Showing papers on "Benzaldehyde published in 2002"

Oxidation, ignition and combustion of toluene: Experimental and detailed chemical kinetic modeling

Abstract: The oxidation of toluene was studied in a jet-stirred reactor at 1 atm. New experimental results were obtained over the high temperature range 1000–1375 K, and variable equivalence ratio (0.5 ⩽ φ ⩽ 1.5). Concentration profiles of reactants, stable intermediates and final products were measured by probe sampling followed by on-line and off-line GC analyses. These experiments were modeled using a detailed kinetic reaction mechanism (120 species and 920 reactions, most of them reversible). This kinetic scheme was also used to simulate the ignition of toluene–oxygen–argon mixtures and the burning velocities of toluene–air mixtures. The presently proposed mechanism has already been validated by simulating the oxidation of benzene at 0.46 to 10 atm under stirred-reactor conditions, the ignition of benzene–oxygen–argon mixtures and the combustion of benzene in flames. Sensitivity analyses and reaction path analyses, based on species rates of reaction, were used to interpret the results. The routes involved in toluene oxidation have been delineated: toluene oxidation proceeds via the formation of benzyl, by H-atom abstraction, and the formation of benzene, by H-atom displacement yielding methyl and benzene; benzyl oxidation yields benzaldehyde, that further reacts yielding phenyl whereas benzyl thermal decomposition yields acetylene and cyclopentadienyl; further reactions of cyclopentadienyl yield vinylacetylene.

Aldol Condensations on Solid Catalysts: A Cooperative Effect between Weak Acid and Base Sites

Abstract: An amorphous aluminophosphate (ALPO) catalyst containing weak acid and base centers can carry out the aldol condensation of heptanal with benzaldehyde at much higher rates and selectivities than conventional solid acid (amorphous or crystalline aluminosilicates) or base catalysts (MgO, hydrotalcites, KF/Al2O3, nitrurated ALPO). With the weak acid-base catalyst, the reaction occurs through a bifunctional acid-base mechanism that involves the activation of benzaldehyde, by protonation-polarization of the carbonyl group on the acid sites, and the attack of the enolate heptanal intermediate generated on the basic sites. With this type of bifunctional acid-base catalyst, compounds with weak basicities are already able to undergo the reaction with a much higher selectivity than those obtained on stronger acid or base catalysts.

A highly stereoselective asymmetric synthesis of (--)-lobeline and (--)-sedamine.

Abstract: A highly stereoselective asymmetric synthesis of (--)-sedamine and (--)-lobeline is described from benzaldehyde in 16 and 17 steps with an overall yield of 20% and 14%, respectively. The key intermediate syn-3,4-epoxyalcohol was prepared in a highly diastereomeric fashion (>99% ee, dr) and served as a common intermediate for both alkaloids.

Characterization and application of xylene monooxygenase for multistep biocatalysis.

Abstract: During the last few decades, the microbial degradation pathways of aromatic and aliphatic hydrocarbons have received a lot of scientific interest because of the high potential of the enzyme systems involved for environmental (43) and preparative applications (38, 59). These pathways are usually initiated by an oxygenase-catalyzed chemo-, regio-, and stereoselective hydroxylation of the hydrocarbons, a reaction for which often no organic chemical counterpart is known (9, 13). The xylene degradation pathway of Pseudomonas putida mt-2 and its initiating oxygenase, the xylene monooxygenase (XMO), are among the best-studied examples of aromatic hydrocarbon degradation (5, 36, 57, 61). The enzymes for xylene degradation are encoded on a catabolic plasmid, the TOL plasmid pWW0. XMO is the first enzyme in the upper degradation pathway for toluene and xylenes, in which a carboxylic acid is formed (1, 16, 58). The upper pathway also involves benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, which catalyze the oxidation of benzyl alcohols via benzaldehydes to benzoic acids (46-48). The carboxylic acid is then transformed to substrates of the Krebs cycle through the meta cleavage pathway (10, 14, 36, 55). XMO consists of two polypeptide subunits, encoded by xylM and xylA (16, 52). XylA, the NADH:acceptor reductase component, is an electron transport protein transferring reducing equivalents from NADH to XylM (45). XylM, the hydroxylase component, is located in the membrane, and its activity depends on phospholipids and ferrous ion, with a pH optimum of 7 (44, 62). The substrate spectrum of XMO was investigated, with focus on preparative applications. XMO expressed in Escherichia coli oxidizes toluene and xylenes but also m- and p-ethyl-, methoxy-, nitro-, and chloro-substituted toluenes, as well as m-bromo-substituted toluene, to the corresponding benzyl alcohol derivatives (21, 65). Furthermore, styrene is transformed into S-styrene oxide with an enantiomeric excess (ee) of 95% (64, 65). The one-step oxygenation of styrene catalyzed by recombinant XMO in growing cells of E. coli was applied to produce S-styrene oxide on a 2-liter scale with hexadecane as the second organic phase (30). The wild-type strain P. putida mt-2 was used to oxidize methyl groups on aromatic heterocyclics to the corresponding carboxylic acids (20). In large-scale fermentations, a 5-methyl-2-pyrazinecarboxylic acid titer up to 20 g liter−1 was reached. This system exploits the inability of the wild-type strain to further degrade heteroaromatic carboxylic acids. In P. putida mt-2, all three enzyme activities of the upper xylene degradation pathway are responsible for the three-step oxidation. Early reports suggested that XMO also catalyzes alcohol and aldehyde oxidations (15, 16). Later, such activities were attributed to dehydrogenases present in the E. coli host (16, 44). Recently, we verified by in vivo experiments that XMO indeed catalyzes the oxidation of benzyl alcohols and benzaldehydes, both via a monooxygenation type of reaction (4). E. coli cells expressing XMO genes under the control of the alk regulatory system (12, 51, 62, 67) were used for these experiments. Potential preparative in vivo applications of XMO are hampered by low water solubilities and high toxicities of possible substrates and products, limiting the performance of aqueous systems. Nonconventional reaction media such as an aqueous-organic two-liquid-phase system are promising alternatives (8, 40). A second immiscible phase can act as a reservoir for substrate and products, regulating the concentration of such compounds in the biocatalyst microenvironment, minimizing toxicity and simplifying product recovery (24, 60, 63). In the present study, we characterized the multistep oxidation of substrates such as pseudocumene and toluene by whole cells of E. coli containing XMO with the aims of clarifying the natural role of such a multistep catalysis and identifying possible applications. The biotechnological conversion of pseudocumene is of special interest because a controlled regio- and chemospecific multistep oxidation of only one methyl group is difficult to achieve by purely chemical methods. We determined the kinetics of the one-enzyme multistep reaction and analyzed the whole-cell biocatalyst in a two-liquid-phase biotransformation on a 2-liter scale. Our results indicate that, depending on the reaction conditions, product formation may be directed to one specific product, either benzylic alcohols, aldehydes, or acids.

Water-Soluble, Core-Modified Porphyrins as Novel, Longer-Wavelength-Absorbing Sensitizers for Photodynamic Therapy. II. Effects of Core Heteroatoms and Meso-Substituents on Biological Activity

Abstract: Water-soluble, core-modified porphyrins were prepared and evaluated as sensitizers for photodynamic therapy (PDT). The addition of an aromatic aldehyde to 2,5-dilithiothiophene or -selenophene gave diol 3 as a nearly equimolar mixture of meso and d,l diastereomers, which gave a single diastereomer following careful recrystallization. The condensation of pyrrole with a diol 3 using catalytic BF3-etherate gave bispyrrolochalcogenophenes (4). Condensation of a diol 3 with 4 in the presence BF3-etherate gave 21,23-dichalcogenaporphyrins (5). 21-Thiaporphyrins (6) were prepared by condensation of a diol 3 with excess pyrrole and benzaldehyde in the presence of tetrachlorobenzoquinone and catalytic BF3-etherate. Sulfonation of 5 and 6 with concentrated sulfuric acid at 100 °C gave sulfonated derivatives 7−15. Bis-4-methoxy-21,23-dithiaporphyrins 5h and 5l were demethylated with BBr3, and the resulting phenols were alkylated with ethyl bromoacetate. Saponification gave 21,23-dithiaporphyrin dicarboxylate salts 1...

A practical stereoselective synthesis of secondary and tertiary aminonaphthols: chiral ligands for enantioselective catalysts in the addition of diethylzinc to benzaldehyde

Abstract: A practical procedure for the stereoselective synthesis of a wide group of functionalized aminoalkylnaphthols, using inexpensive starting materials, is reported. Selective N-alkylation was carried out by cyclization of secondary aminoalkylnaphthols with formaldehyde, followed by reduction or alkylation with organometallic reagents. The catalytic activity of this class of compounds was tested in the addition of diethylzinc to benzaldehyde, resulting in moderate to good enantioselectivities. It is noteworthy that the aminonaphthols obtained as the major diastereomer in the solvent free synthesis, have the best asymmetric induction properties in the alkylation reaction.

Enzymatic synthesis of all stereoisomers of 1-phenylpropane-1,2-diol

Abstract: A stereoselective two-step enzymatic synthesis of all four stereoisomers of 1-phenylpropane-1,2-diol starting from benzaldehyde and acetaldehyde is described. By using one of four possible combinations of a lyase followed by an alcohol dehydrogenase, each diol is accessible separately.

Oxidative catalysis by Mn4O46+ cubane complexes

Abstract: The oxidation of a variety of substrates (thioethers, hydrocarbons, alkenes, benyzl alcohol and benzaldehyde) by t BuOOH catalyzed by Mn 4 O 4 (O 2 PPh 2 ) 6 ( 1 ) and Mn 4 O 4 (O 2 P( p -MePh) 2 ) 6 ( 2 ) is reported. These reactions illustrate the first examples of oxidative catalysis using a manganese-oxo complex with a Mn 4 O 4 cubane core. These uncharged complexes contain Mn ions in a mixed valence oxidation state, formally Mn 4 (2III, 2IV), and are bridged by bulky diphenylphosphinate chelates across each of the six faces of the cube. Using this system, methyl phenyl sulfide is selectively mono-oxygenated to methyl phenyl sulfoxide with high catalytic efficiency, and no evidence for further oxidation to the thermodynamically preferred sulfone. Toluene is oxidized to a mixture of benzyl alcohol, benzaldehyde, and benzoic acid with high catalytic efficiencies. Lower catalytic efficiencies are observed in the oxidation of styrene to a mixture of styrene oxide and benzaldehyde, of cyclohexene to a mixture of cyclohexene oxide, 2-cyclohexen-1-ol, and 2-cyclohexen-1-one, and of cyclohexane to a mixture of cyclohexanol and cyclohexanone. The observed product distribution from the oxidation of hydrocarbons has the characteristics of a free radical-based oxidation mechanism. However, the sulfoxidation and epoxidation activity of the 1 / t BuOOH system, as well as the observed steric preferences for less congested substrates, suggest that a metal-oxo centered oxidation mechanism is active in the reactions studied here. An intermediate species, characterized by a UV–VIS band centered at 610 nm is observed in all reaction mixtures, and forms upon reaction of 1 or 2 with t BuOOH . Preliminary evidence suggests this reactive intermediate may correspond to a Mn(V)O species. Kinetic studies suggest two pathways for oxidation: one involving an oxygen atom transfer (two-electron branch), and the other involving a hydrogen atom abstraction (one-electron branch).

Asymmetric addition of diethylzinc to aldehydes catalyzed by β-amino alcohols derived from limonene oxide

Abstract: A series of β-amino alcohols, conveniently prepared from limonene oxide, were evaluated as catalysts for the enantioselective addition of dialkylzinc to benzaldehyde. These limonene-based amino alcohols are of particular interest because they are easily synthesized in both enantiomeric forms. Ethylation of benzaldehyde using diethylzinc and catalyzed by limonene derived amino alcohols proceeded with enantioselection of up to 87% ee. This is an unusually high level of induction for amino alcohols possessing a trans relationship between the amino and alcohol functionalities. Both enantiomers of 1-phenyl-1-propanol can be synthesized with equal control since both enantiomers of the chiral catalyst are readily available. When (1S,2S,4R)-limonene amino alcohols are used as chiral catalysts, (R)-1-phenyl-1-propanol is obtained as the major product. A plausible mechanism is proposed to explain the facial selectivity determining the asymmetric induction observed in these reactions.

Study on the adsorption properties of novel crown ether crosslinked chitosan for metal ions

Abstract: We first synthesized N-benzylidene chitosan (CTB) by the reaction of benzaldehyde with chitosan (CTS). Chitosan-dibenzo-18-crown-6 crown ether bearing Schiff-base group (CTBD) and chitosan-dibenzo-18-crown-6 crown ether (CTSD) were prepared by the reaction of 4,4′-dibromodibenzo-18-crown-6 crown ether with CTB and CTS, respectively. Their structures were confirmed by Fourier transform infrared spectral analysis and X-ray powder diffraction analysis. These novel crown ether crosslinked CTSs have space net structures with embedded crown ethers and contain the double structures and properties of CTS and crown ethers. They have stronger complexation with and better selectivity for metal ions than corresponding crown ethers and CTS. Moreover, these novel CTS derivatives can be used to separate and preconcentrate heavy or precious metal ions in aqueous environments. From this practical viewpoint, we studied the adsorption and selectivity properties of CTB, CTBD, and CTSD for Ag+, Cu2+, Pb2+, and Ni2+. The experimental results showed that CTBD had better adsorption properties and higher selectivity for metal ions than CTSD. For aqueous systems containing Pb2+–Ni2+ and Pb2+–Cu2+, the selectivity coefficients of CTSD and CTBD were K/Ni2+ = 24.4 and K/Cu2+ = 41.4 and K/Ni2+ = 35.5 and K/Cu2+ = 55.3, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 29–34, 2002; DOI 10.1002/app.10180

Preparation of Benzylamine by Highly Selective Reductive Amination of Benzaldehyde Over Ru on an Acidic Activated Carbon Support as the Catalyst

Abstract: Ruthenium supported on activated carbon, on which acidic groups were introduced by pre-treatment with (NH4)2S2O8, is a highly active and selective catalyst for the synthesis of benzylamine via the reductive amination of benzaldehyde.

A new ruthenium-catalyzed hydrogen-transfer reaction: transformation of 3-benzyl but-1-ynyl ethers into 1,3-dienes and benzaldehyde.

Abstract: We report a ruthenium-catalyzed reaction for various 3-benzyl but-1-ynyl ethers with suitable functionalities. Treatment of these substrates with TpRu(PPh3)(CH3CN)2PF6 (8.0 mol %) catalyst in 1,2-dichloroethane (80 °C, 12 h) afforded functionalized 1,3-dienes and benzyl aldehyde in good yields. This process is considered to be a tandem dealkoxylation and transfer hydrogenation. Deuterium-labeling experiments reveal that the migration of different hydrogen atoms proceeds regiospecifically. A plausible mechanism is proposed on the basis of the results of isotope experiment.

Highly enantioselective diethylzinc addition to aldehydes catalyzed by D-glucosamine derivatives

Abstract: Synthesis of α-hydroxy sulfonamides derived from d -glucosamine and their application as ligands in the titanium tetraisopropoxide-promoted enantioselective addition of diethylzinc to benzaldehyde and selected aromatic and aliphatic aldehydes is presented. The reaction is highly enantioselective and enantiomeric excesses of up to 97% for benzaldehyde and 88% for n -hexanal were obtained.

Mineralization of aromatic compounds by brown-rot basidiomycetes - mechanisms involved in initial attack on the aromatic ring.

Abstract: Benzaldehyde and its metabolic intermediates were effectively degraded by the brown-rot basidiomycetes Tyromyces palustris and Gloeophyllum trabeum. The pathway of benzaldehyde degradation was elucidated by the identification of fungal metabolites produced upon the addition of benzaldehyde and its metabolic intermediates. The oxidation and reduction occurred simultaneously, forming benzyl alcohol and benzoic acid as major products. Hydroxylation reactions, which seemed to be a key step, occurred on benzaldehyde and benzoic acid, but not on benzyl alcohol, to form corresponding 4-hydroxyl and 3,4-dihydroxyl derivatives. 1-Formyl derivatives were oxidized to 1-carboxyl derivatives at several metabolic stages. All of these reactions resulted in the formation of 3,4-dihydroxybenzoic acid. This was further metabolized via the decarboxylation reaction to yield 1,2,4-trihydroxybenzene, which may be susceptible to the ring-fission reaction. Ring-U-14C-labelled benzaldehyde and benzoic acid were effectively mineralized, clearly indicating that the brown-rot basidiomycetes are capable of metabolizing certain aromatic compounds to CO2 and H2O, despite the fact that brown-rot fungi cannot degrade polymeric lignin. Inhibitor experiments, using hydroxyl radical scavengers, catalase and cytochrome P450 inhibitors, strongly suggested that the aromatic hydroxylation reactions found in the brown-rot fungi are catalysed by intracellular enzyme(s), but not by Fenton-reaction-derived hydroxyl radicals.

Oxidation, Redox Disproportionation and Chain Termination Reactions Catalysed by the Pd‐561 Giant Cluster

Abstract: Redox disproportionation of benzyl alcohol to benzaldehyde and toluene catalysed by the Pd561phen60(OAc)180 (phen=1,10-phenanthroline) giant cluster 1 under anaerobic conditions was found, whereas in an O2 atmosphere cluster 1 catalyses the oxidation of benzyl alcohol to benzaldehyde and inhibits further oxidation of the latter A study of the AIBN-initiated and non-initiated oxidation of benzyl alcohol, sec-butyl alcohol and styrene in the presence of cluster 1 revealed that cluster 1 performs three functions in the oxidation reactions: 1) catalysis of polar oxidation of the substrates with O2, 2) termination of the chains of radical oxidation, and 3) catalysis of redox disproportionation

Oxidative deamination by hydrogen peroxide in the presence of metals.

Abstract: Various amines, including lysine residue of bovine serum albumin, were oxidatively deaminated to form the corresponding aldehydes by a H2O2/Cu2+ oxidation system at physiological pH and temperature. The resulting aldehydes were measured by high-performance liquid chromatography. We investigated the effects of metal ions, pH, inhibitors, and O2 on the oxidative deamination of benzylamine by H202. The formation of benzaldehyde was the greatest with Cu2+, and catalysis occurred with Co2+, VO2+, and Fe3+. The reaction was greatly accelerated as the pH value rose and was markedly inhibited by EDTA and catalase. Dimethyl sulfoxide and thiourea, which are hydroxyl radical scavengers, were also effective in inhibiting the generation of benzaldehyde, indicating that the reaction is a hydroxyl radical-mediated reaction. Superoxide dismutase greatly stimulated the reaction, probably due to the formation of hydroxyl radicals. O2 was not required in the oxidation, and instead slightly inhibited the reaction. We also examined several oxidation systems. Ascorbic acid/O2/Cu2+ and hemoglobin/H2O2 systems also converted benzylamine to benzaldehyde. The proposed mechanism of the oxidative deamination by H2O2/Cu2+ system is discussed.