Abstract
TiO2/SiO2, Cr2O3-NiO/SiO2, and TiO2-Cr2O3/SiO2 were prepared by the impregnation method for alkyl carbamate synthesis using urea as the carbonyl source. Up to 97.5% methyl carbamate yield, 97% ethyl carbamate yield, and 96% butyl carbamate yield could be achieved, respectively. The catalysts were characterized by ICP-AES, BET, XRD, XPS, NH3-TPD, and EPMA. Catalytic activity investigation revealed that TiO2/SiO2, Cr2O3-NiO/SiO2, and TiO2-Cr2O3/SiO2 were effective catalysts for methyl carbamate (MC), ethyl carbamate (EC), and butyl carbamate (BC), respectively. The recycling tests suggested that these silica gel supported catalyst system is active, stable, and reusable. A total of 96–97% alkyl carbamate (methyl, ethyl, and butyl) could be obtained in a 2 L autoclave, and these data suggested that our catalyst system is relatively easy to scale up.
Highlights
Alkyl carbamates are important intermediates and end products in the synthesis of a variety of organic compounds [1–3]
As a potential reaction process in industry, the reusability of the catalyst some time was more shown in Figure 12, methyl carbamate (MC), ethyl carbamate (EC), and butyl carbamate (BC) yields higher than 95.8%, 94%, and 94% were still remained important than the initial catalytic activity
Ammonia produced in the MC (EC, BC) synthesis was vented as followed: firstly, the autoclave was heated to 170 ◦ C within 20 min, after reacted 1.5 h (1 h, 1 h), the reaction was stopped and cooled to the room temperature by cool water; the pressure of the headspace was 0.2 MPa, the valve was opened
Summary
Alkyl carbamates are important intermediates and end products in the synthesis of a variety of organic compounds [1–3]. The alkyl carbamate could be used as carbonyl source to replace phosgene for the synthesis of isocyanates [13–16]. Carbon dioxide is indirectly used as carbonyl source in the whole process for carbamates synthesis with urea as the carbonyl sources. In view the practical application, the development of which should be simple, active, and reusable, for the synthesis of alkyl carbamates from urea is catalysts, which should be simple, active, and reusable, for the synthesis of alkyl carbamates highly desirable. Catalytic performance catalyst prepared by the impregnation method andofused synthesisThe of alkyl carbamates. Ethyl, ethyl, butyl butyl carbamate/dimethyl, carbamate/dimethyl, diethyl, Scheme diethyl, and dibutyl carbonate
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