A compound of the formula: ##STR1## wherein R.sub.1 is a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, a C.sub.3 -C.sub.4 alkenyl group, a C.sub.3 -C.sub.4 alkynyl group, a C.sub.1 -C.sub.4 haloalkyl group, a C.sub.3 -C.sub.4 haloalkenyl group, a C.sub.3 -C.sub.4 haloalkynyl group a C.sub.1 -C.sub.2 alkoxy(C.sub.1 -C.sub.2)alkyl group or a C.sub.1 -C.sub.2 alkoxy(C.sub.1 -C.sub.2)alkoxy(C.sub.1 -C.sub.2)alkyl group, R.sub.2 and R.sub.3 are, the same or different, each a hydrogen atom, a halogen atoms, a C.sub.1 -C.sub.3 alkyl group or a phenyl group, X is a hydrogen atom, a chlorine atom or a fluorine atom and n is an interger of 0 or 1, which is useful as a herbicide.