Synthesis of dibutyl hexamethylenedicarbamate without phosgene

Dibutyl hexamethylenedicarbamate (BHDC) is a precursor of diisocyanatohexane. Through a one-step process, BHDC can be synthesized from 1,6-hexamathylenediamine (HDA) by using butyl carbamate (BC) as the carbonylating reagent to displace the dangerous phosgene, hydrate of yttrium nitrate as catalyst, and n-butanol as solvent. When the reaction was carried out at 180°C for 5 hr using Y(NO₃)₃ · 6H₂O as catalyst, and n(n-butanol):n(BC):n(HDA) = 15:4:1, HDA conversion was nearly 100% and yield to BHDC was 85%. Although transformation of crystalline to amorphous state, loss of crystalline water and existence of yttrium oxide were found in used catalyst, no deactivation was observed after the catalyst was reused for four times.