N-Substituted carbamate synthesis using urea as carbonyl source over TiO₂–Cr₂O₃/SiO₂ catalyst

Abstract

The use of urea as an active form of carbon dioxide is a feasible way to substitute phosgene in the chemical industry. This paper reports an effective route for the syntheses of N-substituted carbamates from amines, urea and alcohols. Under the optimized reaction conditions, several important N-substituted carbamates were successfully synthesized with 95-98% yields over TiO 2 -Cr 2 O 3 /SiO 2 catalyst. The catalyst could be reused for several runs without deactivation. The catalysts were characterized with BET, 10 XPS, XRD, and TPD, which suggested that the strength and amount of the acidic-basic sites might be the major reason for the highly catalytic activity of TiO 2 -Cr 2 O 3 /SiO 2 .Journal Name, [year], [vol], 00-00 | 5 65 nucleophilic substitution mechanism. TiO 2 -Cr 2 O 3 /SiO 2 exhibited relatively stronger basic strengths in comparison with TiO 2 /SiO 2 and Cr 2 O 3 /SiO 2 , and showed the best catalytic performance. The presence of strong basic sites in TiO 2 -Cr 2 O 3 /SiO 2 probably due to strong synergy between TiO 2 and Cr 2 O 3 species on SiO 2 , which 70 was consistent with XRD results. Moreover, the role of the Lewis acid site of M + (M = Ti and Cr, synergistic effect between Ti and

Indirect reduction of CO2and recycling of polymers by manganese-catalyzed transfer hydrogenation of amides, carbamates, urea derivatives, and polyurethanes

“…Notably, the synthesis of carbamates from urea derivatives and alcohols typically requires high reaction temperatures and metal catalysts. [74][75][76] To the best of our knowledge, a basepromoted conversion of urea derivatives to carbamates has not been reported so far. Interestingly, other bases gave only poor or no conversion (For details, see supplementary information, Scheme S1).…”

One-Pot Synthesis of Dialkyl Hexane-1,6-Dicarbamate from 1,6-Hexanediamine, Urea, and Alcohol over Zinc-Incorporated Berlinite (ZnAlPO4) Catalyst

“…On prolonging the reaction timeframe, the selectivity for 5 gradually decreased. These results indicate that prolonging the reaction time promoted the formation of 2 via the further reaction of 5 and butanol [15,20]. The decrease in the yield of 2 at a longer reaction time may be explained by the partial decomposition of 2 to 1, because the synthesis of 2 via the further reaction of 1, urea, and butanol is an equilibrium reaction.…”

“…It is interesting that the main byproducts mixture (1, 3-5) mentioned above can also be directly employed as the raw materials in the synthesis of the desired product 2 by Reactions (5), (6), (8) and (9) [15,16,19,20,26,28].…”

Important Green Chemistry and Catalysis: Non‐phosgene Syntheses of Isocyanates – Thermal Cracking Way

“…Likewise, the co-produced NH 3 could Scheme 4 Possible reaction pathways for the reaction of HDA, urea and ethanol [36] …”

“…However, the use of soluble zirconium compounds as catalyst involved separation and recovery problems. Herein, our group [36] proposed TiO 2 -Cr 2 O 3 /SiO 2 as highly effective and recoverable catalyst for N-substituted carbamates syntheses from amines and urea (Scheme 4). The reaction was conducted at 190 ℃ , 8 h, 8 wt% TiO 2 -Cr 2 O 3 /SiO 2 catalyst, with molar ratio of M HDA ∶ M Urea ∶M ROH ＝1∶2.4∶15, and the yield of diethyl hexamethylenedicarbamate (EHDC) could reach 98%.…”