Solubilities and Glass Formation in Aqueous Solutions of the Sodium Salts of Malonic Acid With and Without Ammonium Sulfate

The
solubility of sodium hydrogen malonate and sodium malonate in water
both with and without ammonium sulfate present has been studied using
differential scanning calorimetry and infrared spectroscopy. The crystals
that form from sodium hydrogen malonate/water solutions were determined
to be sodium hydrogen malonate monohydrate by single-crystal X-ray
diffractometry. The crystals formed in sodium malonate/water solutions
were determined to be sodium malonate monohydrate, a compound whose
structure had not been previously known. When ammonium sulfate is
added to these respective aqueous systems, the precipitation solids
contain sodium sulfate decahydrate under low to moderate ammonium
concentrations and lecontite (NaNH4SO4·2H2O) under high ammonium concentrations, which can be found
under dry atmospheric conditions. Thus, it appears the presence of
malonate and hydrogen malonate ions does not significantly affect
the precipitation of inorganic salts in these systems. The glass transition
temperatures of all solutions were also determined, and it was observed
that the addition of ammonium sulfate slightly lowers the glass transition
temperature in these solutions.