Synthesis of dialkyl hexamethylenedicarbamate from 1,6-hexamethylenediamine and alkyl carbamate over Y(NO₃)₃·6H₂O catalyst

The non-phosgene carbonylation of 1,6-hexamethylenediamine (HDA) with alkyl carbamates using Y(NO₃)₃·6H₂O as a catalyst and the influence of reaction variables on the yields of dialkyl hexamethylenedicarbamate (HDC) were studied. At 453 K and in the presence of 5 wt.% Y(NO₃)₃·6H₂O, nearly 100% HDA conversion and 85% dibutyl hexamethylenedicarbamate (BHDC) isolated yield could be achieved when butyl carbamate (BC) was employed as a carbonyl source. During reaction, an induction period was observed, but it almost disappeared by pretreating the catalyst with n-butanol. The FT-IR, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterizations of the catalyst showed that some transformation occurred when the catalyst was pretreated with n-butanol or employed during reaction, i.e., part decomposition of Y(NO₃)₃ to Y₂O₃, conversion from crystal to amorphous state, changes occurring in chemical state of the active species, as well as some subtle interactions between the catalyst and n-butanol. All these observed changes might be the reason resulting in activation of the catalyst.