Iron chelate composition

Abstract: The composition contains iron EDDHA and for iron EDDHMA in an agriculturally-acceptable organic solvent, preferably ethylene glycol. The composition is used in treating iron deficiency in soils and can have an iron content of up to 40 or 50 g dm⁻³. The composition may also contain considerable amounts of water yet still to be stable at room temperature, the aqueous composition having a significantly reduced viscosity relative to the water-free composition. The iron chelate need not be dry when incorporated into the composition. It may also be synthesised in situ in the solvent of the composition.

Description: This invention relates to iron chelate compositions. Iron chelate compounds include the compounds which contain the anions [Fe (III) EDDHA]⁻ and [Fe (III) EDDHMA]⁻, together with a cation, for example Na⁺ or K⁺. [Fe (III) EDDHA]⁻ is the chelate anion formed between ferric iron and the quadrivalent anion of ethylenediamine-N,N′-di-(o-hydroxyphenyl acetic acid), ethylenediamine-N,N′-di-(p-hydroxyphenyl acetic acid) or ethylenediamine-N-o-hydroxyphenyl acetic acid-N′-p-hydroxyphenyl acetic acid. Commercially-available materials often contain mixtures of the ortho, para and ortho-para isomers mentioned. Although the chelating powers of the three isomers may vary considerably, the expression "iron EDDHA" as used herein covers any compound which contains, in addition to a cation or two or more different cations, a monovalent anion in which ferric iron is chelated by the EDDHA anion in any one or more of its isomeric forms, and mixtures of such compounds. [Fe (III) EDDHMA]⁻ is the chelate anion formed between ferric iron and the quadrivalent anion of either ethylenediamine-N,N′-di-(2-hydroxy-4-methylphenyl acetic acid) or ethylenediamine-N,N′-di-(2-hydroxy-3-methylphenyl acetic acid). The chelating powers of the isomers are again not necessarily equal but the expression "iron EDDHMA" as used herein covers any compound which contains, in addition to a cation or two or more different cations, a monovalent anion in which ferric iron chelated by the EDDHMA anion in any one or more of its ismoeric forms, and mixtures of such compounds. The compounds just mentioned are sometimes identified by names such as sodium ethylenediamine-N,N'-di-(o-hydroxyphenyl) acetato ferrate (III), which corresponds to the compound containing sodium ions and the ortho-ortho form of the chelated anion [Fe (III) EDDHA]-. Iron EDDHA and iron EDDHMA are known to be effective agents for remedying iron deficiency in agriculture, particularly in highly alkaline soils. In the past, powders or granules of iron EDDHA or iron EDDHMA have been applied directly to the soil or have been dissolved in irrigation water. Both compounds however suffer from the disadvantage of low solubility in water; the powder forms are particularly difficult to handle because of their tendency to cake or form lumps in the presence of water. Aqueous solutions of the compounds are correspondingly difficult to prepare. DE-B-2846832 discloses a gelated micronutrient fertiliser composition. DE-A-2138068 discloses in example XVI an iron EDDHA foliar spray composition which is water-based and contains 1% propylene glycol as a penetrant agent. Attempts to make such solutions tend to result in the precipitation of a sticky mass of material in the mixing vessel, unless the addition of the solid iron EDDHA or EDDHMA to the water is accompanied by continuous strong agitation of the contents of vessel. This causes a particular problem when it is desired to dissolve the compounds in irrigation water where agitation to aid dissolution is difficult. Attempts to solve this problem by preparing aqueous solutions of the compounds for direct application to the soil have not been particularly successful because, even if sufficient agitation is used, it is not possible to obtain a solution which is more concentrated in iron EDDHA than about 30% w/v (i.e. about 30g of iron EDDHA chelate in 100 cm³ of solution, an iron EDDHA concentration of about 300 g dm⁻³ ), or more concentrated in iron EDDHMA than about 20% w/v (i.e. about 20g of iron EDDHMA chelate in 100 cm³ of solution, an iron EDDHMA concentration of about 200g dm⁻³). Since commercially available iron EDDHA and EDDHMA chelates are themselves only about 6% iron by weight and normally contain equimolar amounts of salts such as sodium sulphate or sodium chloride, a 30% w/v aqueous solution of iron EDDHA has an iron concentration of only about 1.8g per 100 cm³ (about 18 g dm⁻³) and a 20% w/v aqueous solution of iron EDDHMA has an iron concentration of only about 1.2 g per 100 cm³ (about 12 g dm⁻³). The low iron contents of these solutions, the difficulties in preparing the solutions and the problems which are associated with agricultural use of iron EDDHA and EDDHMA chelates in solid form (even after granulation, itself an expensive process) tend to restrict the agricultural usefulness of what might otherwise be an effective agent for remedying iron deficiency in soils. Similar problems are expected to arise in the agricultural use of other iron chelate compounds. The present invention provides a liquid composition for use in treating iron deficiency in soils, the composition comprising at least one iron chelate compound containing the anion [Fe (III) EDDHA]⁻ or the anion [Fe (III) EDDHMA]⁻, or a mixture of such compounds, in an amount effective, after dilution, to treat iron deficiency in soils, characterised in that the composition contains an agriculturally-acceptable liquid organic solvent, wherein the solvent comprises a polyhydric alcohol, or an ether thereof, and the composition has a viscosity at 20°C in the range from 0.1 to 10 Pa s and is sufficiently concentrated in iron that the relative amounts of iron chelate and organic solvent are such that the mass ratio of organic solvent to iron chelate in the composition does not exceed 3:1, and wherin any water in the composition is present in an amount such that the mass ratio of water to organic solvent does not exceed 10:1. The mass ratio of iron chelate to organic solvent preferably does not exceed 3:1 and most preferably is about 1:1. Typical compositions according to the invention may thus have iron chelate concentrations as high as about 700 g dm⁻³ and iron contents of about 40 or 50 g dm⁻³. The compositions can thus be sufficiently concentrated in iron to be highly useful as remedial agents against iron deficiency in soils. Advantageously, the organic solvent is one which allows the water content of the composition to be significant. The amount of water in the composition is preferably such that the mass ratio of organic solvent to water does not exceed 99:1, more preferably 10:1. Most preferably the mass ratio of water to organic solvent is about 2:1. In all cases the amount of water is such that the stability of the composition is not impaired. In general, as the iron chelate content of the composition increases, the amount of water which can be added whilst still maintaining stability, and, with iron EDDHMA compositions, an acceptable viscosity, decreases. For example, a composition with an iron EDDHA chelate concentration of 700 g dm⁻³ can contain ethylene glycol and water in a mass ratio of from 1:0 to 1:1, preferably in the range of 3:1 to 1.1:1 and more preferably about 2.3:1. Thus, for example, at an iron EDDHA chelate concentration of 700 g dm⁻³, the composition can contain as much as 300 g dm⁻³ of water and only 340 g dm⁻³ of ethylene glycol and still be stable at room temperature. These aqueous compositions can have significantly reduced viscosity relative to the water-free compositions and are accordingly more easily handled and used and, volume for volume, are less expensive than the water-free compositions. Compositions according to the invention preferably have a viscosity at 20°C as close to 0.5 Pa s (500 cP) as possible. A further advantage of the aqueous compositions of the invention is that the iron chelate compound used to prepare the composition need not be entirely dry. Energy which would be expended in drying the chelate compound can thereby be saved. Moreover, the iron chelate compound used to prepare either an aqueous or a water-free composition according to the invention may contain an amount of an agriculturally-acceptable solvent, preferably the same solvent as is contained in the composition. The effort and energy which would otherwise be expended in removing residual solvent from the chelate is thus saved. This is particularly the case when the solvent present in the chelate compound is a solvent in which synthesis of the iron chelate compound has been carried out. The aqueous and water-free solutions are useful as remedial agents against iron deficiency in soil and can be applied to the soil by, for example, direct spraying or by incorporation into irrigation water. The invention will now be explained further by way of the following examples of the preparation and use of EDDHA chelate compositions. EXAMPLE 1 200g of water was introduced into the mixing vessel of a Silverson mixing machine and the mixing machine started at half speed. 450g (403 cm³) of ethylene glycol was then added to the water in the mixing vessel. To the water-ethylene glycol mixture, 700g of commercial iron EDDHA powder was added over a period of about 5 min. After addition was complete, stirring was continued for about 10 min, after which the mixing machine was stopped. The composition produced was a dense blood-red solution having an iron EDDHA concentration of 700 g dm⁻³, corresponding to an iron concentration of 42 g dm⁻³. The solution was apparently stable for an indefinite period over a temperature range of from 40°C to -15°C. The composition was found to be effective as an agent for remedying iron deficiency when applied to the soil by spraying. EXAMPLE 2 The procedure of Example 1 was followed except that 500g of commercial iron EDDHA powder was added to a mixture of 200 g of water and 510 g of ethylene glycol to give a composition having an iron EDDHA concentration of 500 g dm⁻³ (corresponding to a 30 g dm⁻³ iron). This composition was effective in the way stated for the composition of Example 1. EXAMPLE 3 The procedure of Example 1 was repeated omitting the water, increasing the amount of ethylene glycol to 660 g and using 700 g of iron EDDHMA to give a solution of corresponding strength. The composition was similarly effective in remedying iron deficiency in soils. EXAMPLE 4 The procedure of Example 2 was repeated using 500 g of commercial iron EDDHMA powder in place of the iron EDDHA powder to give a composition having an iron EDDHMA concentration of 500 g dm⁻³. EXAMPLE 5 This example describes the preparation in an agriculturally-acceptable solvent of iron EDDHA. Any residual amount of the solvent need not be removed from the iron EDDHA product before its use in a composition according to the invention. The known reaction between 2 moles of phenol, 2 moles of glyoxylic acid, 1 mole of ethylenediamine and 4 moles of sodium hydroxide proceeds according to the equation: Addition of Fe³⁺ ions at a pH of 7.0 to 8.5 leads to formation of Na[FeEDDHA]. The reaction, when carried out in ethylene glycol as solvent, leads to formation of a composition according to the present invention. Details of the reaction procedure are as follows, all parts being by weight: A reaction vessel fitted with a condenser, dropping funnels and a mechanical agitator was charged with 9.4 parts phenol (0.1 mol) and 18 parts ethylene glycol as solvent. These were heated to 40 to 45°C and 3 parts of ethylenediamene (0.05 mol) and 8 parts 50% w/w aqueous sodium hydroxide solution (0.1 mol) added. The reaction mixture was stirred constantly and maintained at 40 to 45° C. 14.8 parts of 50% w/w glyoxylic acid were added over a period of 15 minutes. After complete addition of the glyoxylic acid the reaction mixture was stirred constantly and maintained at 70 to 75° C for 2 hours. 13.51 parts of ferric chloride hexahydrate (0.05 mol iron) were dissolved in 5 parts of water. This solution was added slowly to the cooled reaction mixture with constant stirring. The pH was monitored throughout this addition and maintained between 7.0 and 8.5 using 50% w/w sodium hydroxide solution. After complete addition, the mixture was stirred for a further 30 minutes still maintaining the pH at 7.0 to 8.5 using 50% w/w sodium hydroxide solution. The resultant liquid was the characteristic deep red of iron EDDHA and contained solid sodium chloride which was removed by centrifuge. Approximately 62 parts of liquid concentrate were recovered containing 1.93% w/w iron with a relative density of 1.237, equivalent to an iron content of 2.39% w/v or 23.9 g dm⁻³. This was increased to 4.2% w/v (42 g dm⁻³) by removal of water by distillation. The presence of iron EDDHA was confirmed by gel permeation chromatography. EXAMPLE 6 Example 5 was repeated with 0.1 moles of p-cresol instead of 0.1 moles of phenol, the resulting iron EDDHMA compound being predominantly the ortho isomer, i.e. ethylenediamine-N,N′-di-(2-hydroxy-4-methylphenyl acetic acid). It has been noted that the viscosity of iron EDDHMA compositions can be unacceptably high if water is present in iron EDDHMA compositions of iron concentration as high as 40 or 50 g dm⁻³. As much water as possible should preferably be distilled out of the reaction mixture for iron EDDHMA compositions of greater iron concentration than 35 g dm⁻³. If possible, water should be avoided altogether in the synthesis. EXAMPLES 7,8,9, and 10 The procedures of Examples 1,2,3 and 4 were repeated using ethylene glycol monoethyl ether instead of ethylene glycol and taking the standard precautions necessary due to the low flashpoint of the solvent. The compositions so produced were less viscous than the corresponding ethylene glycol compositions. EXAMPLE 11 A composition according to Example 1 was tested under replicated glasshouse conditions (treatment 3) and compared with the powder chelate of 6% iron content by weight (treatment 2) and a control containing no iron (treatment 1). Conditions were as follows: A wheat test crop was watered daily with an iron-free but otherwise balanced nutrient solution. In treatment 1, no iron was added. In treatment 2, commercially-available iron EDDHA (6% by weight iron) was dissolved in water and watered into the soil at an application rate of 50 kg ha⁻¹ iron EDDHA (6% Fe) and a water rate of 1000 dm³ ha⁻¹. In treatment 3, the composition of Example 1 was applied at a rate of 83.3 dm³ ha⁻1 and a water rate of 1000 dm³ ha⁻¹, to give the same rate of application of iron as in treatment 2. The experimental design was a randomised block, with four replicates of each treatment. The following results were obtained: Treatment Leaf Iron Level (ppm) (% increase over the nil) Grain Dry Yield (g/pot) (% increase over the nil) 1. Nil 53.5 24.39 2. 50 kg/ha Fe EDDHA (6% Fe) 82.8 (54.8%) 26.24 (7.6%) 3. 83.3 1/ha Composition of example 1 (4% Fe) 78.5 (46.7%) 27.01 (10.7%) The results showed the composition from Example 1 to be as effective on an iron for iron basis, within experimental error, in correction of iron deficiency as powdered iron chelate (6% Fe) when applied to the soil by watering. Preparation and application was however much more convenient.

Claims: A liquid composition for dilution and subsequent use in treating iron deficiency in soils, the composition comprising at least one iron chelate compound containing the anion [Fe (III) EDDHA]⁻ or the anion [Fe (III) EDDHMA]⁻, or a mixture of such compounds, in an amount effective, after dilution, to treat iron deficiency in soils, characterised in that the composition contains an agriculturally-acceptable liquid organic solvent, wherein the solvent comprises a polyhydric alcohol, or an ether thereof, and the composition has a viscosity at 20°C in the range from 0.1 to 10 Pa s and is sufficiently concentrated in iron that the relative amounts of iron chelate and organic solvent are such that the mass ratio of organic solvent to iron chelate in the composition does not exceed 3:1, and wherein any water in the composition is present in an amount such that the mass ratio of water to organic solvent does not exceed 10:1. A composition according to claim 1, in which the solvent comprises ethylene glycol or the monoethyl ether thereof. A composition according to claim 1 or 2, in which the mass ratio of iron chelate to organic solvent does not exceed 3:1. A composition according to claim 3, in which the mass ratio of iron chelate to organic solvent is about 1:1. A composition according to any preceding claim, containing water in such an amount that the mass ratio of organic solvent to water does not exceed 99:1. A composition according to claim 5, in which the mass ratio of organic solvent to water does not exceed 10:1. A composition according to claim 6, in which the mass ratio of organic solvent to water is about 2:1. A method of preparing a composition according to any of claims 5 to 7, using iron chelate material as specified in claim 1, the iron chelate material containing water which forms in the composition at least some of the water specified in claim 5, 6 or 7. A method of preparing a composition according to any of claims 1 to 7, in which at least one iron chelate compound as specified in claim 1 is synthesised in an agriculturally-acceptable liquid organic solvent as specified in claim 1, the chelate compound(s) not being subsequently removed from the solvent which forms at least some of the organic solvent of the composition. Treatment of iron deficiency in soils by use, after dilution, of a composition according to any of claims 1 to 7.

Inventors: DAWSON JOHN MERVYN, WARNE VIVIAN BEVERLEY, DAWSON, JOHN MERVYN, WARNE, VIVIAN BEVERLEY
Applicants: PHOSYN PLC
Application year: 1989
Main classification: C05G3
IPC codes: C05F11