scholarly journals New insights into the Lewis acidity of guanidinium species: Lewis acid interaction provides reactivity

2020 ◽  
Vol 23 (2) ◽  
pp. 185-199
Author(s):  
Muhammad Ageel Ashraf ◽  
Cheng Li ◽  
Fataneh Norouzi ◽  
Dangquan Zhang
Keyword(s):  
Lewis Acid ◽  
Lewis Acidity ◽  
Acid Interaction

scholarly journals Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 887
Author(s):  
Rujeeluk Khumho ◽  
Satit Yousatit ◽  
Chawalit Ngamcharussrivichai
Keyword(s):  
Natural Rubber ◽  
Lewis Acid ◽  
Value Added ◽  
Acid Sites ◽  
Superior Performance ◽  
Lewis Acidity ◽  
Lewis Acid Sites ◽  
Niobium Oxides ◽  
Silica Nanocomposite ◽  
Loading Amount

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

scholarly journals Fluorosilane Activation by Pd/Ni→Si–F→Lewis Acid Interaction: An Entry to Catalytic Sila-Negishi Coupling

2020 ◽  
Vol 142 (33) ◽  
pp. 14039-14044
Author(s):  
Hajime Kameo ◽  
Hiroki Yamamoto ◽  
Koki Ikeda ◽  
Tomohito Isasa ◽  
Shigeyoshi Sakaki ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Acid Interaction ◽  
Negishi Coupling

scholarly journals Unique reactivity of B in B[Ge9Y3]3 (Y = H, CH3, BO, CN): formation of a Lewis base

2019 ◽  
Vol 21 (42) ◽  
pp. 23301-23304
Author(s):  
G. Naaresh Reddy ◽  
Rakesh Parida ◽  
R. Inostroza-Rivera ◽  
Arindam Chakraborty ◽  
Puru Jena ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Lewis Base ◽  
Lewis Acidity ◽  
Boron Compounds ◽  
Zintl Ion ◽  
Acid Nature ◽  
Boron Center

Boron compounds usually exhibit Lewis acidity at the boron center due to the presence of vacant p-orbitals. But using Zintl-ion based groups (Ge9Y3, Y = H, CH3, BO, CN), we can alter Lewis acid nature of B to a Lewis base.

An umpolung of Lewis acidity/basicity at nitrogen by deprotonation of a cyclic (amino)(aryl)nitrenium cation

2018 ◽  
Vol 54 (35) ◽  
pp. 4390-4393 ◽  
Author(s):  
Jiliang Zhou ◽  
Liu Leo Liu ◽  
Levy L. Cao ◽  
Douglas W. Stephan
Keyword(s):  
Lewis Acid ◽  
Lewis Acidity ◽  
Acid Base ◽  
Neutral Compound

The cyclic (amino)(aryl)nitrenium cation 2 is Lewis acidic at nitrenium N1, reacting with PMe3 affording a Lewis acid/base adduct 3, while deprotonation of 2 provides the neutral compound 4 which is Lewis basic at N1.

Elucidating the secondary effect in the Lewis acid mediated anodic shift of electrochemical oxidation of a Cu(ii) complex with a N2O2 donor unsymmetrical ligand

2019 ◽  
Vol 48 (39) ◽  
pp. 14898-14913 ◽  
Author(s):  
Souvik Maity ◽  
Soumavo Ghosh ◽  
Ashutosh Ghosh
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Oxidation ◽  
Lewis Acid ◽  
Linear Dependence ◽  
Lewis Acidity ◽  
Secondary Effect ◽  
Vis Spectroscopy ◽  
Electrochemical Signal

The causes behind the fluctuations from a linear dependence of the electrochemical signal of a guest bound metalloligand [CuL] with the Lewis acidity of redox-inactive cations were established by using UV-vis spectroscopy and cyclic voltammetry.

scholarly journals Regenerable Acidity of Graphene Oxide in Promoting Multicomponent Organic Synthesis

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Virgilio D. Ebajo ◽  
Cybele Riesse L. Santos ◽  
Glenn V. Alea ◽  
Yuya A. Lin ◽  
Chun-Hu Chen
Keyword(s):  
Graphene Oxide ◽  
Organic Synthesis ◽  
Lewis Acid ◽  
Photoelectron Spectroscopy ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Epoxide Ring ◽  
Multicomponent Synthesis ◽  
Lewis Acid Sites ◽  
Toxic Reaction

Abstract The Brønsted acidity of graphene oxide (GO) materials has shown promising activity in organic synthesis. However, roles and functionality of Lewis acid sites remain elusive. Herein, we reported a carbocatalytic approach utilizing both Brønsted and Lewis acid sites in GOs as heterogeneous promoters in a series of multicomponent synthesis of triazoloquinazolinone compounds. The GOs possessing the highest degree of oxidation, also having the highest amounts of Lewis acid sites, enable optimal yields (up to 95%) under mild and non-toxic reaction conditions (85 °C in EtOH). The results of FT-IR spectroscopy, temperature-programed decomposition mass spectrometry, and X-ray photoelectron spectroscopy identified that the apparent Lewis acidity via basal plane epoxide ring opening, on top of the saturated Brønsted acidic carboxylic groups, is responsible for the enhanced carbocatalytic activities involving Knoevenagel condensation pathway. Recycled GO can be effectively regenerated to reach 97% activity of fresh GO, supporting the recognition of GO as pseudocatalyst in organic synthesis.

scholarly journals Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines

2015 ◽  
Vol 6 (3) ◽  
pp. 2016-2021 ◽  
Author(s):  
Michael H. Holthausen ◽  
Rashi R. Hiranandani ◽  
Douglas W. Stephan
Keyword(s):  
Lewis Acid ◽  
Lewis Acidity ◽  
Spatial Proximity ◽  
Acid Catalysts ◽  
Lewis Acid Catalysts ◽  
Acid Catalyzed

A series of electrophilic bis-fluorophosphonium dications dervied from diphosphines with naphthalene- and (oligo)methylene-linkers is presented. The resulting Lewis acidity is demonstrated to depend on the spatial proximity between the P moieties as evidenced in several Lewis acid catalyzed transformations.

Lewis acid sites in MOFs supports promoting the catalytic activity and selectivity for CO esterification to dimethyl carbonate

2020 ◽  
Vol 10 (6) ◽  
pp. 1699-1707 ◽  
Author(s):  
Yu-Ping Xu ◽  
Zhi-Qiao Wang ◽  
Hong-Zi Tan ◽  
Kai-Qiang Jing ◽  
Zhong-Ning Xu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Dimethyl Carbonate ◽  
Metal Organic Frameworks ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Catalyst Supports ◽  
Lewis Acid Sites ◽  
Metal Organic

We studied the effect of Lewis acidity in metal–organic frameworks (MOFs) on their activity as catalyst supports for the esterification of CO to dimethyl carbonate.

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