as used throughout the specification , the following terms shall have the following meanings , unless the context clearly indicates otherwise . the term &# 34 ; microbicide &# 34 ; refers to a compound capable of inhibiting the growth of or controlling the growth of microorganisms at a locus . the term &# 34 ; microorganism &# 34 ; includes , but is not limited to , fungi , bacteria , and algae . the term &# 34 ; locus &# 34 ; refers to an industrial system or product subject to contamination by microorganisms . &# 34 ; carrier &# 34 ; refers to any material that can be used to dissolve , disperse or dispense the composition incorporated therewith without impairing the microbicidal effectiveness of the 3 - isothiazolone compound . &# 34 ; alkyl ,&# 34 ; &# 34 ; alkenyl &# 34 ; and &# 34 ; alkynyl &# 34 ; refer to straight chain , branched , or cyclic carbon chains , or any combination thereof . &# 34 ; substituted alkyl ,&# 34 ; &# 34 ; substituted alkenyl &# 34 ; and &# 34 ; substituted alkynyl &# 34 ; mean one or more of the hydrogens on the carbon chain are replaced by another substituent , such as cyano , hydroxy , ( c 1 - c 4 ) alkyl , nitro , mercapto , ( c 1 - c 4 ) alkylthio , halo and ( c 1 - c 4 ) alkoxy . &# 34 ; halo &# 34 ; and &# 34 ; halogen &# 34 ; refer to fluorine , chlorine , bromine and iodine . &# 34 ; substituted aralkyl &# 34 ; means one or more hydrogens on the aromatic ring or alkyl chain are replaced by another substituent , such as cyano , hydroxy , ( c 1 - c 4 ) alkyl , nitro , mercapto , ( c 1 - c 4 ) alkylthio , halo and ( c 1 - c 4 ) alkoxy . &# 34 ; aryl &# 34 ; refers to phenyl , fused aromatic rings , heteroaromatic rings and fused heteroaromatic rings . &# 34 ; substituted aryl &# 34 ; means one or more of the hydrogens on the aryl ring are replaced by another substituent , such as cyano , hydroxy , ( c 1 - c 4 ) alkyl , nitro , mercapto , ( c 1 - c 4 ) alkylthio , halo and ( c 1 - c 4 ) alkoxy . &# 34 ; heteroaromatic &# 34 ; refers to a 5 - 7 membered aromatic ring having one or more heteroatoms in the ring . all amounts are percent by weight (&# 34 ;% wt &# 34 ;), unless otherwise noted . all ranges are inclusive . as used throughout the specification , the following abbreviations are applied : g = gram ; c = centigrade ; hplc = high performance liquid chromatography ; di = deionized ; mw = molecular weight ; and ppm = parts per million . any 3 - isothiazolone compound is useful in the compositions of the present invention . suitable 3 - isothiazolone compounds include , but are not limited to : 5 - chloro - 2 - methyl - 3 - isothiazolone ; 2 - methyl - 3 - isothiazolone ; 2 - ethyl - 3 - isothiazolone ; 5 - chloro - 2 - ethyl - 3 - isothiazolone ; 4 , 5 - dichloro - 2 - methyl - 3 - isothiazolone ; 2 - n - octyl - 3 - isothiazolone ; 4 , 5 - dichloro - 2 - n - octyl - 3 - isothiazolone ; 1 , 2 - benzisothiazolone ; 4 , 5 - trimethylene - 2 - methyl - 3 - isothiazolone ; and mixtures thereof . when mixtures of 5 - chloro - 2 - methyl - 3 - isothiazolone and 2 - methyl - 3 - isothiazolone are used , the weight ratio of 5 - chloro - 2 - methyl - 3 - isothiazolone to 2 - methyl - 3 - isothiazolone is generally 99 : 1 to 1 : 99 , preferably 90 : 10 to 70 : 30 . in general , the amount of 3 - isothiazolone compound useful in the compositions of the present invention is 0 . 5 to 35 % wt , based on the weight of the composition , and preferably 1 to 25 % wt . the azobiscarbonyl compounds useful as stabilizers for 3 - isothiazolone compounds are those of formula ( i ), above . it is preferred that r 1 , r 2 , r 3 and r 4 are hydrogen , ( c 1 - c 12 ) alkyl and substituted ( c 1 - c 12 ) alkyl , and more preferably ( c 1 - c 8 ) alkyl and substituted ( c 1 - c 8 ) alkyl . when r 1 , r 2 , r 3 or r 4 is alkynyl , it is preferred that the alkynyl is propynyl or halopropynyl . preferred azobiscarbonyl compounds are those wherein r = nr 1 r 2 . when r 1 and r 2 are joined to form a 5 - 7 membered ring , such ring may be saturated or unsaturated . these 5 - 7 membered rings may contain one or more additional heteroatoms , such as sulfur and oxygen . suitable 5 - 7 membered rings include , but are not limited to : piperidine , morpholine , and pyrrolidine . when the aryl group is a heteroaromatic ring , it is preferred that the heteroaromatic ring have one or more heteroatoms selected from nitrogen , oxygen and sulfur . suitable heteroaromatic rings include , but are not limited to : thiophene , pyridine and furan . suitable fused aromatic rings useful as aryl groups in the present invention include , but are not limited to : naphthalene , indene and substituted naphthalene , such as naphthalene dicarboxylates . suitable fused heteroaromatic rings include , but are not limited to : benzothiophene , benzothiazole , and indazole . suitable azobiscarbonyl compounds useful in the present invention include , but are not limited to : 1 , 1 &# 39 ;- azobis ( n , n - dimethylformamide ); azodicarbonamide ; n , n &# 39 ;- dicyclohexyl - diazenedicarboxamide ; n , n &# 39 ;- bis ( 2 - methoxyethyl ) diazenedicarboxamide ; n - ethyl - n &# 39 ;- phenyl - diazenecarboxamide ; n , n &# 39 ;- dibutyl - diazenedicarboxamide ; n , n &# 39 ;- bis -( 1 - methylpropyl )- diazenedicarboxamide ; n - butyl - n &# 39 ;- cyclohexyl - diazenedicarboxamide ; n - butyl - n &# 39 ;-( 1 - methylethyl )- diazenedicarboxamide ; n , n &# 39 ;- dihexyl - diazenecarboxamide ; n , n &# 39 ;- bis -( 3 - methylbutyl )- diazenecarboxamide ; n , n &# 39 ;- didodecyl - diazenecarboxamide ; n , n &# 39 ;- bis ( phenylmethyl )- diazenecarboxamide ; bis -( 1 - oxotetradecyl )- diazene ; bis -( 1 - oxodecyl )- diazene ; bis -( 1 - oxododecyl )- diazene ; diethyl diazenedicarboxalate ; dimethyl diazenedicarboxalate ; bis -( 1 , 1 - dimethylethyl ) diazenedicarboxalate ; bis -( phenylmethyl ) diazenedicarboxalate ; and 1 , 1 &# 39 ;-( azodicarbonyl ) dipiperidine . preferred azobiscarbonyl compounds are 1 , 1 &# 39 ;- azobis ( n , n - dimethylformamide ) and azodicarbonamide . any amount of azobiscarbonyl compound sufficient to stabilize the 3 - isothiazolone compound is suitable for use in the present invention . in general , the amount of azobiscarbonyl compound sufficient to stabilize the 3 - isothiazolone compound is 0 . 01 to 15 % wt , based on the weight of the composition . it is preferred that the amount of azobiscarbonyl compound is 0 . 1 to 10 % wt , and more preferably 0 . 5 to 8 % wt . the specific amount of azobiscarbonyl compound will depend upon the particular azobiscarbonyl compound and the amount of the 3 - isothiazolone compound in the composition . more azobiscarbonyl compound is needed when more 3 - isothiazolone compound is present . for example , 0 . 1 to 2 % wt of azobiscarbonyl compound is typically sufficient to stabilize 1 . 5 % wt of 3 - isothiazolone compound while 6 to 10 % wt of azobiscarbonyl compound is typically sufficient to stabilize 14 % wt of 3 - isothiazolone compound . the azobiscarbonyl compounds useful in the present invention are generally commercially available , for example , from aldrich chemical company ( milwaukee , wis .) and may be used without further purification . the compositions of the present invention may optionally contain a carrier . the carriers may be either solids or liquids . suitable solid carriers include , but are not limited to : silicas , diatomaceous earth , inorganic salts and cyclodextrins . liquid carriers include water , organic solvents and mixtures thereof . suitable liquid carriers include , but are not limited to : water , methanol , ethanol , benzyl alcohol , ethylene glycol , diethylene glycol , polyethylene glycol , propylene glycol , dipropylene glycol , polypropylene glycol , phenoxyethanol , phenoxypropanol , xylene , toluene , methyl isobutyl ketone , methyl isoamyl ketone , and mixtures thereof . when the compositions of the present invention contain a solid carrier , they may be added directly to the locus to be protected or may be formed into bricks , tablets , briquettes , blocks , pucks , prills and the like , and then added to the locus to be protected . when the compositions of the present invention contain a liquid carrier , they are typically added directly to the locus to be protected . when a liquid carrier is used in the present invention , the amount of the azobiscarbonyl compound that may be used is not limited to the amount that is soluble in the carrier . thus , an amount of the azobiscarbonyl compound above its solubility limit in the carrier may be used . when an azobiscarbonyl compound is used in excess of its solubility limit in the liquid carrier , the excess compound may be added to the composition in any way that will allow for more of the azobiscarbonyl compound to dissolve as needed . for example , the excess azobiscarbonyl compound may be added to the composition in a liquid permeable bag . thus , a solution of a 3 : 1 mixture of 5 - chloro - 2 - methyl - 3 - isothiazolone and 2 - methyl - 3 - isothiazolone in water can be stabilized by the slightly water - soluble compound azodicarbonamide by adding the azocarbonamide to the solution in a water - permeable bag . the compositions of the present invention may be prepared by combining the 3 - isothiazolone compounds with the azobiscarbonyl compounds in any order . it is preferred that the azobiscarbonyl compound be added to the 3 - isothiazolone compound . when a liquid carrier is used , it is preferred that the 3 - isothiazolone compound is combined with the liquid carrier before the azobiscarbonyl compound is added . the stability of the 3 - isothiazolone compounds may be improved under certain conditions by the addition of one or more other stabilizers . thus , other known 3 - isothiazolone stabilizers may be combined advantageously with the stabilizers of the present invention . any known 3 - isothiazolone stabilizer is suitable for use in combination with the stabilizers of the present invention as long as it does not destabilize , or otherwise react with , the azobiscarbonyl stabilizers of the present invention . other stabilizers suitable for use in combination with the azobiscarbonyl stabilizers of the present invention include , but are not limited to : alkyl disulfides , aromatic disulfides , trialkyl orthoformates , pyridine , pyridine n - oxide , metal nitrate salts , iodic acid , iodic acid salts , periodic acid , periodic acid salts , copper salts , and the like . the compositions of the present invention can be used to inhibit the growth of microorganisms by introducing a microbicidally effective amount of the compositions onto , into , or at a locus subject to microbial attack . suitable loci include , but are not limited to : cooling towers ; air washers ; boilers ; mineral slurries ; wastewater treatment ; ornamental fountains ; reverse osmosis filtration ; ultrafiltration ; ballast water ; evaporative condensers ; heat exchangers ; pulp and paper processing fluids ; plastics ; emulsions and dispersions ; paints ; latexes ; coatings , such as varnishes ; construction products , such as mastics , caulks , and sealants ; construction adhesives , such as ceramic adhesives , carpet backing adhesives , and laminating adhesives ; industrial or consumer adhesives ; photographic chemicals ; printing fluids ; household products , such as bathroom disinfectants or sanitizers ; cosmetics and toiletries ; shampoos ; soaps ; detergents ; industrial disinfectants or sanitizers , such as cold sterilants , hard surface disinfectants ; floor polishes ; laundry rinse water ; metalworking fluids ; conveyor lubricants ; hydraulic fluids ; leather and leather products ; textiles ; textile products ; wood and wood products , such as plywood , chipboard , flakeboard , laminated beams , oriented strandboard , hardboard , and particleboard ; petroleum processing fluids ; fuel ; oilfield fluids , such as injection water , fracture fluids , and drilling muds ; agriculture adjuvant preservation ; surfactant preservation ; medical devices ; diagnostic reagent preservation ; food preservation , such as plastic or paper food wrap ; pools ; and spas . preferred loci are cooling towers ; air washers ; boilers ; mineral slurries ; wastewater treatment ; ornamental fountains ; reverse osmosis filtration ; ultrafiltration ; ballast water ; evaporative condensers ; heat exchangers ; pulp and paper processing fluids ; plastics ; emulsions and dispersions ; paints ; latexes ; coatings ; and metal working fluids . the amount of 3 - isothiazolone compounds suitable to inhibit or control the growth of microorganisms is well known in the art and depends upon the locus to be protected . the amount of 3 - isothiazolone microbicide suitable to inhibit the growth of microorganisms is generally between 0 . 05 and 5 , 000 ppm , based on the volume of said locus to be protected . it is preferred to use between 0 . 1 and 2 , 500 ppm . for example , loci such as a cooling towers or pulp and paper processing fluids require 0 . 1 to 100 ppm of the 3 - isothiazolone microbicides to inhibit microorganism growth . other loci , such as construction products , oilfield fluids or emulsions , require 0 . 5 to 5000 ppm of the 3 - isothiazolone microbicides to inhibit microorganism growth , while loci such as disinfectants or sanitizers may require up to 5 , 000 ppm . it is known in the art that the performance of antimicrobial agents may be enhanced by combination with one or more other antimicrobial agents . thus , other known microbicidal agents may be combined advantageously with the compositions of the present invention . the following examples are presented to illustrate further various aspects of the present invention , but are not intended to limit the scope of the invention in any aspect . in the following examples , samples were considered stable when at least 50 percent of the 3 - isothiazolones remained after 1 week of storage at 55 ° c . five samples of a solution of a 3 : 1 mixture of 5 - chloro - 2 - methyl - 3 - isothiazolone (&# 34 ; cmi &# 34 ;) and 2 - methyl - 3 - isothiazolone (&# 34 ; mi &# 34 ;) in di water were prepared . one sample served as control and the other samples were labeled a - d . the control contained only the 3 - isothiazolone mixture and di water . samples a - d contained the 3 - isothiazolone mixture , di water and 1 , 1 &# 39 ;- azobis ( n , n - dimethylformamide ) as stabilizer . in addition , sample b contained 2 , 2 &# 39 ;- dithiobis ( pyridine - n - oxide ) as a second stabilizer . the amounts of the 3 - isothiazolone and stabilizers in the control and samples a - d are reported in table 1 . the remainder of each sample was di water . an aliquot was removed from each sample for initial analysis . the samples were then placed in a 55 ° c . oven . aliquots were removed after 2 and 4 weeks storage and analyzed by hplc for the total amount of 3 - isothiazolone remaining . the results are reported in table 1 . stabilizer a is 1 , 1 &# 39 ;- azobis ( n , n - dimethylformamide ) and stabilizer b is 2 , 2 &# 39 ;- dithiobis ( pyridine - n - oxide ). table 1______________________________________percent of 3 - isothiazolone remaining after storage cmi + mi initial % stabilizer a stabilizer bsample wt (% wt ) (% wt ) 2 weeks 4 weeks______________________________________control 1 . 5 0 0 0 0a 1 . 5 0 . 9 0 100 100b 1 . 5 0 . 9 0 . 3 100 89c 4 . 7 3 . 0 0 100 100d 1 . 4 0 . 9 0 100 100______________________________________ the above data clearly show that the azobiscarbonyl compounds of the present invention are effective at stabilizing 3 - isothiazolone compounds . six samples of a solution of a 3 : 1 mixture of cmi and mi in di water were prepared . two samples served as controls and the other samples were labeled e - h . the controls contained only the 3 - isothiazolone mixture and di water . samples e - h contained the 3 - isothiazolone mixture , di water and azodicarbonamide as stabilizer . the amounts of the 3 - isothiazolone and stabilizer in the controls and samples e - h are reported in table 2 . the remainder of each sample was di water . due to its limited water solubility , the azodicarbonamide was placed in water - permeable bags having a mw cut off of 3500 . one bag was then placed in each of samples e - h . an aliquot was then removed from each sample for initial analysis . the samples were then placed in a 55 ° c . oven . aliquots were removed after 1 , 2 and 4 weeks storage and analyzed by hplc for the total amount of 3 - isothiazolone remaining . the results are reported in table 2 . table 2______________________________________percent of 3 - isothiazolones remaining after storage cmi + mi stabilizersample initial % wt (% wt ) 1 week 2 weeks 4 weeks______________________________________control 5 . 6 0 19 3 0control 14 . 0 0 43 3 0e 5 . 6 3 . 3 98 97 100f 12 . 2 6 . 0 98 92 40g 5 . 6 3 . 3 100 100 99h 16 . 0 5 . 5 54 15 0______________________________________ the above data clearly show that azobiscarbonyl compounds of the present invention stabilize 3 - isothiazolone compounds even when only slightly soluble in the liquid carrier . one sample , labeled i , of a solution of 0 . 27 g of a 3 : 1 mixture of cmi and mi in 14 . 6 g of di water was prepared . to this solution was added 0 . 2 g of 1 , 1 &# 39 ;-( azodicarbonyl ) dipiperidine as a stabilizer . the sample was mixed , but not all of the stabilizer dissolved . the undissolved stabilizer remained at the bottom of the sample jar . this sample was compared to a control sample containing only a 3 : 1 mixture of cmi and mi in di water . the amounts of the 3 - isothiazolone and stabilizer in the sample and the control are reported in table 3 . an aliquot was removed from the sample for initial analysis . the sample was then placed in a 55 ° c . oven . an aliquots was removed after 1 week of storage and analyzed by hplc for the total amount of 3 - isothiazolone remaining . the results are reported in table 3 . table 3______________________________________percent of 3 - isothiazolone remaining cmi + mi stabilizersample initial % wt (% wt ) 1 week______________________________________control 5 . 6 0 19i 1 . 5 1 . 3 78______________________________________ these data show that the azobiscarbonyl compounds of the present invention stabilize 3 - isothiazolone compounds even when only slightly soluble in the liquid carrier .
disclosed are stable microbicidal compositions of 3 - isothiazolone compounds and azobiscarbonyl compounds . also disclosed are methods of stabilizing 3 - isothiazolone compounds against chemical decomposition by combining with the 3 - isothiazolones a stabilizing amount of an azobiscarbonyl compound .