Atom‐economy Synthesis of N‐Substituted Carbamate from Urea Derivative and Dimethyl Carbonate Catalyzed by La/SiO₂: Characterization and Activity

Abstract

A series of silica gel immobilized lanthanum catalysts were prepared for the atom-economy synthesis of N-substituted carbamates from urea derivatives and dimethyl carbonate. The La/SiO 2 catalysts with lanthanum loadings varied from 1.3 wt% to 8.5 wt% were characterized by AES, BET, XRD, TEM, FT-IR, XPS and TPD. According to the characterization, lanthanum species with particle sizes of 5-10 nm on the surface of silica gel were formed. The catalysts were all amorphous and the surface areas were 336.5-530.2 m 2 /g. NH 3 -TPD analysis showed that all samples exhibited similar acid strength with different acid amounts. FT-IR measurement indicated that the component of lanthanum species on the catalyst surface were La(OH) 3 , LaOOH and hydrated La 2 O 3 . Also, the peak value of the absolute amount of LaOOH was obtained with 4.3 wt% lanthanum loading. The BET surface area decreased dramatically when the lanthanum loading was above 4.3 wt%. In consideration of the results obtained from the catalytic reactions, it could be concluded that LaOOH was the possible active species and high surface area was important for the high catalytic activity.

A new route of CO2 catalytic activation: syntheses of N-substituted carbamates from dialkyl carbonates and polyureas

“…Till now, several catalysts, including silica gel, Bu 2 SnO, NaOCH 3 , PbCO 3 and La/SiO 2 , have been extensively studied for the N-substituted monocarbamate syntheses. [37][38][39][40][41] However, there was no report for N-substituted dicarbamate syntheses from dialkyl carbonates and polyurea derivatives. Another promising approach is the direct syntheses of carbamates from CO 2 , amines and alcohols, however, only monocarbamates could be synthesized with ≤66% to >90% of isolated yields.…”

Non‐isocyanate polyurethanes: synthesis, properties, and applications

“…N‐substituted carbamates have been synthesized by using urea derivatives and dialkyl carbonates as raw materials . Several catalysts, including silica gel, Bu 2 SnO, Zn(OAc) 2 , NaOCH 3 , PbCO 3 , and La/SiO 2 , have been extensively studied for the N‐substituted monocarbamate or dicarbamate syntheses . The reaction with dialkyl carbonate carried out in supercritical carbon dioxide (scCO 2 ) at 90 bar inhibits the formation of N‐methylated by‐products and favors the formation of alkylammonium carbamates …”

Catalytic degradation of polyurea: synthesis of N-substituted carbamates with CuO–ZnO as the catalyst

“…However, transition metal complex catalyzed carbonylation of nitroaromatics or amines using CO as a carbonyl source suffers from some problems such as the poisonous feed gas and the higher cost of the noble metal Pd complex catalyst accompanied by 92.4% carbamate selectivity under 100 bar CO pressure with phosphorous acids or Ph 2 P(O)OH as promoters. [19][20][21][22] Moreover, dimethyl carbonate (DMC) as an attractive eco-friendly alternative to phosgene and CO was used as an environmentally benign method for carbamate production; [31][32][33] however, the higher price of DMC limited its practical applications. Besides, the alcoholysis of substituted ureas resulting in poor atom economy, with amines produced as by-products, decreased the efficiency of the functional group of the reagents.…”