Hydrolysis of Phosphoryl Triamide

Abstract

The hydrolysis of phosphoryl triamide was studied mainly in an acetic acid-acetate buffer solution and an aqueous sodium hydroxide solution by means of ion-exchanged chromatography. General acid-catalysis was effected in the hydrolysis of PO(NH₂)₃ by acetic acid in acetate buffer, and its catalysis constant was 2. 29 × 10^-3 /.mor^-1.sec^-1 (25°C), while the basic catalysis by acetate ion was not detected. In the buffers of 0. 2, 0. 4 mol.l^-1(pH 5∼6), the reaction rate was the first-order function of the concentration, and the first order rate constants for the hydrolysis increased with increasing concentration of acetic acid (Fig. 5). In the buffers of 0. 1 mol.l^-1 (pH 4∼6), the rate was proportional to the concentration of hydrogen ions, and the rate constants increased with increasing concentration of the ions (Fig. 6). In the former case, the acid-catalysis worked as a general type one, and the latter as a special type, in spite of the fact that the initial transfer of a protone was supplied from the undissociated acid. The activation energy and entropy for the hydrolysis of PO(NH₂)₃ in the buffer were 12. 3 kcal . mol^-1, -42.0 e. u. (25°C), respectively. In the aqueous solutions of pH 7 to 10 region, induction periods of 6∼24 hr were observed for the hydrolysis of PO (NH₂)₃ (Fig. 7) . The initial rates of hydrolysis of PO(NH₂)₃ in the aqueous solutions of sodium hydroxide accorded with a first-order equation, and the rates increased in proportion to the increase of the concentration of sodium hydroxide (Fig. 9).
The mechanism of hydrolysis of PO(NH₂)₃ in acetate buffer was discussed through the protolytic mechanism.