WO1994010083A1

WO1994010083A1 - Method of recovering iodine from iodated organic compounds

Info

Publication number: WO1994010083A1
Application number: PCT/EP1993/002822
Authority: WO
Inventors: Jürgen JACKE; Peter Blaszkiewicz
Original assignee: Schering Aktiengesellschaft
Priority date: 1992-10-30
Filing date: 1993-10-13
Publication date: 1994-05-11
Also published as: JPH08502469A; EP0666830A1; CA2147373A1; DE4236724A1

Abstract

The method proposed is characterized in that, in a first step, the substance to be de-iodized is suspended or dissolved in water in a reactor and mixed with sufficient quantities of organic and/or inorganic bases and, following the addition of a catalyst, the de-iodization carried out at room or elevated temperature in the presence of hydrogen, optionally at elevated pressure. After separating off the catalyst in a second stage, the solution is mixed with an organic and/or inorganic acid and the precipitated de-iodized compound filtered off. The iodide present in the acid filtrate is then oxidized in a third step with an oxidizing agent to iodine which is separated from the aqueous reaction mixture by the usual methods.

Description

Process for the recovery of iodine from iodinated organic compounds

The invention relates to a process for the recovery of iodine from production residues which contain iodinated organic compounds.

The increased demands on an ecologically justifiable production method for organic iodine compounds arouse the need for a process for recovering the iodine from the unavoidable production residues. Legal requirements stipulate that residues are to be recycled or re-used. Only when attempts in this regard have been unsuccessful can either the residual material be incinerated or be sent to the waste water. Appropriate attempts must be demonstrated to the authorities.

In modern iodinated X-ray contrast media and their synthetic ionic or non-ionic precursors, iodine is bound so tightly that it is difficult to access even chemical degradation processes.

Because of the relatively large production volume for such compounds, the amounts of solid and liquid production residues in the form of mother liquors, distillation residues from solvent recovery, filter dust and / or waste water are considerable and have to be processed from an ecological and economic point of view.

X-ray contrast media are predominantly derivatives of 2,4,6-triiodo-benzoic acid, 2,4,6-triiodo-isophthalic acid, 2,4,6-triiodo-3-amino-benzoic acid, 2,4,6-triiodo-5 -amino-isophthal- acid, 2,4,6-triiodo-3,5-diamino-benzoic acid, 2,4,6-triiodo-1,3,5-benzenetricarboxylic acid and corresponding di erer.

DE-OS 3 612 504 discloses a process for removing iodinated compounds from carbonylation products, in which the organically bound iodine is converted with oxidizing agents into iodine compounds which can be easily separated off by distillation.

EP 135 085 describes a process for the removal of iodinated compounds in which the carbonylation products are combined with phosphines or heterocyclic nitrogen compounds in the presence of at least one metal, such as, for. B. copper are treated and the reaction product is separated by distillation from the non-volatile iodine compounds.

Further methods of this type are described in European patent specifications 143 179 and 217 182.

These processes have in common that the iodine input concentrations must be kept low.

EP-A-106 934 describes a process for the recovery of iodine from mother liquors and wastewater containing organically bound iodine, the technical further development being to consist in that the addition of catalytic amounts of copper (ions) in the alkaline medium the bound iodine is mineralized. This procedure gives satisfactory results when using dilute solutions (p. 6, line 11). In order to take into account the realities of modern operating processes on the one hand and to keep the amounts to be released to the environment as low as possible, there was still a demand for processes by means of which highly concentrated production residues can be easily, effectively and economically dehalogenated and both iodine and the de-iodinated organic ones Compounds can be recovered and reused for synthesis.

This requirement is met by the method according to the invention.

The present invention relates to a 3-stage process for the recovery of iodine from iodinated organic compounds, which is characterized in that in a first stage the substance to be de-iodinated is suspended or dissolved in water and with sufficient amounts of organic and / or inorganic bases are added and, after addition of a catalyst in the presence of hydrogen, if appropriate at elevated pressure, the deiodination is carried out at room or elevated temperature and after removal of the catalyst in

second stage, the solution is mixed with an organic and / or inorganic acid and then the precipitated, de-iodinated compound is filtered off and

third stage from the acidic filtrate, the iodide present is oxidized to iodine with an oxidizing agent, which is separated from the aqueous reaction mixture using the customary processes. In the process according to the invention, in the first stage the substance to be decoded is hydrogenated in aqueous solution in the presence of bases and a catalyst.

Here, the iodine-containing substrate is dissolved or suspended in at least the same amount by weight of water and mixed with an organic and / or inorganic base in an amount sufficient to keep the organic acid released after the hydrogenation in solution.

According to the invention, the amount is preferably selected so that the hydroiodic acid liberated and the acid groups bound to the organic molecule are neutralized and the pH after the hydrogenation is in particular in the range from 8 to 13.

According to the invention, all compounds with sufficient basicity which are stable under the given reaction conditions and do not act as a catalyst poison can be used as inorganic and / or organic bases.

According to the invention, preference is given to using inorganic bases such as alkali and / or alkaline earth metals as oxides, carbonates or hydroxides and NH3. In order not to unnecessarily increase the amount of water, the bases are preferably used in solid form or as concentrated solutions such as, for example, solid sodium hydroxide, potassium hydroxide, calcium hydroxide.

Ni, Pd, Pt, Rh, if appropriate on support materials, have proven to be useful as catalysts according to the invention, usually in amounts of 0.01-10 % By weight, preferably 0.1-1% by weight, of the pure metal and based on the iodine-containing substrate.

The hydrogenation is carried out at room temperature up to approximately 150 ° C., preferably between 50 ° C. and 90 ° C., and a hydrogen pressure of approximately 1-50 bar. Higher pressures are possible if necessary, but pressures between 1-20, in particular 1-6 bar, are preferred according to the invention.

After the deiodination has ended, the catalyst is separated off, for example by filtration, and the filtrate containing the reaction products is acidified.

The acids used are one or more strong organic and / or inorganic acids such as, for example, oxalic acid, citric acid, acetic acid, sulfuric acid, hydrochloric acid, preferably those with pKa values <_3.5. The amount of acid used must be sufficient for the neutralization of the bases contained in the reaction solution and for the protonation of the deiodinated carboxylic acids.

The respective carboxylic acid precipitates almost quantitatively as a solid precipitate and is separated off.

In the third stage, the iodide remaining in the reaction solution is oxidized with oxidizing agents to iodine, which is then separated off.

The oxidation is carried out using mild oxidizing agents known per se, such as preferably hydrogen peroxide in acidic solution or electrochemically. To carry out the reaction, the pH of the solution is adjusted to <7 using one or more of the above-mentioned inorganic or organic acids. According to the invention, pH values <4, in particular <2, are preferred.

The H ₂ O ₂ preferred according to the invention can be added continuously or in portions to the acidic solution at room temperature as a concentrated solution. The reaction temperature is optionally kept at temperatures of preferably <25 ° C. by cooling.

If the reaction did not start with a large excess of acid, the progress of oxidation can by increasing the pH ^to track. The pH is kept within the intended range by adding acid continuously or in portions. The reaction is complete when the pH of the reaction mixture does not increase further by adding the oxidizing agent.

The iodine formed as a crystalline precipitate at reaction temperatures of preferably <25 ° C. is filtered off. If necessary, the dissolved iodine remaining in the filtrate can be removed by extraction with solvents such as ethyl acetate or by water distillation / sublimation.

The remaining filtrate is largely free of iodine in the various oxidation states such as. B. iodide, iodate, iodine and iodinated and deiodinated organic compounds that after neutralization it can be easily added to biological wastewater treatment. One of the advantages of the process according to the invention lies in the possibility of being able to process highly concentrated solutions, so that all reaction products are precipitated and can therefore be largely separated off in a simple manner.

Accordingly, the volume of the remaining solution is also comparatively small, so that, if necessary, the neutralized solution can be evaporated in whole or in part at low cost and the salts which precipitate out can be isolated.

Example 1 :

500 g (0.59 mol) of Josimid [2,4,6-triiodo-1,3,5-benzenetricarboxylic acid tris [bis (2-hydroxyethyl)] triamide] and 142 g (3.55 mol) of sodium hydroxide are dissolved in 1.5 l of water. After adding 20 g of palladium / carbon catalyst (5% Pd, 54% water), the mixture is hydrogenated at 60-70 ° C./5 bar hydrogen for 80 minutes. After 1 h of stirring, the catalyst is filtered off. From the filtrate are concentrated by adding 290 ml (3.5 mol). Hydrochloric acid 112 g (90% of theory) on white

Precipitation Ki precipitated and filtered off. The mother liquor is mixed with a total of 250 ml of 35% hydrogen peroxide, during which the pH of the solution is concentrated by adding 300 ml (3.6 mol). Hydrochloric acid is kept in the range of pH = 1-2. The temperature is kept at 25 ° C. by cooling. 224 g of nutsche moist, crystalline iodine with a content of 81% (= 81% of theory) precipitate. The mother liquor has a residual iodine content of 2 g / 1.

The residual iodine content of the mother liquor is reduced to 50 mg / l by extraction (2-stage) with the same volume of ethyl acetate.

Analysis Ki: triic acid: calc .: C 51.4%, H 2.9%, found: C 51.1%, H 3.0%

Example 2;

500 g (0.9 mol) of iodamic acid (2, 6-triiod-5-amino-isophthalic acid) are suspended in 1.5 l of water and dissolved by adding 183 g (4.6 mol) of sodium hydroxide. After adding 20 g of palladium / carbon catalyst (5% Pd, 54% water), the mixture is hydrogenated at 60-70 ° C./5 bar hydrogen for 60 minutes. After 1 h After stirring at 60 ° C, the catalyst is filtered off. From the filtrate are concentrated by adding 120 ml (1.4 mol). Hydrochloric acid 191 g of white precipitate Ki precipitated and filtered off. The filtrate is concentrated with 210 ml. Hydrochloric acid was added and crystalline iodine was released by adding 120 ml of 35% hydrogen peroxide. Yield: 343.5 g nutsche moist, with a content of 84.2% {= 85% of theory. Th.). The mother liquor has a residual iodine content of 1 g / l.

The residual iodine content of the mother liquor is reduced to 45 mg / 1 by extraction (2-stage) with the same volume of ethyl acetate.

Analysis Ki: DC / HPLC comparison: 5-aminoisophthalic acid

Example 3:

500 g (0.64 mol) of Jopa idol [5-α-hydroxypropionylamino-2, 6-triiodoisophthalic acid di- (2-hydroxyisopropylamide] and 166 g (4.15 mol) of sodium hydroxide are dissolved in 1.5 l of water After adding 20 g of palladium / carbon catalyst (5% Pd), the mixture is hydrogenated for 120 min at 85 ° C./5 bar hydrogen and after 1 hour of stirring at 75 ° C. The catalyst is filtered off Add 250 ml

(3 mol) conc. Hydrochloric acid 110 g (94% of theory) precipitated on a white precipitate Ki and filtered off. The mother liquor is concentrated with 240 ml (2.9 mol). Hydrochloric acid are added and crystalline iodine is released by adding 120 ml of 35% hydrogen peroxide. Yield: 265 g nutsche moist, with a content of 81.4% (= 88% of theory). The mother liquor has a residual iodine content of 1.5 g / l. The residual iodine content of the mother liquor is reduced to 50 mg / l by extraction (2-stage) with the same volume of ethyl acetate.

Analysis Ki: DC / HPLC comparison: 5-aminoisophthalic acid

Example 4:

500 g of ethanol-moist mother liquor distillation residue from an intermediate X-ray contrast agent synthesis (iodine content: 38%) and 150 g of sodium hydroxide are dissolved in 1.5 l of water. After adding 20 g of palladium / carbon catalyst (5% PD, 54% water), hydrogenation is carried out at 80 ° C./5 bar hydrogen for 90 minutes. After a further stirring time of 1 h, the catalyst is filtered off. From the filtrate are concentrated by adding 200 ml. Hydrochloric acid 145 g precipitated on a cream-colored precipitate and filtered off. A total of 200 ml of 35% hydrogen peroxide is added to the mother liquor, during which the pH of the solution is concentrated by adding 250 ml. Hydrochloric acid is kept in the range of pH = 1-2. The temperature is kept at 25 ° C. by cooling. After a stirring time of 30 min, 182 g of nutsche-moist, crystalline iodine with a content of 84% (= 80% of theory) are filtered off. The mother liquor has a residual iodine content of 4 g / 1.

The residual iodine content of the mother liquor is reduced to 100 mg / l by extraction (2-stage) with the same volume of ethyl acetate.

Claims

1. A process for the recovery of iodine from iodinated organic compounds, characterized in that in a first stage the substance to be de-iodinated is suspended or dissolved in water in a reactor and mixed with sufficient amounts of organic and / or inorganic bases and after the addition of a catalyst in the presence of hydrogen, if appropriate at elevated pressure, the deiodination is carried out at room or elevated temperature and, after the catalyst has been separated off, the solution is mixed in a second stage with an organic and / or inorganic acid and then the precipitated, de-iodinated compound is filtered off and, in a third stage, the iodide present is oxidized from the acidic filtrate to iodine using an oxidizing agent, which is separated from the aqueous reaction mixture using the customary methods.

2. The method according to claim 1, characterized in that alkali and / or alkaline earth oxides or Hydro¬ xides are used as bases.

3. The method according to claims 1 and 2, characterized gekennzeich- net that Ni, Pd, Pt, Rh, where appropriate on catalysts, are used as catalysts.

4. The method according to claims 1-3, characterized in that those with a pKa value of 3.5 are used as acids.

5. The method according to claims 1-4, characterized in that the pH after the oxidation in the third stage is <7.

6. The method according to claims 1-5, characterized in that as acids in the second stage one or more highly concentrated organic or inorganic acids such as

Citric acid, acetic acid, oxalic acid, sulfuric acid, hydrochloric acid can be used.

Process according to claims 1-4, characterized in that hydrogen peroxide is used as the oxidizing agent.