S,S-ethylenediamine-N,N′-disuccinic acid iron alkali...

Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing

Reexamination Certificate

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C544S384000, C544S399000

Reexamination Certificate

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06515159

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt that is a chelate compound usable as a photographic bleaching agent, a fertilizer or the like and has little undesirable influence on the environment because of its good biodegradability, and a process for producing said salt.
BACKGROUND ART
The present inventors have disclosed in JP, 8-34764,A that an S,S-ethylenediamine-N,N′-disuccinic acid iron ammonium salt, which is a compound useful for photographic bleaching and the like, has a high biodegradability. However, in a production process for producing the disclosed compound, it was necessary to obtain a highly viscous and highly slurry concentrate because of the very high solubility of the desired compound, in order to obtain the desired compound in high yield. Therefore, there has been a desire for a production process having a higher productivity as an industrial production process. A process for obtaining the desired compound by a concentration to dryness or a continuous hot gas drying has achieved an improvement in the yield but has been disadvantageous in product quality that, for example, powders obtained by said process were so poor in shelf stability that it was colored or was deteriorated in solubility.
Unlike a production process using an inorganic salt such as iron sulfate, a production process using iron oxide was expected to make it possible to obtain a desired compound having a relatively high purity by evaporating a reaction solution to dryness as it was, unless starting materials are decomposed. However, when a meso/racemic mixture of ethylenediamine-N,N′-disuccinic acid was used, a product obtained by such a process had a very high hygroscopic in some cases and moreover its purity was not sufficient. In addition, also when S,S-ethylenediamine-N,N′-disuccinic acid was used, the resulting solid had a low stability, for example, it was colored or gave an insoluble material with a lapse of time. Furthermore, the solid had a low purity and the mass balance of the S,S-ethylenediamine-N,N′-disuccinic acid used was markedly unsatisfactory.
An object of the present invention is to solve such problems and provide an S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt having a high storage stability and a process for producing the same in high yield.
DISCLOSURE OF THE INVENTION
The present inventors have made extensive studies in order to achieve the above object and consequently found that an S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt contains an impurity that is difficult to detect even under HPLC analysis conditions under which a slight amount of a chelate compound can be analyzed, because the impurity has a much lower chelate ability than that of other components. Additionally, the present inventors found that, as a result of various analyses such as mass spectrometry and NMR, the impurity is a compound derived from S,S-ethylenediamine-N,N′-disuccinic acid by a formation of a lactam ring. The present inventors also found that a coloring and a deterioration of a shelf stability of the S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt are due to the presence of a compound of the following general formula (1) or a compound of the following general formula (2) as reaction by-products and due that an iron complex's stability of these compounds is low that the compounds release a chelated iron with a lapse of time. Thus, the present inventors found that a reduction of an amount of the reaction by-products is important.
(Wherein M is an ammonium ion or an alkali metal ion.)
(Wherein n is an ammonium ion or an alkali metal ion.)
In addition, the present inventors found that even if these compounds are contained in the S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt, this salt is not seriously deteriorated in shelf stability when a content of each of the compounds is 7 wt % or less. The present inventors further found the following: a formation of these impurities can be inhibited by properly controlling a reaction temperature, a reaction period of time and pH at the reaction and adding a reducing agent; of the impurities formed, the lactam compound is easily soluble in a lower alcohol while the S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt is insoluble therein, and therefore only the impurity can be dissolved by utilizing a difference in solubility between the impurity and the lactam compound; and when a continuous hot gas drying method is adopted, a decomposition of S,S-ethylenediamine-N,N′-disuccinic acid during an oxidation can be minimized, and an oxidation of ferrous iron easily proceeds simultaneously with drying. Thus, the present invention has been accomplished.
That is, one aspect of the present invention is directed to an S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt which contains a lactam compound represented by the general formula (1) shown below and an ethylenediaminemonosuccinic acid represented by the general formula (2) shown below in an amount of 7 wt % or less, respectively:
wherein M is an ammonium ion or an alkali metal ion,
wherein M is an ammonium ion or an alkali metal ion,
Another aspect of the present invention is directed to a process for producing the above-mentioned S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt.
BEST MODE FOR CARRYING OUT THE INVENTION
S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salts as such are stable at a room temperature and have a very high water-solubility of 60 g/50 g H
2
O or more, and aqueous solutions thereof are weakly acidic substances having a pH of about 5 and can be stably stored.
On the other hand, S,S-ethylenediamine-N,N′-disuccinic acid used as a starting material in a process for producing an S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt by an iron chelating reaction, is an unstable compound in an acidic solution. It undergoes a lactam ring formation reaction or is decomposed by an amine elimination reaction. Additionally, this compound has a strong acidity of pH 2 or thereabout in an aqueous solution. Therefore, the compound further characterized in that its cyclization gradually proceeds when water is present, without an addition of an acidic substance, even at room temperature. The formation of a cyclization product and a fumaric acid, and a ethylenediaminemonosuccinic acid by an elimination reaction of amine are accelerated by heating.
However, a chelating reaction of iron under basic conditions results in an extreme decrease of a reactivity of iron oxide and a formation of a large amount of iron hydroxide and iron ammine complexes. In addition, when the S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt is obtained in the form of powder, an alkali present in excess undesirably caused a moisture absorption to deteriorate a stability of a product. Therefore, the reaction was unavoidably carried out with heating in a weakly acidic pH region of 3 to 6, so that the above-mentioned by-products were formed. Furthermore, since these by-products, i.e. the cyclization product and the by-products produced by the amine elimination reaction, have a lower chelate ability than that of S,S-ethylenediamine-N,N′-disuccinic acid, they released iron ions, owing to a pH change, a composition change of liquid caused by additives, and a lapse of time, so that a water-insoluble iron hydrate was formed to cause an appearance of turbidity in an aqueous solution.
The present inventors found the following: an appearance of the turbidity can be prevented to such an extent that it does not cause any problem in practice, by reducing a content of each of the above-mentioned by-products to 7 wt % or less; and the content of each of the by-products can be reduced to 7 wt % or less by taking the countermeasure described below. Thus, the present invention has been accomplished.
Since a formation of the decomposition products and the cyclization product is dep

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