Lowering the Activation Energy under Mechanochemical Conditions: The Case of 2,3-diphenylquinoxaline

The kinetics of 2,3-diphenylquinoxaline synthesis was investigated in mechanochemical conditions aiming to estimate the overall activation energy. Arrhenius plot revealed a change in the activation energy around the eutectic melting of the powder mixture under mechanical activation. Below this transition zone the reaction between solids prevails, where the mechanical effects lower the activation energy. Above it, part of the energy is used to induce the eutectic, and the apparent activation energy is higher. DFT calculations showed a reaction barrier similar to the experimental one for higher temperatures. This study is the first that demonstrates the effect of mechanical energy to lower an activation barrier for ball milled organic reaction.