hexamethylenetetramine; stability; hydrolysis; buffer system; buffer capacity


In the current study stability of hexamethylenetetramine (HMTA) aqueous solutions without acid additives (HCl, H2SO4, citrate-phosphate buffer systems, etc.) in the range of temperatures 1.0 ÷ 20.0 °С and concentrations of HMTA 0.10 ÷ 1.0 M (pH0 = 7.05 ÷ 8.25) was investigated by the spectrophotometric and potentiometric (pH and redox) methods. The obtained data indicate the complexity of the mechanism of hydrolytic transformations and acid-base interactions in the studied HMTA solutions. It was noted that the mechanism of disproportionation of HMTA in water significantly depends on temperature and its concentration. The contents of ammonium ions and formaldehyde as the final products of HMTA hydrolysis was determinated. The molar concentration of ammonium ions is no more than 5.0 % of the total content of HMTA and is several times higher than the formaldehyde concentration. It is shown that the dynamics of ammonium ions and formaldehyde accumulation does not correlate with the potentiometric curves. It was established that hydrolytic stability of HMTA aqueous solutions increases with it concentration. Recommendations for the preparation of buffer solutions based on HMTA are formulated. It is noted that it is desirable to prepare aqueous HMTA solutions of high concentration (³ 0.50 M) and store them at room temperature. An algebraic equation that describes the ratio of volumes of solutions of 1.00 M (2.50 M) HMTA and 0.10 M HCl, which are required for the preparation of buffer solutions with a certain pH in the range of 4.30 ÷ 7.40 (5.00 ÷ 7.50) was obtained. Mathematical model that describes the concentration dependence of the HMTA – HCl – H2O buffer solutions capacity and the influence of dilution on the change in pH has been proposed. It is noted that the buffer capacity of the studied buffer system depends significantly on the concentration and ratio of the components in the solution.


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