Method for producing platinum complexes for plating

Abstract

The present specification describes a method of making a plating bath comprising a platinum (II) complex, the method comprising the steps of: (i) preparing an acidic aqueous solution comprising a chloride-free platinum (IV) compound and a source of nitrous acid (HNO2) as a reducing agent; (ii) heating the solution from step (i) to promote the reduction of platinum (IV) to platinum (II) and the decomposition of residual nitrous acid. Platinum plating baths produced by a method are also described.

Description

Technical Field

[0001] The present invention relates to a process for the preparation of platinum(II) complexes and their use in plating. Background Art

[0002] Plating using platinum (IV) and (II) salts is well known. Common classes of platinum salts contain one or more nitro ligands, and these complexes can be written by general formula (I):

[0003] M x [Pt(NO 2 ) a L b ] Formula I

[0004] wherein M is H, a metal or nonmetal cation, L is a ligand, and x, a and b are integers whose values ​​vary depending on M, L and the oxidation state of the platinum.

[0005] An example of a complex of formula I is dihydrodinitrosulfate platinum(II)H 2 [Pt(NO 2 ) 2 (SO 4 )], which is also known in the literature as dinitrothioplatinic acid, PtDNS or simply DNS. This complex has been described for platinum electroplating, see GB2059440A (Johnson Matthey), and is commercially available from Johnson Matthey and others (CAS 12033-81-7).

[0006] Dinitrosulfatoplatinic acid (hereinafter referred to as "H.DNS") and related complexes such as potassium dinitrosulfatoplatinate (hereinafter referred to as "K.DNS") and potassium tetranitroplatinate K 2 [Pt(NO 2 ) 4 ] are used to produce thin platinum films on various substrates. For example, the article "The Electrodeposition of Platinum and Platinum Alloys" (Platinum Metals Rev., 1988, 32, (4), 188-197) describes that these electrolytes can be used to coat platinum onto a wide range of materials including copper, brass, silver, nickel, lead and titanium. CN105132964A (Wuxi Qingyang) describes a method comprising coating K 2 [Pt(NO 2 ) 4], water-soluble phosphate, dialkyltrimethylammonium bromide and sulfuric acid plating solution. The article "Hot corrosion behaviour of single-phase platinum-modified aluminide coatings: Effect of Pt content and pre-oxidation" (Corrosion Science 2017, 127, 82-90) describes K.DNS (K 2 [Pt(NO 2 ) 2 (SO 4 )] Used for electroplating Ni-based super alloys.

[0007] The preparation of H.DNS and K.DNS is also reported in the literature. GB897690 (Johnson Matthey) describes that H.DNS can be prepared by tetranitroplatinic acid H 2 [Pt(NO 2 ) 4 ] and sulfuric acid. In this reference, K 2 [Pt(NO 2 ) 4 The complex H was prepared by passing a solution of ] through a cation exchange column with sulfuric acid. 2 [Pt(NO 2 ) 4 Complex K 2 [Pt(NO 2 ) 4 ] itself is usually prepared from platinum chloride salts. For example, the article "The Stereoisomerism of Complex Inorganic Compounds. XIV. Studies upon the Stereochemistry of Saturated Tervalent Nitrogen Compounds" (J. Am. Chem. Soc. 1952, 74, 14, 3535-3538) and "Molecular Photocrystallography: A Study of Metastable and Transient Species by Non-Ambient Crystallographic Techniques" (Hatcher, L., Doctoral Thesis 2014, University of Bath) describes the use of K 2 PtCl 4 and KNO2 The reaction between 2 [Pt(NO 2 ) 4 ].

[0008] The article Platinum Metals Rev., 1988, 32, (4), 188-197 describes that H.DNS can be prepared from platinum nitro salts such as K 2 [Pt(NO 2 ) 3 Cl], K 2 [Pt(NO 2 ) 2 Cl 2 ] or K 2 [Pt(NO 2 ) 2 SO 4 ] (K.DNS). These in turn must be prepared from precursor platinum salts, which are usually platinum chloride salts.

[0009] The article "Hot corrosion behavior of single-phase platinum-modifiedaluminide coatings: Effect of Pt content and pre-oxidation" (CorrosionScience2017,127,82-90) describes K.DNS (K 2 [Pt(NO 2 ) 2 (SO 4 )] for electroplating Ni-based super alloys. K.DNS by K 2 PtCl 6 and KNO 2 Aqueous reaction at 80 °C to obtain K 2 [Pt(NO 2 ) 4 ] crystal, and then by K 2 [Pt(NO 2 ) 4 ] and sulfuric acid.

[0010] Existing routes to H.DNS, K.DNS and related complexes involve several steps and generally require the use of sensitized platinum halide complexes. A simpler, safer and scalable method is needed to produce platinum (II) complexes such as H.DNS, K.DNS and related complexes. The present invention satisfies this need. Summary of the invention

[0011] The present inventors have found that platinum (II) complexes can be synthesized in a simple manner by reacting a chloride-free platinum (IV) compound with nitrous acid (HNO 2 ) sources. Nitrite ions reduce Pt(IV) to Pt(II) and are oxidized to nitrates and / or nitrogen oxides, particularly nitrogen dioxide. Other nitrite ions can complex with the Pt(II) center to produce a nitro complex. A heating step is performed to promote the reduction of platinum(IV) to platinum(II) and to promote the decomposition of residual nitrous acid. An exemplary reaction is:

[0012] H 2 [Pt(OH) 6 ]+3KNO 2 +H 2 SO 4 →K 2 [Pt(NO 2 ) 2 (SO 4 )]+KNO 3 +5H 2 O

[0013] This process offers several advantages over known processes for producing Pt(II) complexes, in particular H.DNS and K.DNS.

[0014] First, a Pt(II) complex is prepared from a Pt(IV) compound in a single step. This provides a higher yield route to the desired complex compared to the complex multi-step route described above. The single-step process also allows for simplification of manufacturing equipment and requires less space in the factory.

[0015] Secondly, with the reducing agents previously used to reduce Pt(IV) to Pt(II), such as H 2 、N 2 / H 2 Compared with hydrazine or nitrite, nitrite is relatively easy to handle materials. In addition, nitrite does not further reduce Pt(II) to Pt(0).

[0016] Third, reduction and subsequent processing are rapid, allowing for increased throughput compared to existing alternative approaches.

[0017] Fourth, the preferred sources of platinum (IV) used in this route are hexahydroxyplatinic acid and hexahydroxyplatinum salts, which are non-sensitized, unlike the platinum chloride salts used in prior methods to prepare H.DNS / K.DNS and related complexes.

[0018] It is known to use Pt(IV) compounds as precursors for Pt(II) salts. US2015 / 0315224 (Umicore) describes a method in which H2 [Pt(OH) 6 ] is reacted with an uncharged donor ligand L in the presence of a reducing agent and at least one of the hydroxyl ligands is replaced. A preferred reducing agent is H 2 、N 2 / H 2 mixtures, hydrazine, formaldehyde, oxalic acid and formic acid. Typically, the ligand L is a monodentate or bidentate amine or phosphine. However, this reference does not describe the use of HNO 2 As a reducing agent.

[0019] Combinations of platinum (IV) compounds and nitrites are described in US4200626 (Toyo Seiyaku Kasei Co Ltd), which describes dental compositions comprising water-soluble haloplatinates and a pharmaceutical carrier or diluent. Examples 2 and 3 of this reference describe combinations of sodium hexachloroplatinate hexahydrate and sodium nitrite (Example 2) or sodium hexachloroplatinate hexahydrate, sodium nitrite and sodium chloride (Example 3) at pH 5.5 or 3.5. However, the absence of sodium nitrite is sufficient to complete the reduction of Pt (IV) to Pt (II), and even if some reduction occurs, the heating step is not performed.

[0020] The book "Handbook of Preparative Inorganic Chemistry" (Vol. 1, 2nd edition, Academic Press Inc, 1963) describes on pages 1579-1580 the preparation of cis-dinitrodiammineplatinum(II) based on the method described in US Pat. No. 1,779,436. In the first step, potassium hexachloroplatinate(IV) (K 2 PtCl 6 ) and sodium nitrite are dissolved in water and heated with stirring. NO 2 As small bubbles are released. When no more gas is released, the 2 [Pt(NO 2 ) 4 The solution was cooled and filtered. The solution was then reacted with a stoichiometric amount of 20% aqueous ammonia to produce the desired complex [Pt(NO 2 ) 2 (NH 3 ) 2 ], which can be recrystallized from hot water. This route uses chloride-containing and sensitized K 2 PtCl 6 .

[0021] In a first aspect, the present invention relates to a method for producing a plating solution comprising a platinum (II) complex, the method comprising the following steps:

[0022] (i) preparing a platinum (IV) compound containing no chloride and nitrous acid (HNO) as a reducing agent 2 )

[0023] an acidic aqueous solution of a source;

[0024] (ii) heating the solution from step (i) to promote the reduction of platinum (IV) to platinum (II) and the decomposition of residual nitrous acid.

[0025] In the present invention, Pt(IV) compounds can be converted into a different range of Pt(II) nitro complexes depending on the choice of acid and nitrous acid source.

[0026] In a second aspect, the present invention relates to a plating solution produced by the method described herein. Without wishing to be bound by theory, it is believed that the new method can produce a plating solution similar to that previously described in this document as H 2 [Pt(NO 2 ) 2 (SO 4 )] or K 2 [Pt(NO 2 ) 2 (SO 4 )] have solutions with different species formation compared to those of DETAILED DESCRIPTION

[0027] Any sub-headings are for convenience only and are not intended to limit the invention.

[0028] Step (i)

[0029] The method of the present invention uses a Pt(IV) compound as a starting material. The Pt(IV) center is usually surrounded by a ligand, and the Pt(IV) compound may also be referred to herein as a complex. The Pt(IV) compound is usually a salt in which the anion contains Pt(IV).

[0030] Platinum chloride salts and complexes such as K 2 PtCl 6 and K 2 PtCl 4 is usually sensitized. Therefore, the Pt(IV) compound used in step (i) is chloride-free. By "chloride-free" it is meant that the compound does not include a chloride complexed with platinum, such as K 2 PtCl 6 or H 2 PtCl 6 etc. The Pt(IV) compound is preferably halide-free, i.e. the compound does not include any halide complexed with platinum. A particularly preferred Pt(IV) compound is hexahydroxyplatinic acid, H 2Pt(OH) 6 This compound is commercially available and is considered to be a non-sensitized Pt(IV) compound. Hexahydroxyplatinates containing hexahydroxyplatinate ions are also preferred Pt(IV) compounds. The counter ion of the hexahydroxyplatinate may be a metal ion or a non-metal ion, such as ammonium or alkylammonium ions.

[0031] The effect of nitrous acid source is to form nitrous acid in original position under acidic conditions, and thus Pt (IV) is reduced to Pt (II).Preferably, add nitrous acid source with the amount that is enough to reduce all Pt (IV) to Pt (II).Although excessive reductant is desirable for fast reaction conversion, for cost reasons and in order to avoid excessive NOx release, too much reductant is undesirable.

[0032] The reducing agent is referred to herein as "nitrous acid" for convenience, but it should be understood that the active reducing agent may be more complex and may be nitrous acid (HNO 2 ) and nitrous anhydride (N 2 O 3 ), which are known to exist in equilibrium in aqueous solution according to the following equation:

[0033] 2HNO 2 →N 2 O 3 +H 2 O

[0034] Under the acidic conditions in steps (i) and (ii), nitrite will be used as N 2 O 3 , HNO 2 and NO 2 - and possibly mixtures of other substances are present, depending on the pH of the solution.

[0035] In one embodiment, the nitrous acid source is, for example, a a+ (NO 2 ) a )] provided by nitrite, wherein M a+ is a metal or non-metal cation and a is an integer. Nitrous acid is formed by nitrite under acidic conditions. One type of preferred salt is Group I nitrite, preferably lithium nitrite, sodium nitrite or potassium nitrite. Another type of preferred salt is Group II nitrite, preferably magnesium nitrite, calcium nitrite, strontium nitrite or barium nitrite. Another preferred salt is silver nitrite. In a preferred embodiment, the nitrous acid source is a metal nitrite selected from magnesium nitrite, calcium nitrite, strontium nitrite, barium nitrite and silver nitrite. These salts are preferred because the metal ions (Mg 2+ , Ca2+ , Sr 2+ , Ba 2+ 、Ag + ) form insoluble salts with many minerals and some organic acids, which means that they can be precipitated from solution in step (i) or in optional step (iii). For example, adding phosphoric acid in step (i) or in optional step (iii) will precipitate the residual metal ions as magnesium phosphate, calcium phosphate, strontium phosphate, barium phosphate or silver phosphate. Magnesium nitrite, calcium nitrite and strontium nitrite are preferred over barium nitrite because the latter is toxic, and are preferred over silver nitrite because the latter is expensive. Therefore, a preferred nitrite source is a metal nitrite selected from magnesium nitrite, calcium nitrite and strontium nitrite. Ammonium nitrite is a preferred nitrite source with non-metallic cations.

[0036] Alternative nitrous acid sources may also be used. In one embodiment, the nitrous acid source is M x [Pt(NO 2 ) 4 ] salt, wherein x=2 when M has a charge of +1, and x=1 when M has a charge of +2, such as potassium tetranitroplatinate (II) (K 2 [Pt(NO 2 ) 4 ]).

[0037] If there is an excess of nitrite, it is released as brown nitrogen dioxide gas as the reaction heats up. If a metal nitrite is used as the nitrous acid source, it may not be desirable to have excess counter cations remaining in solution after step (i) / (ii). The molar ratio of Pt(IV):nitrous acid source at the start of step (i) will depend on the choice of nitrous acid source. For example, one equivalent of KNO 2 、Ca(NO 2 ) 2 or K 2 [Pt(NO 2 ) 4 ] contain 1, 2 and 4 equivalents of nitrite, respectively. When the nitrite source is nitrite, it is preferred that the molar ratio of Pt(IV):nitrite at the beginning of step (i) is between 1:2 and 1:10, preferably between 1:2 and 1:8.

[0038] In one embodiment, the nitrous acid source is pure HNO 2 The so-called "pure HNO 2" means that the solution is substantially free of metal ions. Pure nitrous acid can be prepared by treating a solution containing nitrite in an aqueous organic polar solvent solution with an ion exchange resin. Examples include the procedures reported in US 3113837 and the article "Preparation of Solutions of Pure Nitrous Acid" (J. Am. Chem. Soc. 1963, 85, 23, 3888). Pure nitrous acid can also be prepared by electrolyzing nitric acid solution using a platinum electrode, as described in the article "Alternative Electrode Reactions. Part I. Reactions ata platinum cathode in nitric acid solutions" (J. Chem. Soc. 1932, 1565-1579). In the use of pure HNO 2 In the case of , the solution in step (i) is substantially free of metal ions other than those from the Pt(IV) compound, the optional acid (described later) and the optional salt (which is dissolved to produce the acidic solution (described later)).

[0039] The nitrous acid source can also exchange with the ligand on the Pt(IV) or Pt(II) center to form a nitro complex. As used herein, "nitro complex" should be understood in its broadest sense and includes nitrous acid sources that are ligands on the Pt(IV) or Pt(II) center to form a nitro complex. 2 ) or via oxygen (Pt–ONO).

[0040] Some Pt(IV) compounds are not appreciably soluble in water at room temperature, such as hexahydroxyplatinic(IV) acid which is insoluble in water at room temperature. Therefore, it is preferred to stir the mixture to promote dissolution during steps (i) and (ii). Stirring is preferably achieved by moderate stirring. Rapid stirring, if necessary, should be limited to short pulses as it promotes nitrogen dioxide loss. The inventors have found that an aqueous suspension of hexahydroxyplatinic(IV) acid dissolves rapidly in the presence of nitrous acid, presumably due to the reduction of Pt(IV) to Pt(II) by nitrite.

[0041] The concentration of Pt in step (i) should be selected considering process economics (dilute solutions require more energy to heat). Typically, the Pt concentration is 5 g / L to 100 g / L, such as 10 g / L to 100 g / L. The upper limit is determined by the solubility of the Pt (IV) compound. When manufactured on a commercial scale, a Pt concentration of 30 g / L to 80 g / L may be appropriate.

[0042] The reaction is carried out under acidic conditions, i.e. pH <7, preferably pH <6, more preferably pH <5, more preferably pH <4. ​​The lowest pH is not particularly limited, but is preferably not less than -1, preferably not less than 0. Typically, the reaction is carried out at pH <4, such as pH 0-4. Acidic conditions promote nitrous acid (HNO 2 ), which is considered to be the main species responsible for the reduction of Pt(IV).

[0043] Depending on the Pt (IV) compound and nitrous acid source used, it is not necessary to add any additional acid. However, in some embodiments, an acid is added in step (i) to promote the formation of nitrous acid. The acid is different from the Pt (IV) compound or the nitrous acid source. It will be appreciated by those skilled in the art that if the conjugate base of the acid is strongly coordinated with platinum (II), it is likely to be incorporated into the platinum (II) complex. For example, if sulfuric acid is added as an acid, it is likely to form a sulfate-containing platinum (II) complex. Therefore, the selection of acid will be guided by the desired platinum (II) complex. The acid can be a mineral acid or an organic acid. Preferred mineral acids include phosphoric acid, sulfuric acid and nitric acid. Preferred organic acids include carboxylic acids and aldehydes that often contain carboxylic acid impurities when aging, such as glyoxal.

[0044] Adding phosphoric acid or sulfuric acid as the acid in step (i) has the additional advantage that they form insoluble salts with various metal ions. Thus, if the nitrous acid source is a metal nitrite, where the metal forms an insoluble salt with a phosphate or sulfate, the solution can be acidified and the metal phosphate or sulfate precipitated simultaneously in step (i).

[0045] In one embodiment, the nitrite source is a metal nitrite, the acid is phosphoric acid, and the metal phosphate is precipitated. In a preferred embodiment, the nitrite source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is phosphoric acid, and in step (i) magnesium phosphate, calcium phosphate or strontium phosphate is precipitated.

[0046] In one embodiment, the nitrous acid source is a metal nitrite, the acid is sulfuric acid, and the metal sulfate is precipitated. In a preferred embodiment, the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is sulfuric acid, and magnesium sulfate, calcium sulfate or strontium sulfate is precipitated in step (i). The use of calcium nitrite or strontium nitrite with sulfuric acid is superior to the use of magnesium nitrite because the insolubility of calcium sulfate and strontium sulfate is much greater than that of magnesium sulfate.

[0047] Preferred organic acids include acetic acid, oxalic acid and oxalic acid. These acids dissolve in aqueous solution to provide the formation of HNO 2And Pt (IV) is reduced to the necessary acidic conditions of Pt (II). These acids, particularly oxalic acid, also form precipitation with some metal ions, and are particularly advantageous when metal nitrites are used as nitrite sources. Oxalic acid is a particularly preferred organic acid. In one embodiment, the nitrite source is a metal nitrite, and the acid is oxalic acid, and precipitates metal oxalate. In a particularly preferred method, the nitrite source is magnesium nitrite, calcium nitrite or strontium nitrite, and the organic acid is oxalic acid, and precipitates magnesium oxalate, calcium oxalate or strontium oxalate.

[0048] When the product from step (ii) is used for electroplating, the use of excess oxalic acid tends to result in darkening and matte effects. Although dark colors and matte effects are desirable in some cases, avoiding excess oxalic acid and / or adding a mixture of oxalic acid and sulfuric acid alleviates this and results in a bright platinum plate.

[0049] In some embodiments, the acid is provided in step (i) by a salt dissolved in an aqueous solution to produce an acidic solution. This may replace or supplement a mineral acid or an organic acid. It is preferred that the salt is dissolved in the solution to produce a pH below 6. This helps to ensure that N 2 O 3 / HNO 2 / NO 2 – Balance in favor of N 2 O 3 / HNO 2 , which is believed to be the active species for reducing Pt(IV) to Pt(II). Examples of suitable salts include Group I metal sulfates, Group I metal hydrogen sulfates, Group I metal dihydrogen phosphates, and Group I metal hydrogen oxalates, in each case sodium or potassium salts being preferred due to their commercial availability. Preferred salts are those that dissolve in solution to produce a pH below 4.

[0050] The addition of the Pt(IV) compound, nitrous acid source and any acid should be controlled to avoid exotherm.If necessary, the solution may be cooled to a temperature of 0°C to 10°C, such as 0°C to 5°C.

[0051] The order in which the Pt(IV) compound, nitrous acid source and any additional acid are added in step (i) is not particularly important unless the acid is capable of reducing Pt(IV) to Pt(0), in which case the acid should be added after or at the same time as the Pt(IV) compound and nitrous acid source are combined. This is particularly true for oxalic acid which is capable of completely reducing Pt(IV) to Pt(0).

[0052] Step (ii)

[0053] In step (ii), the reaction mixture is heated. The purpose of step (ii) is to promote the reduction of Pt(IV) to Pt(II) and to promote the decomposition of any residual nitrous acid to nitrogen oxides.

[0054] In some embodiments, heating is initiated only when both the chloride-free platinum (IV) compound and the nitrous acid source are present in solution.

[0055] In an alternative embodiment, a solution of a chloride-free platinum (IV) compound is preheated and a nitrous acid source is added to the preheated solution. In this embodiment, steps (i) and (ii) occur simultaneously. The nitrous acid source may be added as a solid or as a solution.

[0056] In the present invention, it is found that excess nitrous acid escapes as brown nitrogen dioxide gas in the range of 50°C-80°C. Therefore, it is preferred that the reaction is heated to a temperature of at least 50°C, preferably at least 80°C during step (ii). The reaction is usually heated to a temperature of at least 90°C to ensure any conversion based on a final solution color change (e.g., reddening). However, in many cases, solutions maintained for an extended duration at lower temperatures (e.g., 60°C) will be successfully plated. If a nitrous acid source is added to a preheated solution of a chloride-free platinum (IV) compound, it is preferred that the temperature of the preheated solution be at least 50°C.

[0057] Step (iii)

[0058] Step (iii) is an optional step. If an excess of metal nitrite is included in step (i), it will be appreciated that the resulting solution will contain residual metal ions unless these metal ions have been precipitated in step (i). In order to limit the possibility of metal ions interfering with subsequent plating, for example by contaminating the coating, it may be desirable to remove the metal ions. Therefore, in some embodiments, the nitrite source is selected so that the salt MX can be precipitated in a subsequent step after steps (i) and (ii). The method involves step (iii): adding an acid or salt so that the counter cation of the metal nitrite is precipitated as the corresponding metal salt. [M a+ ] ions to form insoluble salts.

[0059] As described above, step (i) may involve adding a mineral acid or an organic acid to acidify the solution and simultaneously precipitate the metal ions (e.g., from a nitrite source) as the corresponding metal salt. It should be understood that if the metal ions are precipitated in step (i), step (iii) is generally not necessary.

[0060] In one embodiment, oxalic acid is added in step (iii) and metal oxalate is precipitated. In a preferred embodiment, the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is oxalic acid, and magnesium oxalate, calcium oxalate or strontium oxalate is precipitated in step (iii).

[0061] In one embodiment, phosphoric acid is added in step (iii) and the metal phosphate is precipitated. In a preferred embodiment, the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is phosphoric acid, and in step (iii) magnesium, calcium or strontium phosphate is precipitated.

[0062] In one embodiment, sulfuric acid is added in step (iii) and metal sulfate is precipitated. In a preferred embodiment, the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is sulfuric acid, and magnesium sulfate, calcium sulfate or strontium sulfate is precipitated in step (iii). The use of calcium nitrite or strontium nitrite with sulfuric acid is superior to the use of magnesium nitrite because the insolubility of calcium sulfate and strontium sulfate is much greater than that of magnesium sulfate.

[0063] To ensure maximum removal of metal salts, the solution may be concentrated, cooled, and / or the pH may be adjusted prior to adding the acid to maximize removal of metal salts.

[0064] The solution produced after step (ii) or after step (iii) in the case of performing step (iii) is suitable for plating, such as electroplating. In some embodiments, the concentration can be adjusted (concentrated or diluted) according to the [Pt] required for electroplating. Typically, reactions (i)-(iii) are carried out at a relatively high [Pt] and then diluted, for example, with deionized water. The Pt concentration in the "ready-to-use" solution for electroplating is typically 0.5 g / L to 30 g / L. Therefore, in some embodiments, after step (ii) (or if applicable, after step (iii)), the concentration of Pt is adjusted to 0.5 g / L to 30 g / L.

[0065] Example

[0066] Example 1-H 2 [Pt(OH) 6 ]+K 2 [Pt(NO 2 ) 4 ](1.04 equivalent)+H 2 SO 4

[0067] A suspension of hexahydroxyplatinic acid (0.75 g, 2.51 mmol) and potassium tetranitroplatinate (1.2 g, 2.62 mmol) in 30 mL of water was stirred. Concentrated sulfuric acid (1.0 mL) was added dropwise, causing some yellowing of the color. The stirred mixture was heated to boiling, causing the color to change through yellow and orange until a clear cherry red solution was produced. Some bubbling occurred around 70°C-80°C due to residual nitrogen dioxide release, but it quickly subsided. After boiling for a few minutes to ensure that no residual nitrogen oxides remained, the beaker was removed from the hot plate and cooled to room temperature without further discoloration. The final cherry red liquid was diluted to 200 mL with distilled water to obtain a concentration of 5.0 g / L Pt, and the resulting solution was used to plate formed stainless steel coupons at 9.3 ASF and 90°C for 90 minutes, producing a silver bright Pt coating with a cathode current efficiency of 20% for the first plate to pass through the bath. The red plating solution was continuously stirred during plating. A circular Pt / Ti grid anode surrounds the cathode test piece. During early plating, the red liquid darkens slightly to a reddish brown color.

[0068] Example 2-H 2 [Pt(OH) 6 ]+K 2 [Pt(NO 2 ) 4 ](1.5 equivalents)+H 2 SO 4

[0069] Hexahydroxyplatinic acid pellets (1.5 g, 5.0 mmol) in a 150 ml glass beaker were crushed into a fine powder with a spatula, potassium tetranitroplatinate (3.4 g, 7.4 mmol) and 40 mL of water were added, and the mixture was stirred magnetically. Concentrated sulfuric acid (2.5 mL) was quickly added dropwise to the stirred suspension at room temperature, causing it to turn yellow first and then orange as a large amount of solution was dissolved. The orange suspension was then heated with stirring to give a brown suspension at 60°C and an almost clear red solution at 85°C, in which a small amount of brown nitrogen dioxide was observed in the beaker below the watch glass placed on top. The solution was boiled for a few minutes to form a clear red solution, which was used for electroplating and turned brown during use. Using 8-10 ASF at 55 or 80°C, the bath showed a cathode current efficiency of 15%-25% and produced a continuous bright plate.

[0070] Example 3-H 2 [Pt(OH) 6 ]+Ca(NO 2 ) 2 (3.5 equivalents) + HNO 3

[0071] Stir hexahydroxyplatinic acid H 2 [Pt(OH) 6] (3.0g, 10.0mmol), calcium nitrite solution (4.005g calcium nitrite, 30.3mmol) and 50mL water suspension, while using ice bath to cool to less than 5 ℃. Dilute nitric acid (about 20%, 20mL, 6.3mmol) is added in batches under stirring. The dissolved suspension is added as the final part to obtain a lemon yellow solution. Additional diluted calcium nitrite solution (0.667g calcium nitrite, 5.1mmol) and concentrated nitric acid (0.3g) are added, but there is no further change in the solution. The yellow solution is removed from the ice bath, replenished to 120mL and stirred overnight. The clear yellow solution is then heated under stirring to drive off any residual nitrogen dioxide gas. Above 90 ℃, the yellow solution turns into a clear orange. Stop heating, and cool the solution to less than 5 ℃ with an ice bath. Oxalic acid dihydrate (3.7 g, 29.3 mmol) dissolved in 50 mL of warm water was slowly added to the cooled solution with rapid stirring, producing a thick white precipitate of calcium oxalate, which was filtered off, leaving a clear orange solution. The oxalic acid added was slightly less than 1 equivalent relative to the calcium content to avoid the presence of excess oxalic acid, which would reduce the platinum (II) ions. The orange solution was used to electroplate steel parts at 8-10 ASF, producing bright plates at 55°C or 80°C, with a cathodic current efficiency of 10%-20%.

[0072] Example 4-H 2 [Pt(OH) 6 ]+Ca(NO 2 ) 2 (3 equivalents) + HNO 3

[0073] A suspension of hexahydroxyplatinic acid (3.0 g, 10.0 mmol), calcium nitrite solution (4.005 g calcium nitrite, 30.3 mmol) and 50 mL of water was stirred in a 250 mL glass beaker cooled in an ice bath below 5°C. 70% nitric acid solution (6 g, diluted to 20 mL) was added to the stirred cold white suspension in four 4×5 mL aliquots over 40 minutes to give a yellow suspension which formed a turbid yellow solution shortly after the third nitrite addition. The beaker containing the contents was removed from the ice bath and allowed to warm to room temperature, producing a very slightly turbid yellow solution which became a clear yellow solution after stirring at room temperature for 5 minutes. The solution was stirred at room temperature overnight without change. It was then heated to 90°C with stirring to drive off any residual nitrogen oxides (almost none), turning into an orange solution. The stirred solution was then cooled, refrigerated in an ice bath and oxalic acid dihydrate (3.7 g, 29 mmol) dissolved in water (50 mL) was added to precipitate the calcium as insoluble white calcium oxalate. The calcium oxalate was removed by vacuum filtration, washed, dried and 3.97 g was weighed (consistent with the expected weight of calcium oxalate hydrate, about 3.9 g). 125 mL of the clear orange filtrate was diluted to 200 mL and boiled for four hours while replacing with water to prevent liquid loss. The resulting clear reddish-brown solution was used to electroplate steel and titanium parts at 8-10 ASF, producing bright plates at 55°C or 80°C with cathodic current efficiencies in the 10%-20% range.

[0074] Example 5-H 2 [Pt(OH) 6 ]+KNO 2 (3.4 equivalents) + H 2 SO 4

[0075] Hexahydroxyplatinic acid H 2 Pt(OH) 6A suspension of (6.06g, 20.3mmol), 3.5g of concentrated sulfuric acid and 160mL of water was stirred in a 400mL glass beaker cooled in an ice bath below 5°C. Potassium nitrite (5.77g, 67.6mmol) dissolved in 40mL of water was added to the stirred ice-cold suspension in batches within 30 minutes at room temperature. During this addition, the white suspension in the beaker turned yellow and then began to dissolve. After adding potassium nitrite, the beaker containing the contents was removed from the ice bath and allowed to warm up to room temperature naturally. At 16°C, the suspension was almost completely dissolved, leaving a slightly turbid yellow-orange solution. The solution was heated to 52°C under stirring, and a weak intensity brown vapor was observed to appear for the first time in the beaker, which was equipped with a watch glass on top. Continue heating and convert the orange-yellow solution into a bright orange solution at a temperature higher than 75°C. No brown gas was observed to exist or bubble above 80°C. Finally, the bright orange solution was boiled for a few minutes without further color change. The solution was vacuum hot filtered through a combined paper and glass fiber filter to remove small amounts of possible orange insoluble hydrated platinum oxide formed during the process. 200 mL of the clear orange filtrate was diluted to 600 mL and electroplated, initially two boards at 80°C, then 13 boards over the next 10 days at about 55°C, replenished from another identical orange bath. During extended plating without replenishment, the orange color faded to form an almost colorless solution. All boards were bright with efficiencies in the 10%-20% range for primarily 8-10 ASF, with the highest efficiencies obtained at higher temperatures.

[0076] Example 6-H 2 [Pt(OH) 6 ]+KNO 2 (4 equivalents) + H 2 SO 4

[0077] Stir the white suspension of hexahydroxyplatinic acid (6.03g, 20.0mmol) and potassium nitrite (5.75g, 67.6mmol) in 100mL water in a 400mL glass beaker, then cool in an ice bath below 5°C. Add concentrated sulfuric acid (3.6g in 20mL water) in batches at room temperature within 10 minutes to produce a yellow suspension. After adding the acid, the beaker containing the contents is removed from the ice bath and allowed to warm to room temperature naturally under stirring. This causes most of the yellow suspension to dissolve to form a yellow translucent solution. The beaker and its contents are cooled again with an ice bath below 5°C and treated with potassium nitrite (1.0g, 12.0mmol, dissolved in 10mL water), and 0.75g of concentrated sulfuric acid is added dropwise to the stirred cold translucent solution. This addition causes the translucency to disappear rapidly, resulting in a clear orange-yellow solution. The beaker containing the contents was removed from the ice bath and heated to 50°C with stirring, producing an almost clear light orange solution with a volume of about 130 mL. Heating between 50°C-80°C resulted in excess nitrous acid being lost as brown nitrogen dioxide gas, as seen in the beaker with a watch glass on top. At around 80°C, a slight translucency appeared in the clear orange solution due to the formation of insoluble orange hydrated platinum oxide, which was filtered out. Boiling the bright orange solution for 15 minutes did not produce further changes. Boiling the orange solution for several hours (circulating water to replace evaporated water) turned it red. Further heating of the red solution without electroplating, but more rapidly electroplating at 80°C or higher, resulted in a dark red brown solution, and finally a brown solution whose color was very similar to the currently commercially available H.DNS solution. In the case of long-term use of the plating bath without replenishment, the new brown solution slowly faded to almost colorless. At 8-10 ASF, 55°C or 80°C, plates from this reddish brown bath gave cathode current efficiencies in the range of 10%-20%.

[0078] Example 7-H 2 [Pt(OH) 6 ]+Ca(NO 2 ) 2 (3 equivalents) + oxalic acid

[0079] Hexahydroxyplatinic acid (2 g crushed powder, 6.6 mmol), calcium nitrite (30% solution, 2.75 g calcium nitrite, 20.8 mmol) and 50 mL of water were stirred together in a 250 mL beaker in an ice bath below 5°C. Oxalic acid dihydrate (2.64 g in 40 mL of water, 21.0 mmol) was carefully added all at once, but this resulted in the loss of some brown nitrogen dioxide from the cold stirred suspension, which quickly turned yellow. After 30 minutes, the beaker and its contents were removed from the ice bath and heated to 40°C, causing a small amount of brown nitrogen dioxide to be released. Further slight release was observed up to 85°C. Heating and stirring were then stopped, and a white suspension settled out of the bright yellow solution, which was separated by vacuum filtration. Upon prolonged heating above 80°C, the yellow solution turned orange. The orange solution was used to electroplate steel parts at 8-10 ASF, producing bright plates at 55°C or 80°C with a cathodic current efficiency of 10%-20%.

[0080] Example 8-H 2 [Pt(OH) 6 ]+Ca(NO 2 ) 2 (3 equivalents) + oxalic acid

[0081] In the 250mL beaker contained in the ice bath, oxalic acid dihydrate (2.53g, 20.1mmol dissolved in 40mL water under slight warming) is stirred and added into hexahydroxyplatinic acid (2g crushed powder, 6.6mmol). Below 5 ℃, calcium nitrite solution (2.63g calcium nitrite, 19.9mmol) in 40mL water is added in batches within a few minutes to minimize any loss of brown nitrogen dioxide. The stirred white suspension turns yellow quickly. After 45 minutes, the suspension is removed from the ice bath and warmed to 35 ℃, causing slight brown nitrogen dioxide loss, and the yellow solution is quickly separated from the sedimented precipitation when standing. After standing for four days, the yellow solution turns into orange. The stirred orange solution is treated with calcium nitrite solution (0.26g, 2.0mmol), and then treated with oxalic acid dihydrate (0.26g, 2.06mmol dissolved in 20mL water at room temperature). At 80°C some brown nitrogen dioxide is released but the color of the solution remains unchanged. This solution and the white suspension are separated by vacuum filtration. The orange solution is used to electroplate steel parts at 8-10 ASF to produce bright plates at 55°C or 80°C with a cathodic current efficiency of 10%-20%.

Claims

1. A method for producing a plating solution comprising a platinum (II) complex, the method comprising the following steps: (i) preparing an acidic aqueous solution comprising a chloride-free platinum (IV) compound and a source of nitrous acid (HNO2) as a reducing agent; (ii) heating the solution from step (i) to promote the reduction of platinum (IV) to platinum (II) and the decomposition of residual nitrous acid.

2. The method according to claim 1, wherein the nitrous acid source in step (i) is a metal nitrite.

3. The method of claim 2, wherein the molar ratio of Pt(IV):nitrite at the beginning of step (i) is between 1:2 and 1:

10.

4. The method of any one of claims 1 to 3, wherein the nitrous acid source is a Group I or Group II nitrite.

5. The method according to any one of claims 1 to 4, wherein the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite.

6. The method according to claim 1, wherein the nitrous acid source is M x [Pt(NO2)4] salt, wherein x=2 when M has a charge of +1, and x=1 when M has a charge of +2.

7. The method of claim 6, wherein the nitrous acid source is potassium tetranitroplatinate (II) (K2[Pt(NO2)4]).

8. The method according to any one of claims 1 to 7, wherein the platinum (IV) compound is hexahydroxyplatinic (IV) acid (H2Pt(OH)6) or a salt thereof.

9. The method according to any one of claims 1 to 8, wherein the pH of the solution in step (i) is <6.

10. The method according to any one of claims 1 to 9, wherein the pH of the solution in step (i) is <4.

11. The process according to any one of claims 1 to 10, wherein an acid is added in step (i).

12. The method of claim 11, wherein the acid is selected from the group consisting of phosphoric acid, sulfuric acid and nitric acid.

13. The method of claim 11, wherein the acid is oxalic acid.

14. The method of claim 11, wherein the acid is a salt that dissolves in an aqueous solution to produce an acidic solution having a pH below 6.

15. The method according to any one of claims 1 to 14, wherein the concentration of Pt in step (i) is between 5 g / L and 100 g / L.

16. The process according to any one of claims 1 to 15, wherein in step (ii) the mixture from step (i) is heated to a temperature of at least 50°C.

17. A method according to any one of claims 1 to 16, comprising the subsequent step of using the product of step (ii) for plating.

18. A method according to any one of claims 1 to 16, wherein the nitrous acid source is a metal nitrite and comprises the step (iii) of adding an acid or salt and precipitating the metal counter cation of the nitrous acid source as a salt.

19. The method of claim 18, wherein the acid is oxalic acid and metal oxalates are precipitated.

20. The method of claim 18, wherein the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is oxalic acid, and magnesium oxalate, calcium oxalate or strontium oxalate is precipitated in step (iii).

21. The method of claim 18, wherein the acid is phosphoric acid and a metal phosphate is precipitated.

22. The method of claim 18, wherein the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is phosphoric acid, and magnesium phosphate, calcium phosphate or strontium phosphate is precipitated in step (iii).

23. The method of claim 18, wherein the acid is sulfuric acid and metal sulfates are precipitated.

24. The method of claim 18, wherein the nitrous acid source is selected from magnesium nitrite, calcium nitrite or strontium nitrite, the acid is sulfuric acid, and magnesium sulfate, calcium sulfate or strontium sulfate is precipitated in step (iii).

25. The method of claim 18, wherein the nitrous acid source is selected from calcium nitrite or strontium nitrite, the acid is sulfuric acid, and calcium sulfate or strontium sulfate is precipitated in step (iii).

26. A method according to any one of claims 18 to 25, comprising the subsequent step of using the product of step (iii) for plating.

27. A platinum plating solution produced by the method according to any one of claims 1 to 26.