Tetrahedron Green Chem最新文献

Nanostructured TiO₂ catalysts were synthesised via the sol-gel method using solvent-free titanium (IV) n-butoxide and acidified water at pH 1 in a continuous flow spinning disc reactor (SDR). The influence of disc rotational speed, total flow rate of the reagents, and molar hydrolysis ratio (molar ratio of the acidified water to the titanium (IV) n-butoxide) on the particle size, phase distribution, band gap energy and photocatalytic activity for CO₂ reduction was studied. Increasing the disc rotational speed from 400 ​rpm to 1400 ​rpm results in highly sheared, uniformly mixed thin films where small particles (up to ca. 40 ​nm mean diameter) with narrow particle size distribution (polydispersity index of up to 0.5) are formed even at the lower molar hydrolysis ratio of 113. Increasing the molar hydrolysis ratio from 113 to 301 favours anatase phase transformation to rutile phase, thus improving photocatalytic activity. Larger TiO₂ particles from the SDR are associated with an increase in their band gap energy whilst doping with copper narrows the band gap energy from 3.00 ​eV down to 2.53 ​eV.

The photocatalytic performance of the TiO₂ nanoparticles was evaluated for CO₂ reduction in the form of bicarbonate ions using a meso-structured photocatalytic reactor at a TiO₂ loading of 0.5 ​g L^-1 and flow rate of 4 ​mL min^-1. A formate production rate of 500 ​μmol ​g^-1 ​h^-1 is achieved after 2 ​h of irradiation (λ ​= ​254 ​nm) on a bare TiO₂ catalyst, with no apparent trend observed with SDR operating conditions used in the production of the nanoparticles. However, for copper-doped TiO₂, there is a clear correlation between the anatase to rutile ratio and formate production rate.

The synthesis of functionalized azetidines from azetines is poorly explored. Here, we report the safe and sustainable continuous flow hydrogenation of 2-azetines using ethyl acetate and CPME as environmentally responsible solvents. The chemoselective saturation of the endocyclic double bond of 2-azetines bearing additional functional groups sensitive to hydrogenation has been additionally disclosed. Moreover, the protocol has been successfully combined with the continuous flow preparation of the substrates, accessing to a bio-relevant azetidine through a telescoped multistep approach.

This study investigates acylation of chitin in deep eutectic solvents (DESs) as analogous solvents of ionic liquids (ILs), because we have already reported that such reaction smoothly progresses using acyl chlorides in the presence of pyridine/N,N-dimethyl-4-aminopyridine (DMAP) as base/catalyst in the IL, that dissolves chitin. In addition to a DES composed of 1-allyl-3-methylimidazolium chloride (AMIMCl) and thiourea (TUA) as hydrogen bond acceptor and donor (HBA and HBD), respectively, which we previously reported to dissolve chitin, several DESs were prepared from AMIMCl and different HBDs, that is, urea (UA), acetylthiourea (AcTUA), acetylurea (AcUA), and 1,1,3,3-tetramethylguanidine (TMG). These DESs were found to also dissolve chitin. Hexanoylation of chitin in the AMIMCl/TUA-DES under the same conditions, as those previously performed in the IL, i.e., using hexanoyl chloride in the presence of pyridine/DMAP at 100 ​°C for 24 ​h, gave the product with the low degree of substitution (DS). As this was speculated to be due to the high nucleophilicity of TUA, which had a potential to react with hexanoyl chloride, the other HBDs with lower nucleophilicity, mentioned above, were employed to be combined with AMIMCl in the DESs. When hexanoylation of chitin was carried out in the DESs composed of UA, AcTUA, AcUA, and TMG under the same conditions as above, the higher DS products were obtained. In particular, the reaction in the AMIMCl/TMG-DES efficiently occurred in the absence of pyridine/DMAP to produce the high DS product, probably owing to the high basicity and low nucleophilicity of TMG. The structure of the chitin hexanoate produced was evaluated by the IR and ¹H NMR measurements. Accordingly, acylation of chitin using various acyl chlorides was performed in the AMIMCl/TMG-DES under the conditions without the use of pyridine/DMAP to give the corresponding chitin acylates with the high DSs. This study achieves the facile and efficient acylation method of chitin in the DES.

The development of effective methodologies for the sustainable production of chemicals and biofuels from lignocellulosic biomass has attracted immense attention from the scientific community. However, it is challenging due to the highly complex nature of biomass sources. Over the past few decades, numerous reports targeting various catalytic biomass transformation reactions highlighting the vital role of the catalysts in substrate activation and product selectivity have appeared in the literature. Through this perspective, we present recent advances in metal complexes-based molecular catalysis for transforming biomass-derived 5-hydroxymethylfurfural (5-HMF) and furfural (FAL) to various industrially important chemicals, materials, pharmaceuticals, and biofuels. This article focuses on the catalytic transformation of 5-HMF and FAL involving hydrogenation, ring opening, hydrogenolysis, oxidation, and amination over molecular catalysts, to provide insights into the role of molecular catalytic systems explored in biomass transformation and allied areas.

This mini-review discusses Mg–Al hydrotalcite-based catalyst systems used for modified Friedländer quinoline synthesis. The metal-grafted Mg–Al hydrotalcites consist of both active metal species and base sites capable of advancing catalytic activity. The Ru-grafted catalysts are active for the oxidative dehydrogenation of 2-aminobenzyl alcohol to 2-aminobenzaldehyde, followed by the base-catalyzed condensation with ketones to 2-substituted quinolines. Fe-grafted Mg–Al hydrotalcites also act as heterogeneous catalysts for the one-pot synthesis at a slightly higher reaction temperature. For pure Mg–Al hydrotalcite, hydrogen transfer reactions occur to afford 2-aminobenzaldehyde intermediate with an alcohol, resulting in the consequent production of the corresponding quinolines. The reaction mechanism and substrate scope of each catalyst system are also discussed.

Gold photocatalysis includes a diverse set of gold-catalyzed processes with essentially distinctive fundamental stages. When photocatalysis and gold catalysis are combined, then it results to change the valence of the gold centre by electron transfer and radical addition without the usage of exogenous oxidants that are stoichiometrically sacrificed. A number of significant organic transformations are made possible by radicals' exceptional compatibility with gold catalysts. The photocatalysis using gold complexes opens up new opportunities for gold chemistry and complements the existing photoredox catalysis techniques admirably. In this review, the achieved transformations for mononuclear gold(I) catalysts (both those with and without a photosensitizer) and dinuclear gold(I) photocatalysts are discussed with a number of fascinating techniques, as well as their significance for organic chemists.

An organic solvent-free synthesis of sulfonyl hydrazides has been achieved in water. The reactions of equimolar amount of sulfonyl chlorides and hydrazines afforded a series of substituted sulfonyl hydrazides at 60 ​°C for 1 ​h in water as a solvent in the presence of triethylamine when hydrazines are hydrochlorides. Moderate to good yields were observed for this transformation by the simple operation (46–93%). The reaction of amines, anilines, alcohol, and phenol have also been investigated in water.

A metal-free, efficient, and eco-friendly on-water protocol for the synthesis of quinazolinone derivatives via a tandem one-pot three-component reaction using a novel, efficient, and recyclable heterogeneous catalyst, [CA@MIP] – melamine-based covalent organic polymer supported citric acid, has been described. The catalyst has been synthesized by a simple procedure and is well characterized by numerous spectroscopic techniques such as Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM), Powder X-ray diffraction (PXRD), Brunauer-Emmett-Teller (BET), Energy Dispersive X-ray (EDX), and Thermal Gravimetric (TG) analyses. [CA@MIP] showed excellent catalytic potential offering quinazolinones in excellent yields (>85%) in a short reaction time period and was reusable for up to five successive runs.

The use of biobased polymers or natural inorganic materials in place of synthetic polymers or liquid crystals derived from petroleum to fabricate optical components establishes the concept of “sustainable optics”, at least for what concerns the environmental dimension of sustainability as these polymers are renewable and often biodegradable or compostable. To identify the main obstacles to be addressed prior to industrial uptake of these polymeric resins in the optics industry, we focus on two promising and widely studied biobased polymeric materials, namely nanocellulose and poly(limonene carbonate). The conclusions have implications also for the emerging bioeconomy and the undergoing reshaping of the chemical industry driven by sustainability megatrend.