Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The thermochemistry of a-D-xylose(cr) was studied by means of oxygen bomb calorimetry and a Physical Property Measurement System (PPMS) in zero magnetic field. The sample of a-D-xylose(cr) used in this study was one well-characterized by HPLC, Karl Fischer analysis, NMR, and by carbon dioxide analysis. The standard molar enthalpy of combustion was found to be The thermochemistry of a-D-xylose(cr) was studied by means of oxygen bomb calorimetry and a Physical Property Measurement System (PPMS) in zero magnetic field. The sample of a-D-xylose(cr) used in this study was one well-characterized by HPLC, Karl Fischer analysis, NMR, and by carbon dioxide analysis. The standard molar enthalpy of combustion was found to be (2342.2 +- 0.8) kJ*mol^-1 at T = 298.15 K and at the standard pressure p = 0.1 MPa. The standard molar heat capacity for a-D-xylose(cr) was measured with the PPMS over the temperature range 1.9001 to 303.66. At T = 298.15 K, C_p,m = (178.1 +- 1.8) J*K^-1*mol^-1. The values of C_p,m were fit as a function of T by using theoretical and empirical models for appropriate temperature ranges. The results of these fits were used to calculate values of C_p,m, the entropy increment change in entropy, change in enthalpyThe results of these fits were used to calculate values of Cop ;m, the entropy increment DT 0So m, DT 0Ho m, and Uo m 1/4 oDT 0So m DT 0Ho m=T) from T = 0.5 K to T = 300 K. Derived quantities for a-D-xylose(cr) are the standard molar enthalpy of formation DfHo m = (1054.5 +- 1.1) kJ mol 1, the third law standard molar entropy So m = (175.3 +- 1.9) J K 1 mol 1, and the standard molar Gibbs energy of formation DfGo m = (750.5 +- 1.0) kJ mol 1. A comparison of values of DcHo m and So m for the five-carbon aldoses demonstrated a striking similarity in the values of these respective properties for a-D-xylose(cr), D-ribose(cr), and D-arabinose(cr). Thermochemical network calculations were performed that led to values of the standard formation properties at T = 298.15 K for a variety of biochemical substances: D-xylose(aq), D-xylose (aq), D-xylose2 (aq), D-lyxose(cr and aq), D-lyxose (aq), D-xylulose(aq), xylitol(aq), 1,4-b-D-xylobiose(am and aq), and 1,4-b-D-xylotriose(am and aq).