NZ202108A - Method for the detection and removal of substitution labile transition metal ions - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £02108 Piic.Uy Date(s}: .'A'.".

Complete Specification Filedf7..T/7 Class: « ur • 31 MAY 1985 Publication Date: P.O. Journal, No: .... 33 i NEW ZEALAND PATENTS ACT, J953 //". ••> No.: Date: COMPLETE SPECIFICATION METHOD FOR THE DETECTION AND REMOVAL OF SUBSTITUTION LABILE TRANSITION METAL IONS H/We, BRISTOL-MYERS COMPANY, a State of Delaware corporation having offices at 345 Park Avenue, New York, New York, United States of America, hereby declare the invention for which X / we pray that a patent may be granted to fSfflfi/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - (followed by la) 202108 - la - METHOD FOR THE DETECTION AND REMOVAL OF SUBSTITUTION ; LABILE TRANSITION METAL IONS 1. Description: FIELD OF INVENTION The present invention relates to the detection and/or removal of substitution labile transition metal ions present in aqueous solutions. More specifically, the method described herein concerns the use of a 2-pyridinethiol-l-oxide anion to determine the presence or absence of the said transition metal ions and to facilitate their removal from solution by chelation. Most specifically, the present invention relates to the detection/removal of said transition metal ions from an aqueous solution also containing other chelating agents, or from aqueous solutions into which other chelating agents will be added, the use of a 2-pyridinethiol-1-oxide alkali salt being compatible with said other chelating agents.

BACKGROUND OF THE INVENTION Industrial, household and cosmetic preparations are often sensitive to the presence of heavy metal ions, which ions interfere with active agents resulting in a dimunition or loss of product effectiveness. The nature of the interference caused by the metal ions is varied, for example, the breaking of emulsions in furniture polishes, hand creams or lotions, Friedel-Crafts reactions that affect fragrance stability, or reduction in peroxide stability.

Metal ions which behave in this manner are the substitution labile transition metal cations, for example, some complexes of ferric and ferrous, and cupric ions. Substitu- n % 0 :8' tion inert cations, for example, the chromic ion, do not complex or transthelate with organic ligands, and therefore do not require removal from the aqueous solution. Whether an ion is substitution labile or substitution inert depends on the d orbital configuration, substitution inert ions being characterized by 3 and 8 d electrons in their outer shell. Transition metal ions having 4, 5 and 6 d electrons in the outer shell are also substitution inert if complexed with strong- field ligands such that "the electrons in those " d orbits are paired.

Substitution labile ion contamination in the preparation of these products typically occurs during manufacture, the ions being present in the process water arriving from outside the facility battery limits. The contamination may also occur because of the nature of piping and equipment materials used witin the battery limits of the processing facility. Of course, if the magnitude of in-plant contamination is too great, replacement of equipment may be more economical than removal of the ions by chemical/physical means. Product contamination may occur during storage or shipment from the product containers, especially metal containers having a polymeric film that can be scratched.

Past practice has sought to control the dimunition/ loss in product effectiveness caused by ion contamination by several means. Process water- entering the facility can be treated by distillation or ion exchange, thereby removing the contaminants. A second method, often used in conjunction with water treatment, has been to incorporate within the product composition a chelating agent that complexes the substitution labile transition metal ion thereby reducing offending physical or chemical interference. Typical chelating agents are alkali salts of nitrilotriacetic acid, ethylenediaminetriacetic acid and the like. In certain formulations the incorporation of these chelating agents are also necessary even though the processing water and facility have been successfully purged of the substitution labile ions. Instances where the chelating agent would be required are where the product is shipped in containers which may allow the ions to enter into the product solution, where the product is used in an aqueous environment that may contain the-metal ions, or where- the chelating agent itself is an active ingredient of the formulation.

Greater flexibility in the manufacture of the aforesaid chemical preparations could be achieved if there was a simple method whereby the substitution labile ions could be identified prior to the use of the process water in the product batch. Similarly, the manufacture of these formulations would be simplified if the ions could be removed without resorting to expensive distillation and/or ion exchange methods. Because the formulations themselves may contain a chelating agent, it is critical that the method used to detect or remove the substitution labile metal ions does not itself deactivate other chelating agents present in solution or that are to be added to the final product formulation. The detection/removal means should also be inert to the other active and non-active constituents of the formulation, should be usable over a wide pH range, and should not exhibit off odors.

SUMMARY OF INVENTION It is an object of this invention to provide a method for the detection and/or removal of substitution labile heavy metal transition ions from an aqueous solution.

It is a further object of this invention to provide a 2021,08 4 method for the detection or removal of the aforesaid ions from an aqueous solution, which method is compatible with the presence of other chelating and sequesterinq agents.

The primary object of the invention is to detect or remove the aforesaid metal ions from an aqueous solution by the addition of an effective amount of an ionizable salt of a 2-pyridi'nethiol-l-oxide compound, specifically an alkali salt of 2-pyridimethiol-l-oxide, the presence of which does not interfere with the use of or incorporation of other chelating or sequestering agents.

These and other objects and advantages of the present invention will be readily apparent upon a reading of the detailed description of invention, a summary of which follows.

The method of detecting the presence or absence of a substitution labile metal ion comprises the step of adding an effective amount of an ionizable salt of 2-pyridinethiol-l-oxine, the presence of said salt being compatible with the presence or subsequent addition of chelating or sequesterinq agents having a higher equilibrium constant for the ion to be detected than said salt anion. The presence of said ion is confirmed by the formation of a precipitate which typically is highly colored. Removal of the complexed ion from the aqueous solution may then be accomplished by distillation, filtration, centrifuging, or other means used to separate a solid from an aqueous phase.

In accordance with this invention, it has been found that ionizable salts of 2-pyridinethiol-l-oxide (hereinafter pyridinethiol) when added to an aqueous &ol~ ' DETAILED DESCRIPTION OF INVENTION containing substitution labile transition metal ions, for example Co+^f Ti+^,V+^,Mo+^,Mo+^/Cu+^ ions, forms a highly colored precipitate thereby indicating the presence of said ions. It has also been found, that the presence of the pyridinethiol in the aqueous solution is compatible with many chelating and sequestering agents used currently in the production of household, industrial, and cosmetic preparations, which compatibility is not predicted by chemicaL or thermodynamic rate laws. ~ - ^ .

The preferred form of pyridinethiol used in the detection of the substitution labile ions has the structural formula in tautomeric form as follows: x@ S* where X is an alkali Group I metal of sodium, postassium, and lithium. Pyridinethiol compounds are sold under the Omadine trademark, e.g., Sodium OmadineTM, by Olin Chemicals, Stamford, Connecticut. As disclosed in "Rate and Mechanisms, of _Sub,sti tut ion of Inorganic Complexes in Solution", H.Taube, Chemical Reviews, pages 69-126 (1952), the kinetics governing rates of chelation are determined . primarily by d orbital configuration. Metal complexes requiring positive crystal field stabilization energy in their activated complex exchange inner sphere ligands very slowly. Such complexes are substitution inert.

Metal complexes possessing 3 and 8 d electrons in their outer shell are substitution inert. Finally, transition metal ions possessing 4, 5 and 6 d electrons in their outer shell that are complexed with strong field ligands, for example, metal complexes wherein 4, 5 and 6 d electrons are paired, are also substitution inert. Substitution + 2 +3 +3 +3 +4 +4 inert metals, e.g. V ,Cr ;Mo ;W ; Re ; Mn , are not 202108 subject to transchelation, and do not interfere in the . chemical preparation under consideration. Metal transition ions not within the above definition of substitution inert ions are considered to be substitution labile, and will adversely affect the effectiveness of the household, industrial or cosmetic preparation. Depending upon the active ingredients in said preparations, the substitution labile ions can cause emulsified preparations to split into two phases, may combine chemically with expensive dyes, perfumes, or aromatic materials or may reduce the stability of other active ingredients. For this reason, many preparations include in their formulation a chelating agent or sequestering agent that sacrificially complex with these ions to decrease their interference. Even though the chelating or sequestering agents are added to the preparation formula, flexibility in manufacture of these composi-' • tions would be enhanced if the manufacturer could determine a priori whether the process water contains the substitution labile ions. For example, if the process water does not contain these ions, the addition of the chelating agent may be dispensed with or a lesser amount of the chelating agent could be used. Alternatively, if substantial amounts of the ions are present in the process water, the manufacturer could attempt to remove the ions by ion exchange or by the method of the present invention. However, the method of the present invention for detecting the presence or absence of the ions does place into solution and into the. preparation an effective amount of the pyridinethiol, a relatively weak chela-' ting agent, and subsequent addition of other chelating or sequestering agents should not result in transchelation of these materials especially where the chelating or sequestering agent is an active ingredient of the formulation.

The rate of chemical conversion of reactants to products is determined empirically, and is described by chemical DEC 1984* 202108 kinetics. Observed reaction rates are quantified as rate laws. Conversely, thermodynamic equilibrium measures the potential or driving force of a chemical reaction; i.e. it predicts the tendency to form one reaction product over another. The potential or driving force of the chemical reaction is measured by equilibrium constants, the larger the equilibrium constant, the greater the driving force to obtain equilibrium. The table below provides equilibrium constants.for. several transition metal chelating agents commonly used and various metal ions, as well as the equilibrium constants for pyridinethiol.

Equilibrium Constants for Chelating Ligands H+ ^ +2 Co Fe+2 Zn+2 2-Pyridinethiol-l-Oxide 4. .0 4.7 11.3 Thioglycolic Acid 13. 2 12.4 .9 .9 Dithizone . 0 13.0 - - Sodium Nitrolotriacetate(NTA) 13. 0 14.2 8.8* .4* Sodium Ethylenediamine. tetracetate (EDTA) . 2 16. 2 14.3 16.-4 Ethylene Diamine 17. 14.0 9.6 11.5 1, 10-phenanthroline 4. 9 19.9 21.0 18.5 ♦Value for K, Inspection of this Table indicates that the pyridinethiol anion is a relatively weak ligand, and thermodynamically, a metal complex of the pyridinethiol should react with another chelating agent having a higher equilibrium constant to form the metal complex of that chelating agent. Hence, an analysis of the thermodynamic data would predict that when pyridinethiol is in solution with another chelating agent specified in the table, complex formation would always favor the chelating agent at the expense of pyridinethiol. That is the use of the pyridinethiol to provide an indication of the presence of metal complexes would subsequently, after the addition of one of the above chelating agents, reduce or eliminate the effects of pyridinethiol. Based upon thermodynamic considerations, the following chemical reactions should take place with octahedral metal complexes: [»xp3]x 3 y — +nC MC +3P (1) Transchelation of —- .. n pyridinethiol Mx + 3p~ +nC———— MCX + 3P~ (2> CoraPetin9 equilibrium n favoring the thermo- dynamically more stable chelating agent while the reaction below should not be favored: ,x . 1 x-3 MC * + 3P —=—=^= JmpJ X + Transchelation to form the pyridine-thiol complex where 11 is the substitution labile ion, C is a chelating agent, and P is a pyridinethiol anion, and where x is the* charge of the substitution labile ion and n is the coordinating power of the chelating agent.

Equation. 1 indicates that pyridinethiol complexed with a substitution labile transition metal ion and in a solution: with a chelating agent (C) having a higher equilibrium constant than the metal-pyridinethioj.. complex should trans-chelate to form a metal complex of said ^helating agent. Equation 2 indicates that a solution of metal ions, pyridinethiol, and a chelating agent should preferentially form the chelating agent-metal complex. Equation 3 indicates that a chelating agent-metal complex in solution should not transchelate with pyridinethiol to form the pyridinethiol complex.

These arguments are based upon equilibrium constant data and provide a good basis for predicting the outcome of a chemical reaction. Thermodynamics can predict the stability of a complex but cannot assure that a given reaction will in fact occur. As previously stated, chemical kenitics emperically measures a reaction and quantifies it as a rate law whereas thermodynamics can only predict how fast equilibrium is obtained if the reaction takes place. Analysis of the above principals with respect to stability and transchelation has not been considered heretofore, apparently because there has been no particular interest in the rate and equilibrium aspects of pyridinethiol chemistry vis-a-vis other chelating agents. From the examples hereinafter described, it was found that the pyridinethiol anion behaves in an unusual and unexpected way. In the competing reaction of Equation 2, it was found that the substitution labile ion did not complex with the chelating agent, but rather formed an insoluble precipitate with the pyridinethiol: . « MX + nC + 3P~ a- [mP3]X"3 j+ Cn (4) while the transchelation reaction of Equation 3 did in fact take place forming the pyridinethiol metal complex: MCX + 3P" »-[MPJX~3 J+ nC (5) Again, the complex formed was insoluble. Thus, it can be seen that pyridinethiol, which formed a highly colored precipitate of the substitution labile metal ion, could be used to indicate the presence of the ion, yet would not subsequently react or transchelate with sequestering agents or chelating agents placed into solution.

Detection of substitution labile transition metal ions can be accomplished by adding to the aqueous solution an effective amount of the pyridinethiol anion, followed by visual or instrument observation of the formation of the precipitate, typically also associated with a color change. Precipitates possess a range of colors: green (cupric); blue (ferrous); blue-grey (ferric). To remove the ions from solution, the pyridinethiol can be added to the process water to form the precitptate, followed by removal of the precipitate by conventional means, for example, by distillation, filtration or centrifuging. The amount of pyridinethiol anion added to the process water is dependent upon whether detection or removal is desired. Where detection is the primary purpose of the addition, the pyridinethiol can be added in small concentrations, it only being necessary to obtain the color change and the formation of the precipitate. Where removal of the substitution labile ions is desired, the pyridinethiol should be added in excess to ensure complete precipitation of all substitution labile ions in solution.

The following examples illustrate reactions (4) and (5) described above. - 11 - .

.J*** EXAMPLE I 0L02fC Two solutions were prepared; solution A and solution B described below: Solution A Item Parts by Weight Deionized Water 85.20 Sodium 2-Pyridinethiol-l-0xide (40%) 0.03 Disodium Ethylenediaminetetra- acetate Hydrate (EDTA salt) 0-. 04 85. 27 Solution B Item Parts by Weight Deionized water 14.705 Fe2 (S04)3-9H20 0. 025 14.730 Solution B was added to a buret and titrated into Solution A. Immediately after addition, a blue color appeared due to the formation of the ferric 2-pyridinethiol-l-oxide complex. The order of addition was then reversed and the chelating agents were added to a solution of ferric sulfate. As before, the results were the same. Shortly after addition, the formation of an insoluble dark precipitate was noted. It was concluded that the ferric ion did not preferentially complex with EDTA, even though equilibrium constant data would suggest thermodynamic driving force according to Equation 2 was in favor of the EDTA complex. > / EXAMPLE II 1 o This example was conducted to test transchelation of a substitution labile metal ion. Two solutions were prepared; solutions C and D described below: Solution C Item Parts by Weight Deionized water Disodium EDTA . 2^0 Fe2(S04)3-9H2° 89.905 0.040 0.025 89.970 Solution D Item Parts by Weight Deionized water Sodium 2-Pyridinethiol-l-Oxide (40%) .000 0.030 10.030 Ferric EDTA was formed and solution D containing the pyridinethiol anion titrated into solution C. Immediately after addition, a violet color was observed and a precipitate formed. As before, the order of addition was reversed, and with the same results. The conclusion is that the substitution labile ferric EDTA complex transcheilated to form the insoluble ferric 2-pyridinethiol-l-oxide complex which subsequently precipitated from solution .according to reaction (5). 0 EXAMPLE III To test the substitution inertness of the ferrous and ferric ion when complexed with strong field ligands, the following experiment was conducted: Solution E Item Parts by Weight Deionized water K3Fe(CN)6 89.94 0.03 89.97 Solution F Item Parts by Weight Deionized water K4Fe(CN)6.3H20 89.93 0 .04 89. 97 Solution G Item Parts by Weight Deionized water Sodium 2-Pyridinethiol-l-Oxide (40%) .10: 000 0.030 10.030 Solution G was added to solution E and solution F. Unlike the results obtained with Examples I and II, after 40 minutes no color change or precipitate was observed. \ 14 C ) ' .V^ 1 0 This led to the conclusion that cyanide is a strong field ligand and will make the ferrous/ferric complexes substitution inert; i.e. cyanide causes the 5d and 6d electrons to be paired. When these compounds were added to a solution plex formation and subsequent precipitation can only occur with substitution labile transition metal ions. This was confirmed by preparing a solution of chromic chloride, which was added to a disodium EDTA solution. When solution G was added to this mixture, no color change or precipitate was observed after 30 minutes. This was because the chromic 3 ion, d , is substitution inert and like ferric cyanide and ferrous cyanide will not transchelate with pyridinethiol.

EXAMPLE IV The industrial application of the invention was tested by the following experiment in which solutions H, I, J and K were prepared. of pyridinethiol anion, no reaction occurred because com- Solution H Item Parts by Weight Deionized water Union Carbide Silicone Emulsion 70.00 LE- 45 8 (60%).

Fragrance Sodium 2-Pyridinethiol-l-0xide (40%) .00 0.20 0.03 75. 23 Solution I Item Parts by Weight Deionized water CuSO..5H-0 4 2 14.710 0. 020 14.730 Solution J Item Parts by Weight Deionized water Sn C12.2H20 FeS04.7H20 14.685 0. 020 0.025 14.730 Solution K Item Parts by Weight Deionized water Fe2(S04)3.9H20 14.705 0. 025 14.730 When solution I, J, or K containing substitution labile ferric, ferrous, or cupric ions was added to solution H containing the pyridinethiol, an immediate color change was noted and a precipitate formed. The odor of the resulting mixture was noted after 30 minutes and after 18 hours, and such organoleptic condition was comparable to the control. The colored precipitate ranged from green (cupric) to blue (ferrous) to grey (ferric). Solution H is typical of a light duty polishing cleaner containing a silicone emulsion • 108 Typically transition metal ions would destabilize the silicone emulsion so that the water used in the formulation must be controlled.

The above description of the invention is exemplary only, the scope of the invention not being limited except as described in the claims that follow. 202108

Claims (12)

WHAT WE CLAIM IS:

1. A method of detecting the presence or absence of substitution labile transition metal ions in process water, the method comprising the step of adding an effective amount of an ionizable salt of 2-pyridinethiol-l-oxide, the presence of said salt anion being compatible with the presence or subsequent addition of chelating or sequestering agents having a higher equilibrium constant for the ion to be detected than the salt anion, whereby the presence of the ion is confirmed by the formation of a precipitate and whereby the absence of the ion is confirmed by the absence of a precipitate.

2. A method for the removal of substitution labile c transition metal ions from an aqueous solution, the method comprising the steps of adding an effective amount of an ionizable salt of 2-pyridinethiol-l-oxide, the transition metal ions being chelated thereby and forming a precipitate, the addition of said pyridinethiol being compatible with the presence of or the subsequent addition of chelating or sequestering agents of higher equilibrium constants, and removing said precipitate from solution.

3. The method of claim 1 or 2 wherein the ionizable salt of 2-pyridinethiol-l-oxide is the sodium salt.

4. The method of claim 1, 2 or 3 wherein the chelating or sequestering agents are ammonia, ammonium salts, phosphate salts, citrate salts, nitrilotriacetic acid and salts thereof, ethylenediaminetetraacetic acid and salts thereof. 'va ia.

5. The method of any one of claims 1 to 4 wherein the | substitution labile transition metal ions are selected from the group consisting of ions with Od, Id, 2d, 7d, 9d and lOd electrons and combinations of same. 202 ICS - 18 - 6.

The method of claim 5 wherein said ion is Ti .+3 Cu Hg +1 i + 2 Au +1 Co + 2 Ag + 1 Os +6 Mo + 5 Mo + 6 Zn+2, Cd '+3. + 2 or a mixture thereof.

The method of any one of claims 1 to 4 wherein the substitution labile transition metal ions are selected from, the group consisting of ions with 4d, 5d and 6d electrons complexed in such manner that the d electrons are unpaired and combinations of the same.

8. +2 +3 The method of claim 7 wherein said ion is Fe , Fe ' + 2 +3 +2 Mn , Mn , Cr or a mixture thereof.

9. The method of claim 2 wherein the method for removal of the precipitate is centrifuging.

10. The .method of claim 2 wherein the method for removal of the precipitate is filtration.

11. The method of claim 2 wherein the removal of the precipitate is by distillation.

12. The method of claim 1 or claim 2 when performed substantially as hereinbefore described with particular reference to any one of the foregoing Examples I to IV. DATED THIS Co DAY OF U 6C D. A. J. PARK & SON PEA AGENTS fOll THi APPLICANTS -Q—1