The reaction mechanism for synthesizing dibutyl toluene-2,4-dicarbamate (BTDC) catalyzed by γ-Al2O3 from toluene-2,4-diamine, urea, and n-butyl alcohol has been investigated by means of Fourier transform infrared spectroscopy, liquid chromatograph–mass spectrometry, and experimental observations. The results show that (1) the nitrogen atom of C═NH in the tautomer of urea is absorbed on the acidic site of γ-Al2O3, causing the carbon atom to be charged more positively; (2) toluene-2,4-diamine as a nucleophilic reagent attacks the positively charged carbon atom of C═NH to produce an intermediate, 3-amino-4-methyl phenylurea or 2-methyl-5-amino phenylurea (TU); (3) a nucleophilic C4H9O– coming from an n-butyl alcohol molecule attacks the ureido carbon atom in a TU molecule to generate another intermediate, butyl 3-amino-4-methyl-N-phenyl carbamate or butyl 2-methyl-5-amino-N-phenyl carbamate (TMC); and (4) another −NH2 group in a TMC molecule follows the same steps as mentioned above, and then BTDC is obtained.