The invention relates to a synthesis of a manganese complex useful as a bleach catalyst.

Peroxide bleaching agents have been used for many years in laundry compositions. Such agents are effective in removing stains, such as tea, fruit and wine stains, from clothing at or near the boiling temperatures of the laundry composition. The efficacy of peroxide bleaching agents diminishes sharply when laundry compositions are used at temperatures below 60°C.

It is known that many transition metal ions catalyse the decomposition of H ₂ 0 ₂ and H ₂ 0 ₂ -liberating percompounds, such as sodium perborate. It has also been suggested that transition metal salts together with a chelating agent be employed to activate peroxide compounds to render them usable for satisfactory bleaching at lower temperatures. However, not all combinations of transition metals with chelating agents are suitable for improving the bleaching performance of peroxide compound bleaches. Many combinations indeed show no effect, or even an adverse effect, on the bleaching performance. A recent advance in this technology was reporting in European Patent Specification No. 458397. Therein was reported a class of highly active bleaching catalysts in the form of a manganese complex having the general formula:

[ L _n Mn _m X _p ] ^z Y _q and

especially the species:

[Mn ^IV ₂ (μ-0) ₃ (Me-TACN) ₂ ] (PF ₆ ) ₂ H ₂ 0

Several of the aforementioned complexes were first synthesised and described by K Wieghardt in the "Journal of the American Chemical Society", 1988, Vol. 110, No. 22, page

7398, as well as in the "Journal of the Chemical Society - Chemical Communications", 1985, page 1145.

The synthesis route as described in the above art involved the reaction, in aqueous medium, of a manganese (III)- compound, e.g. Mn (III) -triacetate, with a nitrogen- containing ligand, e.g. 1,4,7-trimethyl-l,4,7- triazacyclononane, using an ethanol/water mixture as the solvent. A disadvantage of this route is that only low yields of the dinuclear Mn (III)-complex are obtained. Another disadvantage associated with the process of the art is that, owing to the slow crystallisation of the product, long reaction times are necessary. Still another disadvantage is that, besides crystallisation of the desired product, decomposition also seemed to occur, yielding manganese dioxide which contaminates the product. Therefore, a purification process is required when the product is to be converted into the dinuclear Mn (IV) -complex.

More recently there was reported a process for the preparation of manganese complex catalysts, co-pending European Patent Application No. 92310720.5, in which a four- step procedure was outlined. In this procedure a manganese II salt and a ligand L are first reacted to form a manganese coordinated substance. In the second and third step, the substance is oxidised and then basified to a pH of at least 10.5. In the final step the basified reaction mixture is contacted with a further oxidising agent to form the manganese complex catalyst. Yields in the range of 60% range are achieved by this procedure. Improvements in yield and reduction in processing costs would be desirable.

The present invention seeks to provide an improved method for the preparation of manganese (III)- and manganese (IV)- dinuclear complexes of high purity and in high yield.

These and other objects of the present invention will become more readily apparent from the detailed description and examples given hereafter.

Accordingly, the present invention provides a process for the preparation of a manganese complex catalyst having the formula:

wherein Mn is manganese in a III or IV oxidation state;

each X is independently a coordinating or bridging species selected from:

H ₂ 0, 0 ₂ ^2' , 0 ² \ OH ^" , H0 ₂ ^" , SIT, S ^2" , SO, Cl ^" , N ₃ ^" , SCN ^" , N ^3" , RCOO ^" , NH ₂ ^" and NR ₃ , where R is a radical selected from the group consisting of H, alkyl and aryl radicals;

L is an organic ligand containing at least two nitrogen atoms that coordinate with the Mn;

z is an integer ranging from -4 to +4;

Y is a monovalent or multivalent counterion leading to charge neutrality; and

q is an integer from 1 to 4;

the process comprising the steps of:

i) reacting, in an aqueous medium a manganese (II) salt with the ligand L or a precursor thereof to form a manganese coordinated substance, a counterion salt M ₂ Y _q

being present wherein M is selected from the group consisting of metallic, ammonium and alkanolammonium ions; and

ii) oxidising the manganese coordinated substance with an oxidising agent while simultaneously maintaining a pH of at least 12 to thereby form the manganese complex catalyst.

It has been found that high yields of dinuclear manganese complexes of relatively high purity can be obtained at a much shorter reaction time and essentially, in a single pot reaction through the use of simple manganese (II) inorganic salts.

The counterion Y needed for charge neutrality of the complex is generally provided by carrying out the complexation reaction in the presence of a counterion-forming salt. Though the type of the counterion-forming salt, e.g. chlorides; sulphates; nitrates; methylsulphates; surfactants such as alkyl sulphates, alkyl sulphonates, alkylbenzene sulphonates, tosylates, trifluoro-methyl sulphonates; perchlorates; NaBH ₄ ; and KPF ₆ , is not critical for the conversion, some salts are more preferred than others in terms of product properties and/or safety. For example, small counterions will produce oily liquids. Perchlorates are potentially explosive and could become a severe hazard upon large-scale preparation. Preferred counterions are the large molecules from surfactants, especially tosylate. A particularly preferred counterion is PF ₆ ^" , which is conveniently obtained from KPF ₆ . Dinuclear manganese (III) and manganese (IV) complexes having PF ₆ ^" as the counterion, are solid crystalline products which are easy to handle and to form into a granulated catalyst product. A most preferred counterion is sulfate.

Suitable and preferable ligands for use in the present invention are those which contain three nitrogen atoms all of which coordinate to one of the manganese centers. Preferably the ligand is also macrocyclic in nature.

The nitrogen atoms in the ligand can be part of not only tertiary, secondary or primary amine groups, but also of aromatic ring systems, e.g. pyridines, pyrazoles, etc. or combinations thereof.

Examples of the most preferred ligands are those having the following structures:

III IV

VI

VII VIII

The most preferred ligands are ligands I-V, with I being particularly preferred.

Ligand (I) is 1,4,7-trimethyl-l,4,7-triazacyclononane, coded as 1,4,7-Me ₃ -TACN; ligand (II) is 1,4,7-triazacyclononane, coded as TACN; ligand (III) is 1,5, 9-trimethyl-l, 5, 9- triazacyclododecane, coded as 1,5, 9-Me ₃ -TACD; ligand (IV) is 2-methyl-1,4,7-trimethyl-l,4,7-triazacyclononane, coded as 2- Me,l,4,7-Me ₃ TACN; and ligand (V) is 2-methyl-1,4,7- triazacyclononane, coded as 2-Me-TACN.

Any of these complexes, either performed or formed in situ during the washing process, are useful catalysts for the bleach activation of peroxy compounds over a wide class of stains at lower temperatures, i.e. below 60°C, in a much more effective way than the Mn-based catalysts of the art hitherto known. Furthermore, these catalysts exhibit high stability against hydrolysis and oxidation, even in the presence of oxidants such as hypochlorite.

Manganese complexes which are the object of the present synthesis and which are particularly preferred are those in which each X is 0 ^2~ and which have the following structures:

[LMn(IV) (μ-0) ₃ Mn(IV)L] ^z Y _q

wherein L, Y, q and z are as described above.

Specifically preferred is a complex of the structure:

abbreviated as [Mn ^IV ₂ ( μ-O) ₃ ( 1 , 4 , 7 -Me ₃ -TACN) ₂ ] ( PF ₆ ) ₂ H ₂ 0.

A particular advantage of the process according to the invention is that it can be performed in a single reactor without isolation of any intermediate products as was previously required.

The first step of the process involves reacting a manganese (II) salt with a ligand L in the presence of a counterion salt M ₂ Y _q . Suitable as manganese (II) salts are manganese chloride, manganese sulphate, manganese bromide and manganese nitrate, with the manganese chloride being preferred.

The molar ratio of manganese (II) salt to ligand may range anywhere from 4:1 to 1:2, preferably from about 2:1 to about 1:1, and most preferably about 1.5:1 to 1:1. Relative molar ratios of the manganese (II) salt to the counterion salt will range from about 4:1 to 1:4, preferably from about 2:1 to about 1:2, and most preferably between about 1:1 and 1:2. In the second and final step of the process of the invention, the manganese coordinated substance formed in the first step is oxidised. Oxidation can be performed with air, pure oxygen, hydrogen peroxide, potassium permanganate or any combination thereof. Most preferred as an oxidising agent is aqueous hydrogen peroxide or solid sodium peroxide.

In the second step of the reaction the reaction medium must be held at a pH of at least 12 and preferably is at least 12.5. Sodium hydroxide is the preferred basifying agent. It is important that the reaction mixture of the second step simultaneously be provided with both the oxidising and the basifying agents. Only under such conditions will high and reproducible yields be achieved.

Advantageously, upon reaction completion the resultant mixture is quenched by lowering the pH to pH 9 or below, preferably between pH 7 and 9. Decomposition of the desired manganese complex catalyst is thereby avoided.

For purposes of the process of this invention, there need be no isolation of any coordinated manganese intermediates. In fact, isolation of a coordinated manganese intermediate may have an adverse effect. Further, for purposes of the invention, it is advantageous to employ a protic solvent system. Particularly useful is a combination of a alkanol and water in a ratio of about 10:1 to 1:10, preferably 4:1 to 1:1, and most preferably about 2:1. The preferred alkanol is ethanol.

With the process of the invention it is no longer necessary nor desirable that a preliminary oxidation is carried out between formation of a manganese coordinated substance and before basification. In the process of the present invention, the intermediate oxidation step is eliminated and basification and oxidation is performed concurrently in a single final step.

The following examples will more fully illustrate the embodiments of this invention. All concentrations presented are by weight unless otherwise indicated.

EXAMPLES

Example 1

Synthesis of Mn, (1,4,7-Me,TACN)-,(ii-O) ■_ (PF , via Mn(II) Salts and Sodium Peroxide

In a 2L round-bottom flask was dissolved 18.4g MnCl ₂ (0.146 mole) in 1000 ml ethanol/water (67:33). To the resultant solution, under agitation, was added 25g 1,4,7"Me ₃ TACN (0.146 mole) and 26g NaPF ₆ (0.156 mole). This solution was stirred at room temperature for 20 minutes and then chilled to about 5°C in an ice bath. To the chilled solution, whilst maintaining stirring, was slowly added (over 3 minutes)

10.75g of solid sodium peroxide (0.146 mole) . The pH of the solution was greater than 12. After complete addition of the

sodium peroxide, the reaction mixture was stirred, whilst surrounded by an ice bath, for one hour and then warmed to room temperature. The mixture was then stirred at room temperature for an additional 45 minutes. Finally, the pH of reaction mixture was lowered to pH 8-9 with 1.2N sulfuric acid. The resulting mixture was then filtered through a medium porosity glass frit to remove manganese by-product and washed with water until the filter pad rinsed colourless (to remove any red precipitated Mn(IV) product) . The cherry red coloured solution was then concentrated to 1/10 of the original solvent volume causing crystallisation of the product. This concentrated solution was filtered and the red crystalline product was washed with ethanol (25 ml) and dried under vacuo. Yield was 34.8g Mn(IV) ₂ l,4,7-(Me ₃ TACN) ₂ (μ- 0) ₃ (PF ₆ ) ₂ H ₂ 0 (Purity = 97%).

Example 2

Synthesis of Mn,(1,4,7-Me,TACN),(li-O)-,(PF _C ), via Mn(II) Salts and Hydrogen Peroxide

In a 2L round bottomed flask was dissolved 11.lg MnCl ₂ (0.088 mol) in 600 ml ethanol/water (67:33). To this solution, whilst stirring, was then added 15g 1,4,7-Me ₃ TACN (0.088 mole) and 17.5g KPF ₆ (0.095 mole). This solution was stirred at room temperature for 20 minutes and then chilled to about 5°C in an ice bath. To the chilled solution, whilst stirring, was added one mole equivalent hydrogen peroxide (3%) and 1.5 mole equivalent sodium hydroxide (20% aqueous solution) . This corresponds to adding a mixture of 99ml of hydrogen peroxide (3%) and 26.3ml sodium hydroxide (20% solution) to the reaction mixture. The pH of the resulting solution was greater than 12. After complete addition of the peroxide premix, the resultant reaction mixture was stirred whilst surrounded by an ice bath for one hour and then warmed to room temperature. The mixture was stirred at room temperature for an additional 45 minutes. Finally, the pH of the reaction mixture was lowered to pH 8-9 with 1.2N

sulphuric acid and filtered through a medium porosity glass frit to remove manganese by product. It was then washed with water until the filter pad rinsed colourless (to remove any red precipitated Mn(IV) product). The cherry red coloured solution was then concentrated to 1/10 the original solvent volume causing crystallisation of the product. This concentrated solution was then filtered and the red crystalline product was washed with ethanol (25 ml) and dried under vacuo. Yield was 25.8g Mn(IV) ₂ (1,4,7-Me ₃ TACN) ₂ (μ- 0) ₃ (PF ₆ ) ₂ H ₂ 0 (Purity = 97%).

Example 3

Comparison of Various Oxidising Agents

Various combinations of oxidising agents were used to prepare Mn ₂ (l,4,7-Me ₃ TACN) ₂ (μ-0) ₃ (PF ₆ ) ₂ and the results of these preparations are recorded in the following table. The first three entries were performed via two oxidation steps. The first oxidation was performed at pH 7. Thereafter, the pH was raised to greater than 10.5 with triethyl amine whereupon the second oxidation was performed. The last two entries report results from Examples 1 and 2.

Example 4

The synthesis of Mn ₂ (1,4,7-Me ₃ TACN) ₂ (μ-0) ₃ (PF ₆ ) ₂ can be performed with a variety of Mn(II) salts. Results obtained with two Mn(II) compounds are shown in the following table.

Example 5

Simultaneous addition of the base and peroxide has been found to produce higher yields of the desired product than sequential addition of the two reactants. As shown in the following table, addition of sodium peroxide or a NaOH/H ₂ 0 ₂ mixture (pH greater than 12) gave more product than addition of H ₂ 0 ₂ followed by addition of NaOH (pH greater than 12) or vice versa.