Abstract:
Effective stabilization of aqueous hydrogen peroxide solutions is achieved by the addition of a stabilizing phosphonate compound of the general formula: ##STR1## wherein n=1-4; and X=H or a water-soluble cation. The stabilizing phosphonate compound is particularly effective for use with alkaline hydrogen peroxide solutions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the stabilisation of aqueous hydrogen peroxide solutions, especially under alkaline conditions. The invention also relates to the preparation of storage-stable alkaline hydrogen peroxide solutions which can be used as a base for liquid bleach products. 
     Hydrogen peroxide decomposes to water and oxygen and cannot be kept for long unless it is properly stabilised. 
     Decomposition of hydrogen peroxide occurs mainly in a catalysed reaction, of which the active catalysts are trace amounts of indigenous transition metal ions, such as copper, iron, cobalt and manganese ions, and as such can in principle be reduced by adding suitable metal complexing agents. Indeed many stabilisers for hydrogen peroxide known in the art are complexing agents and just as many stabilisers have been suggested and used for solving, at least partially, the decomposition problem of hydrogen peroxide solutions. 
     While the stabilisation of hydrogen peroxide is relatively easy in acid solution, i.e. at pH&lt;&lt;7, where the concentration of reactive HO 2   -  ions--the active form of hydrogen peroxide--is minimal, it has heretofore been considered as practically impossible to achieve a satisfactory stabilisation of hydrogen peroxide under alkaline conditions. The term &#34;alkaline&#34; as used here is meant to indicate alkaline pH values of above 7, particularly between 8 and 14. 
     Indeed many complexing agents developed heretofore as stabilisers for use with hydrogen peroxide solutions and which give satisfactory stabilisation of hydrogen peroxide under acid conditions, are poor stabilisers and hence unsuitable when used with hydrogen peroxide under alkaline conditions, particularly at pH above 8. 
     For this reason hydrogen peroxide is presented commercially as product concentrates having a pH lying generally within the range of 2-5, mostly between 2 and 3. Acid hydrogen peroxide is, however, unsuitable for use as a bleach due to the low concentration of HO 2   -  ions, the active form of hydrogen peroxide. For effective bleaching an alkaline pH is a necessary requirement, the higher the pH the higher the HO 2   -  ion-concentration to provide for more effective bleaching. The selection of pH used will generally depend upon the substrate which is to be bleached. For textile bleaching a suitable pH is within the range of 8-12.5, preferably between 9 and 11.5, as higher pH&#39;s will tend to cause excessive fabric damage. 
     When said commercial acid hydrogen peroxide solution is made alkaline, e.g. with sodium hydroxide, to a suitable bleaching pH with or without dilution with water to any desired concentration, it becomes unstable and cannot be stored without quickly losing its activity. 
     Stabilisers which have been suggested for use with hydrogen peroxide solutions include dipicolinic acid (DPA) as described in U.S. Pat. No. 2,624,655; ethylenediamine tetra acetic acid compounds (EDTA) as described in British Pat. No. 1,285,151; amino tri-(lower alkylidene phosphonic acid) compounds, e.g. sodium nitrilo tri-(methylene phosphonate) as described in British Pat. No. 1,119,221; alkylidene-diphosphonic acid derivatives, e.g. ethane-1-hydroxy-1,1-diphsophonate (EHDP) as described in British Pat. No. 925,373; and ethylenediamine tetra methylene phosphonic acid) as described in U.S. Pat. No. 3,701,825. 
     Most of these known stabilisers, though having some ability to inhibit decomposition of hydrogen peroxide under acid conditions, are however poor stabilisers for alkaline hydrogen peroxide solutions, and are suitable or even unsuitable for producing satisfactory storage-stable alkaline hydrogen peroxide solutions. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to improve the stability of hydrogen peroxide solutions, especially under alkaline conditions. 
     It is another object of the invention to provide a stabiliser for hydrogen peroxide which is much better than the hitherto known stabilisers for use with alkaline hydrogen peroxide solutions. 
     Still another object of the invention is to provide alkaline hydrogen peroxide solutions which are sufficiently stable on storage to achieve an acceptable shelf-life. 
     It has now been found that these and other object which will be apparent hereinafter can be achieved if the hydrogen peroxide solution includes a stabilising phosphonate compound of the following general formula: ##STR2## wherein n=1-4; and X=H or a water-soluble cation. The various X groups may be the same or different. Typical examples of useful cations are alkali metals, ammonium, substituted ammonium and alkaline earth metals, such as calcium and magnesium. 
     DESCRIPTION OF THE INVENTION 
     The invention therefore provides an aqueous hydrogen peroxide solution stabilised against decomposition, containing a stabilising amount of a phosphonate compound of the following general formula: ##STR3## wherein n=1-4; and X is H or a water-soluble cation, selected from the group consisting of alkali metals, ammonium, substituted ammonium and alkaline earth metals. 
     Preferred compounds have n=1-2 and preferably X is hydrogen, ammonium, sodium or potassium or mixtures thereof. 
     The addition of any amount of the above-described stabilising phosphonate compound to hydrogen peroxide solutions of any pH and of any concentration, results in the beneficial effect of inhibiting the hydrogen peroxide decomposition. The invention is however of particular importance for inhibiting the decomposition of hydrogen peroxide solutions under alkaline conditions. Advantageously the stabilising phosphonate compound can be used with alkaline solutions of hydrogen peroxide of a concentration of about 5-20% by weight and having a pH of about 8-14. 
     The preferred amount of stabilising phosphonate compound depends upon the pH of the hydrogen peroxide solution and the anticipated amount of impurities that may enter the hydrogen peroxide solution to be stabilised. 
     Generally the amount of stabilising phosphonate compound used will be at least 0.01% by weight of the hydrogen peroxide in the aqueous hydrogen peroxide solution. Preferably an amount of between 0.03 and 1.0% by weight is used for stabilising an acid hydrogen peroxide solution, and from 0.1-10% by weight, more preferably from 0.2-5.0% by weight for stabilising an alkaline hydrogen peroxide solution, the percentages being of the weight of the hydrogen peroxide in the aqueous hydrogen peroxide solution. 
     The maximum amount of the stabilising phosphonate compound that can be present in the hydrogen peroxide solution is limited only by practical and economic considerations in that concentrations beyond the above upper levels, although functional, impart little or no advantage over lower percentages. Higher levels of the stabilising compound would also tend to give a reduced bleachng due to interaction between the bleaching species and the stabilising compound. 
     The stabilised hydrogen peroxide solutions of the invention can be of any desired concentration and of any desired pH; however preferred practice is to stabilise bleaching hydrogen peroxide solutions having a concentration of from about 5 to 20% by weight and an alkalinity of from about pH 8 to pH 12.5. The preferred concentration of the stabilised hydrogen peroxide solution is from about 5-10% by weight; the preferred pH of the stabilised hydrogen peroxide is between 9 and 11.5. 
    
    
     EXAMPLES 
     Stability studies were carried out on 5% w/v H 2  O 2  solutions at pH of around 10 and a temperature of 40° C. At the 5% level the H 2  O 2  has a similar oxidising capacity to (a) 10% NaOCl used in liquid chlorine bleach, or (b) 25% sodium perborate used in fabric washing powders. The comparatively high temperature of 40° C. was chosen deliberately to accelerate the test. The 5% w/v H 2  O 2  test solution was made by diluting a 28% w/v H 2  O 2  solution sample (ex Hopkins and Williams) with dionised water. As received the 28% w/v H 2  O 2  -solution had a pH˜2 and for test purposes this was raised to about 10 with NaOH. The residual H 2  O 2  in the test solution was monitored periodically during storage at 40° C. using the iodine/thiosulphate method. From the plot of % residual H 2  O 2  vs. time the half decomposition time of the solution was found. The experiments were carried out with two members of the stabilising phosphonate compound of formula I within the invention(Runs 19 and 20) and compared with a variety of other known stabilisers and metal ion complexing agents (Runs 2-18), added in most cases at a levdel of 0.03% by weight of the solution. 
     Run 1 with no stabiliser added was used as a control. The results showing average half decomposition lives of each solution from repeated tests are given in the Table below. 
     
                                           TABLE__________________________________________________________________________                            Half                            decompo-                            sition                            time                  Trade name                         Initial                            at 40° C.Run  Additive          (if known)                         pH (hours)__________________________________________________________________________1.   None              --     9.82                            ˜12.   0.03% w/v ethylenediamine tetra(ethoxyphosphonic acid)                  --     9.94                            ˜13.   0.1% w/v dipicolinic acid DPA                  --     9.78                            ˜14.   0.03% w/v ethylendiamine di-(o-hydroxyphenyl acetic acid)                  Chel DP                         9.85                            55.   0.03% w/v hydroxypropylenedia-mine tetra acetic acid                  Chel U 9.95                            36.   0.03% w/v hexamethylenediaminetetra (methylene phosphonicacid)             Dequest 2051                         9.94                            37.   0.1% w/v nitro triacetic acid-NTA               --     9.80                            68.   0.03% w/v dodecylamine di-(methylene phosphonic acid)                  Dequest 2071                         9.95                            79a.  0.03% w/v ethylenediamine tetraacetic acid-EDTA  Various                         9.84                            109b.  0.40% w/v ethylenediamine tetraacetic acid-EDTA  Various                         9.87                            810.  0.03% w/v diethylenetriaminepenta acetic acid-DETPA                  Chel 330                         9.82                            1211.  0.03% w/v sodium nitrilo tri-(methylene phosphonate)                  Dequest 2006                         9.92                            2412.  1.0% w/v sodium silicate                   --    10.12                            2813a. 0.03% w/v ethane hydroxy di-phosphonate-EHDP  Dequest 2010                         9.80                            2913b. 0.4% w/v ethane hydroxy di-phosphonate-EHDP  Dequest 2010                         10.1                            20314a. 0.03% w/v ethylenediamine tetra(methylene phosphonic acid)EDTMP             Dequest 2041                         9.90                            41714b. 0.30% w/v ethylenediamine tetra(methylene phosphonic acid)EDTMP             Dequest 2041                         10.43                            23215a. 0.18% w/v N,N-bis(carboxymethyl)-aminomethane diphosphonic acid                  --     10.05                            2915b. 0.24% w/v N,N-bis(carboxymethyl)-aminomethane diphosphonic acid                  --     10.02                            22315c. 0.40% w/v N,N-bis(carboxymethyl)-aminomethane diphosphonic acid                  --     9.96                            18815d. 0.75% w/v N,N-bis(carboxymethyl)-aminomethane diphosphonic acid                  --     10.02                            14316a. 0.012% w/v N,N-bis(carboxymethyl)-aminoethane 1,1-diphosphonicacid              --     10.08                            716b. 0.16% w/v N,N-bis(carboxymethyl)-aminoethane, 1,1-diphosphonicacid              --     10.02                            6816c. 0.4% w/v N,N-bis(carboxymethyl)-aminoethane, 1,1-diphosphonicacid              --     9.98                            12416d. 0.75% w/v N,N-bis(carboxymethyl)-aminoethane 1,1-diphosphonicacid              --     9.96                            24617a. 0.03% w/v aminoethane 1,1-diphos-phonic acid       --     10.18                            1.517b. 0.40% w/v aminoethane, 1,1-diphos-phonic acid       --     10.14                            3.318a. 0.06% w/v 1,3,5-tricarboxypentane-3-phosphonic acid --     10.16                            0.6518b. 0.8% w/v 1,3,5-tricarboxypentane-3-phosphonic acid --     10.20                            0.2519.  0.03% w/v diethylenetriamine pen-ta (methylene phosphonic acid)                  Dequest 2060                         9.85                            93220.  0.03% w/v triethylenetetraminehexa (methylene phosphonicacid)             --     9.91                            812__________________________________________________________________________ 
    
     &#34;Dequest&#34; is a trade name used by Monsanto for their phosphonate complexing agents. 
     &#34;Chel&#34; is a trade name used by Ciba-Geigy. 
     The results show the outstanding stability of the hydrogen peroxide solutions of the invention (Runs 19 and 20) as compared with the other hydrogen peroxide solutions outside the invention (Runs 2-18).