5,6-Dihydro-5-oxo-1,4-dithiino (2,3-d) pyridazine-2,3-dicarbonitriles
SUMMARY OF THE INVENTION 
     The novel compounds of the present invention, hereinafter alternatively referred to as active compounds, correspond to the formula ##STR2## wherein R is either H or an alkyl group having from 1 to about 7 carbon atoms. Examples of suitable alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl and n-hexyl. 
     The active compounds, directly or as active ingredients in formulations and compositions, exhibit, in antimicrobially-effective amounts, antimicrobial activity against fungi and bacteria. Hereinafter the terms &#34;antimicrobial&#34; and &#34;antimicrobially-effective&#34;, when used in conjunction with the active compounds, will be employed to identify their activity against fungi and/or bacteria. 
     The active compounds are prepared by adding a corresponding 4,5-dihalo-3-pyridiazone to disodiumdimercaptomaleonitrile in dimethylformamide (DMF) as exemplified by the following equation: ##STR3## wherein R is as defined hereinbefore, and R&#39; is a halogen selected from Br or Cl. 
     The reaction mixture is stirred from about 10° C. to about 50° C. until substantial completion of the reaction, usually from about 0.25 to about 1 hour. Upon completion of the reaction, the mixture is poured into water and allowed to stand for at least about 4 hours, during which time a solid product will precipitate. The solid is recovered by filtration, washed and dried. The compound can be used as prepared, however if desired it can be further purified by conventional techniques known to one skilled in the art. 
     Either of the starting materials can be used in excess of the stoichiometric requirements. However, ordinarily substantially equimolar proportions are employed. 
     The active compounds are slightly soluble in acetone and chloroform and are insoluble in water. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following examples illustrate the present invention and the manner by which it can be practiced but as such should not be construed as limitations upon the overall scope of the same. 
     EXAMPLE 1 - Preparation of 5,6-Dihydro-5-oxo-1,4-dithiino(2,3-d)-pyridazine-2,3-dicarbonitrile (Compound 1) 
     To a stirred solution of 20 g (0.1 mole) disodiumdimercaptomaleonitrile in 250 ml of DMF was added 16.5 g (0.1 mole) of 4,5-dichloro-3-pyridiazone. The reaction mixture was stirred at room temperature (approximately 20° C.) for 0.25 hours and was thereafter poured with stirring into 1.5 liters of water. The resulting mixture was allowed to stand for four hours during which time a brown precipitate slowly formed. This precipitate was separated by filtration, washed with water, and dried in vacuo to yield 10.2 g (43% yield from the pyridiazone) of a brown solid, m.p. (decomposition) 240°-260° C. 
     A sample was subjected to elemental analysis. The results obtained were as follows: 
     
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Analysis for C.sub.8 H.sub.2 N.sub.4 OS.sub.2 :                           
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Calcd.:    C, 41.01; H, 0.86;  N, 23.92.                                  
Found:     C, 41.30; H, 1.11;  N, 23.69.                                  
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     Infra-red spectrophotometry confirmed the assigned structure. 
     EXAMPLE 2 - Preparation of 5,6-Dihydro-6-methyl-5-oxo-1,4-dithino(2,3-d)-pyridazine-2,3-dicarbonitrile (Compound 2) 
     To a stirred solution of 10.2 g (0.05 moles) of disodiumdimercaptomaleonitrile and 250 ml of DMF was added 9 g (0.05 moles) of 4,5-dichloro-2-methyl-3(2-H)-pyridiazone. The reaction mixture was stirred for 1 hour at approximately 50° C. and then poured with stirring into 1.5 liters of water. The resulting mixture was allowed to stand for 63 hours during which time a red brown precipitate slowly formed. The precipitate was separated by filtration, washed with water, and dried in vacuo to yield 4.6 g (37% yield) of a red brown solid, m.p. 175.7° C. 
     A sample was subjected to elemental analysis. The results obtained were as follows: 
     
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Analysis for C.sub.9 H.sub.4 N.sub.4 OS.sub.2 :                           
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Calcd.:    C, 43.54; H, 1.62;  N, 22.57.                                  
Found:     C, 43.40; H, 1.88;  N, 22.38.                                  
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     Infra-red spectrophotometry confirmed the assigned structure. 
     Following the same procedures as set forth in Examples 1 and 2 other compounds of the present invention, wherein the substituent R represents straight chain or branched chain moieties having from two to seven carbon atoms, can readily be prepared from disodiumdimercaptomaleonitrile and the appropriate 4,5-dihalo-2-alkyl-3(2-H)pyridiazone. 
     The active compounds of the invention are suitable for use as antimicrobials for the control of bacteria and fungi. This is not to suggest that the active compounds and mixtures thereof with usual additives are equally effective against all such organisms at the same concentration. The active compounds can be employed in an unmodified form or dispersed on a finely divided solid and employed as a dust. Such mixtures can also be dispersed in water with the aid of a surface-active agent and the resulting emulsion employed as a spray. In other procedures, the active compounds can be employed as the active constituents in solvent solutions, oil-in-water or water-in-oil emulsions. The augmented compositions are adapted to be formulated as concentrates and subsequently diluted with additional liquid or solid adjuvants to produce the ultimate treating compositions. Good control and kill have been realized with compositions wherein antimicrobially-effective amounts of from about 1 to about 500 parts by weight of one or more of the active compounds per million parts of such compositions are employed. As stated hereinbefore the active antimicrobially-effective amount to be employed against a given organism or in a certain composition can be determined by one skilled in the art. 
     Incorporation of the active compounds of this invention into materials which are subject to fungal attack inhibits the growth of the fungi and preserves the original value of the materials. The active compounds are sufficiently nonvolatile and water-insoluble so that they will persist on or in such materials for long periods of time. Examples of materials which are adversely affected by fungal growth are latex and alkyl paint films, wood and wooden products. The active compounds are sufficiently active against fungi that only small quantities are required to prevent mildew on paint films or wood rot. The active compounds are therefore useful for long-term protection against fungal growth in or on materials having a wood basis or a protective or decorative paint film or other coating or covering subject to fungal attack. 
     In a standard activity test, samples of Compound 1 and Compound 2 were individually dispersed in warm melted nutrient agar which was poured into petri dishes and allowed to solidify, the active compounds being employed in an amount sufficient to provide from 1 to 500 parts by weight thereof per million parts (ppm) of the ultimate agar composition. The surface of the agar was inoculated with a variety of bacterial and fungal pest organisms, and the inoculated plates incubated under conditions conducive to bacterial and fungal growth. Similar check plates in which the agar did not contain the active compounds or other toxic compounds were similarly inoculated and incubated. 
     In these studies, Compounds 1 and 2 gave 100% growth inhibition (kill) and control of the following organisms, as set forth in the Table, at the indicated concentrations in parts per million (ppm); 
     
                       TABLE                                                       
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Antimicrobial Activity                                                    
             Concentration in ppm                                         
Organism       Compound 1   Compound 2                                    
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S. aureus      1            5                                             
S. typhosa     1            5                                             
A. niger       100          10                                            
A. Fumigatus   50           10                                            
C. pelliculosa 100          5                                             
C. albicans N  50           50                                            
C. albicans D  50           50                                            
B. subtilis    1            5                                             
A. aerogenes   10           100                                           
P. aeruginosa  50           500                                           
P. sp. strain 10                                                          
               10           100                                           
E. coli        5            10                                            
S. marcesens   10           50                                            
T. sp. med. col. VI                                                       
               500          50                                            
C. ips         100          10                                            
Tri. sp. mad. P-42                                                        
               50           50                                            
T. mentagrophytes                                                         
               50           5                                             
P. chrysogesum 100          50                                            
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