THE SUBLIMATION ENTHALPY OF DIMETHYL OXALATE

The sublimation enthalpy of dimethyl oxalate has been measured by calo rimetric and head space analysis. These results along with vaporizatio n enthalpy measured by correlation gas chromatography and fusion entha lpy measurements are compared to results predicted by two estimation t echniques. A previous experimental measurement was found to be in erro r. A mean value of (75.2 +/- 0.5) kJ/mol was obtained which results in a corrected molar value of (-681.5 +/- 0.8) kJ/mol for the enthalpy o f formation of gaseous dimethyl oxalate, Delta(f)H(m) degrees (g, 298. 15 K). This new value of Delta(f)H(m) degrees (g, 298.15 K) for dimeth yl oxalate, in combination with other enthalpies of formation, suggest s that the ground state of oxalates are destabilized relative to alpha -diketones by approximately 25 kJ/mol.