A Mechanistic Study on Alcohol Oxidations with Oxygen Catalysed by TPAP-Doped Ormosils in Supercritical Carbon Dioxide (original) (raw)
Related papers
Continuous heterogeneous catalytic oxidation of primary and secondary alcohols in scCO2
Green Chemistry, 2010
A miniature catalytic reactor has been developed for the oxidation of alcohols with O 2 in supercritical CO 2 . Particular attention has been given to ensuring good mixing of O 2 and CO 2 prior to contact with the substrate. The reactor was optimised using the oxidation of 2-octanol over 5% Pt + 1% Bi on Al 2 O 3 and the mass balance was measured. The reactor was then evaluated for the oxidation of a series of secondary alcohols, and also the primary alcohol, 1-octanol.
Journal of Catalysis, 2006
Cinnamyl alcohol was oxidized to cinnamaldehyde in a continuous fixed-bed reactor with molecular oxygen over an alumina-supported palladium catalyst in supercritical carbon dioxide modified with toluene. A strong dependence of the reaction performance on pressure and oxygen concentration in the feed was found. Optimization of the reaction conditions resulted in a higher catalytic activity than in the liquid phase. At 120 bar, 80 • C, and double stoichiometric oxygen concentration, a turnover frequency of 400 h −1 at a selectivity of 60% to cinnamaldehyde was achieved. Spectroscopic investigations and the knowledge of the selectivity pattern turned out to be crucial for a deeper understanding of the reaction allowing a rational optimization. Under almost all experimental conditions (even at high oxygen concentration) hydrogenated byproducts, stemming from internal hydrogen transfer reactions, were detected in the effluent. This indicated that alcohol dehydrogenation was the first reaction step; this finding was further confirmed by spectroscopic investigations. In situ XANES and EXAFS revealed that in the entire experimental range investigated, the palladium constituent was mainly in a reduced state, and its surface could be oxidized only in the absence of cinnamyl alcohol in the feed. Bulk-phase behavior studies and investigations at the catalyst-fluid interface, performed by visual inspection and combined transmission and ATR-IR spectroscopy, demonstrated that the reaction performed best in the biphasic region. Moreover, cinnamaldehyde and carbon dioxide, but hardly any toluene and cinnamyl alcohol, were detected inside the porous catalyst, indicating a significantly different product composition inside the porous catalyst compared with the bulk phase. (J.-D. Grunwaldt).
Advanced Synthesis & Catalysis, 2004
Hybrid organic-inorganic fluorinated silica glasses doped with the ruthenium species TPAP (tetra-n-propylammonium perruthenate) are effective catalysts for the aerial oxidation of benzyl alcohol to benzaldehyde in dense phase CO 2 . Moderate silica fluorination (10%) by short-chain fluoroalkyl-containing monomers in the sol-gel polycondensation with TMOS affords highly active catalysts which at 75 8C and 220 bar selectively dehydrogenate the alcohol with oxygen as primary oxidant. Both the activity and the stability of the fluorinated materials vary with the degree of fluorination and the nature of the fluoroalkyl residue attached to the silica polymeric network. An explanation of the behaviour of doped sol-gel oxides in supercritical carbon dioxide is proposed which is thought to be of general validity for future practical applications to heterogeneously catalysed aerobic oxidations eliminating the current need for both organic solvents and stoichiometric oxidants. Figure 4. TPAP-doped fluorinated silica gels (here are shown 50,000Â micrographs) show a smooth, compact geometry surface at lower fluorinations (C3F-10 and C8F-25: a and b, respectively) while the 50% fluoroalkyl-modified gel C8F-50 shows a globular non uniform surface (c).
FluoRuGel: a versatile catalyst for aerobic alcohol oxidation in supercritical carbon dioxide
Organic & Biomolecular Chemistry, 2006
FluoRuGel-a hybrid fluorinated silica glass doped with TPAP (tetra-n-propylammonium perruthenate)-is a versatile catalyst for the aerobic oxidation of different alcohols in dense phase CO 2 with marked stabilization and activity enhancement of perruthenate upon its confinement in the sol-gel fluorinated silica matrix. A brief competitive analysis shows large potential rewards.
Sol-Gel Entrapped TPAP: An Off-the-Shelf Catalyst Set for the Clean Oxidation of Alcohols
Current Organic Chemistry, 2008
Whether in supercritical CO 2 or in organic solvent and using O 2 or aqueous H 2 O 2 as primary oxidants, the series of sol-gel entrapped TPAP hybrid silica gels is a versatile class of oxidation catalysts suitable for the highly selective conversion of alcohols to carbonyls. These materials are generally more stable and active than traditional polymersupported analogues. This report summarizes recent findings showing the large potential of this technology for synthetic chemistry.
European Journal of Inorganic Chemistry
The oxidation of allylic and benzylic alcohols to aldehydes oxygen, in the presence of the bifunctional rutheniumcopper system (nPr 4 N)(RuO 4)-CuCl acting as the catalyst. can be carried out at room temperature with molecular The oxidation of alcohols to aldehydes and ketones is a species [RuCl 2 (PPh 3) 3 ] [6] , RuO 2 •xH 2 O [7] , the binuclear [Ru 2 O 6 (C 5 H 5 N) 4 ] • 3.5H 2 O [8] , the bimetallic system fundamental reaction in organic synthesis, and numerous oxidizing reagents are available to effect this key transfor-RuCl 3 ϪCo(OAc) 2 [9] and the triple catalytic system [Ru-Cl(OAc)(PPh 3) 3 ]ϪhydroquinoneϪ[Co(salophen)(PPh 3)] [10] mation. [1] In most instances, these reagents are used in stoichiometric amounts and are very often toxic such as the where H 2 salophen ϭ N,NЈ-bis(salicylidene)-O-phenylenediamine. However, these catalysts are rarely selective and are chromium oxidants used in vast amounts in both the laboratory and industry. [1] However, with the ever-growing en-often limited as rather high reaction temperatures and high pressures of molecular oxygen are required and low turn-vironmental and economic concerns the development of catalytic processes for alcohol oxidation is becoming in-over numbers are observed. Recently, during the preparation of our manuscript creasingly important. A particularly noteworthy process has been described by Ley [11] and Markó [12] have communicated the use of tetran-propylammonium perruthenate, (nPr 4 N)(RuO 4), in the Griffith et al. [2] who reported the use of the high oxidation state oxoruthenium compound tetra-n-propylammonium presence of molecular oxygen, as a catalytic oxidant of both primary and secondary alcohols. Markó [12] has also ob-perruthenate (nPr 4 N)(RuO 4), TPAP, as a mild catalyst for the oxidation of alcohols with N-methylmorpholine N-ox-served that the presence of CuCl • phenanthroline (5 mol-%) and K 2 CO 3 (200 mol-%) produced a retarding effect in the ide, NMO, as the secondary oxidizing source. More recently, we reported the catalytic oxidation of primary al-oxidation of 4-chlorobenzyl alcohol. We wish to communicate some of our recent results on a similar (nPr 4 N)(RuO 4) cohols to aldehydes with cis-dioxymolybdenum(VI) complexes and sulfoxides as the co-oxidant. [3] Although both of ϪCuCl bimetallic system which is a selective and efficient catalytic system for the oxidation of alcohols with molecu-the above function well as catalytic systems, unpleasant and harmful by-products, amine and sulfide respectively, are lar oxygen under mild conditions (25°C), producing water as the only stoichiometric by-product, Scheme 1. produced. This limits the use of these catalysts on an industrial scale. The quest for catalytic systems that use inexpen-The catalytic oxidation of various alcohols takes place smoothly at 25°C with (nPr 4 N)(RuO 4) (1 mol-%), CuCl (1 sive, nontoxic, molecular oxygen in the air as the secondary oxidant remains a particularly important goal for the devel-mol-%), and 2-aminopyridine (5 mol-%) in the presence of 1 atm of molecular oxygen in toluene, dichloromethane, or opment of a "green method" for converting alcohols to carbonyl products on an industrial scale. [4] acetonitrile. The results are presented in Table 1. The addition of powdered 4-Å molecular sieves results in slightly Relatively few ruthenium-based catalytic systems using air or molecular oxygen have been reported for the dehydro-increased rates, as previously observed in oxidations with (nPr 4 N)(RuO 4) and NMO. [2] This may be because the water genation of alcohols. These include the trinuclear ruthenium carboxylates [Ru 3 O(O 2 CR) 6 L 3 ] n (R ϭ CH 3 or formed as a by-product in the reaction degrades the catalyst. Allylic and benzylic alcohols are oxidized with nearly C 2 H 5 ; L ϭ H 2 O or PPh 3 ; n ϭ 0, ϩ1) [5] , the ruthenium(II) Scheme 1
Cinnamyl alcohol was oxidized to cinnamaldehyde in a continuous fixed-bed reactor with molecular oxygen over an alumina-supported palladium catalyst in supercritical carbon dioxide modified with toluene. A strong dependence of the reaction performance on pressure and oxygen concentration in the feed was found. Optimization of the reaction conditions resulted in a higher catalytic activity than in the liquid phase. At 120 bar, 80 • C, and double stoichiometric oxygen concentration, a turnover frequency of 400 h −1 at a selectivity of 60% to cinnamaldehyde was achieved. Spectroscopic investigations and the knowledge of the selectivity pattern turned out to be crucial for a deeper understanding of the reaction allowing a rational optimization. Under almost all experimental conditions (even at high oxygen concentration) hydrogenated byproducts, stemming from internal hydrogen transfer reactions, were detected in the effluent. This indicated that alcohol dehydrogenation was the first reaction step; this finding was further confirmed by spectroscopic investigations. In situ XANES and EXAFS revealed that in the entire experimental range investigated, the palladium constituent was mainly in a reduced state, and its surface could be oxidized only in the absence of cinnamyl alcohol in the feed. Bulk-phase behavior studies and investigations at the catalyst-fluid interface, performed by visual inspection and combined transmission and ATR-IR spectroscopy, demonstrated that the reaction performed best in the biphasic region. Moreover, cinnamaldehyde and carbon dioxide, but hardly any toluene and cinnamyl alcohol, were detected inside the porous catalyst, indicating a significantly different product composition inside the porous catalyst compared with the bulk phase. (J.-D. Grunwaldt).
DESALINATION AND WATER TREATMENT
Porous carbon xerogels were prepared from the sol-gel polymerization of resorcinol with formaldehyde (RF) followed by carbonization at a high temperature under argon atmosphere. The capacity of the carbon xerogels for direct immobilization of metal complexes was tested with a vanadium(IV) complex, [V IV O(HL)(H 2 O)(CH 3 OH)], which possesses an extended ligand π system and reactive hydroxyl groups on the L-tyrosine fragment. Textural characterization of the CXG and CXG/[V IV O(HL)(H 2 O)(CH 3 OH)] have been investigated using N 2 adsorption-desorption at −196°C. Chemical surface groups were analyzed by FT-IR spectroscopy. Nano-particle size and morphology of CXG and CXG/[V IV O(HL)(H 2 O)(CH 3 OH)] nano-particles have been characterized by scanning electron microscopy (SEM). Catalytic activity of CXG/[VO(HL)(H 2 O)(CH 3 OH)] was investigated in the aerobic oxidation of olefins. The reaction conditions have been optimized for solvent and temperature. CXG/[VO(HL)(H 2 O)(CH 3 OH)] showed higher catalytic activity for the epoxidation of unfunctionalized olefins with molecular oxygen in the presence of isobutyraldehyde. Comparison of the heterogenized catalyst, CXG/[VO(HL)(H 2 O)(CH 3 OH)], with the corresponding homogeneous catalyst, [VO(HL)(H 2 O)(CH 3 OH)], showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous counterpart. The heterogeneous catalyst was easily recovered from the reaction medium and could be re-used for other five runs without significant loss of activity.
Sol-Gel Ormosils Doped with TEMPO as Recyclable Catalysts for the Selective Oxidation of Alcohols
Advanced Synthesis & Catalyis, 2002
Organically modified silicas doped with TEMPO prepared via the sol-gel method are highly recyclable catalysts of the selective Montanari-Anelli oxidation of 1-nonanol; They show a notable ∫positive feedback∫ effect of matrix alkylation on the catalyst activity which is typical of doped sol-gel materials and markedly differentiates the behaviour of these materials from that of analogous silicasupported TEMPO.