Pyrimidine or triazine derivatives and herbicides

A compound of the formula (I) or its salt:

• ##STR642## wherein A is a heterocyclic ring of the formula:
• ##STR643## wherein R is a hydrogen atom, a hydroxyl group, an imidazolyl group, a C.sub.1 -C.sub.6 alkoxy group, a C.sub.3 -C.sub.6 alkenyloxy group, a C.sub.3 -C.sub.6 alkynyloxy group, a C.sub.1 -C.sub.6 alkylthio group, a C.sub.3 -C.sub.7 cycloalkoxy group, a benzyloxy group, a substituted benzyloxy group, a benzylthio group, a substituted benzylthio group, a C.sub.3 -C.sub.6 cycloalkylthio group, a C.sub.1 -C.sub.4 alkoxy C.sub.1 -C.sub.4 alkoxy group, a furyloxy group, a tetrahydrofuryloxy group, a phenoxy group, a substituted phenoxy group, a C.sub.2 -C.sub.4 aralkyloxy group, a C.sub.1 -C.sub.4 alkylthio C.sub.1 -C.sub.4 alkoxy group, a cyano C.sub.1 -C.sub.4 alkoxy group, a C.sub.1 -C.sub.4 alkoxycarbonyl C.sub.1 -C.sub.4 alkoxy group, an N,N-di C.sub.1 -C.sub.3 alkylamino C.sub.1 -C.sub.3 alkoxy group, an N,N-diC.sub.1 -C.sub.3 alkylamino C.sub.1 -C.sub.3 -alkylthio group, a C.sub.3 -C.sub.9 linear or cyclic alkylidene aminoxy group, a C.sub.1 -C.sub.4 alkylsufonylamino group, a phenylsulfonylamino group, a substituted phenylsulfonylamino group, a trimethylsilylethoxy group, a group of the formula --NR.sup.4 R.sup.5 (wherein each of R.sup.4 and R.sup.5 which may be the same or different, is a hydrogen atom, a hydroxyl group, a C.sub.1 -C.sub.6 alkyl group, a C.sub.1 -C.sub.6 alkoxy group, a C.sub.3 -C.sub.6 alkenyl group, a phenyl group, a substituted phenyl group, a C.sub.3 -C.sub.6 cycloalkyl group, a C.sub.1 -C.sub.3 alkoxy C.sub.1 -C.sub.3 alkyl group, a C.sub.1 -C.sub.3 acyl group, a C.sub.3 -C.sub.6 alkynyl group, a C.sub.3 -C.sub.5 alkenyloxy group, a C.sub.3 -C.sub.5 alkynyloxy group, a benzyloxy group, a substituted benzyloxy group, a C.sub.1 -C.sub.4 alkoxycarbonyl C.sub.1 -C.sub.3 alkyl group, a C.sub.1 -C.sub.4 alkoxycarbonyl C.sub.1 -C.sub.3 alkoxy group, an amino group, a dimethylamino group, a cyano group, a C.sub.1 -C.sub.4 alkylsulfonyl group, a phenylsulfonyl group, a substituted phenylsulfonyl group, an acetylamino group or an anilino group, or R.sup.4 and R.sup.5 may together form a ring which may contain an oxygen atom),
• each of R.sup.1 and R.sup.2 which may be the same or different, is a hydrogen atom (provided that a case where R.sup.1 and R.sup.2 are both hydrogen is excluded), a halogen atom, a C.sub.1 -C.sub.6 alkyl group, a C.sub.1 -C.sub.6 haloalkyl group, a C.sub.1 -C.sub.6 alkoxy group, a C.sub.1 -C.sub.6 haloalkoxy group, a C.sub.1 -C.sub.6 alkylthio group, a phenoxy group, a substituted phenoxy group, a C.sub.1 -C.sub.3 alkoxy C.sub.1 -C.sub.3 alkyl group, a C.sub.3 -C.sub.6 cycloalkyl group, a C.sub.2 -C.sub.5 alkenyl group, a C.sub.3 -C.sub.5 alkenyloxy group, a C.sub.2 -C.sub.4 alkynyl group, a C.sub.3 -C.sub.5 alkynyloxy group, a C.sub.1 -C.sub.3 alkylthio C.sub.1 -C.sub.3 alkyl group, a group of the formula --NR.sup.6 R.sup.7 (wherein each of R.sup.6 and R.sup.7 which may be the same or different, is a hydrogen atom, a hydroxyl group, a C.sub.1 -C.sub.4 alkyl group, a C.sub.1 -C.sub.4 alkoxy group, a C.sub.2 -C.sub.4 alkenyl group, a C.sub.3 -C.sub.5 alkenyloxy group or a C.sub.3 -C.sub.5 alkynyloxy group, or R.sup.6 and R.sup.7 may together form a ring which may contain an oxygen atom),
• X is a phenyl group,
• W is an oxygen atom, a sulfur atom or a group of the formula --NR.sup.10 (wherein R.sup.10 is a hydrogen atom, a C.sub.1 -C.sub.3 alkyl group, a C.sub.2 -C.sub.5 alkenyl group, a C.sub.2 -C.sub.4 alkynyl group, a C.sub.1 -C.sub.3 alkoxy C.sub.1 -C.sub.3 alkyl group, a C.sub.1 -C.sub.3 alkylsulfonyl group, a phenylsulfonyl group, a substituted phenylsulfonyl group, a C.sub.1 -C.sub.3 acyl group, a benzoyl group or a substituted benzoyl group),
• Z is a methine group, and
• n is an integer of from 1 to 2.