9003-31-0Relevant articles and documents
Mechanisms of Methylenecyclobutane Hydrogenation over Supported Metal Catalysts Studied by Parahydrogen-Induced Polarization Technique
Salnikov, Oleg G.,Burueva, Dudari B.,Kovtunova, Larisa M.,Bukhtiyarov, Valerii I.,Kovtunov, Kirill V.,Koptyug, Igor V.
, (2022/03/15)
In this work the mechanism of methylenecyclobutane hydrogenation over titania-supported Rh, Pt and Pd catalysts was investigated using parahydrogen-induced polarization (PHIP) technique. It was found that methylenecyclobutane hydrogenation leads to formation of a mixture of reaction products including cyclic (1-methylcyclobutene, methylcyclobutane), linear (1-pentene, cis-2-pentene, trans-2-pentene, pentane) and branched (isoprene, 2-methyl-1-butene, 2-methyl-2-butene, isopentane) compounds. Generally, at lower temperatures (150–350 °C) the major reaction product was methylcyclobutane while higher temperature of 450 °C favors the formation of branched products isoprene, 2-methyl-1-butene and 2-methyl-2-butene. PHIP effects were detected for all reaction products except methylenecyclobutane isomers 1-methylcyclobutene and isoprene implying that the corresponding compounds can incorporate two atoms from the same parahydrogen molecule in a pairwise manner in the course of the reaction in particular positions. The mechanisms were proposed for the formation of these products based on PHIP results.
A mild method for the replacement of a hydroxyl group by halogen: 3. the dichotomous behavior of α-haloenamines towards allylic and propargylic alcohols
Munyemana, Fran?ois,Patiny, Luc,Ghosez, Léon
, (2021/06/07)
A study of the deoxyhalogenation of allylic and propargylic alcohols with tetramethyl-α-halo-enamines is reported. Primary allylic and primary and secondary propargylic alcohols gave the corresponding halides in high yields. Secondary allylic and propargylic alcohols yielded the corresponding secondary halides but the reaction also produced some rearranged primary halides (I > Br > Cl). The reactions with tertiary allylic and tertiary propargylic alcohols gave several products and was therefore of little synthetic value. However, the addition of triethylamine to the reaction mixture or the use of lithium alkoxide instead of alcohol brought about a major change of the course of the reaction which led to amides carrying an allyl or an allenyl group at C2. This was shown to result from a Claisen-Eschenmoser rearrangement of an intermediate α-allyloxy- or propargyloxy-enamine.
Study on heteropolyacid-based catalysts with high activity and reusability for isoprene synthesis from formaldehyde and isobutene
Wang, Qingxue,Luo, Xu,Liu, Li,Tao, Shenghui,Xu, Shan
, p. 5371 - 5381 (2021/04/06)
Silica-supported heteropolyacid catalysts with different pore structures were synthesizedviaimpregnation method using silicalite-1 with three-dimensional MFI structure, two-dimensional hexagonal SBA-15 and amorphous silica as supports. Moreover, these catalysts were employed for the gas phase one-step synthesis of isoprene from isobutene and formaldehyde. The result showed that the activity of silicotungstic acid supported on silicalite-1 (SiW/S-1) catalysts was significantly better than that on other supports, which indicates that the three-dimensional MFI structure and suitable pore size of silicalite-1 were more conducive to the production of isoprene. Furthermore, the formation rate of isoprene over 20% SiW/S-1 catalyst reached up to 8.5 times that on the bulk silicotungstic acid catalyst, which could be attributed to the highly dispersed silicotungstic acid and the suitable acidity produced by the strong interaction between silicotungstic acid and silicalite-1. In addition, the 20 wt% SiW/S-1 catalyst exhibited excellent reusability and was reused 10 times without obvious loss of activity.
Method for preparing isoprene
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Paragraph 0039-0111, (2021/04/14)
The invention relates to a method for preparing isoprene by catalyzing isobutene and a formaldehyde solution through metal-doped cerium dioxide. Isobutene and a formaldehyde solution are used as reaction substrates, and under the action of a doped cerium dioxide catalyst, isoprene is prepared through Prins condensation, hydrolysis and dehydration. According to the method, isoprene can be obtained from isobutene and a formaldehyde solution in one step, and the catalyst is good in stability.
Piperazine-promoted gold-catalyzed hydrogenation: The influence of capping ligands
Barbosa, Eduardo C. M.,Camargo, Pedro H. C.,Fiorio, Jhonatan L.,Hashmi, A. Stephen K.,Kikuchi, Danielle K.,Rossi, Liane M.,Rudolph, Matthias
, p. 1996 - 2003 (2020/04/22)
Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold-ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand-metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.
Isoprene Synthesis from Formaldehyde and Isobutylene in the Presence of Aluminum- and Niobium-Containing BEA Catalysts
Chistov, D. L.,Drozhzhin, V. R.,Ivanova, I. I.,Kots, P. A.,Ponomareva, O. A.,Rodionova, L. I.
, p. 942 - 949 (2020/09/02)
Abstract: A single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of Al–BEA and Nb–BEA zeolite catalysts containing different amounts of aluminum and niobium has been studied. The physicochemical properties of the catalysts have been studied by low-temperature nitrogen adsorption, infrared spectroscopy of adsorbed CO, X-ray fluorescence analysis, and ammonia TPD methods. Catalytic tests have shown that, at similar formaldehyde conversion values, the isoprene selectivity is higher in the presence of the Al-containing BEA catalysts. It has been found that Al–BEA with Si/Al = 12 exhibits the highest activity in isoprene synthesis.
Effects of steam on toluene hydrogenation over a Ni catalyst
Atsumi, Ryosuke,Kobayashi, Keisuke,Xieli, Cui,Nanba, Tetsuya,Matsumoto, Hideyuki,Matsuda, Keigo,Tsujimura, Taku
, (2019/12/23)
The catalytic toluene hydrogenation over Ni/SiO2 was carried out using H2 or a H2/H2O mixture. The toluene conversion and MCH selectivity were evaluated under partial steam pressures 0?10 kPa, at H2/t
Highly efficient synthesis of isoprene from methyl tert-butyl ether and formaldehyde over activated carbon supported silicotungstic acid catalysts
Wang, SaiSai,Chen, Xingkun,Tan, Yuan,Zhao, Ziang,Yang, Wenshao,Huang, Chuanqi,Wang, Xuepeng,Chen, MiaoMiao,Du, Zhongnan,Ding, Yunjie
, (2020/02/28)
In this contribution, we reported the liquid single-stage synthesis of isoprene from methyl tert-butyl ether (MTBE) and formaldehyde over activated carbon supported silicotungstic acid (STA/AC) catalysts. In comparison with the corresponding homogeneous STA catalysts, the STA/AC catalysts exhibited much higher activity of the prins condensation reaction under the same conditions. The results could be attributed to the highly dispersed STA, the relative weaker acidity resulting from the strong interaction between STA and AC and the structural collapse of STA. Additionally, the catalyst could be reused at least 3 times with only a slight decrease of activity. The physical and chemical properties of the STA/AC catalysts were characterized by means of DRIFT, HRTEM, HAADF-STEM, NH3-TPD, XRD, XPS and TG techniques. The excellent catalytic reactivity and easy recycling advantages make the STA/AC catalyst to be an attractive candidate of the prins reactions in the future.
Thermal Behavior Analysis of Two Synthesized Flavor Precursors of N-alkylpyrrole Derivatives
Ai, Lvye,Liu, Mengzhen,Ji, Xiaoming,Lai, Miao,Zhao, Mingqin,Ren, Tianbao
, p. 2389 - 2397 (2019/08/01)
To expand the library of pyrrole-containing flavor precursors, two new flavor precursors—methyl N-benzyl-2-methyl-5-formylpyrrole-3-carboxylate (NBMF) and methyl N-butyl-2-methyl-5-formylpyrrole-3-carboxylate (NUMF)—were synthesized by cyclization, oxidation, and alkylation reactions. Thermogravimetry (TG), differential scanning calorimeter, and pyrolysis–gas chromatography/mass spectrometry were utilized to analyze the thermal degradation behavior and thermal degradation products of NBMF and NUMF. The TG-DTG curve indicated that the maximum mass loss rates of NBMF and NUMF appear at 310 and 268°C, respectively. The largest peaks of NBMF and NUMF showed by the differential scanning calorimeter curve were 315 and 274°C, respectively. Pyrolysis–gas chromatography/mass spectrometry detected small molecule fragrance compounds appeared during thermal degradation, such as 2-methylpyrrole, 1-methylpyrrole-2-carboxylic acid methyl ester, limonene, and methyl formate. Finally, the thermal degradation mechanism of NBMF and NUMF was discussed, which provided a theoretical basis for their application in tobacco flavoring additives.
Isoprene Synthesis from Formaldehyde and Isobutylene over Zeolite Catalysts
Ponomareva,Chistov,Kots,Ivanova
, p. 711 - 718 (2019/08/13)
Abstract: Single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of zeolite catalysts of the MFI, BEA, and FAU(Y) framework types and Al–BEA, Zr–BEA, Sn–BEA, and Nb–BEA catalysts synthesized by isomorphous substitution methods has been studied. Catalytic tests have shown that the isoprene yield increases in the following order: Zr–BEA Sn–BEA Nb–BEA Al–BEA, which is in agreement with the content of Br?nsted acid sites in the samples, whereas the formation of the major byproduct—carbon monoxide resulting from the decomposition of formaldehyde—increases with an increase in the number of Lewis acid sites. Comparison of the catalytic properties of zeolites of the different framework types has shown that the highest isoprene selectivity is exhibited by medium-pore MFI zeolites with a pore diameter of 5.5 ?.
