Solvent-free Catalysis Research Articles

Environmentally Benign Organic Synthesis Based on Solvent-free Catalysis

Environmentally Benign Organic Synthesis Based on Solvent-free Catalysis

Graphdiyne anchored ultrafine Ag nanoparticles for highly efficient and solvent-free catalysis of CO2cycloaddition

Composite catalysts of 3D sponge-like porous Pyr-GDY anchored capping agent free ultrafine Ag NPs were constructed, which displayed a record-high catalytic activity towards solvent-free CO2cycloaddition with propargylamines.

Integrated fast-mass transfer and high Ti-sites utilization into hybrid amphiphilic TS@PMO catalyst towards efficient solvent-free methyl oleate epoxidation

For solvent-free catalytic oxidations, low efficiency resulted from poor mass transfer and insufficient utilization of active centers remains a tough problem. Herein, we demonstrate a novel hybrid core-shell catalyst (TS@PMO) with an amphiphilic shell and a Ti-surface-enriched mesoporous TiO2-SiO2 (TS) core to address this challenge. Such TS@PMO realizes its amphiphilicity via an ex situ formed periodic mesoporous organosilica (PMO) shell. Simultaneously, by a unique etching effect induced by organic precursor growth on [SiO4] tetrahedra in TS core, active Ti sites are facilely enriched in near-surface layer of core and extra mesoporous cavities are introduced for substrate reservation. When applied for solvent-free epoxidation of methyl oleate (MO) with H2O2, TS@PMO exhibits remarkably boosted catalytic activity (X = 90.2%) and epoxide selectivity (S = 70.2%), overwhelming the unmodified titanosilicate (X = 63.7%, S = 49.2%) and Ti-containing organosilica (X = 39.8%, S = 25.0%). Such result benefits from an evidently enhanced interphase mass transfer and sufficiently accessible active Ti sites in TS@PMO. On the one hand, amphiphilic PMO shell can efficiently collect hydrophobic substrate and H2O2, while abundant mesopores in the shell offer open-path for them to access active sites in the core; on the other hand, an increased framework Ti (IV) density and their surface-enrichment in TS core greatly improve the utilization of active Ti sites. This study effectively makes up for the deficiencies of slow mass transfer and insufficient utilization of conventional titanosilicates in biphasic reactions, which paves a new avenue to exploit other hybrid catalysts for high-efficiency solvent-free catalysis.

Feasibility Study on the Etherification of Fermentative-Produced Isobutylene to Fully Renewable Ethyl Tert-Butyl Ether (ETBE)

This work evaluates the direct etherification of bio-sourced isobutylene with ethanol forming fully renewable ethyl tert-butyl ether (ETBE). Challenge was the use of the fermentative produced substrate in a solvent-free catalysis using the acidic ion exchanger Amberlyst-15. CO2 impurities have a significant influence on the liquid phase process. The conversion at a ratio that is based on molarities of isobutylene to ethanol of 1:0.9 results in yields up to 97 mol% ETBE. Purities up to 99 wt.% could be achieved by subsequent water extraction in order to ensure qualities for technical application as high performance fuel additive.

Magnetic nanoparticle-supported ferrocenylphosphine: a reusable catalyst for hydroformylation of alkene and Mizoroki–Heck olefination

This study was focused on regioselective, re-usable and solvent-free catalysis using Fe3O4@dop-BPPF nanomaterials.

Theoretical Studies on Muti‐Hydroxyimides as Highly Efficient Catalysts for Aerobic Oxidation

N,N-dihydroxypyromellitimide (NDHPI) and N,N',N''-trihydroxyisocyanuric acid (THICA) have been recently demonstrated to act as better carbon-radical-producing catalysts than the popular N-hydroxyphthalimide (NHPI). To gain a mature understanding of these particular catalysts, herein their geometrical, electronic, and thermochemical properties, as well as their catalytic activities, have been systemically investigated by a theoretical analysis. It appears that THICA, unlike NDHPI and NHPI, is unsuitable for solvent-free catalysis or catalysis in aprotic solvents due to its favorable coexistent planar conformer. Besides, the more remarkable catalytic efficiencies of NDHPI and THICA compared to NHPI can be ascribed to the lower barriers and the endothermicity in the H-abstraction processes by their radicals, especially by their multi-radicals which show stronger electron-withdrawing effects. Furthermore, the generation of THICA radicals would be much feasible at high temperature without co-catalysts. This study provides a new perspective towards the rational design of reactive hydroxyimide organocatalysts for industrial applications.

Enzyme catalysis with small ionic liquid quantities

Enzyme catalysis with minimal ionic liquid quantities improves reaction rates, stereoselectivity and enables solvent-free processing. In particular the widely used lipases combine well with many ionic liquids. Demonstrated applications are racemate separation, esterification and glycerolysis. Minimal solvent processing is also an alternative to sluggish solvent-free catalysis. The method allows simplified down-stream processing, as only traces of ionic liquids have to be removed.

Triphase, solvent-free catalysis over the TS-1/H 2O 2 system in selective oxidation reactions

Solvent-free, triphase conditions (solid-liquid-liquid) used in the oxidation of various organic substrates over the TS-1/H 2O 2 system (vis-à-vis conventionally used biphase conditions in the presence of a co-solvent) exhibit: (i) significant enhancement (3–10 times) in the reaction rates in the hydroxylation of aromatics (such as benzene, toluene, anisole and benzyl chloride), along with a reversal in regioselectivity of the products of substituted benzenes; and (ii) Baeyer-Villiger (BV) oxidation/rearrangement of cyclohexanone and acetophenone. In the case of benzyl chloride, triphase conditions resulted in the ring hydroxylation forming p-hydroxy and o-hydroxy benzyl chloride (75%) ( para:ortho ratio 85:15) along with side-chain oxyfunctionalization followed by HCl removal directly forming benzaldehyde (no formation of benzyl alcohol through hydrolysis). During BV oxidation, cyclohexanone and acetophenone gave caprolactone and phenyl acetate, respectively, as major products (70–90% selectivity). The other reaction was ring oxidation (30-10%) to hydroxy cyclohexanone and corresponding diketones (cyclohexanone) or hydroxy-acetophenones (acetophenone). Addition of a catalytic amount of mineral acid (H 2SO 4) significantly increased the conversion. Such reaction routes do not occur at all in the presence of co-solvent under biphase conditions. Factors responsible for enhancement in activity, change in regioselectivity and new routes are: (i) relative hydrophobic nature and restricted pore dimensions of titanium silicates; (ii) competitive diffusion of substrate with co-solvent; and (iii) Brönsted acidity of titanium silicates in the presence of H 2O 2 and water. Thus the present study opens up a new area where titanium silicate will be quite useful in various organic transformations, in an eco-safer way.