Abstract: Novel thiadiazole compounds are produced having the following general formula: ##STR1## wherein X is S or SO.sub.2R.sub.1 is a lower alkyl (cyclic or non-cyclic) radicalR.sub.2 is hydrogen or a lower acyclic hydrocarbon radicalR.sub.3 is a lower acyclic hydrocarbon or cycloalkyl radical or alkoxy radical, andR.sub.4 is hydrogen, a lower acyclic hydrocarbon radical or cycloalkyl radical, provided R.sub.3 and R.sub.4 are not both cycloalkyl, and[B] Tautomers of [A] wherein R.sub.2 is hydrogen.Synthesis of these compounds is disclosed, including synthesis of those compounds which exhibit tautomerism.The compounds show particular utility as agricultural pesticides and most favorably as herbicides.