novel antibacterial agents ; namely , 7 -- cephalosporanic acid derivatives having the formula : ## str1 ## wherein r 1 is thienyl , 2 - furyl , phenyl , substituted thienyl or substituted phenyl ; r is hydroxyl ; r 2 is hydrogen , hydroxy , acetoxy , carbamoyloxy , n - pyridyl , azido or heterocyclic thio group ; r and r 2 when taken together represent an oxygen atom ; r 3 is sulpho or coor 4 &# 39 ; wherein r 4 &# 39 ; is hydrogen or r 4 wherein r 4 is lower alkyl , 5 - indanyl , naphthyl , phenyl , or substituted phenyl , conr 5 r 6 , wherein each of r 5 and r 6 is hydrogen , lower alkyl or cycloalkyl ; or r 5 and r 6 together with the nitrogen atom to which they are attached form a saturated heterocyclic group ; x is oxygen or sulphur , a direct link , carbonyl , methylene , hydroxymethylene , sulphinyl , sulphonyl or an imino group of the formula -- nr 7 --, wherein r 7 is hydrogen , lower alkyl , lower alkenyl , or benzyl ; and each of alk 1 and alk 2 is a divalent saturated aliphatic hydrocarbon group containing from 1 to 3 carbon atoms ; the pharmaceutically acceptable salts thereof , and methods for their preparation .