Ionization of Buthidazole, VEL 3510, Tebuthiuron, Fluridone, Metribuzin, and Prometryn

Aqueous solutions of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, VEL 3510 {1-β,β-dimethoxyethyl-1-methyl-3-[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl] urea}, tebuthiuron { N -[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl]- N,N ′-dimethylurea}, fluridone 1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1 H )-pyridinone, metribuzin [4-amino-6- tert -butyl-3-(methylthio)- as -triazin-5(4 H )-one], and prometryn [2,4-bis(isopropylamino)-6-(methylthio)- s -triazine] were spectrophotometrically titrated to obtain pK A values. Ionizing properties of the chemicals were compared with other related compounds reported in the literature. The pK A values for the six herbicides were 0.6 and 11.3, 0.9 and 9.0, 1.2, 1.7, 1.1, and 4.1, respectively.