a compound having the structural formula ## str1 ## wherein : y is selected from o and s ; r 1 and r 4 are independently selected from fluorinated methyl , chlorofluorinated methyl , and c 1 - c 4 alkyl , provided that not both r 1 and r 4 may be c 1 - c 4 alkyl ; r 2 is selected from hydrogen , lower alkyl , haloalkyl , alkenyl , alkynyl , haloalkenyl , and a cation ; r 3 is selected from c 1 - c 5 alkyl , cycloalkyl , cycloalkylalkyl , hydroxy , and alkoxy ; and x is selected from ## str2 ## in which r 8 is selected from h , alkyl and cf 3 and r 10 is selected from f , cl , -- or 1 , -- sr 1 , -- nhr 1 , -- n 2 , phenyl , substituted phenyl , and -- p 2 where r 1 is as defined above ; ## str3 ## wherein r 1 is as defined above ; ## str4 ## wherein r 14 and r 15 are independently selected from hydrogen and alkyl ; and -- n ═ c ═ o and their use as herbicides .