7.2. NH4H2PO4-Organic Compound-H2O The NH4H2PO4-CS(NH2)2-H2O system is described in two articles.1,2 The 298 K isotherm and the complete phase diagram are given for the system. All these data are consistent with each other, but no critical evaluation can be made because there are no other data available for this system.
The same group of investigators also presented some information on the NH4H2PO4-methionine-H2O system.3 The phase diagrams for the systems, Fig. 14 and Fig. 15, provide an illustration of the problem involved in the so-called α- and β-NH4H2PO4 discussed on page 1335. The authors are convinced that these two allotropes do exist and state that the transition point between them is at about 306 K. However, the evidence for these claims appears to be weak. There is no clear break where the curves for those systems in which both these solid allotropes are in equilibrium with the saturated solution join the curves for solutions in which the organic component is also an equilibrium solid phase. Furthermore, there is an insufficient number of data points for solutions in equilibrium with both the solid a-NH4H2PO4 and b-NH4H2PO4.
Other systems containing an organic compound that is both solid and water-soluble under ordinary room conditions and thus analogous to the systems described above are the NH4H2PO4-(C2H4)3NKHCl-H2O system4,5 and the NH4H2PO4-(C4H9)2NHKHCl-(C4H9)3NKHCl-H2O system6. These systems were studied by the same group of investigators, but no other data for these systems are available. Therefore, the information in these articles cannot be evaluated. This is true also for the NH4H2PO4-Biuret-H2O system7.