Synthesis of Diethyl Toluene Diamine by Zeolite-Catalyzed Ethylation of 2,4-Toluene Diamine

A novel route for the environmentally friendly synthesis of diethyl toluene diamine (DETDA) was developed by the ethylation of 2,4-toluene diamine (2,4-TDA) over acidic zeolites using ethene and ethanol as the alkylation reagents. Different types of zeolites and reaction conditions were examined. Monoethyl toluene diamine (ETDA) was first generated and then DETDA was formed by ethylation of ETDA. Triethyl toluene diamine (TETDA) was the excessive ethylation product. The acidic zeolites were characterized by NH₃ temperature-programmed desorption, pyridine adsorption Fourier transform infrared spectroscopy, argon/nitrogen physisorption and scanning/transmission electron microscopy. The acidity, especially the Brønsted acid sites on the external surface of zeolites, plays a more important role in the ethylation than the pore channel does. A small crystal size exposing more acid sites on the external surface is beneficial for the producing of DETDA. The treatment with NaOH generating meso- and macropores and increasing external surface area can also improve the catalytic activity of ZSM-5.