(S,S)-Ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt and process for its preparation

Abstract: (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt represented by the formula: wherein C* is an asymmetric carbon atom. This compound has a very high biodegradability and it is not accumulated in the environment even when used as a photographic processing agent or the like. Therefore, the compound is advantageous for the protection of environment.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a novel optically active (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt usable as, for example, a photographic processing agent, and a process for production thereof. Description of the Related Art Red prussiate (potassium hexacyanoferrate (III)) was widely used in the past as an oxidizing agent contained in a bleaching solution and a bleaching and fixing solution which were used for printing of color photographs. But owing to the pollution problem, i.e., the presence of cyanogen in a waste solution after development, there are now used iron chelate compounds such as ethylenediaminetetraacetic acid (EDTA) iron (III) complex salts, diethylenetriaminepentaacetic acid (DTPA) iron (III) complex salts, propanediaminetetraacetic acid (PDTA) iron (III) complex salts, etc. However since these iron chelate compounds have a strong chelate bond strength between each acid and iron ions but are poor biodegradability, they continue to be accumulated in the environment as industrial wastes. Therefore, they have been disadvantageous for use from the viewpoint of the protection of environment. EP-A-0581197 discloses a method for processing silver halide photographic light-sensitive materials which describes the use of certain alkylene diamine (N,N')-disuccinic acid ligands as bleaching agents in the processing method. DE-A-2334034 relates to a process for synthesising ferric-aminopolycarboxylic acid complex compounds and aqueous solutions thereof. These compounds find applications as components of bleach-fixing solutions for colour photography. The process comprises mixing an amino polycarboxylic acid and metallic iron in an aqueous medium and reaching the mixture with oxygen in the presence of a water-soluble iron salt. On the other hand, there have been proposed several chelating agents which are used as a photographic agent and have biodegradability. They include, for example, β-alanine N,N-diacetic acid (EP-A-0574829) and isoserine N,N-diacetic acid (US-A-5,238,791). These chelating agents, however, have been disadvantageous for use because they have a low iron chelate stability constant of about 10, so that when they are used as a photographic developing agent, iron remains in a film or a print. SUMMARY OF THE INVENTION An object of the present invention is to provide a novel iron chelate complex which is rapidly degraded by microorganisms and has a chelate-forming ability similar to that of the conventional chelate compounds (the EDTA iron (III) complex salts, etc.), and a process for producing the same. The present inventors produced a novel alkylenediamine-N-N'-disuccinic acid iron (III) complex salt. This complex salt is a compound having a chelate-forming ability (iron chelate stability constant: about 20) similar to that of the EDTA iron (III) complex salts, the conventional chelate compounds and a high biodegradability, as compared with β-alanine N,N-diacetic acid and isoserine N,N-diacetic acid. Aforesaid alkylenediamine-N,N'-disuccinic acid iron (III) complex salt, however, has two asymmetric carbon atoms, so that a conventional process for producing the complex salt via alkylenediamine-N,N'-disuccinic acid produced from an alkylenediamine and maleic acid gives the complex salt as a mixture of racemic modification and mesoisomer in which 3 optical isomers, i.e., (S,S) form, (R,R) form and (S,R) form are present in a ratio of 1 : 1 : 2. Of these optical isomers, the (R,R) form requires a conditioning period for biodegradation. Accordingly, the present inventors investigated in further detail the biodegradation of the alkylenediamine-N,N'-disuccinic acid iron (III) complex salt consisting of mesoisomer and racemic modification by microorganisms and consequently found that the alkylenediamine-N,N'-disuccinic acid iron (III) complex salt of (S,S) form, in particular, (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt is easily biodegradable compound which is much more rapidly degraded by microorganisms than the alkylenediamine-N,N'-disuccinic acid iron (III) complex salt of meso form and that of (R,R) form. The present invention was made on the basis of this finding. That is, the present invention is directed to (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt represented by the formula (I): wherein C* is an asymmetric carbon atom. Another aspect of the present invention is directed to a process for producing (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt represented by the above formula (I) which comprises reacting (S,S)-ethylenediamine-N N'-disuccinic acid with [A] iron or an iron compound and [B] ammonia in an aqueous medium, and oxidizing the reaction product if necessary. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an IR spectrum obtained by a KBr tablet method of (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt synthesized in Example 1. PREFERRED EMBODIMENTS OF THE INVENTION The present invention is explained below in The (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt of the present invention has a structure represented by the above formula (I) and has such a high biodegradability that it is easily degradable for utilization when tested by the degradability test method, No. 301C Modified MITI Test (1) prescribed in the item of "degradation, concentration" in Chapter 3 of the guidelines for chemicals test of OECD (Organization for Economic Cooperation and Development). Furthermore, this compound has a chelate stability similar to that of ethylenediaminetetraacetic acid iron complexes. The compound of the present invention can be produced as follows. First, (S,S)-ethylenediamine-N,N'-disuccinic acid is reacted with ammonia or an alkali metal hydroxide and metallic iron or an iron compound to give an (S,S)-ethylenediamine-N,N'-disuccinic acid iron complex salt. This reaction is carried out in an aqueous medium at a temperature of 5 - 100°C, preferably 10 - 90°C. The amount of ammonia used may be properly chosen in a range of 0.5 to 5 moles, preferably 0.8 to 4.5 moles, per mole of (S,S)-ethylenediamine-N,N'-disuccinic acid. The amount of iron (metallic iron powder) or the iron compound used may be properly chosen in a range of 0.25 to 1.5 moles, preferably 0.3 to 1.2 moles, in terms of iron atoms, per mole of (S,S)-ethylenediamine-N,N'-disuccinic acid. The (S,S)-ethylenediamine-N,N'-disuccinic acid used in the present invention can be synthesized by a conventional method. For example, it can be synthesized by heating a 1,2-halogenoethane and L-aspartic acid in the presence of an alkali metal hydroxide (Inorganic Chemistry, 7 (11), 2405 (1968)). The iron source in the present invention is iron powder and iron compounds. The iron compound includes divalent and trivalent iron compounds, and there can be used iron sulfates; iron halides such as iron chlorides, etc.; iron oxides such as diiron trioxide (i.e. iron (III) oxide) (Fe 2 O 3 ), triiron tetraoxide (i.e., black iron oxide) (Fe 3 O 4 ), iron (III) hydroxide oxide (FeO(OH)), etc.; and hydrated iron oxides. Of these, triiron tetraoxide is preferable from the viewpoint of reactivity. The above-exemplified iron compounds may be used singly or as a mixture of two or more thereof. The presence of a reducing agent makes it possible to carry out the reaction more rapidly. Subsequently, when the (S,S)-ethylenediamine-N,N'-disuccinic acid iron complex salt obtained by the reaction contains an iron (II) salt, the iron (II) salt is oxidized into the corresponding ion (III) salt. This oxidation reaction can be carried out by using the aqueous solution of the aforesaid produced iron complex salt as it is, and reacting therewith an oxidizing agent such as molecular oxygen or a peroxide. The molecular oxygen includes air, oxygen-enriched air, oxygen, etc. Air is usually preferable from an economic viewpoint. The amount of air used is approximately 5 - 50 times, preferably approximately 10 - 25 times as large as the theoretical equivalent amount with respect to the aforesaid iron (II) salt. As the peroxide, persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate, etc. are preferable. The amount of the peroxide used may be properly chosen in a range of 0.9 to 2.0 equivalents, preferably 1.0 to 1.5 equivalents, per equivalent of the aforesaid iron (II) salt. Although the oxidation reaction can be carried out in an arbitrary pH range of the reaction solution from the acidic range to the alkaline range, it is preferably carried out at pH 4 to 10, more preferably pH 5.0 to 8.0. As a pH adjustor, aqueous ammonia, (S,S)-ethylenediamine-N,N'-disuccinic acid or sulfuric acid is preferably used. The oxidation reaction temperature is 5 - 90°C, preferably approximately 10 - 50°C. After completion of the reaction, the pH of the reaction solution is adjusted to 3.5 to 6.5, preferably 4.5 to 5.5. As the pH adjustor, (S,S)-ethylenediamine-N,N'-disuccinic acid or sulfuric acid is preferably used. This adjustment facilitates crystallization of a desired product from the reaction solution. The reaction solution is concentrated and then cooled to precipitate (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt as crystals. The reaction solution is preferably concentrated until its weight becomes 1.5 to 5 times, preferably 1.5 to 3.5 times, as large as the weight of the (S,S)-ethylenediamine-N,N'-disuccinic acid used in the reaction. The precipitated crystals are separated from the mother liquor by means of a centrifuge or the like, washed with ice water and then dried, whereby the compound of the above formula, i.e., the desired product can be obtained. The thus obtained (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt has a molecular weight of 362 and is very rapidly degradable by microorganisms. The present invention is explained with reference to the following examples. Example 1 Into a 1-liter cylindrical three-necked flask fitted with a stirrer and a thermometer were charged 146.1 g of (S,S)-ethylenediamine-N,N'-disuccinic acid, 350 g of water and 56.7 g of 15% aqueous ammonia, and stirred at room temperature. Thereto was added 39.1 g of triiron tetraoxide (purity: 98.5%), and the resulting mixture was heated at 85°C for 30 minutes and then matured as it was for 15 minutes. The reaction mixture was cooled to room temperature and adjusted to pH 7.0 with aqueous ammonia. Air was blown through the reaction mixture at a rate of 7 liters/minute at room temperature for 4 hours to carry out oxidation reaction. Subsequently, the reaction mixture was adjusted to pH 5.0 with (S,S)-ethylenediamine-N,N'-disuccinic acid and then concentrated under reduced pressure until crystals were sufficiently precipitated. The reaction mixture was cooled to 5°C to precipitate (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt further. The precipitated crystals were separated with a centrifuge. The wet crystals were washed with a small amount of ice water and then dried at 70°C for 1 hour and 30 minutes. The thus obtained (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt was yellow crystals, and its amount was 126.7 g and its yield 70.0% (based on the amount of triiron tetraoxide). The results of measurement of the elemental analysis values, ammonia content, chelating agent percentage, and infrared absorption spectrum of the crystals are described below: 1. Elemental analysis values (%) C H N Fe Found 33.272 4.556 11.444 15.359 Calculated 33.171 4.447 11.606 15.426 2. Ammonia content Found 4.646% (JIS K8960 Kjeldahl distillation method) Calculated 4.701% 3. Chelating agent percentage Found 79.1% (chelatometoric titration using Zn-XO) Calculated 79.6% 4. Infrared absorption spectrum Fig. 1 The spectrum in Fig. 1 shows absorptions due to carbonyl and ammonia at 1600 - 1700 cm -1 and near 3200 cm -1 , respectively. The above results of measurement of the elemental analysis values, ammonia content, chelating agent percentage and infrared absorption spectrum agree with the theoretical values obtained on the basis of the compositional formula C 10 H 16 N 3 O 8 Fe of (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt, within the limits of analytical error. Thus, it was confirmed that the compound obtained was that of the present invention. The specific rotation of the compound was [α] 20 D + 30.8 (C = 1, 6N·HCl). Example 2 The (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt (hereinafter referred to as "(S,S)-EDDS iron ammonium salt") obtained in Example 1 was tested for utilization according to Modified MITI Test. The results obtained are shown in Table 1. Comparative Example 1 Into a 1-liter cylindrical three-necked flask fitted with a stirrer and a thermometer were charged 146.1 g of ethylenediamine-N,N'-disuccinic acid composed of a mixture of mesoisomer and racemic modification, 500.0 g of water, 24 g of 28% aqueous ammonia and 47.5 g of triiron tetraoxide, and heated at 80 - 85°C for 30 minutes, and the resulting mixture was matured as it was for 15 minutes. The reaction mixture was cooled to 60°C and the remaining iron oxide was filtered off, after which air was blown through the residue at a rate of 7 liters/minute for 3 hours by means of a ball filter to oxidize the remaining divalent iron into trivalent iron. After completion of the reaction, the reaction mixture was adjusted to pH 5.5 with ammonia and then concentrated under reduced pressure until crystals were sufficiently precipitated. The precipitated crystals were filtered and washed with a small volume of water to obtain 80.3 g of primary crystals. The filtrate and the washing were reconcentrated to obtain 83 g of secondary crystals. The primary crystals and the secondary crystals were combined and then dried at 70°C for 1 hour to obtain 160.0 g of ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt. The thus obtained ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt composed of a mixture of mesoisomer and racemic modification (hereinafter abbreviated as "meso-racemic mixture-EDDS iron ammonium salt") was tested for utilization according to Modified MITI Test. The results obtained are shown in Table 1. Degree of degradation after 28 days TOC BOD Example 2 (S,S)-EDDS iron ammonium salt 98% 71.6% Comparative Example 1 Meso, racemic mixture-EDDS iron ammonium salt 24.9% 16.8% Reference Aniline 100% 73.1% Example 3 Into a 1-liter cylindrical three-necked flask fitted with a stirrer and a thermometer were charged 146.1 g of (S,S)-ethylenediamine-N,N'-disuccinic acid, 250 g of water and 195 g of 15% aqueous ammonia, and they were stirred at room temperature. Then, 139 g of iron (II) sulfate heptahydrate was dissolved therein with heating, and the resulting solution was cooled to room temperature and adjusted to pH 7.5 with aqueous ammonia. To the reaction solution was added a solution of 57 g of ammonium per sulfate in 150 ml of water with stirring at 20 - 25°C over a period of 30 minutes to carry out oxidation reaction. Subsequently, the reaction solution was concentrated under reduced pressure to adjust the ammonium sulfate concentration to about 25 wt%. The concentrate was adjusted to pH 5.0 with sulfuric acid and then cooled to 15°C to precipitate an iron (III) complex ammonium salt. The precipitated crystals were separated with a centrifuge. The wet crystals were washed with a small amount of ice water and then dried at 70°C for 1 hour and 30 minutes. IR spectrum of the obtained crystals agreed with that of the (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt obtained in Example 1, and its amount was 100.6 g and its yield 55.6% (based on the amount of iron (II) sulfate). Example 4 Into a 1-liter cylindrical three-necked flask fitted with a stirrer and a thermometer were charged 146 g of (S,S)-ethylenediamine-N,N'-disuccinic acid and 250 g of water, and 195 g of 15% aqueous ammonia was added dropwise with stirring to effect dissolution. A solution of 105.5 g of iron (III) chloride tetrahydrate in 200 g of water was added dropwise with stirring and ice-cooling, and the resulting solution was stirred at room temperature for 2 hours to complete the reaction. Then, the reaction solution was adjusted to pH 5.5 with 15% aqueous ammonia and concentrated until its weight became 560 g. The concentrate was cooled to 15°C and allowed to stand for 24 hours to precipitate crystals. The precipitated crystals were separated with a centrifuge, washed with a small amount of water, and then dried at 40°C for 3 hours. IR spectrum of the obtained crystals agreed with that of the (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt obtained in Example 1, and its amount was 82.9 g and its yield 50.9% (based on the amount of iron (III) sulfate).

Claims: (S,S)-ethylenediamine-N,N'-disuccinic acid iron (III) ammonium salt represented by the formula (I): wherein C* is an asymmetric carbon atom. A process for producing (S,S)-ethylenediamine-N.N'-disuccinic acid iron (III) ammonium salt which comprises reacting (S,S)-ethylenediamine-N,N'-disuccinic acid with iron or an iron compound and ammonia in an aqueous medium. A process according to claim 2, which further comprises oxidizing a reaction product after the reaction in the aqueous medium. A process according to claim 2 or claim 3, wherein the iron compound is selected from the group consisting of iron sulfates, iron chlorides, diiron trioxide, triiron tetraoxide and iron (III) hydroxide oxide. A process according to claim 2 or claim 3, wherein the iron is used in the form of iron powder.

Inventors: SAKAI HARUO, SATO TAKASHI, YAMAKAWA TOSHITAKE, SAKAI, HARUO, SATO, TAKASHI, YAMAKAWA, TOSHITAKE, SAKAI, HARUO, C/O NITTO CHEM. IND. CO., LTD., SATO, TAKASHI, C/O NITTO CHEM. IND. CO., LTD., YAMAKAWA, TOSHITAKE, C/O NITTO CHEM. IND. CO., LTD
Applicants: NITTO CHEMICAL INDUSTRY CO LTD, NITTO CHEMICAL INDUSTRY CO., LTD.
Application year: 1995
Main classification: C07C229
IPC codes: C07C229, C07F15, G03C7