Pyridine-3-percarboxylic acid monopersulfate

Abstract: Pyridine-3-percarboxylic acid monopersulfate of formula: the process for its preparation and the use thereof as bleach­ ing agent are described.

Description: The present invention relates to pyridine-3-percarboxylic acid monopersulfate having the formula (I): and, moreover, its preparation and the use thereof as bleaching agent. Pyridine-3-percarboxylic acid monopersulfate represents a product which is highly interesting from an industrial point of view, particularly due to its high content of active oxygen per weight unit. More specifically, pyridine-3-percarboxylic acid monopersulfate can be employed in a particularly efficient manner, e.g., in the field of bleaching, in the industry of detergence. In the past few years organic peracids have attracted increasing interest in the industrial field, particularly due to their excellent employability as bleaching agents in formulations for medium-low temperature washing and, even more important, also due to energy-saving considerations. Therefore the research activity is aimed at finding organic peracid compounds endowed with the required properties of high bleaching activity, thermal stability and storage stability (shelf life). Therefore, many (cyclo)aliphatic mono- or di-percarboxylic acids are already known and used, among others, in the detergent field. From "Ullmanns Encyklopädie der technischen Chemie" (4. Edition, vol.17, pages 720-721) it is furthermore known to use monopersulfate salts as bleaching agents optionally together with halide ion or α,β unsaturated carboxylic acids. Already described percarboxylic acids are, e.g., diperdodecanedioic acid, monoperphthalic acid, diperazelaic acid and substituted diperglutaric and adipic acids, etc. The conventional percarboxylation processes comprise the oxidation of the substrate with a solution of hydrogen peroxide in concentrated H₂SO₄. The strong acidity of the reaction medium and the presence of a salifiable nitrogen atom of basic character in the substrate used as starting material renders said substrate highly soluble in said acidic medium, making it impossible to apply any of the conventional processes for the isolation of the resulting percarboxylic acid derivative, such as precipitation by dilution with water or extraction with an organic solvent selective for the percarboxylic acid product and not miscible with the remaining reaction mixture. Surprisingly, it has now been found that the pyridine-3-percarboxylic acid monopersulfate having the above formula (I), salified on the nitrogen atom with persulfuric acid, may be obtained by means of a novel process which is also a part of the present invention. One object of the present invention is to provide, as per se novel compound, pyridine-3-percarboxylic acid monopersulfate having the above formula (I). Another object is to provide a simple and inexpensive process for the preparation of the monopersulfate of formula (I). A further object is the use of 3-pyridine-percarboxylic acid monopersulfate as bleaching agent in detergent formulations, especially those intended for low-medium temperature use. These and still other objects which will become even clearer for those skilled in the art from the following detailed disclosure, are achieved, according to the present invention, by 3-pyridine-percarboxylic acid monopersulfate and the process for the preparation thereof wherein nicotinic acid (pyridine-3-carboxylic acid) or its N-sulfate salt is reacted with H₂O₂ in concentrated H₂SO₄ and the resulting monopersulfate (I) is then separated from the reaction mixture by the addition of ethyl acetate. In this way the compound of formula (I) is obtained as a crystalline solid through its insolubilization in the reaction medium by ethyl acetate. More specifically, the process according to the present invention comprises the percarboxylation reaction of pyridine-3-carboxylic acid or the N-sulfate salt thereof in an acid medium of concentrated H₂SO₄ with H₂O₂ and the subsequent addition, at the end of the process, of ethyl acetate. This leads to the separation of the pyridine-3-percarboxylic acid monopersulfate in a stable solid form. As mentioned above, the pyridine-3-carboxylic acid substrate used as the starting material may optionally already be salified as sulfate on the nitrogen atom. The substrate used as the starting material is a per se known compound (nicotinic acid). The obtained product is then filtered off, washed with the solvent, dried etc., according to per se known techniques. According to a preferred embodiment, the percarboxylation of pyridine-3-carboxylic acid or its N-sulfate is carried out by gradually adding H₂O₂ (having a concentration of from 70% to 90% by weight) to a solution of the substrate in concentrated H₂SO₄ (96-98%), maintaining the reaction temperature throughout the reaction within the range of from 0 to 25°C. It has been found that it is also possible to prepare in advance the salt of the substrate, in the form of the N-sulfate, by working under the same conditions as described above, but in the absence of H₂O₂ and by separating the salt thus obtained which then is peroxidized. The amount of H₂SO₄, determined at a concentration of 100%, preferably is substantially equal to 9 moles per mole of substrate. The hydrogen peroxide is used in an amount which is in excess with respect to the substrate, substantially equal to 5.5 moles per mole of substrate. The amount of ethyl acetate used suitably is at least equal to 4 liters/per mole of substrate and, furthermore, is advantageously added at a temperature not higher than 0°C. The pyridine-3-percarboxylic acid monopersulfate usually is solid at room temperature. It may be especially useful in formulations of detergent compositions, e.g., granular formulations, as bleaching agents in solution over a wide temperature range. The detergent compositions may be formulated according to conventional methods, together with other components and/or additives, etc. The present invention will now be described in still more detail in the following examples, which are given for purely illustrative purposes. The pyridine-3-percarboxylic acid monopersulfate was characterized by elemental analysis, by determining tis content of active oxygen (by iodometric titration), and by using Fourier Transform Infrared Spectroscopy (FT-IR). EXAMPLE 1 59.6 g (0.583 mole) of H₂SO₄ (96%) were placed in a beaker equipped with stirrer, thermometer, and external bath. The internal temperature was brought to 0°C and 14.4 g (0.36 mole) of H₂O₂ at 85% were slowly added under stirring, maintaining the temperature below 5°C. 8 g (0.0650 mole) of pyridine-3-carboxylic acid (nicotinic acid) were then gradually added and the reaction was continued for 4 hours at 20 - 25°C. At the end, the reaction mixture was poured into 250 ml of ethyl acetate maintained under stirring at between -10° and 0°C. After 2 hours of reaction at this temperature, the crystalline product was filtered, under vacuum, over a porous septum. The product was directly washed on the filter with ethyl acetate (50 ml) and ethyl ether (50 ml) and then dried over CaCl₂ under vacuum and at room temperature for 1 hour. Obtained were 12.5 g of crystalline product having an active oxygen content of 11.75% (theoretical value for pyridine-3-percarboxylic acid monopersulfate: 12.64%). Yield 70%. Elemental Analysis Calculated for C₆H₇O₈NS: C = 28.47%; H = 2.78%; N = 5.53%; O (active) = 12.64%; H₂SO₅ = 45.07%. Found: C = 28.90%; H = 2.86%; N = 5.69%; O (active) = 11.75%; H₂SO₅ = 42.30%. Melting Point: 85°C (with decomposition). EXAMPLE 2 (Application example) Bleaching with pyridine-3-percarboxylic acid monopersulfate Bleaching tests were carried out with a detergent formulation containing pyridine-3-percarboxylic acid monopersulfate in the amount reported in the following Table 1 (composition A) and a similar comparative formulation containing, as bleaching agent, H 48 peracid (Mg salt of monoperphthalic acid, a known commercial product, manufactured by INTEROX Chemical Ltd London, U.K., for use in the detergent art) (composition B). Compositions A and B were obtained by dry blending of a detergent base (identical for both compositions) with the above bleaching agents. As detergent base a granular composition was used which contained all of the conventional components of a detergent for washing machines (surfactants, builders, etc.), except the chemical bleaching agents, and was obtained by atomization of the component mixture. The detergent base employed had the following composition: Weight % Total surfactants 15.4 Sodium alkyl (C₁₂) benzenesulphonate, soap, ethoxylated (EO) alcohol (C₁₆-C₁₈) Total sodium phosphates 8.8 Zeolite A 19.8 Silicate (SiO₂/Na₂O=2) 4.4 Sodium sulphate 36.6 Sodium carbonate 6.6 Carboxymethylcellulose 1.1 Anti-encrusting copolymers 4.8 Water 2.2 Optical bleaching agents 0.3 The metering of the compositions A and B was carried out in a way such as to introduce into the washing machine a constant amount of detergent base (corresponding to 120 g) and an amount of bleaching agent such as to introduce into the washing machine a quantity of total initial active oxygen of about 2g of oxygen for each washing cycle, identical for all operations. Specifically, the compositions A and B given in the following Table 1 were used in the bleaching tests. Composition A Detergent base 120 g Pyridine-3-percarboxylic acid monopersulfate having 11.1% of active oxygen 18 g Composition B Detergent base 120 g H 48 having 5.5% of active oxygen 39 g The tests were carried out in a commercial IGNIS® Mod. 644 washing machine by introducing into the machine two cotton specimens (15 x 15 cm) stained with standard stains or red wine at the EMPA INSTITUTE of St. Gallen (Switzerland) and marked with the "EMPA 114" mark, together with 3 kg of cleaned cotton wipers as ballast for each washing operation. The washing operations were carried out by using a conventional low temperature program (about 40°C). Normal tap water, having a hardness of 14°F, was used. The results of the tests are reported in the following Table 2, wherein the data are expressed as % Bleaching, defined as: wherein: A = degree of whiteness (%) of the specimen bleached after the test; B = degree of whiteness (%) of the specimen before the test; C = degree of whiteness (%) of the completely bleached specimen. The degree of whiteness was measured by means of an Elrepho Zeiss Reflectometer, using a filter No. 6 ( λ = 464 nm) and assuming MgO = 100% of whiteness. % Bleaching Composition A 57 Composition B 52 The data show the higher bleaching power of the claimed peracid in comparison to that of H 48. EXAMPLE 3 (Application example) Bleaching tests were carried out with the pyridine-3-percarboxylic acid monopersulfate at an acid pH in comparison to H 48. The results are listed in the following Table 3. All tests were carried out at constant temperature of 60°C with an initial concentration of total active oxygen in the bleaching solution of 200 mg/l, identical for both products. Process For each test 500 ml of deionized water, contained in a 1000 ml flask equipped with a condenser, were heated to a temperature of 60°C. The bleaching product was dissolved under stirring in the amounts shown in the following Table 3 and immediately thereafter two cotton specimens (10 x 10 cm) stained with standard stains of red wine at the EMPA INSTITUTE of St. Gallen (Switzerland), and marked with the "EMPA 114" mark, were added to the solution having a pH value of 3 - 4. Thereafter the system was kept stirred for 60 minutes and finally the specimens, rinsed under running water, dried and ironed, were subjected to an evaluation of the bleaching effect by determining the degree of whiteness by reflectometry. The results are reported in the following Table 1, expressed in terms of % Bleaching as defined in example 2 above. The data in Table 3 show that the acid salt of the present invention, in acid solution, has a particularly high bleaching activity, and a much higher one than H 48. This is particularly surprising in consideration of the fact that peroxy compounds generally show a very modest bleaching activity under these conditions. Tests Carried out at Acid pH (3-4) Compound Amount used in the tests (grams) Initial concentration of total active oxygen (mg/l) % Bleaching at 60°C Example 1 (TITER = 11.75% of active oxygen) 0.86 200 74.0 H 48 (TITER = 5.5% of active oxygen) 1.86 200 60

Claims: Pyridine-3-percarboxylic acid monopersulfate having the formula: Process for preparing pyridine-3-percarboxylic acid monopersulfate, wherein pyridine-3-carboxylic acid or its N-sulphate salt is reacted in concentrated H₂SO₄ with H₂O₂ in an amount which is substantially equal to 5,5 moles per mole of pyridine-3-carboxylic acid and the resulting percarboxylic acid salt is separated from the reaction mixture by the addition of ethyl acetate. Process for preparing pyridine-3-percarboxylic acid monopersulfate wherein pyridine-3-carboxylic acid is converted into the corresponding HSO₄ salt which is then reacted in concentrated H₂SO₄ with H₂O₂ in an amount which is substantially equal to 5.5 moles per mole of pyridine-3-carboxylic acid, and the resulting product is separated from the reaction mixture by the addition of ethyl acetate. Process according to any one of claims 2 and 3 wherein the pyridine-3-carboxylic acid or its N-sulfate salt is graduallly reacted in concentrated H₂SO₄ and at a temperature of from 0° to 25°C with H₂O₂ in an amount of substantially equal to 5.5 moles per mole of pyridine-3-carboxylic acid, the H₂O₂ have a concentration of from 70% to 90% by weight. Process according to any one of claims 2 to 4, wherein the amount of H₂SO₄ is substantially equal to 9 moles per mole of pyridine-3-carboxylic acid. Process according to any one of claims 2 to 5, wherein the amount of ethyl acetate used is at least equal to 4 litres per mole of pyridine-3-carboxylic acid. Process according to any one of claims 2 to 6, wherein the ethyl acetate is added at a temperature not higher than 0°C. Use of pyridine-3-percarboxylic acid monopersulfate as bleaching agent in detergent formulations.

Inventors: CAVALLOTTI CLAUDIO, VENTURELLO CARLO DR, CAVALLOTTI, CLAUDIO, VENTURELLO, CARLO, DR.
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1989
Main classification: C07D213
IPC codes: C07D213, C11D3, D06L3