1,3,4-thiadiazoles useful as herbicides
This invention concerns thiadiazolyloxyacetamides having herbicidal activity, processes for preparing them and compositions containing them. 
     In one aspect, the invention provides the thiadiazolyloxyacetamides of the formula: ##STR2## wherein: R is an optionally-substituted alkyl, cycloalkyl or aryl group; R 1  and R 2 , which may be the same or different, each represent hydrogen, alkyl, cycloalkyl, alkoxy, alkenyl, aryl, aralkyl or aryloxy, any alkyl or aryl moiety thereof being optionally substituted; or R 1  and R 2 , together with the nitrogen atom to which they are attached, represent a heterocyclic or benzheterocyclic group, the heterocyclic ring of which is 5- or 6-membered, and which may be substituted by one or more alkyl groups; and X is oxygen, sulphur or --S(O) n  -- where n is 1 or 2. 
     When any of R, R 1  and R 2  is or contains an alkyl moiety, it is preferably of 1 to 8, particularly 1 to 6, carbon atoms. It is preferably unsubstituted, though if substituted is preferably substituted by one or more halogen atoms, especially fluorine, chlorine or bromine atoms, or by an alkoxy group of 1 to 4 carbon atoms, especially a methoxy or ethoxy group. 
     When any of R, R 1  and R 2  is or contains a cycloalkyl group, it is preferably of 3 to 7, and desirably of 5 or 6 carbon atoms, specific preferred cycloalkyl groups being cyclopentyl and cyclohexyl. 
     When any of R, R 1  and R 2  is or contains an aryl moiety, that moiety is preferably phenyl. If substituted, it is preferably substituted by one or more halogen atoms, especially chlorine or bromine atoms, or by one or more alkyl or alkoxy groups of 1 to 4 carbon atoms, especially methyl, ethyl, methoxy or ethoxy groups, or by one or more nitro groups. 
     When R 1  and/or R 2  represents aralkyl, it is preferably a benzyl group, which is desirably unsubstituted. 
     When R 1  and/or R 2  represents alkenyl, it is preferably of 2 to 6 carbon atoms, especially allyl. 
     When R 1  and R 2 , together with the nitrogen atom to which they are attached, form or include a heterocyclic ring, that ring may if desired be further substituted, e.g. by alkyl of 1 to 4 carbon atoms, especially by methyl or ethyl, or may contain a further heteroatom, especially an oxygen atom or a further nitrogen atom. The ring may be saturated or unsaturated. 
     R preferably represents alkyl of 1 to 6 carbon atoms, cycloalkyl of 5 or 6 carbon atoms, alkenyl of 2 to 6 carbon atoms, phenyl, or phenyl substituted by one or more halogen atoms or alkyl groups of 1 to 4 carbon atoms. 
     Specific preferred groups which R may represent include methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, t-amyl, 2-methylbutyl, cyclohexyl, allyl, phenyl, 2-chlorophenyl, 4-chlorophenyl, 4-fluorophenyl, 3-methylphenyl and 2,4-dichlorophenyl. 
     R 1  and R 2  are preferably both other than hydrogen. When R 1  and R 2 , together with the nitrogen atom to which they are attached, form a ring, it is preferably a 6-membered saturated ring, especially a piperidine ring, and particularly a piperidine ring substituted by one or more alkyl groups of 1 to 4 carbon atoms, e.g. 2-methylpiperidine, 3-methylpiperidine, 4-methylpiperidine, 2-ethylpiperidine, 2,6-dimethylpiperidine or 3,5-dimethylpiperidine. When, however, R 1  and R 2  represent independent groups, each is preferably unsubstituted alkyl of 1 to 6 carbon atoms, cycloalkyl of 5 or 6 carbon atoms, allyl, phenyl, or phenyl substituted by one or more halogen atoms or alkyl groups of 1 to 4 carbon atoms. Specific preferred such groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, cyclohexyl, allyl, phenyl, 2-chlorophenyl, 4-chlorophenyl, 2-methylphenyl, 3-fluorophenyl, 4-methylphenyl and benzyl. 
     Specific preferred compounds of formula I are those of the Examples provided hereinafter, especially: 
     1-[5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine; 
     N,N-diallyl-2-[5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazol-2-yloxy]acetamide; 
     2-[5-(ethylthio)difluoromethyl]-1,3,4-thiadiazol-2-yloxy]-N-methylacetanilide; 
     N,N-diallyl-2-[5-[t-butylthiodifluoromethyl]-1,3,4-thiadiazol-2-yloxy]acetamide; 
     2-[5-(ethylthio)difluoromethyl]-3&#39;-fluoro-1,3,4-thiadiazol-2-yloxy]-N-methylacetanilide; and 
     2&#39;-chloro-2-[5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazol-2-yloxy]-N-methylacetanilide. 
     The compounds of formula I may be prepared by reacting a 2-halothiadiazole of the formula: ##STR3## wherein R and X are as defined hereinbefore, and Y is chlorine or bromine, with a compound of the formula: ##STR4## wherein R 1  and R 2  are as defined hereinbefore, in the presence of a base, to give the desired compound. 
     The base is preferably an inorganic base, particularly a hydroxide, alkoxide, hydride or carbonate of an alkali-metal, especially of sodium, lithium or potassium. 
     The compounds of formula II may be prepared from the corresponding 2-aminothiadiazoles of the formula: ##STR5## by a conventional diazotisation technique, e.g. with sodium nitrite in the presence of a suitable solvent, e.g. acetic acid, and the appropriate hydrohalic acid HY. 
     In turn, the compounds of formula IV may be prepared from the known compound 2-amino-5-chlorodifluoromethylthiadiazole by reaction thereof with the appropriate alkali-metal alkoxide, aryloxide or mercaptide in a suitable solvent medium, e.g. ethanol. 
     The compounds of formula I where X represents S(O) n  may be prepared from the corresponding compounds of formula I where X represents S by oxidation techniques known per se. For example, the compounds may be subjected to the action of an oxidising agent, for example a permanganate, chromate, peroxide or peracid, particularly potassium permanganate, potassium chromate, hydrogen peroxide or metachloroperbenzoic acid. 
     The compounds of formula I have herbicidal activity. They are active in particular against grass weeds, though they do also possess significant activity against many broad-leaved species. In addition, they are comparatively safe to many crop species, particularly non-temperate crop species such as cotton, soybeans, rice and maize, but also to cereals such as wheat and barley, which may make them of use as selective herbicides. 
     Accordingly, in another aspect, the invention provides a method of combating weeds which comprises applying to a locus infested or liable to be infested therewith an effective amount of one or more compounds of formula I as defined hereinbefore. 
     Amongst the weed species combatted are barnyardgrass, crabgrass, johnsongrass, foxtails, speedwells, mayweeds, cleavers and blackgrass. 
     The compounds may be used either pre- or post-emergence of the crop and weed species. They are usually employed at a rate of from 0.005 to 2 kg/ha, preferably from 0.05 to 1 kg/ha, and are generally employed in the form of a composition. 
     In another aspect, the invention therefore provides a herbicidal composition which comprises one or more compounds of the invention in association with a suitable carrier and/or surface active agent. 
     The compositions usually contain from 0.01 to 99% by weight of the present compounds, and are normally produced initially as concentrates containing from 0.5 to 99%, preferably from 0.5 to 85%, and especially from 10 to 50% by weight thereof. Such concentrates are diluted if necessary before application to the locus to be treated such that the active ingredient comprises from 0.01 to 5% by weight of the formulation applied. 
     The carrier may be water, in which case an organic solvent may also be present, though this is not usually employed. A flowable suspension concentrate may be formed by grinding the compound with water, a wetting agent and a suspending agent, e.g. xanthan gum. 
     The carrier may alternatively be a water immiscible organic solvent, e.g. a hydrocarbon which boils within the range 130°-270° C., e.g. xylene, in which the compound is dissolved or suspended. An emulsifiable concentrate containing a water immiscible solvent may be formed with a surface active agent so that the concentrate acts as a self-emulsifiable oil on admixture with water. 
     The carrier may alternatively be a water-miscible organic solvent e.g. 2-methoxy ethanol, methanol, propylene glycol, diethylene glycol, diethylene glycol monoethyl ether, methylformamide or dimethylformamide. 
     The carrier may alternatively be a solid, which may be finely divided or granular. Examples of suitable solids are limestone, clays, sand, mica, chalk, attapulgite, diatomite, perlite, sepiolite, silicas, silicates, lignosulphonates and solid fertilizers. The carrier can be of natural or synthetic origin or can be modified natural material. 
     Wettable powders soluble or dispersible in water may be formed by admixing the compound in particulate form with a particulate carrier or spraying molten compound on to the particulate carrier, admixing a wetting agent and a dispersing agent and finely grinding the whole powder mixture. 
     An aerosol composition may be formed by admixing the compound with a propellant, eg a polyhalogenated alkane eg dichlorofluoromethane, and suitably also with a solvent. 
     The term `surface active agent` is used in the broad sense to include materials variously called emulsifying agents, dispersing agents and wetting agents. Such agents are well known in the art. 
     The surface active agents used may comprise anionic surface active agents, for example mono- or di-esters of phosphoric acid with a fatty alcohol ethoxylate, or salts of such esters, fatty alcohol sulphates such as sodium dodecyl sulphate, ethoxylated fatty alcohol sulphates, ethoxylated alkylphenol sulphates, lignin sulphates, petroleum sulphonates, alkylaryl sulphonates such as alkyl-benzene sulphonates or lower alkylnaphthalene sulphonates, salts of sulphonated naphthaleneformaldehyde condensates, salts of sulphonated phenolformaldehyde condensates, or more complex sulphonates such as the amide sulphonates, e.g. the sulphonated condensation product of oleic acid and N-methyl taurine or the dialkyl sulphosuccinates e.g. the sodium sulphonate of dioctyl succinate. 
     The surface active agents may also comprise non-ionic agents, for example condensation products or fatty acid esters, fatty alcohols, fatty acid amides or alkyl-substituted phenols with ethylene oxide, fatty esters of polyhydric alcohol ethers e.g. sorbitan fatty acid esters, condensation products of such esters with ethylene oxide e.g. polyoxyethylene sorbitan fatty acid esters, block copolymers of ethylene oxide and propylene oxide, acetylenic glycols such as 2,4,7,9-tetramethyl-5-decyn-4,7-diol, or ethoxylated acetylenic glycols. 
     The surface active agents may also comprise cationic agents, for example alkyl- and/or aryl-substituted quaternary ammonium compounds such as cetyl trimethylammonium bromide, or ethoxylated tertiary fatty amines. 
     Preferred surface active agents include ethoxylated fatty alcohol sulphates, lignin sulphonates, alkyl-aryl sulphonates, salts of sulphonated naphthaleneformaldehyde condensates, salts of sulphonated phenolformaldehyde condensates, sodium oleoyl N-methyltauride, dialkyl sulphosuccinates, alkyl phenol ethoxylates, and fatty alkyl ethoxylates. 
     If desired, the compounds of the invention may be employed in combination with a pesticide or further herbicide, especially such a compound which is useful in the location or crop concerned. 
    
    
     The invention is illustrated by the following Examples. 
     EXAMPLE 1 
     1-[5-[Difluoro(isopropylthio)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine 
     (a) 2-Amino-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole 
     2-Amino-5-chlorodifluoromethyl-1,3,4-thiadiazole (59.6 g) was added, in one portion, to a stirred solution of 2-propanethiol (24.5 g) and sodium hydroxide (12.9 g) in ethanol (300 ml) at -40° C. The mixture was stirred at -15° C. for 2 hours and then allowed to warm to room temperature. It was then poured into water (3.5 l) and filtered to give 61.4 g of 2-amino-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole as a pale yellow solid m.p. 119°-121° C. (d). 
     (b) 2-Chloro-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole 
     2-Amino-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole (190 g) was dissolved in a mixture of acetic acid (880 ml) and concentrated hydrochloric acid (216.5 ml) at 60° C. A solution of sodium nitrite (171.3 g) in water (300 ml) was then added dropwise over 30 minutes at 65°-70° C. The mixture was stirred at 65° C. for 15 minutes and then allowed to cool. It was then poured onto water (3 L) and extracted with ether, the combined extracts being washed with water, dried (MgSO 4 ) and evaporated to give an orange liquid, which was distilled under vacuum to give 150 g of 2-chloro-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole, bp 75°-77° C. at 0.7 mmHg. 
     (c) 1-[5-[Difluoro(isopropylthio)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine 
     Lithium hydroxide monohydrate (9.93 g) was added portionwise to a stirred solution of 2-chloro-5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazole (36.67 g) and 1-hydroxyacetyl-2-ethylpiperidine (25.65 g) in methyl isobutyl ketone (150 ml) at 20°-24° C. over 15 minutes, and the mixture was stirred at room temperature for 2 hours, then treated with ether (200 ml) and washed with dilute hydrochloric acid. The ether solution was then dried (MgSO 4 ) and evaporated to give an orange oil, which was purified by chromatography to give 30.2 g of 1-[5-[difluoro(isopropylthio)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine. 
     
         ______________________________________                                    
Analysis for C.sub.15 H.sub.23 F.sub.2 N.sub.3 O.sub.2 S.sub.2            
       C           H      N                                               
______________________________________                                    
Theory   47.47         6.11   11.07%                                      
Found    48.82         6.26   10.62%                                      
______________________________________                                    
 
    
     EXAMPLE 2 
     1-[5-[Difluoro(phenoxy)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine 
     (a) 2-Amino-5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazole 
     2-Amino-5-chlorodifluoromethyl-1,3,4-thiadiazole (92.7 g) was added portionwise to a stirred solution of phenol (47 g) and sodium hydroxide (20 g) in ethanol (400 ml) at 10° C. After stirring at 5° C. for 11/2 hours, the solid was filtered off, washed with water and dried to give 89.6 g of 2-amino-5-[difluoro(phenoxy)-methyl]-1,3,4-thiadiazole, m.p. 149°-151° C. 
     (b) 2-Bromo-5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazole 
     A solution of sodium nitrite (33 g) in water (60 ml) was added dropwise to a stirred solution of 2-amino-5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazole (39.5 g) in acetic acid (175 ml) and 48% hydrobromic acid (40 ml) at 60° C. over 30 minutes. The mixture was stirred at 70° C. for 15 minutes and allowed to cool. 
     The mixture was then poured into water (2 l) and the product was extracted into ether, and the combined extracts were washed with water and dried (MgSO 4 ). The ether was then evaporated to give 40 g of 2-bromo-5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazole as an orange oil. 
     (c) 1-[5-[Difluoro(phenoxy)methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine 
     2-Bromo-5-[difluoro(phenoxy)methyl]-1,3,4-thiadiazole (6.14 g) was added portionwise to a stirred solution of 1-hydroxyacetyl-2-ethylpiperidine (3.44 g) and potassium t-butoxide (2.25 g) in t-butanol (15 ml) at 25° C. over 5 minutes, and the mixture was stirred at 25° C. for 2 hours. It was then treated with ether (200 ml) and washed with 2N hydrochloric acid and saturated sodium chloride solution. 
     The ether solution was dried (MgSO 4 ) and evaporated to give an orange oil, and purified by chromatography to give 2.8 g of 1-[5-[difluoro(phenoxy)-methyl]-1,3,4-thiadiazol-2-yloxyacetyl]-2-ethylpiperidine as a yellow oil. 
     
         ______________________________________                                    
Analysis for C.sub.18 H.sub.21 F.sub.2 N.sub.3 O.sub.3 S                  
       C           H      N                                               
______________________________________                                    
Theory   54.39         5.33   10.57%                                      
Found    53.93         5.25   10.28%                                      
______________________________________                                    
 
    
     EXAMPLES 3-150 
     The following compounds of formula I were prepared by processes analogous to those of Examples 1 and 2: 
     
         ______________________________________                                    
                                        M. Pt                             
No   R           X     R.sup.1                                            
                              R.sup.2   (°C.)                      
______________________________________                                    
 3   phenyl      O     phenyl ethyl     102-103                           
 4   phenyl      O     ethyl  ethyl     oil                               
 5   phenyl      O     phenyl methyl    82-83                             
 6   phenyl      O     allyl  allyl     oil                               
 7   ethyl       S     phenyl methyl    74-75                             
 8   ethyl       S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 9   isopropyl   S     2,4-dimethylpentane-                               
                                      oil                                 
                       1,5-diyl                                           
 10  isopropyl   S     allyl  allyl     oil                               
 11  isopropyl   S     2-methylpentane-1,5-diyl                           
                                      oil                                 
 12  isopropyl   S     1-methylpentane-1,5-diyl                           
                                      oil                                 
 13  isopropyl   S     ethyl  ethyl     oil                               
 14  isopropyl   S     n-propyl                                           
                              n-propyl  oil                               
 15  isopropyl   S     methyl cyclohexyl                                  
                                        oil                               
 16  t-butyl     S     allyl  allyl     oil                               
 17  t-butyl     S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 18  isopropyl   S     3-methylpentane-1,5-diyl                           
                                      oil                                 
 19  isopropyl   S     n-butyl                                            
                              methyl    oil                               
 20  t-butyl     S     1-methylpentane-1,5-diyl                           
                                      oil                                 
 21  n-butyl     S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 22  n-butyl     S     allyl  allyl     oil                               
 23  t-butyl     S     ethyl  ethyl     oil                               
 24  n-butyl     S     1-methylpentane-1,5-diyl                           
                                      oil                                 
 25  isopropyl   S     1,5-dimethylpentane-                               
                                      40-44                               
                       1,5-diyl                                           
 26  n-butyl     S     n-propyl                                           
                              n-propyl  oil                               
 27  ethyl       S     allyl  allyl     oil                               
 28  ethyl       S     n-propyl                                           
                              n-propyl  oil                               
 29  isopropyl   S     pentane-1,5-diyl                                   
                                      oil                                 
 30  phenyl      O     n-propyl                                           
                              n-propyl  oil                               
 31  isopropyl   S     methyl phenyl    99.5-101                          
 32  t-butyl     S     methyl phenyl    58-60                             
 33  isopropyl   S     hexane-1,6-diyl                                    
                                      oil                                 
 34  ethyl       S     methyl n-butyl   oil                               
 35  ethyl       S     1-methylpentane-1,5-diyl                           
                                      oil                                 
 36  ethyl       S     ethyl  ethyl     oil                               
 37  phenyl      O     pentane-1,5-diyl                                   
                                      96-98                               
 38  phenyl      O     1-methylpentane-1,5-diyl                           
                                      68-70                               
 39  phenyl      O     hexane-1,6-diyl                                    
                                        50-52.5                           
 40  phenyl      O     allyl  n-propyl  oil                               
 41  2,4-dichloro-                                                        
                 O     allyl  allyl     oil                               
     phenyl                                                               
 42  2,4-dichloro-                                                        
                 O     1-ethylpentane-1,5-diyl                            
                                      oil                                 
     phenyl                                                               
 43  isopropyl   S     phenyl ethyl     92-93                             
 44  n-butyl     S     phenyl methyl    38-40                             
 45  phenyl      O     benzyl methyl    oil                               
 46  4-chlorophenyl                                                       
                 O     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 47  phenyl      O     isopropyl                                          
                              isopropyl   82-83.5                         
 48  isopropyl   S     isopropyl                                          
                              isopropyl 70-72                             
 49  4-chlorophenyl                                                       
                 O     allyl  allyl     oil                               
 50  2-chlorophenyl                                                       
                 O     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 51  3-methylphenyl                                                       
                 O     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 52  2-chlorophenyl                                                       
                 O     allyl  allyl     oil                               
 53  isobutyl    S     phenyl methyl    60-61                             
 54  isobutyl    S     1-ethylpentane-1,5-diyl                            
                                      56-57                               
 55  isobutyl    S     1-methylpentane-1,5-diyl                           
                                      oil                                 
 56  s-butyl     S     phenyl methyl    63-64                             
 57  s-butyl     S     n-butyl                                            
                              methyl    oil                               
 58  n-butyl     S     n-butyl                                            
                              methyl    oil                               
 59  s-butyl     S     allyl  allyl     oil                               
 60  phenyl      O     allyl  isopropyl oil                               
 61  isopropyl   S     isopropyl                                          
                              allyl     oil                               
  62 s-butyl     S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 63  4-fluorophenyl                                                       
                 O     n-propyl                                           
                              n-propyl  oil                               
 64  4-fluorophenyl                                                       
                 O     n-propyl                                           
                              allyl     oil                               
 65  4-fluorophenyl                                                       
                 O     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 66  4-fluorophenyl                                                       
                 O     allyl  allyl     oil                               
 67  3-methylphenyl                                                       
                 O     allyl  allyl     oil                               
 68  isobutyl    S     n-propyl                                           
                              n-propyl  oil                               
 69  ethyl       S     methyl 4-methylphenyl                              
                                        oil                               
 70  t-butyl     S     methyl 4-methylphenyl                              
                                        oil                               
 71  isopropyl   S     methyl 3-methylphenyl                              
                                        oil                               
 72  n-butyl     S     methyl 3-methylphenyl                              
                                        oil                               
 73  s-butyl     S     methyl 3-methylphenyl                              
                                        oil                               
 74  phenyl      O     methyl 4-methylphenyl                              
                                         99-100                           
 75  ethyl       S     hexane-1,6-diyl                                    
                                      oil                                 
 76  ethyl       S     methyl 2-chlorophenyl                              
                                        77-78                             
 77  ethyl       S     methyl 2-methylphenyl                              
                                         99-100                           
 78  isopropyl   S     allyl  n-propyl  oil                               
 79  isobutyl    S     allyl  allyl     oil                               
 80  2,4-dichloro-                                                        
                 O     allyl  n-propyl  oil                               
     phenyl                                                               
 81  cyclohexyl  S     phenyl methyl    90-91                             
 82  phenyl      O     methyl 2-chlorophenyl                              
                                        oil                               
 83  phenyl      O     methyl 2-methylphenyl                              
                                        oil                               
 84  ethyl       S     methyl 4-chlorophenyl                              
                                        85-86                             
 85  t-butyl     S     methyl 2-methylphenyl                              
                                         99-100                           
 86  t-butyl     S     methyl 2-chlorophenyl                              
                                        88-89                             
 87  t-butyl     S     n-propyl                                           
                              n-propyl  oil                               
 88  t-butyl     S     allyl  n-propyl  oil                               
 89  cyclohexyl  S     1-ethylpentane-1,5-diyl                            
                                      76-77                               
 90  cyclohexyl  S     allyl  allyl     oil                               
 91  cyclohexyl  S     1-methyl-pentane-1,5-diyl                          
                                      oil                                 
 92  t-butyl     S     methyl 4-chlorophenyl                              
                                        78-79                             
 93  t-butyl     S     hexane-1,6-diyl                                    
                                      49-50                               
 94  phenyl      O     methyl 4-chlorophenyl                              
                                        110-111                           
 95  t-butyl     S     isopropyl                                          
                              allyl     oil                               
 96  isopropyl   S     methyl 4-chlorophenyl                              
                                        oil                               
 97  ethyl       S     methyl 4-methylphenyl                              
                                        46-47                             
 98  n-propyl    S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
 99  n-propyl    S     allyl  allyl     oil                               
100  t-amyl      S     phenyl methyl    52-54                             
101  t-butyl     S     methyl 3-chlorophenyl                              
                                        67-68                             
102  ethyl       S     methyl 3-chlorophenyl                              
                                        oil                               
103  n-propyl    S     phenyl methyl    67-68                             
104  n-propyl    S     allyl  isopropyl oil                               
105  n-propyl    S     1-methylpentane-1,5-diyl                           
                                      oil                                 
106  t-amyl      S     allyl  allyl     oil                               
107  t-amyl      S     allyl  n-propyl  oil                               
108  t-butyl     S     2-methylpentane-1,5-diyl                           
                                      61-63                               
109  phenyl      O     methyl 3-chlorophenyl                              
                                        48-52                             
110  t-butyl     S     s-butyl                                            
                              allyl     oil                               
111  phenyl      O     s-butyl                                            
                              allyl     oil                               
112  ethyl       S     s-butyl                                            
                              allyl     oil                               
113  cyclohexyl  S     hexane-1,6-diyl                                    
                                      71-72                               
114  t-amyl      S     1-ethylpentane-1,5-diyl                            
                                      oil                                 
115  t-amyl      S     isopropyl                                          
                              allyl     oil                               
116  t-amyl      S     n-propyl                                           
                              n-propyl  oil                               
117  2-chlorophenyl                                                       
                 O     pentane-1,5-diyl                                   
                                      88-90                               
118  2-chlorophenyl                                                       
                 O     n-propyl                                           
                              n-propyl  oil                               
119  t-amyl      S     3-methylpentane-1,5-diyl                           
                                      oil                                 
120  n-propyl    S     n-propyl                                           
                              allyl     oil                               
121  phenyl      O     isobutyl                                           
                              n-butyl   oil                               
122  ethyl       S     isobutyl                                           
                              n-butyl   oil                               
123  phenyl      O     isopropyl                                          
                              n-propyl  oil                               
124  t-amyl      S     pentane-1,5-diyl                                   
                                      oil                                 
125  t-amyl      S     1-methylpentane-1,5-diyl                           
                                      oil                                 
126  n-butyl     S     n-propyl                                           
                              isopropyl oil                               
127  t-amyl      S     n-propyl                                           
                              isopropyl oil                               
128  isobutyl    S     n-propyl                                           
                              isopropyl oil                               
129  t-butyl     S     n-propyl                                           
                              isopropyl oil                               
130  ethyl       S     isopropyl                                          
                              n-propyl  oil                               
131  t-amyl      S     2-methylpentane-1,5-diyl                           
                                      oil                                 
132  2-methylbutyl                                                        
                 S     phenyl methyl    oil                               
133  2-methylbutyl                                                        
                 S     1-methylpentane-1,5-diyl                           
                                      oil                                 
134  ethyl       S     methyl 4-fluorophenyl                              
                                        80-84                             
135  phenyl      O     methyl 4-fluorophenyl                              
                                        90-93                             
136  t-butyl     S     methyl 4-fluorophenyl                              
                                        72-74                             
137  ethyl       S     methyl 3-fluorophenyl                              
                                        69-72                             
138  phenyl      O     methyl 2-fluorophenyl                              
                                        62-64                             
139  2-fluorophenyl                                                       
                 O     allyl  allyl     oil                               
140  3-fluorophenyl                                                       
                 O     allyl  allyl     oil                               
141  3-fluorophenyl                                                       
                 O     1-methylpentane-1,5-diyl                           
                                      60-62                               
142  3-methylbutyl                                                        
                 S     methyl phenyl    75-77                             
143  3-methylbutyl                                                        
                 S     allyl  allyl     oil                               
144  methyl      S     methyl 3-methylphenyl                              
                                        oil                               
145  methyl      S     hexane-1,6-diyl                                    
                                      44-46                               
146  methyl      S     n-propyl                                           
                              n-propyl  oil                               
147  methyl      S     methyl 2-methylphenyl                              
                                        82-84                             
148  methyl      S     methyl phenyl    74-80                             
149  2-fluorophenyl                                                       
                 O     allyl  n-propyl  oil                               
150  2-fluorophenyl                                                       
                 O     1-methylpentane-1,5-diyl                           
                                      68-72                               
______________________________________                                    
 
    
     EXAMPLE 151 
     2-[5-(ethylsulphonyldifluoromethyl)-1,3,4-thiadiazol-2-yloxy]-N-methyl-N-phenylacetamide 
     A solution of potassium permanganate (3.16 g) in water (75 ml) was added dropwise to a stirred solution of the product of Example 7 (5.36 g) in acetic acid (20 ml) at 25°-30° C. The mixture was stirred at room temperature for 5 minutes and was poured into water (100 ml). Sodium metabisulphite was added portionwise until the mixture was colourless. The resulting white solid was filtered off, washed with water and crystallised from propan-2-ol to give 2.8 g of desired product as a white solid, mp 103°-104° C. 
     EXAMPLE 152-154 
     The following compounds were prepared by methods analogous to that of Example 151: 
     
         ______________________________________                                    
No  R          X      R.sup.1 R.sup.2  M. Pt (°C.)                 
______________________________________                                    
152 2-methylbutyl                                                         
               SO.sub.2                                                   
                      1-methylpentane-1,5-diyl                            
                                     oil                                  
153 ethyl      SO.sub.2                                                   
                      hexane-1,6-diyl                                     
                                     79-80                                
154 methyl     SO.sub.2                                                   
                      hexane-1,6-diyl                                     
                                     87-88                                
______________________________________                                    
 
    
     EXAMPLE 155-156 
     The following compounds were prepared by methods analogous to that of Example 1: 
     155. 1-[5-(isopropylthiodifluoromethyl)-1,3,4-thiadiazol-2-yloxyacetyl]-1,2,3,4-tetrahydroquinoline, oil. 
     156. 4-[5-(t-butylthiodifluoromethyl)-1,3,4-thiadiazol-2-yloxyacetyl]-3,4-dihydroquinoxalin-2-(1H)-one, oil. 
     EXAMPLE A 
     Seeds of the plant species listed below were sown in 750 mm diameter plastic pots containing sterilised sandy loam. They were watered and then sprayed with the compounds of the Examples listed below formulated as a solution in 3:1 by volume of acetone:water containing the wetting agent polyoxyethylene (20 mols) monolaurate solution (0.25 g per liter). 
     The concentration of each test compound and volume of application were calculated to give a rate of application of the compound of 0.25 kg/ha in 200 liters per hectare. After 22 days growth in the glasshouse (minimum temperature 15° C., maximum 25° C.) the plants were visually assessed for any herbicidal response. All differences from an untreated control were scored. 
     In the table below, the following letters are used to denote the plant species: 
     a--Gossypium hirsutum (cotton) 
     b--Glycine max (soybeans) 
     c--Helianthus annuus (sunflower) 
     d--Zea mays (maize) 
     e--Oryza sativa (rice) 
     f--Alopecurus myosuroides (blackgrass) 
     g--Echinochloa crus-galli (barnyardgrass) 
     h--Sorghum halepense (Johnsongrass) 
     i--Setaria faberii (giant foxtail) 
     j--Digitaria sanguinalis (crabgrass) 
     k--Panicum capillare (witchgrass) 
     l--Setaria viridis (green foxtail) 
     Percentage control was as follows: 
     
         ______________________________________                                    
Species                                                                   
Ex                                                                        
                            No a b c d e f g h i j k l                    
______________________________________                                    
1   5     0     5   10  15  95   99  99   95  95   95                     
                            97                                            
                            2 0 0 0 5 10 98 99 85 90 98 98 80             
                            4 5 0 0 20 15 90 98 97 93 80 99 85            
                            5 5 0 0 15 20 70 99 90 85 95 90 95            
                            6 20 0 10 10 0 85 99 97 95 100 99 95          
                            7 15 0 0 5 5 65 95 90 85 95 97 95             
                            8 0 0 0 0 0 60 93 75 75 95 97 80              
                            10 5 0 0 5 0 75 90 90 90 98 95 97             
                            11 0 0 5 0 0 75 90 90 65 60 92 60             
                            12 15 0 0 20 0 97 95 85 85 98 97 97           
                            14 5 5 0 10 0 75 99 99 90 85 98 85            
                            16 0 0 0 0 0 100 98 95 92 95 100 95           
                            17 10 0 0 40 0 90 97 85 97 99 99 97           
                            18 10 0 0 20 0 97 80 90 85 85 95 98           
                            20 5 0 0 0 0 100 99 95 90 98 100 98           
                            27 0 0 0 0 0 70 35 60 0 85 85 80              
                            32 0 0 0 15 5 80 95 95 99 97 99 99            
                            37 10 0 0 5 0 50 70 65 60 85 80 65            
                            38 10 0 0 0 5 90 97 95 93 99 100 85           
                            40 0 0 0 0 10 85 98 98 90 99 99 98            
                            53 15 0 0 0 0 75 93 95 90 95 93 99            
                            54 5 0 0 15 0 35 80 85 85 95 97 80            
                            56 5 0 0 5 0 70 97 80 85 93 97 95             
                            59 5 0 0 10 0 85 90 95 85 99 97 95            
                            60 0 0 0 0 0 90 99 100 90 85 97 75            
                            61 0 0 10 10 15 98 97 95 90 95 98 97          
                            62 0 0 10 0 15 90 97 85 95 97 95 90           
______________________________________                                    
 
    
     EXAMPLE B 
     An emulsifiable concentrate was prepared by dissolving 500 g of the compound of Example 1, 50 g of Arylan CA (calcium dodecylbenzene sulphonate) and 50 g of Ethylan C40AH (condensation product of ethylene oxide and castor oil) in sufficient xylene to produce 1 liter. Analogous formulations were also prepared containing 5 g, 50 g, 200 g and 750 g of the compounds of Examples 1-156.