The present invention relates to a method for the preparation of aqueous solutions containing performic acid formed by reaction of formic acid and hydrogen peroxide in the presence of a catalyst.

Such a method is known from the book Organic Peroxides, Vol. 1, ed. by B. Swern in 1970 (Wiley Interscience) . Dilute performic acid solutions suitable for disinfection are most conveniently prepared by mixing 70-90 wt. % of formic acid and 35-50 wt.% of hydrogen peroxide. Performic acid is unstable at higher concen¬ trations and therefore it is usually prepared by mixing solutions of formic acid and hydrogen peroxide just prior to use (in situ prepa¬ ration) . According to Swern an acid catalyst may be used. The bactericidal and sporicidal disinfectant properties of performic, peracetic and perproponic acid has been described by erka et al., in J.Hyg.Epidem.Microbiol.Immunol. 1965 (IX) 220. Per¬ formic acid has demonstrated superior results in the studies concerning the fungicidal (mycocidal) properties of these acids (J.Hyg.Epidem.Microbiol.Immunol. 1968. 12, 115).

The exceptional microbicidal properties of performic acid have later been described in EP-A-0231 623.

A specific use of aqueous performic acid containing solutions is described in not prepublished Dutch patent application 9300445. This reference relates to a method for preventing and combating harmful microorganisms such as fungi, viruses, bacteria, yeasts and algae in water circulation systems, wherein the water including feed solutions and drain water, has a disinfectant added to it which at least comprises performic acid. The contents of this Dutch patent application is incorporated here by reference.

It is an object of the present invention to increase the equilibrium concentration of performic acid in aqueous solution of formic acid and hydrogen peroxide.

This object was achieved by the use of a compound containing at least one ester group and/or 0 ^• C-0- group differing from a carboxylic acid group as a catalyst.

Consequently, the present invention relates to a method for the preparation of aqueous solutions containing performic acid formed by reaction of formic acid and hydrogen peroxide in the presence of a catalyst, characterized in that the catalyst is a compound containing at least one ester group and/or 0 ^• C-0- roup differing from a carboxylic acid group.

The compound may be used in catalytic amounts, which expression is well-known to men skilled in the art. However, it is preferred that a minimum amount of 10 ppm, calculated on the aqueous solution, is used. In general an amount of more than 10.000 ppm will not bring additional advantages. The particularly preferred range is 200-5000 ppm, again calculated on the total aqueous solution containing the reactants. Preferably, the catalytic compound is a carboxylic acid ester which is not toxic. However, other ester compounds such as sulfate esters, sulfonate esters/lactones and phosphate esters and similar compounds may be successfully used.

According to a preferred embodiment of the method of the invention the catalytic compound is selected from the group consisting of carboxylic acid esters where the carboxylic acid is: a) aromatic or aliphatic C ₁ -C ₂₀ carboxylic acid; b) aromatic or aliphatic di- or pol functional carboxylic acid; and wherein the alcohol part is a) aliphatic or aromatic C^-C^ mono- of polyfunctional alcohol, b) sugar alcohol , c) polymer containing hydroxyl groups .

Suitable are a.o. compounds like glyceryl mono-, di- and tri- esters, wherein the carboxylic acid is C-r-Cgo carboxylic acid, poly- mers such as (partially hydrolysed) polyvinylacetate.

The use of the catalyst in accordance with the invention causes an enormous increase, e.g. of 100-300 % of the concentration of performic acid. Consequently, performic acid containing preparations prepared in accordance with the invention are more efficient than the prior art solutions.

The present invention also relates to an aqueous solution containing performic acid, formic acid, hydrogen peroxide as well as

a compound containing at least one ester group and/or 0

•C - 0- group differing from a carboxylic acid group. The same preferences as mentioned with respect to the method of the invention can be mentioned here.

Further, the invention relates to the use of the above aqueous solutions of the invention for sterilization, sanitization and disinfection purposes. In this respect reference is e.g. made to the above cited EP-A-0231 623 and NL 9300445. It appeared from many tests that any compound of the ester type may be used with a certain degree of success. An average chemist will immediately understand what is meant by "ester type".

The inventors find the effect of the ester type compound on the amount of performic acid in the solution surprising. The invention is explained in more detail in the following examples.

Example 1

A 35 % (w/w) solution of hydrogen peroxide (515 gι 5-38 mol) is added dropwise with stirring in 98 % (w/w) formic acid (100 ml, 122 g, 2.65 mol) at room temperature. The resulting solution was stirred for 30 minutes at room temperature and diluted with de- ionized water (1911 g) • The solution was divided into 0 ml portions and 50 mg of the following alkyl esters of carboxylic acids were added into each solution:

Sample Carboxylic acid ester

1. no additives

2. caproic acid mono- and diglyceride (Grinstedt TS-T 104)

3. 1,2,3-triacetoxypropane 4. ethyl acetate

5. methyl formate

6. sorbitan monolaurate (ICI Span 20)

7. dibutyl phthalate

The solutions were allowed to stand at room temperature and the concentrations of hydrogen peroxide and performic acid were determined by titration with Ceric sulfate and sodium thiosulfate, respectively, according to the method of Swern et al. (Swern,

Organic Peroxides, Vol. 1, page 501, Wiley Interscience, 1970). The concentrations obtained by titrations are collected in tables 1 and 2.

Table 1 Concentrations of performic acid obtained from the samples 1-6,

1 hour after dilution.

Sample No. additive 1) performic acid (g/1)

1. no additives 3.41

2. monoglyceride 6.51

3- 1,2,3-triacetoxypropane 6.51

4. ethyl acetate 6.51

5. methylformate 6.20

6. sugar ester 6.82

7. dibutyl phthaiate ^1>2 11.16

1) concentration 2500 mg/1

2) titrated after 4 hours stirring at room temperature.

Table 2

Concentrations of performic acid obtained from the samples

24 hours after dilution

Sample No. additive performic acid (g/1)

1. no additives 2.63

2. monoglyceride 6.36

3- 1,2,3-triacetoxypropane 7-13

4. ethyl acetate 7.29

5- methylformate 6.66

6. sugar ester 5.43

Example 2

A 30 wt.# solution of hydrogen peroxide (610 g, 5«3δ mol) was added dropwise into & wt.% formic acid (100 ml, 122 g, 2.65 mol).

The solution was stirred at room temperature for 30 minutes, where¬ after it was divided into five portions. Carboxylic acid esters listed in Table 3 _t were added into the solutions and they were stirred at room temperature for 4 hours. Concentrations of performic acid and hydrogen peroxide were determined by using the method mentioned above.

Table 3

Concentrations of performic acid obtained from the samples

4 hours after dilution.

Sample additive (mg/1) performic acid (mg/1)

1. no additives 27.28

2. ethyl acetate 1300 31.00

3. ethyl propionate 1500 28.52

4. dibutyl phthalate 2500 31.93

6. glycolic acid butyl ester 1500 44.64