稳固的钾 L-threonate 水合物, K (C4H7O5 ) 莇菧 ? 蟩讵 ?? 鮼 ? 邈髧螠蟥 ??? 蒚菧?蟩?
The solid potassium L-threonate hydrate, K(C4H7O5)·H2O, was synthesized by the reaction of L-threonic acid with aqueous potassium hydrogen carbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat capacity of K(C4H7O5)·H2O has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 78 to 395 K. An obvious process of the dehydration occurred in the temperature region of 364-382 K. The peak temperature of the dehydration of the compound has been observed to be (380.524±0.093) K by means of the heat capacity measurements. The molar enthalpy, △dHm, and molar entropy, △dSm, of the dehydration of K(C4H7O5)·H2O were calculated to be (19.655 ± 0.012) kJ/mol and (51.618 ± 0.051) J/(K·mol) by the analysis of the heat-capacity curve. The experimental molar heat capacities of the solid from 78 to 362 K and from 382 to 395 K have been respectively fitted to two polynomial equations of heat capacities against the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, △cUm, has been determined to be (- 1749.71 ±0.91) kJ·mol^-1 by an RBC-Ⅱ precision rotary-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, △fHm , has been calculated to be (- 1292.56± 1.06) kJ·mol^-1 from the combination of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.