the compounds of the present invention may be readily prepared by reacting a compound of the formula ## str2 ## wherein r 1 is hydrogen , alkyl of one to six carbon atoms or benzyl and l is fluorine or chlorine with piperazine or n - methylpiperazine , and , when r 1 is other than hydrogen , converting by known methods the ester to the free acid , and , if desired , converting by known methods the free acid to a pharmaceutically acceptable acid addition or base salt thereof . for purposes of this reaction , the piperazines may , if desired , be protected by a group which renders it substantially inert to the reaction conditions . thus , for example , protecting groups such as the following may be utilized : carboxylic acyl groups such as formyl , acetyl , trifluoroacetyl ; alkoxycarbonyl groups such as ethoxycarbonyl , t - butoxycarbonyl , β , β , β - trichloroethoxycarbonyl , β - iodoethoxycarbonyl ; aryloxycarbonyl groups such as benzyloxycarbonyl , p - methoxybenzyloxycarbonyl , phenoxycarbonyl ; silyl groups such as trimethylsilyl ; and groups such as trityl , tetrahydropyranyl , vinyloxycarbonyl , o - nitrophenylsulfenyl , diphenylphosphinyl , p - toluenesulfonyl , and benzyl , may all be utilized . the protecting group may be removed , after the reaction between compound ii and the piperazine , if desired , by procedures known to those skilled in the art . for example , the ethoxycarbonyl group may be removed by acid or base hydrolysis and the trityl group may be removed by hydrogenolysis . the reaction between the compound of structural formula ii and a suitably protected or unprotected piperazine , may be performed with or without a solvent , preferably at elevated temperature for a sufficient time so that the reaction is substantially complete . the reaction is preferably carried out in the presence of an acid acceptor such as an alkali metal or alkaline earth metal carbonate or bicarbonate , a tertiary amine such as triethylamine , pyridine , or picoline . alternatively an excess of the piperazine may be utilized as the acid acceptor . convenient solvents for this reaction are nonreactive solvents such as acetonitrile , tetrahydrofuran , ethanol , chloroform , dimethylsulfoxide , dimethylformamide , pyridine , picoline , water , and the like . solvent mixtures may also be utilized . convenient reaction temperatures are in the range of from about 20 ° to about 150 ° c . ; higher temperatures usually require shorter reaction times . the removal of the protecting group may be accomplished either before or after isolating the product . alternatively , the protecting group need not be removed . the starting compounds having structural formula ii are known in the art or , if new , may be prepared from known starting materials by standard procedures or by variations thereof . compounds of the formula ii may be prepared by a series of reactions starting with 3 , 4 , 5 , 6 - tetrafluoroanthranilic acid . the acid is reacted with acetic anhydride and acetic acid to form 2 - acetylamino - 3 , 4 , 5 , 6 - tetrafluorobenzoic acid . this compound is reacted with oxalyl chloride and dichloromethane in the presence of n , n - dimethylformamide catalyst to form 2 - acetylamino - 3 , 4 , 5 , 6 - tetrafluorobenzoyl chloride . this product is treated with n - butyl lithium and malonic half acid ester to form 2 - acetylamino - 3 , 4 , 5 , 6 - tetrafluoro - β - oxobenzene - propanoic acid ethyl ester . this product can be converted to 5 - acetylamino - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxoquinoline - 3 - carboxylic acid ethyl ester by a three step reaction . the 2 - acetylamino - 3 , 4 , 5 , 6 - tetrafluoro - β - oxobenzene - propanoic acid ethyl ester is first treated with triethylorthoformate and acetic anhydride . after removal of the solvent the residue is treated with a solution of cyclopropylamine in t - butanol . after the reaction is complete a solution of potassium t - butoxide in t - butanol is added . the resulting product is 5 - acetylamino - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxoquinoline - 3 - carboxylic acid ethyl ester . the ester is hydrolyzed to form 1 - cyclopropyl - 5 - amino - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxo - 3 - quinolinecarboxylic acid . an alternate pathway to the compounds of formula ii begins with 2 - nitro - 3 , 4 , 5 , 6 - tetrafluorobenzoyl chloride . this starting material is treated with n - butyl lithium and malonic half acid ester to form 2 - nitro - 3 , 4 , 5 , 6 - tetrafluoro - β - oxobenzene propanoic acid ethyl ester . this product can be converted to 5 - nitro - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxoquinoline - 3 - carboxylic acid ethyl ester by a three step reaction . the starting material is first treated with triethylorthoformate and subsequently with cyclopropyl amine in t - butyl alcohol . the product is ring closed with potassium t - butoxide to form 5 - nitro - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxoquinoline - 3 - carboxylic acid ethyl ester . this product is hydrogenated to form the corresponding 5 - amino compound . this is then hydrolyzed to form 1 - cyclopropyl - 5 - amino - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxo - 3 - quinoline carboxylic acid . the compounds of the invention display antibacterial activity as shown in the following table when tested by the microtitration dilution method as described in heifetz , et al , antimicr . agents & amp ; chemoth ., 6 , 124 ( 1974 ), which is incorporated herein by reference . a comparison of the compounds of the present invention to ciprofloxacin , 1 - cyclopropyl - 6 - fluoro - 1 , 4 - dihydro - 4 - oxo - 7 - piperazinyl - 3 - quinoline - carboxylic acid , shows clear superiority of the present compounds especially against pseudomonas aeruginosa and the gram - positive bacteria . ______________________________________in vitro antibacterial activityminimal inhibitory concentrationmic ( μg / ml ) com - compound pound cipro - organisms ex . 1 ex . 2 floxacin______________________________________enterobacter cloacae ma 2646 0 . 013 0 . 013 0 . 05escherichia coli vogel 0 . 013 0 . 013 0 . 05klebsiella pneumoniae mgh - 2 0 . 025 0 . 013 0 . 1proteus rettgeri m 1771 0 . 05 0 . 05 0 . 1pseudomonas aeruginosa ui - 18 0 . 025 0 . 1 0 . 4staphylococcus aureus h 228 0 . 05 0 . 05 3 . 1staphylococcus aureus uc - 76 0 . 013 0 . 025 0 . 2streptococcus faecalis mgh - 2 0 . 05 0 . 1 0 . 8streptococcus pneumonia sv - 1 0 . 05 0 . 2 1 . 6streptococcus pyogenes c - 203 0 . 2 0 . 4 0 . 8______________________________________ the compounds of the invention can be prepared and administered in a wide variety of oral and parenteral dosage forms . it will be obvious to those skilled in the art that the following dosage forms comprise as the active component , either a compound of formula i or a corresponding pharmaceutically acceptable salt of a compound of formula i . for preparing pharmaceutical compositions from the compounds described by this invention , inert , pharmaceutically acceptable carriers can be either solid or liquid . solid form preparations include powders , tablets , dispersable granules , capsules , cachets , and suppositories . a solid carrier can be one or more substances which may also act as diluents , flavoring agents , solubilizers , lubricants , suspending agents , binders , or tablets disintegrating agents ; it can also be an encapsulating material . in powders , the carrier is a finely divided solid which is in admixture with the finely divided active compound . in the tablet the active compound is mixed with carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired . the powders and tablets preferably contain from 5 to 10 to about 70 percent of the active ingredient . suitable solid carriers are magnesium carbonate , magnesium sterate , talc , sugar , lactose , pectin , dextrin , starch , gelatin , tragacanth , methyl cellulose , sodium carboxymethyl cellulose , a low melting wax , cocoa butter , and the like . the term &# 34 ; preparation &# 34 ; is intended to include the formulation of the active compound with encapsulating material as carrier providing a capsule in which the active component ( with or without other carriers ) is surrounded by carrier , which is thus in association with it . similarly , cachets are included . tablets , powders , cachets , and capsules can be used as solid dosage forms suitable for oral administration . liquid form preparations include solutions suspensions and emulsions . as an example may be mentioned water or water - propylene glycol solutions for parenteral injection . such solutions are prepared so as to be acceptable to biological systems ( isotonicity , ph , etc ). liquid preparations can also be formulated in solution in aqueous polyethylene glycol solution . aqueous solutions suitable for oral use can be prepared by dissolving the active component in water and adding suitable colorants , flavors , stabilizing , and thickening agents as desired . aqueous suspension suitable for oral use can be made by dispersing the finely divided active component in water with viscous material , i . e ., natural or synthetic gums , resins , methyl cellulose , sodium carboxymethyl cellulose , and other well - known suspending agents . preferably , the pharmaceutical preparation is in unit dosage form . in such form , the preparation is subdivided into unit doses containing appropriate quantites of the active component . the unit dosage form can be a packaged preparation , the package containing discrete quantities of preparation , for example , packeted tablets , capsules , and powders in vials or ampoules . the unit dosage form can also be a capsule , cachet , or tablet itself or it can be the appropriate number of any of these packaged forms . the quantity of active compound in a unit dose of preparation may be varied or adjusted from 1 mg to 100 mg according to the particular application and the potency of the active ingredient . in therapeutic use as agents for treating bacterial infections the compounds utilized in the pharmaceutical method of this invention are administered at the initial dosage of about 3 mg to about 40 mg per kilogram daily . a daily dose range of about 6 mg to about 14 mg per kilogram is preferred . the dosages , however , may be varied depending upon the requirements of the patient , the severity of the condition being treated , and the compound being employed . determination of the proper dosage for a particular situation is within the skill of the art . generally , treatment is initiated with smaller dosages which are less than the optimum dose of the compound . thereafter , the dosage is increased by small increments until the optimum effect under the circumstances is reached . for convenience , the total daily dosage may be divided and administered in portions during the day if desired . the following nonlimiting examples illustrate the inventors &# 39 ; preferred methods for preparing the compounds of the invention . a suspension of 1 . 0 g ( 3 . 35 mmole ) of 5 - amino - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxo - 3 - quinolinecarboxylic acid , 1 . 15 g ( 13 . 4 mmole ) of piperazine , 1 . 36 g ( 13 . 35 mmole ) of triethylamine and 60 ml of acetonitrile is refluxed for three hours and then stirred at room temperature for 16 hours . the precipitate is removed by filtration , washed with acetonitrile and dried in vacuo at 60 ° c . to give 5 - amino - 1 - cyclopropyl - 6 , 8 - difluoro - 1 , 4 - dihydro - 4 - oxo - 7 -( 1 - piperazinyl )- 3 - quinolinecarboxylic acid , mp 257 °- 259 ° c . a suspension of 1 . 0 g ( 3 . 35 mmole ) of 5 - amino - 1 - cyclopropyl - 6 , 7 , 8 - trifluoro - 1 , 4 - dihydro - 4 - oxo - 3 - quinolinecarboxylic acid , 1 . 36 g ( 13 . 35 mmole ) of triethylamine and 60 ml of acetonitrile is refluxed for eight hours and stirred at room temperature for 16 hours . the precipitate is removed by filteration , washed with acetonitrile , and dried in vacuo at 45 ° c . to give 5 - amino - 1 - cyclopropyl - 6 , 8 - difluoro - 1 , 4 - dihydro - 7 -( 4 - methyl - 1 - piperazinyl )- 4 - oxo - 3 - quinoline - carboxylic acid , mp 247 °- 248 ° c .