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Cs2CO3-catalyzed transamination of primary amines and ethylene carbonate proceeds to form 1,3-disubstituted symmetrical/unsymmetrical ureas in excellent yields. The effect of different reaction parameters such as influences of bases, temperature, and reaction time were investigated for the title reaction. 相似文献
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Andrey V. BogolubskySergey V. Ryabukhin Sergey E. PipkoOleg Lukin Alexander Shivanyuk Dmytro MykytenkoAndrey Tolmachev 《Tetrahedron》2011,67(20):3619-3623
A facile and versatile method for the synthesis of unsymmetrical ureas from readily available reagents is reported. In the first step trifluoroethylchloroformate is reacted with a stoichiometric amount of a primary amine to give an intermediate trifluoroethyl carbamate. The addition of a second amine (primary or secondary) to the trifluoroethyl carbamate furnishes corresponding unsymmetrical ureas in 75-85% yield. A simple workup procedure, the high yields obtained, and the purity of the isolated products are suitable for the parallel synthesis of combinatorial libraries of unsymmetrical ureas with high structural and functional diversity. 相似文献
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Jun Jie Gao Hui Quan Li Yi Zhang Institute of Process Engineering Chinese Academy of Sciences P.O. Box Beijing China Graduate University of Chinese Academy of Sciences Beijing China 《中国化学快报》2007,18(2):149-151
Synthesis of methyl N-phenyl carbamate from dimethyl carbonate and 1,3-diphenyl urea was investigated under atmospheric pressure. The results showed that homogenous catalyst sodium methoxide had the excellent activity to efficiently catalyze the synthesis of methyl N-phenyl carbamate under atmospheric pressure. 相似文献
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Hammond C Lopez-Sanchez JA Ab Rahim MH Dimitratos N Jenkins RL Carley AF He Q Kiely CJ Knight DW Hutchings GJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(15):3927-3937
The reaction of glycerol with urea to form glycerol carbonate is mostly reported in the patent literature and to date there have been very few fundamental studies of the reaction mechanism. Furthermore, most previous studies have involved homogeneous catalysts whereas the identification of heterogeneous catalysts for this reaction would be highly beneficial. This is a very attractive reaction that utilises two inexpensive and readily available raw materials in a chemical cycle that overall, results in the chemical fixation of CO(2). This reaction also provides a route to up-grade waste glycerol produced in large quantities during the production of biodiesel. Previous reports are largely based on the utilisation of high concentrations of metal sulfates or oxides, which suffer from low intrinsic activity and selectivity. We have identified heterogeneous catalysts based on gallium, zinc, and gold supported on a range of oxides and the zeolite ZSM-5, which facilitate this reaction. The addition of each component to ZSM-5 leads to an increase in the reaction yield towards glycerol carbonate, but supported gold catalysts display the highest activity. For gold-based catalysts, MgO is the support of choice. Catalysts have been characterised by XRD, TEM, STEM and XPS, and the reaction has been studied with time-on-line analysis of products via a combination of FT-IR spectroscopy, HPLC, (13)C NMR and GC-MS analysis to evaluate the reaction pathway. Our proposed mechanism suggests that glycerol carbonate forms via the cyclization of a 2,3-dihydroxypropyl carbamate and that a subsequent reaction of glycerol carbonate with urea yields the carbamate of glycerol carbonate. Stability and reactivity studies indicate that consecutive reactions of glycerol carbonate can limit the selectivity achieved and reaction conditions can be selected to avoid this. The effect of the catalyst in the proposed mechanism is discussed. 相似文献
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Natarajan A Guo Y Arthanari H Wagner G Halperin JA Chorev M 《The Journal of organic chemistry》2005,70(16):6362-6368
A thiophile-promoted synthesis of disubstituted 4H-[1,2,4]triazole-3-yl-amines as urea mimetics from the corresponding 1,3-disubstituted thioureas has been studied, and the scope and limitations of this reaction are presented. The reaction proceeds through the formation of a carbodiimide, followed by a sequential addition--dehydration with acyl hydrazides. 1,3-Branched dialkylthioureas result in the formation of the corresponding ureas. The electronic and steric effects of the substitution on the phenyl rings of the 1,3-diarylthioureas play an important role in the formation of the intermediary carbodiimde and the direction of the subsequent ring closure of the N-acyl hydrazide adduct. 相似文献
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Propylene carbonate (PC) was produced from 1,2-propylene glycol (1,2-PG) and urea in a continuous-flow fixed bed reactor over
heterogeneous ZnO catalyst supported on NaY. Among different ZnO loadings of ZnO/NaY catalysts, 5 wt% ZnO loadings of ZnO/NaY
showed the highest activity. Characterization and reaction results indicated that the catalysts with a balanced strength of
acid and base sites performed well for the synthesis of propylene carbonate from urea and 1,2-PG. 相似文献
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Wooyong Seong Hyungwoo Hahm Seyong Kim Jongwoo Park Khalil A. Abboud Sukwon Hong 《Molecules (Basel, Switzerland)》2021,26(13)
Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding. 相似文献
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Per-Anders Enquist 《Tetrahedron letters》2005,46(19):3335-3339
Fast cobalt carbonyl-mediated generation of ureas from primary amines was performed using high-density microwave irradiation. This enhanced method permitted the preparation of symmetrical ureas in good yields and unsymmetrical ureas in moderate yields. The reaction times varied between 10 s and 40 min. The proposed mechanism for the reaction includes in situ generation of an intermediate isocyanate that subsequently traps the free amine, producing the urea product. 相似文献
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The reaction of 1,3-disubstituted ureas and 1-arylsulfonyl-3-alkylureas with phosgene permits the preparation of a number of isocyanates and sulfonyl isocyanates that had not previously been described, or that were difficult to prepare. 1,3-Disubstituted thioureas and 1-aryl-(or alkyl)sulfonyl-3-alkylthioureas give carbodiimides. Thionyl chloride and phosphorus pentachloride react with the urea derivatives in the same way as phosgene. Oxalyl chloride reacts with ureas to form parabanic acid derivatives, whereas with thiourea it gives 2-imino-1,3-thiazolidine-4,5-diones, which can isomerize to parabanic acid derivatives. 相似文献
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Oxidative coupling of methane over La-promoted CaO catalysts: Influence of precursors and catalyst preparation method
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The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO (La/Ca = 0.05) catalysts, prepared using different precursor salts for CaO and La2O3 (viz. acetates, carbonates, nitrates and hydroxides) and catalyst preparation methods (viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent), under different reaction conditions (temperature: 700-850℃, CH4/O2 ratio: 4.0 and 8.0, and GHSV: 51360 cm3 g-1 h-1)... 相似文献
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Farzad Nikpour Sajjad Mohebbi Touraj Paibast Mahdi Beigvand 《Monatshefte für Chemie / Chemical Monthly》2008,7(2):663-667
A regio- and stereoselective synthesis of functionalized 4,5-disubstituted oxazolidin-2-ones is reported with moderate to
good yields from the reaction of α-epoxyketones with urea in the presence of p-toluenesulfonic acid as the catalyst. 相似文献
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以碳酸丙烯(PC)和甲醇为原料,经酯交换反应合成的多功能、环保的碳酸二甲酯(DMC)是一种绿色、节能的合成方法。CaO固体碱催化剂对该反应具有良好的催化性能,但其再生性不理想。以F-Ca-Mg-Al水滑石(LDHs)为原料,制备了一系列不同Na F用量的固体碱催化剂,并对其进行了表征和酯交换反应测试。与不加氟的FCMA-0催化剂相比,经氟改性后的催化剂的比表面积、碱量、催化活性等性能均有明显提高。催化活性由高到低依次为:FCMA-0.8> FCMA-0.4>FCMA-1.2> FCMA-1.6> FCMA-0,这与总碱位量和强碱位量一致。FCMA-0.8催化剂活性最好,与纯CaO催化剂的相当,PC转化率为66.8%,DMC选择性为97.4%,DMC收率为65.1%。在10次循环使用后,FCMA-0.8催化剂的DMC收率仅下降3.9%(CaO催化剂下降33.2%)。FCMA-0.8在PC与甲醇酯交换制DMC方面具有良好的工业应用前景。 相似文献
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Noboru Yamazaki Tadao Iguchi Fukuji Higashi 《Journal of polymer science. Part A, Polymer chemistry》1979,17(3):835-841
Selective formation of biscarbamates from diphenyl carbonate (DPC) and diamines and the preparation of polyurethanes from the carbamates and diols under mild conditions were studied. The reaction of DPC and diamines was significantly affected by catalysts, biscarbamates being exclusively prepared in high yields in the presence of 2-hydroxypyridine. The polycondensation reaction of the biscarbamates with diols was facilitated by catalysts such as metal salts; among the catalysts examined magnesium chloride in pyridine gave the best results. Metal chlorides in pyridine also promoted the reaction of DPC with aromatic amines to give the corresponding ureas, and the direct synthesis of polyureas was achieved by the polycondensation of DPC with diamines in the presence of the chloride. 相似文献
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The coordinatively unsaturated 12-electron complex dichloro t-butylimido bispyridine titanium(IV) (2a) has been shown to react with CO(2) to give N,N-bis-t-butyl urea. Two analogous sterically hindered coordinatively saturated 14-electron complexes dichloro t-butylimido trispyridine titanium(IV) (10a) and dichloro 2,6-(i-Pr)(2)phenylimido trispyridine titanium(IV) (10b) also gave their corresponding symmetrical ureas upon treatment with CO(2). Further experiments support the intermediary of metallocycles formed from heterocumulene metathesis reactions. The unsymmetrical urea N-benzyl, N-t-butyl urea (11) was produced from treatment of 2,6-(i-Pr)(2)phenylimido trispyridine titanium(IV) (10b) with CO(2) and interception with BnNH(2). Equimolar quantities of N,N-bistrimethylsilybenzylamine or N,N-bistrimethylsilyphenethylamine were shown to promote the reaction between t-butylimido bispyridine titanium(IV) (2a) and CO(2) to give near quantitative yields of symmetrical urea. Other symmetrical ureas could be produced from TiCl(4), amine and CO(2) in moderate to quantitative yields depending on the stoichiometry of amine present. 相似文献
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催化选择氧化还原羰基化合成脲* 总被引:2,自引:0,他引:2
本文概述了胺硝基物选择氧化还原羰基化生成脲的新工艺路线。对催化剂体系、羰基化反应机理和反应的选择性作了比较全面的评述,着重介绍了金属钯和非金属硒催化的选择氧化还原羰基化反应合成对称脲、非对称脲和环脲,讨论了该方法的应用前景。 相似文献
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Gerald O. Schulz H. James Harwood 《Journal of polymer science. Part A, Polymer chemistry》1974,12(7):1451-1460
Pyrolysis of poly(tert-butyl N-vinylcarbamate) at 185–200°C in bulk yields a rigid foam containing cyclic urea units, primary amine units, and a small amount of urea crosslinks. The yield of primary amine units (ca. 13%) and the yields of carbon dioxide (ca. 57%), isobutylene (ca. 57%), and tert-butanol formed in this reaction indicate that it involves pairwise decomposition of adjacent carbamate units to form cyclic urea units, tert-butanol, carbon dioxide, and isobutylene. The vinyl amine units are formed from carbamate units that become flanked by urea units. The amounts of amine units and residual carbamate units were determined as a function of degree of pyrolysis by an ion-exchange technique and agreed with values expected for a random cyclization process. The pyrolyzed polymers are useful as ion-exchange resins and as rigid foams having good thermal stability. 相似文献
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Summary A two-step synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), carbon dioxide and methanol using heterogeneous
anion exchange resins as catalysts is reported. The first step is the reaction of EO with CO2 to form ethylene carbonate (EC), and the second one the transesterification of EC with methanol to yield DMC. Effect of various
reaction parameters on the activity and selectivity of the catalysts used was investigated. After the first step, the crude
mixture containing EC was directly reacted with methanol in the presence of a heterogeneous anion exchange resin catalyst
to produce DMC in high yield and selectivity. Our process is highly economic. 相似文献