1972 Volume 45 Issue 7 Pages 2070-2074
For the crystallization of aminomalonic acid with several amino acids from an aqueous solution, solid complex formation was studied by means of an X-ray diffractometer. No complex formation of aminomalonic acid with α-alanine, dl-α-amino-n-butyric acid, l-isoleucine, l-leucine, dl-serine, dl-norleucine, α-amino-iso-butyric acid, dl-valine, dl-threonine, or dl-norvaline was observed. However, with β-alanine, the formation of a solid complex with a molar ratio of 1:1 was ascertained. When this solid complex was analyzed by the differential thermogravimetric method in air at a heating rate of 1.4°C/min, a decarboxylation reaction, accompanied by endothermic and exothermic peaks, was observed at 115–133°C. On the other hand, the decarboxylation of aminomalonic acid alone occurred in the temperature range of 112–138°C. The areas of the endothermic peak, which was attributed to the decarboxylation, and the endothermic peak, which was attributed to the crystallization energies of γ-glycine and β-alanine, were, respectively, about 3 and 3/2 times those of the peaks observed in the case of aminomalonic acid. It was also observed that the exothermic process proceeded in two steps. The X-ray analysis of the products of the decarboxylation process suggested that the complex first melted to become amorphous to X-rays, and that it was then decarboxylated to amorphous glycine and amorphous β-alanine with these subsequent crystallization. The two-step exothermic process was explained in terms of a somewhat earlier crystallization of amorphous glycine than in terms of that of the amorphous β-alanine. The activation energy of the solid complex was estimated to 119.2 kcal/mol from the thermogravimetric curve. This large value of the apparent activation energy may be considered to result because the solid complex turns to an amorphous phase much more sensitive to decarboxylation prior to decomposition, and the steep slope of the thermogravimetric curve which results from the rapid decarboxylation of the amorphous gives the large apparent activation energy.
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