Copper(I)-Mediated Ligand-Accelerated Ullmann-Type Coupling of Anilines with Aryliodides: Ligand Selection and Reaction Kinetics for Synthesis of Tri-p-Tolylamine

Screening of eight ligands for the copper-catalyzed ligand-accelerated Ullmann condensation of p-toluidine with 4iodotoluene to produce tri-p-tolylamine (TTA) revealed that 2,2ʹ-dipyridyl and 4,4ʹ-dipyridyl gave the highest conversion to TTA in the shortest time. Based on the ligand-screening results, a mechanistic structure of the active reaction complex between copper and the two fastest ligands was proposed. The TTA synthesis reaction kinetics was followed by an HPLC method, and kinetic parameters of the reaction were determined in temperature range 128-196 (degree) C. The condensation of p-toludine with 4-iodotoluene to give TTA was modeled as a parallel-consecutive reaction system composed of two condensation reactions. Reaction orders for the first condensation reaction to give di-p-tolylamine were determined to be 1.18 and 1.16 with respect to 4-iodotoluene and p-toluidine, respectively. For the second condensation reaction, the reaction orders were determined to be 0.13 and 0.11 with respect to 4-iodotoluene and di-p-tolylamine, respectively. Activation energies for the first and second reaction were determined as 53.6 and 53.8 kJ mol-1, respectively. The preexponential constants (ko) in the Arrhenius equation for the first and second reaction were determined as 1774.4 min^-1(mol/L)^-1.34 and 5657.8 min^-1(mol/L)^0.76, respectively. Finally, the model predictions gave very good agreement with experimental results for low, medium, and high reaction temperature.