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.

The methanolysis rate constants and dissociation constants have been measured of benzoyl derivatives of substituted phenylureas and phenylthioureas. The dissociation constants of the thio derivatives are higher by 1 order of magnitude and the rate constants are higher by 2 orders of magnitude than the respective values of the oxygen analogues. Logarithms of the rate and dissociation constants have been correlated with the Hammet σ constant; the ρ constant of the methanolysis of the oxygen derivatives is almost 2x higher than that of the thio derivatives, which is explained by a change in the rate-limiting step. Methylation of the phenyl nitrogen atom increases the acidity by almost 2 orders of magnitude. This effect is due obviously to steric hindrance to the conjugation with the adjacent carbonyl or thiocarbonyl group.

N-Benzoyl-N'-(2-carboxy- and 2-methoxycarbonylphenyl)thioureas have been obtained by the reaction of N-benzoyl isothiocyanate with anthranilic acid and methyl anthranilate, respectively. Kinetics of cyclization of these compounds into 2-mercapto-3,4-dihydro-4-quinazolone have been studied in water and in methanol. In the base-catalyzed cyclization of N-benzoyl-N'-(2-carboxyphenyl)thiourea the proper cyclization is preceded by solvolysis of the benzoyl group. In the case of N-benzoyl-N'-(2-methoxycarbonylphenyl)thiourea the reaction rate is limited by the base-catalyzed cyclization of the starting benzoyl derivative; the benzoyl group is split off in a subsequent rapid step.

Die Kinetik der basenkatalysierten Cyclisierung des Thioharnstoffs (IIb) [bei höherer Basenkonzentration entsteht neben dem Anion (III) noch das Dianion (IV)] in Methanol und Wasser sowie die Kinetik der Methanolyse und der Hydrolyse von (IIa) und der Cyclisierung des Zwischenprodukts (V) der (IIb)‐Cyclisierung werden untersucht.

Kinetics has been studied of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-betenethioamide (Ia) and 2-acetyl-3-amino-N-benzoyl-2-butenethioamide (Ib) giving 5-acetyl-2-phenyl-1,6-dimethyl-4-(1H)pyrimidinethione (IIa) and 5-acetyl-2-phenyl-6-methyl-4-(3H)-pyrimidinethione (IIb), respectively, in aqueous buffers within pH 2 to 9. Formation of the cyclic intermediate is rate-limiting in the cyclization of Ib within the whole range. In the case of Ia the rate-limiting step consists in acid-catalyzed splitting off of water from the cyclic intermediate above pH 5 and in base-catalyzed splitting off of hydroxyl ion above pH 7.