- Continuous Flow Synthesis of Urea-Containing Compound Libraries Based on the Piperidin-4-one Scaffold
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The advantages of performing reactions in continuous flow vs. the classic batch processes render flow chemistry a suitable technique for library synthesis. Inspired by our recent work to create fluorine-containing nitrogen heterocycles and by the potentia
- Riesco-Domínguez, Alejandra,Blanco-Ania, Daniel,Rutjes, Floris P. J. T.
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supporting information
p. 1312 - 1320
(2018/04/02)
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- Magnesium oxide nanosheets as effective catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol
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A series of MgO catalysts were prepared by thermal decomposition and precipitation methods. Their catalytic performance was evaluated in the synthesis of diethyl carbonate (DEC) from ethyl carbamate (EC) and ethanol. Among them, MgO prepared using sodium carbonate as the precipitant and calcined at 450°C (MgO-SC-450) exhibited much higher catalytic activity. An excellent DEC yield of 58.0% with a high DEC selectivity of 92.1% could be achieved over the MgO-SC-450 catalyst under optimized reaction conditions: 210°C, ethanol/EC molar ratio of 10, and 3 h. Moreover, the catalytic activity could be essentially retained during recycling experiments. The structure and surface basicity of the MgO catalysts were characterized by X-ray diffraction (XRD), Mastersizer 2000, N2 adsorption, field-emission scanning electron microscopy (FE-SEM), and temperature-programmed desorption of CO2 (CO2-TPD). It was found that MgO-SC-450 possessed nanosheet morphology. Furthermore, a larger amount of appropriate medium basic β sites of MgO-SC-450 with the peak located between 225°C and 275°C was favourable for obtaining much superior catalytic activity. Quasi in situ FT-IR experiments were carried out to elucidate the adsorption behaviours of reactants. It was found that EC could be effectively activated and ethanol could be dissociated to a strong nucleophilic ethoxy group by MgO. In addition, theoretical calculation proved the co-adsorption of EC and ethanol on the MgO surface. Based on the results of quasi in situ FT-IR experiments and theoretical calculation, a plausible reaction mechanism has been proposed for the catalytic reaction.
- Li, Fengjiao,Li, Huiquan,Wang, Liguo,He, Peng,Cao, Yan
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p. 1021 - 1034
(2015/02/19)
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- N-substituted carbamates syntheses with alkyl carbamates as carbonyl source over Ni-promoted Fe3O4 catalyst
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A series of catalysts of magnetic iron oxide containing Ni with different nickel content were prepared with co-precipitation method and tested in the syntheses of N-substituted carbamates from various amines and alkyl carbamates. Under the optimized reaction conditions, various N-substituted carbamates were successfully synthesized with 90-98% isolated yield. The catalyst could be recovered based on the magnetic property of the catalyst and reused for five runs without deactivation. The catalysts were characterized with X-ray photoelectron spectroscopy, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption, and Moessbauer spectroscopy analyses. The results showed that the catalytic activity may be derived from the delicate synergy between Ni and Fe species resulted in specific basic sites. Quasi in situ FT-IR and isotopic tracer revealed that the formation of substituted urea was the key step and the N-substituted carbamate was formed via further alcoholysis of the substituted urea.
- Shang, Jianpeng,Guo, Xiaoguang,Shi, Feng,Ma, Yubo,Zhou, Feng,Deng, Youquan
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scheme or table
p. 328 - 336
(2011/05/14)
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- Process for making dialkyl carbonates
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A process for the production of dialkyl carbonates from the reaction of alcohol, for example C1-C3 alcohols, with urea is disclosed wherein the water and ammonium carbamates impurities in the feed are removed in a prereactor. The water is reacted with urea in the feed to produce ammonium carbamate which is decomposed along with the ammonium carbamates originally in the feed to ammonia and carbon dioxide. In addition some of the urea is reacted with the alcohol in the first reactor to produce alkyl carbamate which is a precursor to dialkyl carbonate. Dialkyl carbonates are produced in the second reaction zone. The undesired by-product N-alkyl alkyl carbamates are continuously distilled off from the second reaction zone along with ammonia, alcohol and dialkyl carbonates under the steady state reactor operation. N-alkyl alkyl carbamates can be converted to heterocyclic compounds in a third reaction zone to remove as solids from the system.
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Page/Page column 10; 11
(2008/06/13)
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- Specificity of DNA alkylation by 1-(2-chloroethyl)-3-alkyl-3- acyltriazenes depends on the structure of the acyl group: Kinetic and product studies
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The reactions of calf thymus DNA with ten 1-(2-chloroethyl)-3-alkyl-3- acyltriazenes of varying acyl side chain structure were studied alone, or in the presence of porcine liver esterase in pH 7.0 phosphate buffer. In several of the key triazenes, the acyl substituent contained a free carboxylic acid group. With esterase present in the reaction mixture, the resultant levels of DNA alkylation could be correlated with the kinetic rates of decomposition of the triazenes. Under these conditions, the predominant pathway of decomposition involved deacylation of the parent triazene and eventual production of an alkanediazonium ion. This intermediate subsequently alkylated DNA-guanine to give 7-alkylguanine as the principal reaction product. In the absence of esterase, the order of DNA alkylation for all of the acyltriazenes did not correlate with their respective rates of decomposition, leading to the conclusion that the triazenes did not decompose by the expected mode of uncatalyzed N(2)-N(3) heterolyic cleavage. The major DNA alkylation product from the N(3)-methyltriazenes was 7-methylguanine, instead of the expected 7-(chloroethyl)- and 7-(hydroxyethyl)guanine products, which suggested that the acyl group was being hydrolyzed. However, acyltriazenes with an N(3)-benzyl group rather than a methyl in this position produced very little 7-benzylguanine product, contrary to prediction. An alternative mechanism involving internally assisted hydrolysis of the side chain ester is proposed to explain these results. NMR product analysis and computational studies were carried out to lend support to the postulated mechanism.
- Smith,Schmidt,Czerwinski,Taneyhill,Snyder,Kline,Michejda,Smith Jr.
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p. 466 - 475
(2007/10/03)
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- The reactions of organoboranes with N-chloro-N-sodiocarbamates: A novel synthesis of N-alkylcarbamates
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Trialkylboranes react with N-chloro-N-sodiocarbamates to form N-alkylcarbamates in yields ranging from 50-88%. The reaction is best carried out without intermediate isolation of the N-chlorocarbamate salt. Only one of the alkyl groups of the trialkylborane is utilized.
- Wachter-Jurcsak,Scully Jr.
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p. 5261 - 5264
(2007/10/02)
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- Halogenation Using Quatenary Ammonium Polyhaloides. IX. One-Step Syntheses of Acylureas and Carbamates from Amides by Use of Tetrabutylammonium Tribromide and DBU
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The reaction of amides with tetrabutylammonium tribromide (TBA Br3) (0.5 equiv) and DBU (one equiv) in dichloromethane at room temperature gave N-substituted acylureas in fairly good yields.In the presence of alcohols, the reaction of amides with TBA Br3 (one equiv) and DBU (two equiv) gave N-substituted carbamates.
- Fujisaki, Shizuo,Tomiyasu, Kazushi,Nishida, Akiko,Kajigaeshi, Shoji
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p. 1401 - 1403
(2007/10/02)
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- Orthoamides, XXXVIII. - Contributions to the Chemistry of Orthocarbonic Acid Esters and α,α,α-Trialkoxyacetonitriles
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The reactivity of the orthocarbonates 4 and the nitriles 1 has been investigated.Carboxylic acids are esterified by 4b. Orthocarbonates 4c-f and 9b are prepared by transesterification of 4b.Mixed substituted orthocarbonates 8c-f are obtained from the nitriles 1a,b.The nitriles 2a and 3a react with alkali alcoholate in alcohol to yield the orthocarbamic acid esters 13a,b. Spirocyclic orthocarbonates 17a-d are prepared from 4b and 1,2 or 1,3-dioles, respectively. The reaction of phenol with 1b affords the mixed substituted orthocarbonate 18a. Catechol is converted by 1a into the orthocarbonate 20a.Reactions of 4b with amines and ami ne derivatives are studied. In the course of these investigations guanidines 21, imidocarbonic acid esters 22a-c, 30, carbamic acid esters 25, ureas 26, the isourea derivative 29, as well as the 1,3,4-oxadiazole 31 are prepared. The mechanism of these reactions is discussed. Imidocarbonic acid esters 22d-f, 38, N-cyanocarbamates 39, and isoureas 37 can be prepared from 1b and amines or amine derivatives. 2a as well as 13b react with cyanamide to give the N-cyanoisourea 40. Ureas 26 are formed in the reaction of 1a,b with secondary amines at elevated temperatures.The guanidinium cyanide 41a can be obtained by reaction of pyrrolidine with 1b in ether, whereas under similiar conditions from 1a and pyrrolidine the amidine 42 is produced. o-Aminophenol, o-phenylenediamine and anthranilic acid are cyclized by 4b or 1b to afford the heterocyclic compounds 43-45. α- and β-amino acids are transformed by 4b or 1b into the N-(ethoxycarbonyl)amino acid esters 46 and 47, respectively.
- Kantlehner, Willi,Maier, Thomas,Loeffler, Wolfgang,Kapassakalidis, Joanis J.
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p. 507 - 529
(2007/10/02)
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- Nucleophilic Substitutions to Carbonic Acid Derivates. XII. Kinetics and Mechanism of the Reaction of N-Nitro-N-alkyl-urethanes with Primary Aliphatic Amines
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The aminolysis of N-alkyl-N-nitrourethanes takes place, as the kinetical studies demonstrate, by means of several consecutive steps.The nucleophilic attack of the amine (first step; reaction B), as well as the proton-transfere (second step; reaction C), are quick pre-equilibres, followed by the slow, rate-determining elimination of the nitramino-group (reaction D).During the deprotonation, an intermediate with two to the nitramino-group antiperiplanar orbitals is formed, providing the necessary mesomeric assistance of the elimination.
- Bacaloglu, R.,Prodan-Deac, Y.,Csunderlik, C.,Csomos, P.
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