METHOD FOR STABILIZING ISOTHIAZOLINONES

Abstract: A method is disclosed, for stabilizing 3-isothiazolinones, preferably of the formula (1): wherein X represents hydrogen or a halogen, Y is an alkyl, alkenyl, cycloalkyl, aralkyl or aryl group and R is hydrogen, halogen or an alkyl radical, which comprises adding to a composition containing a 3-­ isothiazolinone or two or more 3-isothiazolinones a stabilizing effective amount of a stabilizing compound of the formula (3): wherein: R, R¹ and R² each independently represents hydrogen, a straight-chained or branched or cyclic alkyl radical, aralkyl or aryl; A is oxygen or nitrogen; Z represents AR x , R¹, R², alkoxy methylene, methylene or alkylidene; n=1 or 2; x=1 or 2; and y=1 or 2; or a derivative thereof.

Description: The present invention relates to a method for stabilizing isothiazolinones. More particularly, the present invention relates to a method for stabilizing 3-isothiazolinones of the formula (1): wherein X represents hydrogen or a halogen, Y is an alkyl, alkenyl, cycloalkyl, aralkyl or aryl group and R is hydrogen, halogen or an alkyl radical. Such compounds are known to possess biocidal and biostatic activity towards a variety of organisms. The isothiazolinones of this type, however, are often not obtained in free form, but as complexes of the formula (2): wherein M is a cation or an amine, X' is an anion forming a compound with the cation M, and the value of n is such that the anion X ' / n satisfies the valence of M. The complexes of formula (2), described in U.S. Patent 4,067,878, are said to be more stable than the 3-isothiazolones of formula (1). The term alkyl group for the substituents R and Y is intended to include both unsubstituted or substituted alkyl, alkenyl, cycloalkyl, aralkyl or aryl groups. Specific examples for preferred groups are C₁₋₁₀alkyl, C₂₋₁₀ alkenyl, C₃-C₈ cycloalkyl, phenyl C₁₋₁₀ alkyl or phenyl groups. In a more preferred embodiment the alkyl group is selected from methyl and n-octyl. Examples of the cation M are metal cations such as calcium, copper, magnesium, manganese, nickel and zinc and complexes of the metal ions such as complexes with ammonia and amines. For bactericidal and fungicidal purposes, particularly useful compositions, described in U.S. Patent 4,105,431, comprise a mixture of N-alkyl-isothiazolin-3-one and N-alkyl-5-chloro-isothiazolin-3-one, in a weight ratio of about 1:3 respectively. A particularly useful mixture of this kind is that in which Y is a methyl group, and such a mixture of referred to hereinafter as MIT (methylisothiazolinones). Formulations of MIT in water or in solvent media containing hydroxylic groups are unstable, decompose rapidly and cannot be stored for long periods of time. The art has searched for ways to overcome this stability problem for a long time. A solution suggested in the art comprises stabilizing 3-isothiazolinones either in liquid formulations or on solid supports, by the addition of metal nitrates. Some such methods are described, e.g., in U.S. Patent 3,870,795, U.S. Patent 4,067,878, EP 0 106 563 and EP 0 166 611. Such methods have the considerable drawback of requiring the addition of metal nitrates in amounts which are usually nearly equimolar - but often even in excess - with respect to the 3-isothiazolinones. Furthermore, the addition of nitrates may lead to the presence of nitrosamines, which are highly undesirable impurities which are suspected of being carcinogens. Therefore, the methods of the art have the added disadvantage of requiring means for removing such nitrosamines or their precursors, as disclosed, e.g., in EP 0 095 907, or for inhibiting their formation. Such operations are complicated, time-consuming and do not afford the certainty that a sufficient amount of nitrosamines or of their precursors has been removed. It is therefore clear that it would be very desirable to provide a method for stabilizing solutions of 3-isothiazolinones, without the need of employing materials which react to give nitrosamines, or at least to reduce the amount of nitrosamines in the formulation to a very low level. Furthermore, certain systems, e.g., petroleum, cannot be treated with the formulations stabilized according to the art, since they cannot be contaminated with large amounts of magnesium nitrate. It has now surprisingly been found, and this is an object of the invention, that it is possible to provide a method by which 3-isothiazolinones and mixtures of two or more 3-isothiazolinones can be stabilized in solid form, in an aqueous medium, or in an organic medium comprising hydroxylic groups, without the need to employ large amounts of metal nitrates as stabilizers. The composition containing one or more 3-isothiazolinones may comprise a solid mixture, or the one or more 3-isothiazolinones may be on a solid support. It is a further object of the invention to provide stable 3-isothiazolinones mixtures of the kind described above, which are substantially free of nitrosamines and of nitrosamine producers. It has further been found, and this is still another object of the invention, that aerating stabilized MIT compositions has a beneficial effect on the final stability of the composition. While it has been known to package and transport MIT solutions according to the known art in containers which are incompletely filled, because of ease and safety in handling and discharge operations, the art has not specifically addressed the question of the influence of aeration to the stability of MIT. Indeed, although the mechanism by which aeration aids stabilization of compositions according to the invention has not been fully elucidated, aeration would not seem to influence the stability of MIT solutions stabilized according to the known art. By "aeration" is meant the exposure of the stabilized MIT solution to air or to another comparable gaseous medium. The method for stabilizing 3-isothiazolinones of the formula (1), according to the invention, is characterized in that a stabilizing effective amount of a stabilizing compound of the formula (3): wherein: R, R¹ and R² each independently represents hydrogen, a C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₃-C₈ cycloalkyl, phenyl C₁-C₁₀ alkyl or phenyl group; A is oxygen or nitrogen; Z represents AR x , R¹, R², alkoxy methylene, methylene or alkylidene; n=1 or 2; x=1 or 2; and y=1 or 2; or a derivative thereof; is added to the composition containing a 3-isothiazolinone or two or more 3-isothiazolinones. A preferred group of stabilizers, which possess enhanced stabilization properties, consists essentially of hydroquinone, quinone and quinhydrone, and their derivatives and homologues. Other representative stabilizing compounds are, e.g., tert-butylcatechol, p-methoxyphenol, and p-phenylenediamine and its derivatives. A considerable advantage of the method of the invention lies in that very low amounts of a stabilizing compound of formula (3), or of a derivative thereof, can be employed. Thus, according to one embodiment of the invention the concentration of the stabilizing compound of the invention in a 3-isothiazolinones - containing liquid composition is lower than 10%, for a solution of about 15% 3-isothiazolinones. Preferably the concentration of the stabilizing compound in the 3-isothiazolinone containing solution is between 0.2 and 5 wt %. According to a preferred embodiment of the said invention, the composition to be stabilized comprises a mixture of N-alkyl-isothiazolin-3-one and N-alkyl-5-chloro-isothiazolin-3-one. Particularly useful mixtures of this kind are those in which the N-alkyl radical is a N-methyl radical. The invention is also directed to stable compositions containing one or more 3-isothiazolinones and a stabilizing effective amount of a compound of the formula (3): wherein: R, R¹ and R² each independently represents hydrogen, a C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₃-C₈ cycloalkyl, phenyl C₁-C₁₀ alkyl or phenyl group; A is oxygen or nitrogen; Z represents AR x , R¹, R², alkoxy methylene, methylene or alkylidene; n=1 or 2; x=1 or 2; and y=1 or 2; or a derivative thereof. Preferred stable compositions of the invention are those which contain a mixture of N-alkyl-isothiazolin-3-one and N-alkyl-5-chloro-isothiazolin-3-one, still more preferably wherein the N-alkyl radical is a N-methyl radical. While the presence of metal nitrate stabilizers in the compositions of the invention is not necessary, such nitrate stabilizers could be also added, together with the stabilizing compound(s) of the invention. It has been surprisingly found that adding to the composition to be stabilized also one or more metal salt(s), selected from metal nitrate stabilizers and salts of metals of groups IA and IIA of the periodic table of the elements, provides a synergistic stabilizing effect, and may be convenient in some cases. In any case, the synergistically effective amount of metal nitrate stabilizers employed in any given composition of the invention can be much lower than amounts used in the known art, and hence the amount of nitrosamines or nitrosamine precursors would be drastically reduced. By "synergistically effective amounts" is meant any amount which, while by itself incapable of effectively stabilizing 3-isothiazolinones, improves the stabilization of 3-isothiazolinone formulations which is provided by the sole addition of stabilizing effective amounts of a stabilizing compound of the invention. Preferred metal salts are selected from the group consisting of magnesium nitrate, K₂HPO₄, KH phthalate, magnesium acetate and potassium permanganate. Preferred stabilizing compounds of the invention comprise hydroquinone, quinone and quinhydrone, and their derivatives and homologues. Stable compositions comprising one or more 3-isothiazolinones, whenever prepared according to the method of the invention, also form part of the present invention. Such compositions comprise solid and liquid formulations comprising one or more 3-isothiazolinones, particularly those in which the solvent medium is essentially water, or a solvent medium containing hydroxylic groups. The above and other characteristics and advantages of the invention will be better understood through the following illustrative examples thereof. The following examples represent stability tests performed at elevated temperatures, in order to accelerate decomposition. For reference purposes it should be noted that a correlation of the elevated temperature testing to ambient temperature is described in EP 0 166 611. For instance, for a formulation containing 1.5% is isothiazolinones one week at 50°C was found to be equivalent to two months of storage at ambient temperature. The results obtained by the inventors confirm the above correlation. All percentages given in the following examples refer to weight percent. The following examples refer to MIT as the representative formulation. MIT concentrations were determined in all cases by HPLC analysis. In the synthesis of MIT, mercaptoamides are cyclochlorinated in the presence of inert liquid media. The major part of the MIT produced generally precipitates. The product can be recovered in several ways, viz., by filtering off the precipitate and recycling the mother liquor, by evaporating the solvent leaving all the products in the residual solid, or by extracting the product into a second liquid phase, such as water, essentially insoluble in the reaction medium. While the method of the invention is valid for stabilizing MIT independent of its source, differences can be found between different samples, depending on their source. Care should therefore be exercised in comparing results, and results obtained in different examples employing different materials may be not comparable. Example 1 A comparative test was run to determine the influence of hydroquinone as a stabilizer, at a concentration of 0.2 wt%. The formulation employed was an MIT aqueous solution, containing a mixture of 5-H / 5-Cl isothiazolinones in a weight ratio of 1:2. The accelerated stability test was run at 50°C. Compositions containing hydroquinone were tested during 30 days, while for compositions free of hydroquinone the test was discontinued after 8 days, due to the very high level of decomposition attained (67%). The results of these tests are shown in Table I and are self-explanatory. Example 2 A series of tests was run with a MIT formulation containing 11.5% MIT in water, to determine the influence of different levels of hydroquinone on the stability of the formulation. The tests were run at 50°C as in Example 1. The results of these tests are shown in Table II. As seen from the data in the table, hydroquinone levels as low as 0.5% were sufficient to insure total stability for at least 40 days, and after 50 days only 5% decomposition occurred. Increasing the amount of hydroquinone from 1% to 4%, on the other hand, increased the stability of the MIT formulation fourfold in terms of time. Example 3 An accelerated stability test was run to determine the relative efficacy of different stabilizers. The formulation tested contained 12.3 wt% MIT in water. The test was run for 8 days at 50°C. The results reported in Table III show that the most effective stabilizer among the ones tested was p-methoxyphenol, which limited the decomposition to 5%, as compared to the 60% decomposition of the control formulation (free of stabilizer). Example 4 The stability of 10.3% MIT formulation in a solvent mixture of 80:20 w/w dipropyleneglycol/water was tested at 50°C, using a 0.5% concentration of two stabilizers: hydroquinone and tert-butylcatechol. The test was run for 4 days and no appreciable difference was found between the stabilizing effects of the two stabilizers tested. The results of this test are shown in Table IV. Example 5 The stability of a 5.7% formulation of MIT in dipropylene glycol was tested at 50°C using N,N′-di-sec-butyl-p-phenylene- diamine as the stabilizer. The formulation so stabilized was tested after 5 days versus an identical control formulation which contained no stabilizer. The decomposition of the stabilized formulation was 17%, while that of the control formulation was 99%. Example 6 Example 5 was repeated, using 2-n-octyl-3-isothiazolinone instead of MIT. After 5 days, only 25% of the stabilized isothiazolinone decomposed, while the control formulation was essentially completely decomposed. Example 7 This example illustrates the synergistic effect of metal nitrates, together with the stabilizing compounds of the invention. An accelerated stability test was carried out as in the previous examples at 50°C, to test the stability of a 10.8 wt% solution of MIT (crude) in water. Four different formulations were tested, containing magnesium nitrate hexahydrate and hydroquinone, both alone and in admixture thereof, as well as a control formulation containing no stabilizers. The results of these tests are reported in Table V. The results of these tests clearly show that hydroquinone was a far better stabilizer than magnesium nitrate at the level used, and their combination provided even better results. Example 8 A mixture of MIT and 4,5-dichloro-2-methyl-isothiazolone (90/10 w/w - total concentration 11.0%) was stabilized using a mixture of 1 wt% Mg(NO₃)₂·6H₂O and 1 wt% Hydroquinone. The results obtained were comparable to those obtained in Example 7 for the same stabilizing mixture. Example 9 A 9.5 wt% crude MIT aqueous formulation was tested in the accelerated stability test at 50°C. The results of this test are set out in Table VI, from which the beneficial effect of hydroquinone on even large amounts of Mg(NO₃)₂ can be seen. Example 10 In order to illustrate the synergistic effect of different salts on the extent of stabilization, four different samples were prepared using the same MIT source, each containing about 10% (±0.8%) MIT (crude). Stability of the composition was tested without any stabilizer, with 1% hydroquinone (HQ) as a stabilizer, and with the addition of a salt to HQ. The salts employed were K₂HPO₄, KH phthalate, Magnesium acetate and KMnO₄. The results of these tests are set out in Tables VII to X, which are self-explicative as to the marked synergistic effect obtained by the addition of these salts. Accelerated stability tests were carried out at 65°C. Example 11 Three identical 10 ml samples of a 11.6% MIT containing 1 wt% Mg(NO₃)₂·6H₂O and each 1 wt% of a different stabilizer selected from among hydroquinone (HQ), quinhydrone (QH) and quinone (Q). Stability was tested at 50°C. A composition was considered as destabilized when more than 10 % MIT decomposition occurred. The results of the comparative test are set forth in Table XI below. Example 12 The compositions of Runs 1 and 3 of Example 11 were tested under a nitrogen atmosphere, to determine the relative potency of quinone and hydroquinone. While different stability periods were obtained with different MIT samples, samples containing quinone were found to be stable for periods almost twice as long as those containing hydroquinone, from which it can be concluded that the synergistic effect with magnesium nitrate hexahydrate is considerably more pronounced with quinone. Example 13 Differently aerated MIT compositions were tested for stability at 50°C. The vessel employed was in all cases a 300 ml glass bottle, and all compositions contained 1 wt% hydroquinone, together with 1 wt% Mg(NO₃)₂·6H₂O. The results of these tests are set forth in Table XII. The above examples have been provided for the purpose of illustration. Many different formulations and solvents can be employed, different concentrations of stabilizers can be employed or different 3-isothiazolinones concentrations can be used. Influence of hydroquinone at 0.2% concentration level No Additive Hydroquinone Added Time (days) MIT Conc. wt% % Decomposition Time (days) MIT Conc. wt% % Decomposition 0 11.6 0 0 11.6 0 4 10.3 10 4 11.6 0 8 3.8 67 8 11.6 0 12 11.6 0 20 11.6 0 30 8.1 30 Influence of Various Additives at 0.2% Concentration Decomposition of Formulation After 8 days No additive : 60% AO 23 : 50% p-MeO-Ph : 5% t-Bu-Cat : 15% BHA : 20% Influence of Additives at 0.5% Concentration Decomposition after 4 days No additive : 70% Hydroquinone : 1% tert-Butylcatechol : 1% Synergistic Effect Decomposition at Time T (days): Additive None Mg HQ Mg+HQ 2HQ 6 60% 46% 0 0 0 30 0 0 0 37 47% 0 18% 48 0 62% 55 8% 60 27% Synergistic Effect on 9.5% MIT Formulation Additive: None 28Mg 28Mg+1HQ Decomposition at time T: T=3 days 63% 0 0 T=14 days 36% 20% T=20 days 42% 20% Synergistic Effect on 10% MIT formulation (65°C) Additive: None 2%K₂HPO₄ 1%HQ 2%K₂HPO₄+1%HQ Decomposition at time T: T=3 days 63% 49% 10% 0 T=6 days 61% 0 T=10 days 4% T=16 days 25% T=20 days 72% Synergistic Effect on 10% MIT formulation (65°C) Additive None 1%KH phthalate 1%HQ 1%KH phthalate+1%HQ Decomposition at time T: T=3 days 63% 47% 10% 0 T=6 days 61% 10% T=10 days 40% Synergistic Effect on 10% MIT formulation (65°C) Additive: None 1%Mg acetate 1%HQ 1%Mg acetate +1%HQ Decomposition at time T: T=3 days 63% 60% 10% 4% T=6 days 61% 14% Synergistic Effect on 10% MIT formulation (65°C) Additive: None 1%KMnO₄ 1%HQ 1%KMnO₄ +1%HQ Decomposition at time T: T=4 days 31% 35% 10% 0 T=7 days 61% 0 T=13 days 17% Relative Influence of HQ, QH and Q on 11.6% MIT formulation (50°C) Run No. Additive Stability Period (days) 1 HQ 60 2 QH 75 3 Q 75 Stability of Aerated Compositions (50°C) Run No. Air (ml) MIT formulation (ml) Air/MIT (ml/mmole) Stability Period (Days) 1 290 10 29.6 50 2 270 30 9.4 45 3 200 100 2.0 12 4 50 250 0.2 <6 5 6 294 0.02 4

Claims: A method for stabilizing compositions containing one or more 3-isothiazolinones, characterized in that a stabilizing effective amount of a stabilizing compound of the formula (3): wherein: R, R¹ and R² each independently represents hydrogen, a C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₃-C₈ cycloalkyl, phenyl C₁-C₁₀ alkyl or phenyl group; A is oxygen or nitrogen; Z represents AR x , R¹, R², alkoxy methylene, methylene or alkylidene; n=1 or 2; x=1 or 2; and y=1 or 2; or a derivative thereof; is added to the composition containing a 3-isothiazolinone or two or more 3-isothiazolinones. A method according to claim 1, wherein the composition containing one or more 3-isothiazolinones comprises a solid mixture or one or more 3-isothiazolinones on a solid support. A method according to claim 1, wherein the composition containing one or more 3-isothiazolinones is a solution of the said 3-isothiazolinones in a liquid solvent medium comprising water or a solvent medium containing hydroxylic groups. A method according to claim 3, wherein the concentration of the stabilizing compound in the 3-isothiazolinones - containing solution is lower than 10 wt%. A method according to claim 4, wherein the concentration of the stabilizing compound in the 3-isothiazolinones - containing solution is between 0.2 and 5 wt%. A method according to claim 2 or 3, wherein the composition to be stabilized comprises a mixture of N-alkyl-isothiazolin- 3-one and N-alkyl-5-chloro-isothiazolin-3-one. A method according to claim 6, wherein the N-alkyl radical is a N-methyl radical. A method according to any one of the preceding claims, wherein the stabilizing compound is selected from the group consisting essentially of hydroquinone, quinone and quinhydrone, and their homologues and derivatives. A method according to any one of the preceding claims, which further comprises adding to the composition to be stabilized a synergistically effective amount of one or more metal salt(s), selected from metal nitrate stabilizers and salts of metals of groups IA and IIA of the periodic table of the elements. A method according to claim 9, wherein the metal salt is selected from the group consisting of magnesium nitrate, K₂HPO₄, KH phthalate, magnesium acetate and potassium permanganate. A method according to any one of claims 1 to 10, wherein the composition to be stabilized is further aerated. A stable composition containing one or more 3-isothiazolinones and a stabilizing effective amount of a stabilizing compound of the formula (3): wherein: R, R¹ and R² each independently represents hydrogen, a C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₃-C₈ cycloalkyl, phenyl C₁-C₁₀ alkyl or phenyl group; A is oxygen or nitrogen; Z represents AR x , R¹, R², alkoxy methylene, methylene or alkylidene; n=1 or 2; x=1 or 2; and y=1 or 2; or a derivative thereof.

Inventors: SEGAL, JEANA, SHORR, LEONARD
Applicants: BROMINE COMPOUNDS LTD.
Application year: 1988
Main classification: C07D275
IPC codes: C07D275, A01N43, A01N25