is carried out in a dilute solution and a diaphragm is required, so the equipment is large-scale and consumes a large amount of electricity. Therefore, it cannot be said that it is an industrially 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 (JP-A-53-73489), iodine is obtained by oxidizing ammonium iodide with oxygen in an ammonia aqueous solution using a copper compound as a total catalyst. In general, a strong acid is required for iodine anio/oxidation (J-Chim, phys, 55, 4
07 (1958),) In this method, the iodine production reaction is carried out under ammoniacal alkaline conditions, so the iodine production rate is extremely slow, and as ammonia is produced along with the iodine production, the reaction is even slower. It is expected that 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 immersing ammonium iodide in acid, but by combining a cum compound and a weak acid, ammonium iodide The present invention was achieved based on the discovery that iodine can be obtained in high yield by total oxidation without by-products such as nitrogen iodide.

That is, the present invention is based on the above knowledge, and when ammonium iodide is oxidized with oxygen or air to obtain molecular iodine, the oxidation reaction is carried out in an aqueous medium containing a vanadium compound and a weak acid. This is the manufacturing method. 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.

In the reaction of the present invention, using a vanadium compound and ammonium dihydrogen phosphate as an example, it is estimated that iodine is produced by the following reaction mechanism.

2I-+V” →I2+V”
(1) V” +jO□+H20, y5++2
0Fr(2)2NI(4H2PO4+ 20H+ 2N
H, II2 (NH,)2HPO4+ 2I-+ 2H
20(3) Therefore, the vanadium compound used as a catalyst is considered to be simply a source of vanadium ions, and the type of anion side of the vanadium compound is considered to be relevant to the essence of the reaction and there are no special restrictions. It will be done. There are no particular limitations on the vanadium compound, and most vanadium compounds can be used, but vanadium oxide, vanadium hydroxide (
■), vanadium dichloride, vanadium(II) sulfate,
K4 (V(CN)6), divanadium trioxide, vanadium hydroxide A (I[), vanadium trifluoride, M2 VF
I, (M-Na, K, NH4), vanadium trichloride, vanadium tribromide, vanadium Misawa, vanadium(III) sulfate, NIN' (804)2 (M-
Na lK, NH4), K3 [V (CN)6
, l l vanadium dioxide, M2V, o, (M=N
a, K, NH4) l vanadium tetrafluoride, M,
[:VOF'4 (OH)2] (M=Na, K,
NHa), vanadium tetrachloride, vanadium oxytrichloride, vanadyl borate, M2 (VO(S04)2
) (M-Na, K, NH4), vanadium pentoxide, sodium metavanadate, potassium metavanadate, ammonium metavanadate, sodium orthovanadate, potassium orthovanadate,
Ammonium orthovanadate, sodium pyrovanadate, potassium pyrovanadate, ammonium pyrovanadate, sodium pentavanadate, potassium pentavanadate, amthonium pentavanadate, vanadium trifluoride, MVFa (M-Na, K, NH4
), vanadium oxytrifluoride, vanadium oxytrichloride, vanadium oxytribromide, VO2Ct1, etc. are preferred.

These vanadium compounds may be used alone or in combination of two or more.

The amount of vanadium compound used is not particularly limited, but
In practice, 3X10-'~0.3mo for 100F of water
t is preferred. Further, the vanadium 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 f with respect to water ioo y.

As for the oxygen used, not only oxygen gas but also air can be used to sufficiently achieve the purpose of spraying water.

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, the temperature is preferably between room temperature and 100°C.

The weak acid is used to prevent the production of ammonia, 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 acids used may be those that release ammonia when the ammonium salt is heated, such as phosphoric acid, ammonium dihydrogen phosphorus, sodium dihydrogen phosphate, potassium dihydrogen phosphate, boric acid, arsenic acid, chromic acid, tellurium. Examples include acids, inorganic acids such as vanadate silicate, and organic acids such as acetic acid and propionic acid, but phosphoric acid, ammonium dihydrogen phosphate, and organic acids are preferred. Furthermore, in the case of ammonium dihydrogen phosphate, when its ammonium salt, ammonium phosphate-hydrogen, is heated.

It is particularly preferred because it releases ammonia quantitatively in a short period of time and returns to ammonium dihydrogen phosphate.

In the present invention, in order to recover the weak acid, 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 ammonium salt of the generated weak acid is extracted. Just heat it. 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.

Decomposition temperature of ammonium salt of weak acid 1 company, the higher the decomposition rate and decomposition rate, preferably 100 to 210'C
, is.

The aqueous medium in the present invention is mainly water alone, but benzene, chlorobenzene, and other substances that do not substantially react with iodine in this system 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 and conditions used, but the higher the hydrogen ion concentration, the faster the iodine production rate tends to be.
゜The method of the present invention has a high production rate of iodine, a good yield, the recovery and reuse of weak acids, and no by-products such as nitrogen iodide.It is an extremely advantageous industrial method for producing iodine that does not generate industrial waste. I can say that. In addition, in the method of the present invention, an iodination reaction is performed simultaneously with the generation of iodine.

It can also be applied to a method for obtaining useful iodides without purifying and isolating iodine. Also, since ammonia is generated when recovering weak acids, this ammonia can be recovered as needed.
It is also possible to use it for other purposes.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

In the following examples, it is assumed that the oxidation reaction follows the following formula (1) when ammonium dihydrogen phosphate is used as an example of a weak acid, and the yield of siiodine was determined according to the formula (2).

÷0. + 2NH4I + 2NH4H,PO4■
! Article Rue.

+ 2 (NH, ), HPO4 + H, 0 (1) 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 the weak acid is calculated as follows: (4) I asked for it.

(N'H4), HPO4+H, H, PO, +NH.

In addition, calculations were also performed using equations (2) and (4) when other weak acids were used.

Example 1 (1) Generation of iodine: 75 t (0J17 mot) of ammonium iodide, 2.4 F (0,0132 mo/,) of vanadium pentoxide, 2 s of ammonium dihydrogen phosphate in a 500-mm lateral pressure glass autoclave. ? (0,217maL
), pure water 50ml1. 50% of benzene was charged, and the reaction was carried out under stirring at an oxygen pressure of 6 to 8 to 9/d (gauge pressure) and a temperature of 70°C. After 4.5 hours, the generated iodine was reduced to 0.
Quantitated with 1N sodium thiosulfate aqueous solution 12
．． It was 4F (0,0488 mot). The yield of iodine was 45%.

(2) Recovery of weak acid After adding 150 nt of pure water to the iodine aqueous solution obtained in (1), iodine was extracted three times with 250-diethyl ether, and almost all of the generated iodine was recovered. . Furthermore, a trace amount of iodine remaining in the aqueous solution was reduced with sodium thiosulfate to obtain an aqueous solution containing no molecular iodine. This aqueous solution was charged into a 500-mm SUS 316 autoclave.

The mixture was heated and stirred at 170 to 210° C. under a nitrogen atmosphere, and ammonia was released together with water vapor through a nozzle provided at the top of the autoclave, and passed through a cooling tube to obtain about 150 marks of aqueous ammonia in 2 hours. The amount of ammonia generated was 1.66 f (0,0976rn) when determined using an IN sulfuric acid aqueous solution.
ot). The recovery rate of weak acid was 100%.

(3) The same amount of ammonium iodide as that consumed in the aqueous solution obtained in reoxidation (2) 14.2? (0,0976m
at J using a pressure-resistant glass autoclave.

The oxidation reaction was carried out again under the conditions of oxygen pressure of 6 to 8 Kp/cJ (gauge pressure) and temperature of 70° C. Next, iodine was obtained in 4 hours with a yield of 40%.

Examples 2 to 7 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.

Examples 8 to 11 Using the compositions shown in Table 1, reactions were carried out in the same manner as in Example 1 (1). The results obtained are shown in Table 1.

Comparative Examples 1 and 2 below: With the composition shown in Table 2 without using a weak acid during the oxidation reaction,
Example 1 (1) (!: When a reaction was carried out in a similar manner, the amount of iodine produced was less than or equal to the amount of the catalyst used. At the start of the reaction, the system was neutral, but As iodine was produced, it became alkaline.Also, Comparative Example 2
In this case, nitrogen iodide was produced, and when the spores dried, they exploded with a slight impact.

Margin below

Claims (1)

[Claims] 1. A method for producing iodine, characterized in that when ammonium iodide is oxidized with oxygen or air to obtain molecular iodine, the oxidation reaction is carried out in an aqueous medium containing a vanadium compound and a weak acid. The manufacturing method according to claim 1, wherein the weak acid is at least partially composed of a weak acid obtained by thermally decomposing an ammonium salt of a weak acid generated in an oxidation reaction.