Stabilization of non-halogenated 3-isothiazolones in aggressive systems

The present invention provides a method of stabilizing non-halogenated 3-isothiazolones in aggressive systems with pH above 8.5. The invention also discloses compositions with pH above 8.5, containing non-halogenated 3-isothiazolones and an effective stabilizing amount of a iodine-containing stabilizer.

This is a nonprovisional application of prior pending provisional 
application Ser. No. 60/007,166, filed Nov. 1, 1995. 
This invention relates to stabilization of 3-isothiazolones in aggressive 
systems. 
Non-halogenated 3-isothiazolones are known to be used for the preservation 
of many loci such as wood, paint, adhesive, caulk, mastic, latex, pulp and 
paper slurries, textile, leather, plastics, cardboard, lubricants, 
cosmetics, detergents, household products, industrial cooling water, metal 
working fluid, pigment slurries, photographic processing fluids, and 
fuels. Some of these loci, particularly metal working fluids, are known to 
be quite aggressive towards 3-isothiazolones due to high pH. Preservation 
of metal working fluids such as cutting oils is difficult due to 
decomposition of the 3-isothiazolones at pH above 8.5. A method of 
stabilizing non-halogenated 3-isothiazolones in aggressive metal working 
fluids with pH above 8.5 is desired. 
The present invention comprises a method of stabilizing 
2-methyl-4-isothiazolin-3-one (MI), 2-n-octyl-4-isothiazolin-3-one (OI), 
or a mixture thereof in a composition having a pH above 8.5 and which is 
free of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI), comprising 
introducing an effective stabilizing amount of an iodine-containing 
compound selected from the group consisting of iodic acid, periodic acid, 
and salts thereof. 
This invention also relates to compositions having a pH above 8.5 
comprising MI, OI, or a mixture thereof and an effective stabilizing 
amount of an iodine-containing compound selected from the group consisting 
of iodic acid, periodic acid, salts thereof, said composition being free 
of chlorinated 3-isothiazolone. 
The preferred concentration of the 3-isothiazolone compound(s) in solution 
is from 750 to 5,000 ppm MI, or from 100 to 2,500 ppm OI, or a mixture 
thereof, based on the total weight of the system. 
The most preferred concentration of the 3-isothiazolone compound(s) in 
solution is from 2,000 to 2,500 ppm MI, or from 500 to 1,000 ppm OI, or a 
mixture thereof, based on the total weight of the system. 
The preferred concentration of the stabilizer(s) in solution is from 100 to 
5,000 ppm, more preferably 1,000 to 3,000 ppm based on the total weight of 
the system. 
Metal salts such as copper sulfate have been disclosed as stabilizers for 
3-isothiazolones in metal working fluids. See "Kathon.RTM. MWC Bulletin 
CS-584", page 6, Rohm and Haas Company 1989. Environmental regulations on 
copper have made the use of copper for stabilizing 3-isothiazolones in 
metal working fluids unacceptable. 
Japanese Tokkyo Koho 05-170608, assigned to Shinto Paint Ltd., disclosed 
antimicrobial compositions for preventing microbiotic contamination of 
aqueous dispersions of synthetic high polymers such as synthetic rubber 
latex, which do not cause coagulation of said dispersions. The 
compositions contain 3-isothiazolones and a stabilizer or stabilizers 
selected from bromic acid, iodic acid, periodic acid or their salts. This 
reference does not teach stabilization of non-halogenated 3-isothiazolones 
in aggressive metal working fluids with pH above 8.5. 
Japanese Kokai Tokkyo Koho 05-286815, assigned to Takeda Pharmaceutical 
LTD., disclosed industrial germicides containing 3-isothiazolones, alkali 
metal salt of bromine acid or iodine acid, and water. Potassium bromate 
was preferred over the other stabilizers. This invention does not teach 
stabilization of non-halogenated 3-isothiazolones in aggressive metal 
working fluids with pH above 8.5. 
In the following examples, the source of MI was a 50% solution of 
2-methyl-4-isothiazolin-3-one in propylene glycol. The source of OI was a 
45% solution of 2-n-octyl-4-isothiazolin-3-one in propylene glycol. The 
source of CMI for Example 1 was a 1.5% solution in water of a 3:1 mixture 
of CMI:MI. The source of CMI for Example 3 was 99% CMI.

EXAMPLE 1 
This example demonstrates that non-chlorinated 3-isothiazolones (MI and OI) 
are stable in glycol/water solutions, while chlorinated isothiazolone 
(CMI) is not stable in the same solution. Samples were prepared in 30 ml. 
screw cap glass vials. Sample 1 was 2.0 g. MI, 4 g. ethylene glycol, and 
14.0 g. deionized (DI) water. Sample 2 was 1.46 g. CMI, 9.0 g. ethylene 
glycol, and 9.54 g. DI water. Sample 3 was 2.20 g. OI, 15.0 g. ethylene 
glycol, and 2.80 g. DI water. Samples were capped and shaken, then stored 
at 45.degree. C. for 4 weeks. Analysis was performed by High Pressure 
Liquid Chromatography (HPLC) with UV detection. Results are shown in Table 
1. 
TABLE 1 
______________________________________ 
% Active Ingredient Remaining 
Al 1 3 1 2 3 4 
Sample (%) Day Days Week Weeks Weeks Weeks 
______________________________________ 
1(MI) 4.51 98.2 100 98.7 99.3 104 99.3 
2(CMI)* 
4.78 96.2 90.2 85.1 76.2 69.2 63.2 
3(OI) 5.08 NA NA 100 98.0 98.2 98.4 
______________________________________ 
NA = Not Analyzed 
* = Comparative 
EXAMPLE 2 
This comparative example demonstrates the effect of pH on the stability of 
non-chlorinated 3-isothiazolones in a metal working fluid. Samples were 
prepared in 30 ml. screw cap glass vials. The low water content of metal 
working fluid concentrates makes direct pH measurement not relevant, so 
pH's of 5% aqueous dilutions were measured. To 1 g. metal working fluid 
was added 19 g. DI water. The pH was measured and the amount of 
hydrochloric acid (HCl) was measured to adjust the pH of the 5% dilution. 
A corresponding amount of HCl (20X) was added to the metal working fluid 
(MWF) itself. The initial pH of the metal working fluid was 9.2. To 
samples 1, 2, 3, 4, 5, and 6 were added 19.92 g. MWF and 0.08 g. MI. The 
pH of the MWF was as follows: sample 1=9.2, sample 2=9.0, sample 3=8.5, 
sample 4=8.1, sample 5=7.6, sample 6=7.0. To samples 7, 8, 9, 10, 11, and 
12 were added 19.91 g. MWF and 0.09 g. OI. The pH of the MWF was as 
follows: sample 7=9.2, sample 8=9.0, sample 9=8.5, sample 10=8.1, sample 
11=7.6, sample 12=7.0. Samples were capped and shaken, then stored at room 
temperature and analyzed by HPLC at 0, 7, 14, 21 and 28 days storage. 
Results are shown in Table 2. 
TABLE 2 
______________________________________ 
Comparative 
% MI Remaining % OI Remaining 
7 14 21 28 7 14 21 28 
Fluid pH 
Days Days Days Days Days Days Days Days 
______________________________________ 
9.2 8 0 0 0 0 NA NA NA 
9 64 30 19 16 0 NA NA NA 
8.5 77 56 43 35 0 NA NA NA 
8.1 90 76 66 60 74 5 3 NA 
7.6 99 90 86 81 100 93 91 92 
7 99 94 95 92 100 100 100 99 
______________________________________ 
EXAMPLE 3 
Effect of Stabilizer of Invention 
This example demonstrates the effects of the stabilizers of this invention 
on the stability of CMI, MI, and OI in a metal working fluid. Metal 
working fluid "A" was used as the fluid for this example. It is a 
semisynthetic metal working fluid with initial pH of 9.22 (as a 4% aqueous 
dilution). Samples were prepared in 30 ml. screw cap glass vials. To 
sample 1 was added 0.04 g. CMI and 19.96 g. MWF "A". To samples 2, 3, 4, 
5, and 6 were added 0.04 g. CMI, 0.04 g. stabilizer, and 19.92 g. MWF "A". 
To sample 2 was added potassium iodate (KIO.sub.3), to sample 3 was added 
sodium periodate (NaIO.sub.4), to sample 4 was added sodium bromate 
(NaBrO.sub.3), to sample 5 was added iodic acid (HIO.sub.3), and to sample 
6 was added periodic acid (HIO.sub.4. To sample 7 was added 0.08 g. MI and 
19.92 g. MWF "A". To samples 8, 9, 10, 11, and 12 were added 0.08 g. MI, 
0.02 g. stabilizer, and 19.90 g. MWF "A". To sample 8 was added KIO.sub.3, 
to sample 9 was added NaIO.sub.4, to sample 10 was added NaBrO.sub.3, to 
sample 11 was added HIO.sub.3, and to sample 12 was added HIO.sub.4. To 
sample 13 was added 0.09 g. OI and 19.91 g. MWF "A". To sample 14, 15, 16, 
17, and 18 was added 0.09 g. OI, 0.04 g. stabilizer and 19.87 g. MWF "A". 
To sample 14 was added KIO.sub.3, to sample 15 was added NaIO.sub.4, to 
sample 16 was added NaBrO.sub.3, to sample 17 was added HIO.sub.3, and to 
sample 18 was added HIO.sub.4. Samples were capped and shaken, then stored 
at 40.degree. C. and analyzed by HPLC at 0, 1, 2, 3, and 4 weeks storage. 
Samples were considered to pass when greater than 50% active ingredient 
remained after storage. Results are shown in Tables 3 and 4. 
TABLE 3 
______________________________________ 
% OI Remaining 
Amount % CMI* 1 2 3 4 
Stabilizer 
(ppm) 1 Week Week Weeks Weeks Weeks 
______________________________________ 
None* 0 0 0 NA NA NA 
KIO.sub.3 
2,000 0 83 73 57 62 
NaIO.sub.4 
2,000 0 77 76 71 71 
NaBrO.sub.3 * 
2,000 0 0 NA NA NA 
HIO.sub.3 
2,000 0 89 78 71 75 
HIO.sub.4 
2,000 0 93 96 84 73 
______________________________________ 
NA = Not Analyzed 
TABLE 4 
______________________________________ 
Amount % MI Remaining 
Stabilizer 
(ppm) 1 Week 2 Weeks 
3 Weeks 
______________________________________ 
None* 0 0 NA NA 
KIO.sub.3 1,000 56 2 NA 
NaBrO.sub.3 * 
1,000 0 NA NA 
HIO.sub.3 2,000 75 74 53 
HIO.sub.4 2,000 79 76 70 
______________________________________ 
* = Comparative 
This example also demonstrates iodic acid, periodic acid, and their salts 
are effective at stabilizing non-chlorinated 3-isothiazolones in 
aggressive metal working fluids at pH above 8.5, where bromate salts are 
ineffective, and that neither iodic acid, periodic acid, their salts, nor 
bromate is effective to stabilize chlorinated 3-isothiazolones in such 
fluids.