Kinetics of Formation of Quantum Dot Solvent N-Oleoylmorpholine

Abstract

The kinetics of the synthesis of noncommercially available quantum dot (QD) solvent N-oleoylmorpholine (NOM) was investigated in a semibatch reactor system to enable scale up. Morpholine was injected into excess oleic acid (OA) at rates of 250 and 500 μL/h at 110, 140, and 170 °C. The reaction was found to be zero order in morpholine, first order in OA, and first order overall for temperatures ≥140 °C. At < 140 °C, the reaction does not follow elementary kinetics with respect to OA. Thermodynamic calculations using the Eyring−Polyani equation determined that the entropy change from the reagents to the transition state was negative, suggesting an associative complex intermediate species. The reaction mechanism was further analyzed via IR and NMR, revealing a carboxyl−amino intermediate, which was long lived (>1 h) at 110 °C but short lived (<30 min) at 170 °C. Conversions of 85% to near completion are achievable for OA, and excess morpholine was removed via rotary evaporation, thus yielding NOM with 70−98% purity.