China
Africa
Explore chapters and articles related to this topic
Imidazolium Hydroxides and Catalysis
Published in Pedro Lozano, Sustainable Catalysis in Ionic Liquids, 2018
Michael additions were the first base catalyzed process to be intentionally studied using an imidazolium hydroxide catalyst, in this case [C4C1im][OH].23 This original study examined 1,3-dicarbonyl compounds as Michael donors with ketone, ester, and nitrile substituted acceptors (Scheme 4.3). Notably, the ester and nitrile substituted acceptors formed bis-addition products, while ketone acceptors formed only the anticipated monosubstituted compounds. Given the use of [C4C1im][OH] at 0.6 equivalents, diluted only by reagents, significant carbene concentrations would likely be present. Similar 1,3-dicarbonyl substrates have been shown to react at comparable rates using only 2.5 mol% of a closely related imidazol-2-ylidine carbene.29 For the carbene catalyzed processes, substrates which were capable of undergoing bis-addition were not examined, so direct comparison with the [C4C1im][OH] conditions cannot be made. While it cannot be conclusively determined whether the reactivity observed is exclusively due to the presence of carbenes, it does indicate that these Michael additions can be catalyzed by the carbenes present in the [C4C1im][OH] solution.
Name Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Using KSF montmorillonite, Bigi et al. (1999b) synthesized compound (4) by heating (1), (2), and (3) at 100°C in water or toluene, and even in the absence of any solvent. Indeed, they were able to obtain 3,4-dihydropyrimidin-2(1H)-one in 82% yield and with 98% selectivity by heating the three components at 130°C for 48 h under solvent-free conditions. Similar results were obtained by substituting different aromatic and aliphatic aldehydes for benzyl aldehyde (Scheme 5.6; compound 1), and β-dicarbonyl compounds for ethyl acetoacetate (Scheme 5.6; compound 2).
Catalytic Asymmetric Michael Addition of Ketones to Nitroalkenes
Published in Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera, Catalytic Asymmetric Reactions of Conjugated Nitroalkenes, 2020
Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera
The reactivity of 1,3-dicarbonyl compounds and aldehydes with nitroalkenes in the presence of various chiral catalysts has been described in the last two chapters. This chapter deals with the similar reaction of ketones as carbon-centered nucleophiles under the influence of a wide variety of chiral organo- and metal-ligand complex as catalysts. Thus, enolates derived from various alkyl and aryl ketones as well as activated ketones, such as α-ketoesters/amides/sulfones/phosphonates and β-ketosulfones, participate in the Michael addition to nitroalkenes to afford synthetically useful δ-nitroketones.
BNPs@Cur-Pd as a versatile and recyclable green nanocatalyst for Suzuki, Heck and Stille coupling reactions
Published in Journal of Experimental Nanoscience, 2020
Muhammed Ali Jani, Kiumars Bahrami
In the BNPs@Cur spectrum, the broad peak at 3416 cm−1 corresponds to the stretching vibrations of hydrogen-bonded OH groups in phenolic rings of Curcumin. The three peaks at 2852, 2924 and 2954 cm−1 indicate the stretching vibrations of sp3 C–H for CH2 alkane groups. The broadening spectrum in the range of 1600–1715 cm−1 is due to C = O enol-keto tautomer and C = C stretching vibrations. The Keto form of dicarbonyl in the Curcumin molecule shows the vibration at 1693 cm−1 while its enolic form appears at 1622 cm−1. The peak at 1454 cm−1 is related to aromatic C–C stretching vibrations as well as bending vibration of alkane C–H. Also, the peak at 1094 cm−1 indicates the Si–O vibration mode in the BNPs@Cur structure. The existence of BNPs indicative bands in the BNPs@Cur-Pd spectra may be related to the presence of free Al–OH which couldn’t react with CPTES due to some spherical hindrances.
Dicarboxylic acids and related compounds in fine particulate matter aerosols in Huangshi, central China
Published in Journal of the Air & Waste Management Association, 2019
Hongxia Liu, Kimitaka Kawamura, Bhagawati Kunwar, Junji Cao, Jiaquan Zhang, Changlin Zhan, Jingru Zheng, Ruizhen Yao, Ting Liu, Wensheng Xiao
Oxalic acid (C2) was detected as the most abundant diacid, followed by phthalic (Ph), terephthalic (tPh), succinic (C4), azelaic (C9), and adipic (C6) acids in PM2.5 samples from Huangshi (HS), central China. Glyoxylic (ωC2) acid was the dominant oxoacid, followed by 9-oxononanoic (ωC9) and pyruvic (Pyr) acids. Glyoxal (Gly) was the dominant α-dicarbonyl. We found seasonal changes in the molecular distributions of DARCs; the highest concentrations were found for C2, ωC2, and C9 in autumn, for C4, Pyr, C3, and C6 in spring, and for Ph, ωC9, and Gly in summer, whereas the lowest values were observed for all the DARCs in winter. Based on monthly variations and correlation coefficients of selected DARCs, this study indicates that primary emissions from anthropogenic sources in winter and spring and secondary SOA formation via the oxidation of unsaturated fatty acids in summer are both important sources of DARCs in HS aerosols.
A novel poly(ethyleneoxide)-based magnetic nanocomposite catalyst for highly efficient multicomponent synthesis of pyran derivatives
Published in Green Chemistry Letters and Reviews, 2018
Ali Maleki, Mojtaba Azizi, Zeynab Emdadi
Heterocycles are an important class of molecules with wide variety. Most of them are biological active molecules. 2-Amino-4H-pyran derivatives are one of the important heterocyclic compounds with various biological and pharmaceutical activities such as antitumor, antibacterial, antiviral, antiallergic, spasmolytic, diuretic, anti-coagulant, and anti-anaphylactic. In addition, these compounds are used in the treatment of Alzheimer, Schizophrenia, and Mycolonous diseases (5–8). Furthermore, they are building blocks of some natural products (9–13). 2-Amino-4H-pyrans are also useful as photoactive materials (14,15). MCR between an aryl aldehyde, malononitriles, and 1,3-dicarbonyl compounds that produce 2-amino-4H-pyrans is widely studied. Some examples of the catalysts used for synthesis are molecular Iodine (16), Ammonia solution (17), Urea (5), MgO (6), Mg/La (18), SiO2 (19), SnCl2/nano-SiO2 (20), Cu(II) oxymetasilicate (21), KF-Al2O3 (22), ionic liquids like [2-aemim][PF6] (23), C4(DABCO-SO3H)2.4Cl (24), and chitosan-CTAB (25). Most of published reports in the literature suffer from disadvantages such as high temperature, non-recyclable catalyst and long reaction time, use of volatile solvent and tedious work-up procedures. Therefore, still finding an efficient method for green synthesis of 4H-pyrans seems necessary.