A facile, highly efficient and phosgene-free synthesis process of dimethyl carbonate (DMC) with nbutanol (BuOH) to dibutyl carbonate (DBC) by transesterification reaction has been studied in detail using tetraethylammonium-based amino acid ionic liquids ([N-2222][AA]) as homogeneous catalysts. The results indicated that tetraethylammonium prolinate ([N-2222]Prol) exhibited the best catalytic activity in compared to other four [N-2222][AA], and DBC could be obtained at a yield of 72% under optimum conditions. Furthermore, quantum-mechanical calculations manifested that such high DBC yield originated from the synergistic dual activation catalysis of [N-2222][Pro]. [N-2222][Pro] could activate BuOH and DMC well at the same time, which enhances the electrophilicity of BuOH and the nucleophilicity of DMC respectively, leading to the excellence catalytic performance. (C) 2014 Elsevier B.V. All rights reserved.