Dissociation constants of m- and p-substituted phenylthioureas and ureas in water and in methanol

Abstract

Dissociation constants of nine m- and p-substituted phenylthioureas, 4-nitrophenylurea, and 1-(4-nitrophenyl)-3,3-dimethylurea have been measured in water and in methanol. The pKa values in methanol are higher than those in water by about 4 units. The Hammett ρ constant has the values 2.6 and 2.35 in water and in methanol, respectively. The pKa difference between 4-nitrophenylurea and 4-nitrophenylthiourea is 2.85 in methanol and 3.25 in water.