Pyrimidine derivatives and their use as herbicides

A pyrimidine derivative has the formula, wherein A is C 3 -C 8 cycloalkyl C 1 -C 6 alkyl, C 3 -C 8 cycloalkyl C 1 -C 6 alkyl substituted with at least one member selected from the group consisting of C 1 -C 6 alkyl and halogen, C 3 -C 6 oxacycloalkyl, C 3 -C 6 oxacycloalkyl substituted with at least one member selected from the group consisting of C 1 -C 6 alkyl and halogen, C 3 -C 6 oxacydoalkyl C 1 -C 6 alkyl, C 3 -C 6 oxacycloalkyl C 1 -C 6 alkyl substituted with at least one member selected from the group consisting of C 1 -C 6 alkyl and halogen, C 3 -C 5 dioxacycloalkyl, C 3 -C 5 dioxacycloalkyl substituted with at least one member selected from the group consisting of C 1 -C 6 alkyl and halogen, C 3 -C 5 dioxacycloalkyl C 1 -C 6 alkyl or C 2 -C 5 dioxacycloalkyl C 1 -C 6 alkyl substituted with at least one member selected from the group consisting of C 1 -C 6 alkyl and halogen ; each of R 1 and R 2 , which may be the same or different, is C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halo C 1 -C 6 alkoxy or halogen ; X is oxygen or sulfur ; Z is nitrogen or CY 4 ; each of Y 1 , Y 2 and Y 3 , which may be the same or different, is hydrogen, halogen, C 1 -C 6 alkyl or C 1 -C 6 alkoxy; and Y 4 is hydrogen, hydroxyl, mercapto, nitro, halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 alkoxy, C 3 -C 6 alkenyloxy, C 3 -C 6 alkynyloxy, halo C 1 -C 6 alkyl, halo C 2 -C 6 alkenyl, halo C 2 -C 6 alkynyl, halo C 1 -C 6 alkoxy, halo C 3 -C 6 alkenyloxy, halo C 3 -C 6 alkynyloxy, C 1 -C 6 alkoxy C 1 -C 6 alkyl, C 3 -C 6 alkenyloxy C 1 -C 6 alkyl, C 3 -C 6 alkynyloxy C 1 -C 6 alkyl, cyano, formyl, carboxyl, C 1 -C 6 alkoxycarbonyl, C 3 -C 6 alkenyloxycarbonyl, C 3 -C 6 alkynyloxycarbonyl, phenyl, phenyl substituted with at least one member