Herbicidal hydroxybenzyl-substituted heteroaryl compounds and derivatives thereof

A compound of the formula ##STR27## wherein:

• Ar is a substituted or unsubstituted pyrazine ring;
• R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently hydrogen, halogen, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, nitro, cyano, hydroxy, thiocyano, --N(R.sup.11)(R.sup.12), C.sub.1 -C.sub.6 haloalkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 haloalkoxy, (C.sub.1 -C.sub.6)alkoxy--(C.sub.1 -C.sub.6)alkyl, halo(C.sub.1 -C.sub.6)alkoxy-(C.sub.1 -C.sub.6)alkyl, --C(X)--R.sup.10 or --S(O).sub.k --R.sup.10 ;
• X is oxygen or sulfur;
• R is hydrogen, hydrocarbyl, hydrocarbyl substituted with one or more of halogen or C.sub.1 -C.sub.6 alkoxy or is of the formula --C(Y)--R.sup.6, --C(O)--C(O)--R.sup.6, --S(O).sub.2 --R.sup.6, --P(Y)(R.sup.11)(R.sup.12), or --Si(R.sup.13)(R.sup.14)(R.sup.15);
• wherein:
• Y is oxygen or sulfur;
• R.sup.6 is hydrocarbyl, substituted hydrocarbyl, hydrocarbyloxy, substituted hydrocarbyloxy, hydrocarbyl-S-, substituted hydrocarbyl-S- or is of the formula --N(R.sup.7)(R.sup.8);
• wherein R.sup.7 and R.sup.8 are each independently hydrogen, hydrocarbyl, substituted hydrocarbyl, hydrocarbyloxy, substituted hydrocarbyloxy, pyridyl, furyl, thienyl, (C.sub.1 -C.sub.6)alkoxycarbonyl(C.sub.1 -C.sub.6)alkyl, hydroxycarbonyl(C.sub.1 -C.sub.6)alkyl, or N(R.sup.9)(R.sup.10) wherein R.sup.9 and R.sup.10 are each independently hydrogen, C.sub.1 -C.sub.6 alkyl or phenyl;
• or R.sup.7 and R.sup.8 together with the nitrogen to which they are bound form an aziridine, piperazine, morpholine, thiomorpholine, thiomorpholine 1-oxide, thiomorpholine 1,1-dioxide fonyl, hexamethyleneimine, piperidine or pyrrolidine ring, any of which may be optionally substituted with C.sub.1 -C.sub.6 alkyl;
• R.sup.11 and R.sup.12 are each independently C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkylthio or C.sub.1 -C.sub.6 alkoxy;
• R.sup.13, R.sup.14 and R.sup.15 are each independently C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 haloalkyl, aryl or arylalkyl;
• and
• k is 0, 1 or 2;
• or an agriculturally acceptable salt thereof;
• wherein hydrocarbyl, whether alone or part of another group, is a member selected from (C.sub.1 -C.sub.6)alkyl, (C.sub.3 -C.sub.6)cycloalkyl, (C.sub.2 -C.sub.6)alkenyl, (C.sub.2 -C.sub.6)alkynyl, phenyl(C.sub.1 -C.sub.6)alkyl, (C.sub.1 -C.sub.6)alkylphenyl, (C.sub.2 -C.sub.6)alkenylphenyl, (C.sub.2 -C.sub.6)alkynylphenyl, (C.sub.1 -C.sub.6)alkylbenzyl, (C.sub.2 -C.sub.6)alkenylbenzyl and (C.sub.1 -C.sub.6)alkynylbenzyl;
• with the proviso that when R is hydrogen or (C.sub.1 -C.sub.6)alkyl, at least one of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is not hydrogen and if one of them is methyl or ethyl at least one of them is other than hydrogen.