This invention also relates to the corresponding phosphine compounds formed by reaction of the above phosphonium compounds with bases. The present invention also relates to a method for the production of such compounds and to their use in a wide variety of applications.

The phosphorus compounds of the present invention have one or more hydroxymethyl groups and one or more hydrophilic groups covalently bonded to the phosphorus atom.

It is known from DE-AS-1045401 to produce phosphorus compounds by reacting tris (hydroxymethyl) phosphine (THP) with aliphatic a, unsaturated carboxylic acids, esters or amides, if necessary in the presence of water, and/or of water-miscible organic solvents and/or acids.

However, THP, and its solutions in water, are unstable and will slowly decompose at ambient temperature to yield flammable materials such as hydrogen. THP can therefore require elaborate and costly handling. We have found that the disadvantages associated with the handling of THP can be avoided by starting from a tetrakis (hydroxyorgano) phosphonium salt (commercially available as a stable solution in water).

According to a first aspect the present invention provides a phosphonium compound having the general formula (1) : [Yn P# (CH2OH)4-n]X- (I) wherein n is a positive integer of from 1 to 4; X is an anion; and Y is an organic residue comprising a hydrophilic group.

The hydrophilic group, for example, may be selected from unsaturated or saturated, aromatic or aliphatic, derivatives of C, to Cl0 carboxylic acids, phosphonic acids, sulphonic acids, acid phosphates, monohydric or polyhydric alcohols.

Suitably, Y may be selected from Cl to Cl0 groups containing polyethylene glycol and/or polypropylene glycol moieties.

General formula (I) shows group"Y"in its unionised form. There will be analogous formulae, readily apparent to those skilled in the art, which represent the ionised forms.

The anion X may be, for example, chloride or sulphate. Alternatively, X may represent any other anion (which results in the product of formula (I) being water-soluble) including for example, bromide, iodide, phosphate, acetate, oxalate, citrate, borate, chlorate, nitrate, fluoride, carbonate and formate.

In a second aspect, the present invention provides a phosphine compound having the general formula (II) : Yn P (CH, OH),, (H) wherein n is a positive integer of from 1 to 3; and Y is as described for formula (I). Such phosphines can typically be generated by action of a base on the phosphonium compound.

A compound of formula (I) or formula (II) may be the reaction product of a tetrakis (hydroxyorgano) phosphonium salt, a base and an unsaturated or saturated, aromatic or aliphatic, Cl to Cl0 carboxylic acid, phosphonic acid, sulphonic acid, acid phosphate or monohydric or polyhydric alcohol.

Preferably the compound is the reaction product of a tetrakis (hydroxyorgano) phosphonium salt, a base and an unsaturated carboxylic acid, or an ester or salt of an unsaturated carboxylic acid.

Alternatively the compound may be the reaction product of a tetrakis (hydroxyorgano) phosphonium salt, a base and an alkyl halide containing at least one reactive halogen and at least one group which imparts hydrophilic character.

Suitably, the substituted alkyl halide comprises from one to ten carbon atoms.

The group which imparts hydrophilic character may be derived from an unsaturated or saturated, aromatic or aliphatic, Cl to Cl0 carboxylic acid,

phosphonic acid, sulphonic acid, acid phosphate or monohydric or polyhydric alcohol.

The compounds of formula (I) and/or formula (II) may also be the reaction product of a tetrakis (hydroxy-organo) phosphonium salt, a base and vinylindene-1, 1-diphosphonic acid (VDPA) or a salt or an ester of VDPA.

Phosphonium compounds produced by this reaction may have the general formula (III): wherein: M is hydrogen, an alkali metal, an alkaline earth metal, a polyvalent metal, ammonium or a quaternised amine radical and each M may be the same or different; X is an anion having the same significance as in formula (I); n is a number having a positive average value of up to 4. The number n need not be an integer.

Examples of polyvalent metals in formula (III) above include transition metals such as copper, chromium, iron, titanium, or zirconium, as well as other metals such as aluminium, while examples of quaternised amine radicals include salts derived from neutralisation with amines e. g. triethanolamine and quaternary ammonium bases e. g. tetrabutyl ammonium hydroxide.

Phosphonium compounds of formula (III) may be readily oxidised, for example, by peroxides or atmospheric oxygen, to the corresponding phosphine oxide, with the loss of formaldehyde and a proton. Phosphine oxides of this type are believed to be novel.

These phosphine oxides may be represented by the general formula (IV): wherein M has the same significance as in formula (III); and n is a number having a positive average value of up to 3.

In a third aspect, the present invention provides a method for the production of phosphonium compounds of formula (1) or formula (III) and/or phosphine compounds of formula (II), by the reaction of a tetrakis (hydroxyorgano) phosphonium salt (THP+ salt), a base and an organic compound including a hydrophilic group, for example, an unsaturated or saturated, aromatic or aliphatic, Cl to Cl0 carboxylic acid, phosphonic acid, sulphonic acid, acid phosphate or monohydric or polyhydric alcohol.

In particular, the THP+ salt and the base may be reacted with an unsaturated carboxylic acid, or an ester or salt of an unsaturated carboxylic acid.

Phosphonium or phosphine compounds according to the present invention may also be prepared by reacting a THP+ salt and a base with an alkyl

halide which contains at least one reactive halogen and at least one group which imparts hydrophilic character.

Preferably, the alkyl halide comprises one to ten carbon atoms. The group which imparts hydrophilic character is preferably derived from an unsaturated or saturated, aromatic or aliphatic, Cl to Cl0 carboxylic acid, phosphonic acid, sulphonic acid, acid phosphate or monohydric or polyhydric alcohol. Alternatively, the group imparting hydrophilic character may be selected from C, to Cl0 groups containing polyethylene glycol and/or polypropylene glycol moieties.

The tetrakis (hydroxyorgano) phosphonium salt (THP+ salt) is preferably a tetrakis (hydroxymethyl) phosphonium salt of formula THPX, where X is an anion as described above with reference to formula (I). The THP+ salt may be, for example, tetrakis (hydroxymethyl) phosphonium chloride (THPC), sulphate (THPS), acetate (THPA) or phosphate (THPP).

Although it is not intended that the method according to the present invention should be construed with reference to any specific theory, it is believed that the reaction proceeds by the in-situ generation of tris (hydroxyorgano) phosphine (THP) under the conditions of the reaction (i. e. in the presence of a base). This type of reaction is well reported in the literature.

Preferably, the conditions of the reaction are optimised to encourage mono, rather than di or tri, substitution of the THP.

In a first preferred embodiment of the method, an unsaturated carboxylic acid, preferably a mono-carboxylic acid such as acrylic acid, is reacted with a THP+ salt in the presence of a base.

Other unsaturated mono-carboxylic acids which may be used to make a compound of formula (I) and/or formula (II) include methacrylic acid, crotonic acid, isocrotonic acid, angelic acid and tiglic acid.

Alternatively, the unsaturated carboxylic acid may be a di-carboxylic acid such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid or glutaconic acid.

In a second preferred embodiment of the method, an alkyl halide, such as 2-bromopropionic acid, is reacted with a THP+ salt in the presence of a base.

Alternatively, there are many alkyl halides, which contain a hydrophilic group, which could be used. These will be readily apparent to those skilled in the art.

In a third preferred embodiment of the method, a phosphonic acid, such as vinylidene-1, 1-diphosphonic acid, is reacted with a THP+ salt in the presence of a base.

Preferred examples of compounds of formula (I) and/or formula (II) include the mono-substituted and di-substituted adducts of THPX and acrylic acid or of THPX and 2-bromopropionic acid.

The reaction may be performed at elevated temperature and under an inert (e. g. nitrogen) atmosphere.

It will be appreciated that for phosphonium compounds of formula (I) or formula (III) where n is less than 3, and for phosphine compounds of formula (II) where n is less than 3, the compounds will contain at least one methylol group. Further reaction of such compounds with other

substitutents is possible; either at the phosphorus atom or at the-CH20H group. For example, a condensation reaction product of the phosphonium compounds with, inter alia, urea, thiourea, dicyandiamide, melamine or guanidine may be formed by such further reaction.

For phosphonium compounds of formula (III), where M is an amine radical, it will be appreciated that further reaction with other substituents is possible at the amine of the phosphonium compound. The amine substituent may include, in addition to a quaternised amine radical, compounds selected from silicones. The silicones are preferably aminosilicones. For example, aminosilicones such as those available under the registered trade mark Rhodorsil@.

Compounds of formula (II) may be formed when a hydroxymethyl group is removed from a phosphonium compound of formula (I). Removal of a hydroxymethyl group can occur due to hydrolysis of a phosphonium compound. Hydrolysis can arise due to the addition of water or an increase in pH.

In a fourth aspect, the present invention provides the use of compounds of formula (I) and/or formula (II) in applications including scale inhibitors, scale dissolvers including iron sulphide dissolvers, corrosion inhibitors, chelating agents, flame retardants, disinfectants, in the surface modification of a wide variety of organic and inorganic substrates e. g. metals and natural or synthetic polymers, as ion exchangers, cement additives, adhesion promoters or gelatine hardening agents for use in, for example, photographic applications.

The compounds can also be used as cross linking agents e. g. in leather tanning. The compounds can also be used as pretanning agents, tanning or retanning agents, as cross-linking agents for leather finishes such as

casein or polyurethane-based finishes and as fixing agents for dyes and amino-derivatives (e. g aminosilicones or amine-derivatised dyes) on to wool, polyester, polyamide or leather substrates.

The compounds can also be used for leather tanning in combination with, pre-blended with, co-applied with or sequentially applied with, other pre- tanning agents such as syntans, aldehydes, THPX or oxazolidine; organic tanning agents such as THPX, aldehydes, oxazolidine, dialdehyde starch or polymeric dialdehydes; mineral tannins such as salts of chromium (III), titanium, zirconium, aluminium or iron; vegetable tannins, both hydrolysable and condensed tannins, such as tara, mimosa, sumac or quebracho; bating enzymes; pickling acids/salts; pickle replacements such as Rhodia ECOETST^ ; protein fillers; all types of syntans, including replacement, auxiliary, neutralising and chrome syntans; resins such as acrylics, styrene/maleics or nitrogen based resins; dyes including direct, reactive and premetallised dyes; fat liquors including anionic, nonionic, cationic, sulphited, sulphated, natural and synthetic types; water proofing agents; oil tannages such as cod oil; splitting/shaving aids such as colloidal silicates; other finish cross linkers such as aliphatic isocyanates, aziridine or carbodiimide.

The advantages of using the phosphonium compounds of formula (I) and/or the phosphine compounds of formula (II), in particular compounds which are the reaction product of THPX, a base and acrylic acid, include lower residual free formaldehyde levels in wet white and crusted skins and in finished leather; whiter and fuller skins and reduced grain tanning, giving a more versatile leather In addition, the phosphonium and/or phosphine compounds, of formulas (I) and (II) respectively, exhibit synergy with mineral tanning agents and display dye enhancement with, for example, premetallised dyes. One

particular aspect of the invention is that the phosphonium and/or phosphine compounds exhibit enhanced compatibility with retannage chemicals, particularly sulphited fat liquors. Wet white leather which has been tanned using compounds of formula (I) and/or formula (II) can be retanned by conventional methods to produce a wide variety of leather skins. The skins are more tolerant to variations in retannage processes for example fat liquor selection is less critical than with conventional tannages.

The compounds can also be used for dye enhancement in textiles.

Phosphonium compounds of formula (I) and/or phosphine compounds of formula (II) can also be used as biocides, for example, as bactericides, fungicides, slimicides, algicides and anti-protozoals in the treatment of water systems.

The water systems to be treated in accordance with the present invention include oilfields, cooling towers, reverse osmotic processes, paper processing plants, non-potable water sources, as well as other industrial applications in which the biocidal treatment of water is necessary.

The present invention also provides the use of compounds of formula (I) and/or formula (II) as preservatives to prevent microbial spoilage of products susceptible to said spoilage.

Preferably, the products to be preserved comprise functional fluids, slurries, emulsions, suspensions and homogeneous solutions, for example, drilling fluids, completion fluids, fracturing fluids, clay slurries, kaolin slurries, silica slurries and calcium carbonate slurries.

The present invention further provides the use of compounds of formula (I) and/or formula (II) as disinfectants.

In the practice of the present invention, the compounds of formula (I) and/or formula (II) may be used in admixture with one or more surfactants. The surfactants may be anionic, cationic, non-ionic or amphoteric.

The present invention still further provides the use of compounds of formula (I) and/or formula (II) in admixture with other water treatment chemicals comprising at least one of scale inhibitors, corrosion inhibitors, dispersants, antifoams, wax inhibitors, asphaltene inhibitors, naphthenate inhibitors, oxygen scavengers, polyelectrolytes, scale dissolvers (including dissolvers for iron sulphide scale) and further biocides. Said further biocides may include poly-quaternary ammonium compounds such as WSCP; quaternary ammonium compounds such as benzalkonium chloride; mono-or poly-aldehydes, such as, formaldehyde and glutaraldehyde; isothiazolones such as chloromethylisothiazolinone (CIT), methylisothiazolinone (MIT), 1, 2-benzisothiazolin-3-one (BIT) or CIT/MIT blends; oxidising biocides such as hydrogen peroxide, peracetic acid, chlorine, bromine, chlorine dioxide; halogenated organics such as 2- bromo-2-nitropropane-1, 3-diol, 2,2-dibromo-3-nitrilopropionamide or 2,2-dibromo-2-nitroethanol ; thio-carbamates; or polymeric biguanidines.

Preferred embodiments of the invention will now be illustrated, by way of the following examples.

Example 1 This Example illustrates the preparation of reaction products of tetrakis (hydroxymethyl) phosphonium chloride (THPC) and acrylic acid.

THPC (80% w/w, 238.4g, l. Omol, 1 equiv), acrylic acid (80% w/w, 90.45g, l. Omol, 1 equiv. ) and water (600g) were charged to a 1-litre jacketed reaction vessel under nitrogen, to give a solution of pH 0 to 1.

Sodium hydroxide solution (47% w/w, 110g) was added to the reactants over a period of 10 minutes during which the temperature reached 44°C.

The pH of the solution was found to be 7.5.

The reactants were heated to 48°C for 6 hours before cooling."P-NMR showed 62% mono-substituted product, 19% di-substituted product and 18% unreacted THPC (and THP acetate) by area. tH-NMR showed less than 1% unreacted acrylic acid remaining.

Further acrylic acid (80% w/w, 9. 0g, O. lmol, 0.1 equiv. ) and sodium hydroxide solution (47% w/w, 0. 48g) was charged to the reactor and the contents were heated at 48°C for 5 hours, after which the reaction mixture was cooled to room temperature. 3lP-NMR showed 69% mono- substituted product, 22% di-substituted product and 9% unreacted THPC (and THP acetate). lH-NMR showed less than 1% unreacted acrylic acid remaining.

The pH of the solution was adjusted to 4 using 36% hydrochloric acid.

The reactor was emptied and the solution stripped on a rotary evaporator using a divac pump to azeotropically remove formaldehyde, adding small amounts of water every hour for 7 hours. The product was stripped further using an oil pump.

The solids (266g) were dissolved in 173g of water to give a 50% w/w solution of mono-and di-substituted products.

Example 2 This Example shows an improved preparation of reaction products of THPC and acrylic acid compared to that of Example 1.

THPC (240g, 80% w/w, acrylic acid (77g, 99%) and water (600g) were added to a 1-litre flask fitted with condenser, temperature probe, nitrogen inlet and dropping funnel. Sodium hydroxide solution (lOOg, 47% w/w) was added dropwise over 60 minutes, ensuring that the temperature did not rise above 40°C. The reaction was allowed to stir at 50°C for 4.5 hours.

The 3'P-NMR spectrum, at this point, showed unreacted THP, so more acrylic acid (15g) was added and the reaction mixture heated for a further 3 hours. The water was stripped over 3.5 days on a rotary evaporator to eliminate formaldehyde. The final product contained 70. 4% THPC/AA mono-substituted adduct, 28. 2% di-substituted adduct and 1.6% tri- substituted adduct. No free, unreacted, THPC was present.

Example 3 This Example illustrates the preparation of reaction products of tetrakis (hydroxymethyl) phosphonium chloride (THPC) and vinylidene- 1,1-diphosphonic acid (VDPA) tetra sodium salt.

Vinylidene-1, 1-diphosphonic acid tetrasodium salt (VDPA, 400g, 0. 79mol, 55% ww/w) was added to a solution of tetrakis-hydroxymethyl phosphonium chloride (THPC, 200g, 80% w/w, 0. 79mol) and water (500ml) in a 3-necked, 2-L round bottomed flask. The mixture was heated under a nitrogen atmosphere with stirring to 75-80°C for 3.5 hours.

A sample was then taken and analysed by"P-NMR. This showed that all of the VDPA had reacted. There was also evidence of a small amount of oxidation of THPC to THPO.

A further 20g of VDPA was added to the reactor, which was maintained at 75°C for a further 2.5 hours. The reactor was then cooled to room temperature and stored under an inert atmosphere overnight. A sample was then taken and analysed by 3lP-NMR. A small trace of THP was detected.

A further 15g of VDPA was added to the reactor, which was then heated to 75°C for 4 hours. After which, analysis by 3lP-NMR showed a small trace of THP still remained. The reaction was complete. The final composition of the reaction was 79% product, 4% of the di-addition product, 9% oxidation, 2% THP and 2. 6% unreacted VDPA.

The mixture was cooled to room temperature and the pH of the product was adjusted from pH8 to pH6 with concentrated hydrochloric acid. The product was then placed on a rotary evaporator to remove water and formaldehyde. Water was continually added back to the flask to help azeotrope out any remaining formaldehyde, this process was continued for three 7-hour days.

The resulting product was a viscous colourless liquid (781g). The residual formaldehyde content was measured to be 2. 3% w/w. The product was estimated to be 40% w/w and was diluted to give a 25% w/w solution in water.

Example 4 This Example further illustrates the preparation of reaction products of tetrakis (hydroxymethyl) phosphonium chloride (THPC) and vinylidene- 1,1-diphosphonic acid (VDPA) tetrasodium salt.

Vinylidene-l, 1-diphosphonic acid tetrasodium salt (VDPA, 442g, 0. 8mol, 50% w/w) was added to a solution of tetrakis- (hydroxymethyl) phosphonium chloride (THPC, 100g, 80% w/w, 0. 4mol) and water (500ml) in a 3-necked, 2-L round bottomed flask. The mixture was heated under a nitrogen atmosphere with stirring to 75-80°C for 7.5 hours. The reaction mixture was then cooled to room temperature and stored overnight under an inert atmosphere.

A sample was taken and analysed by"P-NMR. The spectrum showed that 43% of the VDPA was unreacted, 11% of the THPC had been oxidised to THPO and that there was 45% of the mono addition product.

A further 100g of THPC was added to the reactor, which was heated to 75 ° C for 4 hours. Analysis by"P-NMR showed all the VDPA had

reacted to give a mixture of the mono- (64%) and di- (36%) addition products.

Another 100g of VDPA was added to the reactor, which was maintained at 75 ° C for 4 hours. The reaction mixture was cooled to room temperature and stored overnight under an inert atmosphere. Analysis by 3lP-NMR showed that there was no residual VDPA, and that there was 57% dimer and 43% of the mono addition product.

A further 20g of VDPA was added to the reactor, which was again heated to 75 ° C for 4 hours. A sample was taken and analysed by"P-NMR, no unreacted VDPA was present. The proportion of the dimer had increased to 65% leaving 35% of the mono addition product. The proportion of dimer did not change with further heating and the reaction was concluded as being complete.

The product was placed on a rotary evaporator to remove water and formaldehyde. The resulting product was a mobile colourless liquid with a pH of 7. The moisture content was measured as 23.5% w/w.

The NMR integrals give a ratio of monomer: dimer by area. When these areas are converted into % w/w the product was calculated to be 74% w/w dimer and 26% w/w monomer.

It will be appreciated that examples 1 to 4 can be carried out in polar organic solvents.

Example 5 This Example shows the use of a product obtained according to the invention as a tanning agent using conventional tanning technology.

40g of pickled ovine skin 3g sodium chloride and water to give 100% float 0.2g of sodium formate Rotated for 1 hour. pH measured as 3.2 Next, 1.6g of a 1: 1 THPC/acrylic acid adduct, with an activity of 17%, as determined by iodine titration, was added to give a percentage offer of 4% product.

This was rotated for 3 hours to obtain good penetration (as determined by a selenium indicator previously used with other phosphonium based tanning agents).

Following this, the float was basified gradually by adding 1% (0.4g) sodium bicarbonate and rotated for 30mins between each basification (2 basifications in total).

The final pH after basification was measured as pH 6.0 The shrinkage temperature was measured by standard techniques and a value of 67°C was obtained.

By applying the product at a higher pH, eg. 4.5, a shrinkage temperature of 71°C was obtained.

The wet white produced using the THPC/acrylic acid adduct was whiter and fuller than that usually produced by conventional phosphonium tannages and, upon drying, produced a more malleable skin.

Example 6 This Example shows a further use of a product obtained according to the invention as a tanning agent using conventional tanning technology.

Bovine pickled pelt (lOOg) 8% sodium chloride and water to give 100% float (be°-6) 0. 75% sodium bicarbonate 30 minutes rotation-allow to adjust to float pH5 Next 3% tanning agent, made according to Example 3, was added and left for 90 minutes to allow penetration of the pelt. The shrinkage temperature was measured by standard techniques and a value of 65 °C obtained.

Basification of the float to pH 6.5 was undertaken by adding 1% sodium bicarbonate at 30 minute intervals (sodium bicarbonate was added twice).

The shrinkage temperature was now 68°C.

After leaving to rotate overnight the selenium indicator response was even and dark throughout (this indicates a good"equilibrium tannage"), the leather was flat and tight, and the shrinkage temperature was 76-77°C.

Example 7 This Example shows, using a standard quantitative suspension test, the use as a biocide of a product obtained according to the invention.

Tetrakis (hydroxymethyl) phosphonium sulphate (THPS) and a 1: 1 THPC/acrylic acid product (as per Example 1 above) were each evaluated as 25% active products (300 ppm of product with a 3 hour contact period) against a mixed consortium general aerobic bacteria population. The results are expressed as log reductions of viable bacteria: Product Log reduction THPS 5.2 1: 1 THPC/acrylic acid adduct 4.7 Example 8 The Example further shows, using a standard quantitative suspension test, the use as a biocide of a product obtained according to the invention.

THPS (75% active) and the product of Example 1 above were each evaluated against a general aerobic bacterial population (200ppm of product with a 3 hour contact period) in paper white water. The results are expressed as log reductions of viable bacteria: Product Log Reduction THPS 7.3 1: 1 THPC/acrylic acid adduct 7.3

Example 9 This Example shows, using a standard quantitative suspension test, the use as a biocide of a product obtained according to the invention.

The product of Example 2 was used in this example and is the reaction product of tetrakis (hydroxymethyl) phosphonium chloride (THPC) and acrylic acid. The product was shown by iodine filtration to be 37% active, to have a mono: di: tri substituted species ratio of 83: 4: 11 and to contain 2.5% free THPC. This product was compared to THPS.

THPS and the product described above were each evaluated against a general aerobic bacterial population (37.5 ppm of active product with a 24 hour contact period). The results are expressed as log reductions of viable bacteria: Product Log Reduction THPS 7.3 THPC/acrylic acid adduct 7.3 Example 10 This Example shows the use as an iron sulphide dissolver of a product obtained according to the invention.

In this Example: THPC = tetrakis (hydroxymethyl) phosphonium chloride AA= acrylic acid

Three screw-top glass jars were charged with 100g of the following 1: 1 THPC-Acrylic Acid adduct (THPC-AA) solutions: 1.20g of 1: 1 THPC-AA and 80g deionised water; 2.20g of 1: 1 THPC-AA and 79g deionised water and lg ammonium chloride; 3.20g of 1: 1 THPC-AA and 13. 3g BRIQUESTe 543-25S* and 66.7g of deionised water.

(*25% Diethylenetriaminepentakis (methylenephosphonate, sodium salt)) BRIQUEST is a Registered Trade Mark.

Into each solution was accurately weighed about 3g of an oilfield iron sulphide scale (from a water injection system). The jars were each equipped with a magnetic follower and stirred for 20hrs in a 50°C water bath. Each solution was then filtered through a pre-weighed filter paper.

The residues were washed with water and with acetone. The filter paper and remaining solids were then allowed to dry at room temperature to a constant mass before re-weighting, to give a weight loss. The filtered solutions were also analysed for iron content using the total iron method on a Hach DR2000 Spectrophotometer.

Results _ Solutien 5ta F 0 Wt ; t ; ; i Eron in VVt W Loss Loss, Solution. : L,, oss (1) THPC-AA 3. 00 1. 94 1. 06 35 550 (2) THPC-AA/NH4+ 3. 07 1. 05 2. 02 66 3400 (3) THPC-AA/BRIQUESTO 543-25S* 3. 11 1. 13 1. 98 64 3420 *See above

In a comparative experiment, a blank system (just water) gives a weight loss of 24% and zero iron in solution.