Abstract
The thermal decomposition of the organic free-radical initiator, diethyl peroxydicarbonate (DEPDC), was monitored by in situ ATR-FT-IR in heptane, and in the green solvent supercritical carbon dioxide (scCO 2) both with and without supercritical ethylene. It was observed that the characteristic peaks of DEPDC at 1802–1803 and 1194–1203 cm −1 decreased significantly upon heating corresponding to the decomposition of DEPDC, while two new intense peaks simultaneously appeared at 1747 and 1262 cm −1 in heptane, and similarly at 1756 and 1250 cm −1 in scCO 2. The changes in the absorbance intensity of the characteristic peaks of the initiator during the decomposition were used for the measurement of the decomposition rate constant ( k d) of DEPDC. It was found that the thermal decomposition of DEPDC at low concentration in either heptane under atmospheric N 2 or scCO 2 under high pressure was via the first-order kinetics of unimolecular decomposition. The activation energy of the thermal decomposition of DEPDC was found to be 115 kJ/mol in heptane from 40 to 74 °C and 118 kJ/mol in scCO 2 from 40 to 60 °C. These new peaks revealed the formation of carboxyl groups contained in the decomposed products, indicating incomplete decarboxylation. During removal of CO 2 after the reaction in scCO 2, the instable intermediate monoethyl carbonate was decarboxylated and converted into the major end product, ethanol.
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