Benzimidazole anthelmintic agents

A benzimidazole derivative of the formula:

• ##STR7## or a non-toxic salt thereof, wherein R.sup.1, which is in the 5(6)-position, is either (i) H, benzoyl, phenyloxy, phenylthio, phenylsulfinyl, phenylsulfonyl, phenylsulfonyloxy, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, C.sub.1 -C.sub.6 alkylsulfinyl, C.sub.1 -C.sub.6 alkylsulfonyl or (C.sub.3 -C.sub.7 cycloalkyl) carbonyl, said phenyl groups, and the phenyl portion of said benzoyl group, optionally having 1 to 3 substituents each independently selected from halo, C.sub.1 -C.sub.4 alkyl, halo-(C.sub.1 -C.sub.4 alkyl), C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulfinyl, C.sub.1 -C.sub.4 alkylsulfonyl, C.sub.2 -C.sub.4 alkanoyl, nitro, isothiocyanato, and cyano;
• (ii) a group of the formula:
• ##STR8## where X is O, S, SO, SO.sub.2 or NR.sup.4 in which R.sub.4 is hydrogen;
• C.sub.1 -C.sub.4 alkyl, phenyl or phenyl-(C.sub.1 -C.sub.4 alkyl), wherein said phenyl and the phenyl portion of said phenyl-(C.sub.1 -C.sub.4) alkyl) groups are optionally substituted by 1 or 2 substituents each selected from C.sub.1 -C.sub.4 alkyl, halo, hydroxy and C.sub.1 -C.sub.4 alkoxy;
• and R.sub.5 is H, C.sub.1 -C.sub.4 alkyl, halo, hydroxy or C.sub.1 -C.sub.4 alkoxy;
• or (iii) a group of the formula:
• ##STR9## "alk" is a methylene or ethylene group;
• R.sup.2 is cyano, C.sub.2 -C.sub.4 alkenyl, C.sub.2 -C.sub.4 alkynyl, C.sub.2 -C.sub.4 alkanoyl, C.sub.1 -C.sub.4 alkoxy, C.sub.2 -C.sub.4 alkenoxy, aryl, heteroaryl, aryl-(C.sub.1 -C.sub.4 alkoxy) or heteroaryl-(C.sub.1 -C.sub.4 alkoxy), in which "aryl" means phenyl optionally substituted by 1 to 3 substituents each independently selected from halo, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulphinyl and C.sub.1 -C.sub.4 alkylsulphonyl, and in which "heteroaryl" means thienyl, furyl or pyridinyl all optionally substituted by 1 to 3 substituents each independently selected from halo, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulphinyl and C.sub.1 -C.sub.4 alkylsulphonyl;
• and R.sub.3 is a C.sub.1 -C.sub.4 alkyl group.