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We report a reaction platform for the synthesis of three different high-value specialty chemical building blocks starting from bio-ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde-containing stream active for the production of C4 aldehydes via base-catalyzed aldol-condensation. Then, the resulting C4 adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β-hydroxy acid (3-hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β-dihydroxy acid (2,3-dihydroxybutanoic acid). Crotonic acid, 3-hydroxybutanoic acid, and 2,3-dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl-co-unsaturated acids resins, pharmaceutics, and bio-degradable/ -compatible polymers, respectively.

Abstract: A study of the kinetics of ethanol conversion in the presence of Zr-containing zeolites BEA doped with palladium particles has revealed the order of formation of the main reaction products. It has been shown that the primary processes are ethanol dehydrogenation to acetaldehyde on Pd sites and ethanol dehydration to diethyl ether on the acid sites of the catalyst. After that, acetaldehyde undergoes the aldol–croton condensation reaction to form crotonal, which is hydrogenated to butanol on the metal sites. Butanol, in turn, is dehydrated into butenes, which undergo hydrogenation to butane. The presence of hydrogen in the gas phase leads to the displacement of ethanol from the metal surface and prevents the formation of surface carbonates and acetates. It has been found that hydrogen significantly accelerates ethanol dehydration owing to a decrease in the activation energy, which can be attributed to hydrogen spillover to the zeolite. The addition of water inhibits all acid-catalyzed reactions owing to competitive adsorption on acid sites and thereby decreases the butanol yield and the ethanol conversion.

Structure-guided directed evolution of choline oxidase has been carried out by using the oxidation of hexan-1-ol to hexanal as the target reaction. A six-amino-acid variant was identified with a 20-fold increased kcat compared to that of the wild-type enzyme. This variant enabled the oxidation of 10 mm hexanol to hexanal in less than 24 h with 100 % conversion. Furthermore, this variant showed a marked increase in thermostability with a corresponding increase in Tm of 20 °C. Improved solvent tolerance was demonstrated with organic solvents including ethyl acetate, heptane and cyclohexane, thereby enabling improved conversions to the aldehyde by up to 30 % above conversion for the solvent-free system. Despite the evolution of choline oxidase towards hexan-1-ol, this new variant also showed increased specific activities (by up to 100-fold) for around 50 primary aliphatic, unsaturated, branched, cyclic, benzylic and halogenated alcohols.

Aryl alcohol oxidase (AAO) is a fungal flavoenzyme capable of oxidizing aromatic primary alcohols into their correspondent aldehydes through a stereoselective hydride abstraction. Unfortunately, this enzyme does not act on secondary benzyl alcohols in racemic mixtures due to the strict control of substrate diffusion and positioning at the active site restricted to primary benzyl alcohols. Here we describe the engineering of AAO from Pleurotus eryngii to oxidize chiral benzyl alcohols with high enantioselectivity. The secondary benzyl alcohol oxidase was remodeled at the active site through four cycles of structure-guided evolution, including a final step of in vivo site-directed recombination to address the positive epistatic interactions between mutations. The final variant, with five substitutions and a renovated active site, was characterized at biochemical and computational level. The mutational sculpting helped position the bulkier (S)-1-(p-methoxyphenyl)-ethanol, improving the mutant's catalytic efficiency by three orders of magnitude relative to the native enzyme while showing a high enantioselectivity (ee >99%). As a promising candidate for racemic resolution, this evolved secondary benzyl alcohol oxidase maintained its natural stereoselective mechanism while displaying activity on several secondary benzyl alcohols. (Figure presented.).

Abstract: Processes of catalytic homocondensation of propanal and its cross-condensation with ethanal and methanal in the presence of aniline and amino acids have been studied. The dependence of the conversion of the reactants and selectivity of the homo/heterocondensation process on the catalyst nature and temperature has been revealed. It has been shown that the maximum acrolein selectivity is reached in the case of using benzoyl-substituted derivatives in water, with the proportion of the products of further condensation decreasing. The selectivity for the ethanal homocondensation product 2-butenal decreases simultaneously as a result of the formation of linear and branched oligomers of successive condensation.

Condensation reactions of biomass derived C2 and C4 aldehydes form both ortho- and para-tolualdehydes (2-MB and 4-MB, respectively). The complete reaction network and the detailed mechanisms, however, have not been fully described. H

A novel bioinspired bifunctional ligand incorporating metal-binding site and stable free radical has been synthesized. The catalytic system obtained from the bifunctional ligand with copper(i) iodide in the presence of N-methylimidazole is highly efficient for the oxidation of a broad range of primary benzylic, allylic, alkynyl, aliphatic alcohols and secondary benzylic alcohols to the corresponding aldehydes and ketones in good to excellent yields. The catalyst system exhibits broad functional-group compatibility. The reaction is carried out in acetonitrile as solvent under air balloon at room temperature. The catalyst system features excellent activity for primary aliphatic alcohol oxidation and a high chemoselective oxidation of primary alcohols over the secondary alcohols. This oxidation process is readily amenable to larger-scale application. The interaction of the different components in the reaction mixtures was studied by UV-visible spectroscopy. The data indicated that Cu(i) existed throughout the reaction. A plausible mechanism of the catalytic cycle is proposed.

A new type of catalyst has been designed to adjust the basicity and level of molecular confinement of KNaX faujasites by controlled incorporation of Mg through ion exchange and precipitation of extraframework MgO clusters at varying loadings. The catalytic performance of these catalysts was compared in the conversion of C2 and C4 aldehydes to value-added products. The product distribution depends on both the level of acetaldehyde conversion and the fraction of magnesium as extraframework species. These species form rather uniform and highly dispersed nanostructures that resemble nanopetals. Specifically, the sample containing Mg only in the form of exchangeable Mg2+ ions has much lower activity than those in which a significant fraction of Mg exists as extraframework MgO. Both the (C6+C8)/C4 and C8/C6 ratios increase with additional extraframework Mg at high acetaldehyde conversion levels. These differences in product distribution can be attributed to 1) higher basicity density on the samples with extraframework species, and 2) enhanced confinement inside the zeolite cages in the presence of these species. Additionally, the formation of linear or aromatic C8 aldehyde compounds depends on the position on the crotonaldehyde molecule from which abstraction of a proton occurs. In addition, catalysts with different confinement effects result in different C8 products.

A novel strategy for catalytic oxidation of a variety of benzylic, allylic, propargylic, and aliphatic alcohols to the corresponding aldehydes or ketones by an in situ formed porphyrin-inspired manganese complex in excellent yields (up to 99%) has been successfully developed.

Liquid-phase cross-aldol condensation of acetaldehyde and formaldehyde in the presence of salts of various saturated and unsaturated linear amines, aromatic amines, diamines, and nitrogen bases, as well as in the presence of substituted piperazines, linear and cyclic amino acids and their derivatives, and nitrogen-containing ionic liquids, was studied. The cross-condensation products were formed in considerable amounts when amine hydrochlorides, N-benzoyl amino acids, and amino acid esters were used as catalyst. The formation of cross-condensation products is favored by increased basicity of the amino nitrogen atom in the salt and of the solvent.

The present invention provides novel methods for determining the presence or amount of a hydrolytic enzyme in a sample, based on novel substrates for the enzymes, and also provides compositions and methods that provide highly sensitive assay methods for such hydrolytic enzymes.

We have developed a simple and practical process for the oxidation of alcohols to the corresponding carbonyl compounds by using a low catalytic amount of DDQ, NaNO2 as a cocatalyst, and molecular oxygen as terminal oxidant. Nitric oxide generated in situ by NaNO2 in the presence of AcOH is essential for the realization of the catalytic cycle at room temperature. The practical utility of this catalytic process has been demonstrated in the gram-scale oxidation of cinnamyl alcohol.

Learning from nature: The development of an MoS2/Ta 3N5 nanocomposite as a catalyst for selective aerobic oxidation by O2 activation was inspired by the nitrogenase enzymes in nature. The superior performance of this biomimetic catalyst, which shows potential for the selective oxidation of multifunctional substrates (see picture), results from the integration of Ta3N5 and MoS2 at the nanoscale and the synergistic enhancement of their activity. Copyright

The proline-catalyzed self-condensation of aliphatic aldehydes in DMSO with varying amounts of catalyst was studied by in situ NMR spectroscopy. The reaction profiles and intermediates observed as well as deuteration studies reveal that the proline-catalyzed aldol addition and condensation are competing, but not consecutive, reaction pathways. In addition, the rate-determining step of the condensation is suggested to be the C-C bond formation. Our findings indicate the involvement of two catalyst molecules in the C-C bond formation of the aldol condensation, presumably by the activation of both the aldol acceptor and donor in a Mannich-type pathway. This mechanism is shown to be operative also in the oligomerization of acetaldehyde with high proline amounts, for which the first in situ detection of a proline-derived dienamine was accomplished. In addition, the diastereoselectivity of the aldol addition is evidenced to be time-dependent since it is undermined by the retro-aldolization and the competing irreversible aldol condensation; here NMR reaction profiles can be used as a tool for reaction optimization.

Disclosed are a catalyst including a hydrotalcite and, immobilized on a surface thereof, particles of at least one metal selected from the group consisting of Cu, Ag, and Au; a method for producing a carbonyl compound through dehydrogenation of an alcohol in the presence of the catalyst; and a method for producing a carbonyl compound through dehydrogenation of an alcohol in the presence of a catalyst including a hydrotalcite and, immobilized on a surface thereof, particles of a metal, in which dehydrogenation is performed in the absence of oxygen.

Fungal AAO (aryl-alcohol oxidase) provides H2O2 for lignin biodegradation. AAO is active on benzyl alcohols that are oxidized to aldehydes. However, during oxidation of some alcohols, AAO forms more than a stoichiometric number of H2O2 molecules with respect to the amount of aldehyde detected due to a double reaction that involves aryl-aldehyde oxidase activity. The latter reactionwas investigated using different benzylic aldehydes, whose oxidation to acids was demonstrated by GC-MS. The steady- and presteady state kinetic constants, together with the chromatographic results, revealed that the presence of substrate electron-withdrawing or electron-donating substituents had a strong influence on activity; the highest activity was with p-nitrobenzaldehyde and halogenated aldehydes and the lowest with methoxylated aldehydes. Moreover, activity was correlated to the aldehyde hydration rates estimated by 1H-NMR. These findings, together with the absence in the AAO active site of a residue able to drive oxidation via an aldehyde thiohemiacetal, suggested that oxidation mainly proceeds via the gem-diol species. The reaction mechanism (with a solvent isotope effect, 2H2O kred, of approx. 1.5)would be analogous to that described for alcohols, the reductive half-reaction involving concerted hydride transfer from the a-carbon and proton abstraction from one of the gem-diol hydroxy groups by a base. The existence of two steps of opposite polar requirements (hydration and hydride transfer) explains some aspects of aldehyde oxidation by AAO. Site-directed mutagenesis identified two histidine residues strongly involved in gem-diol oxidation and, unexpectedly, suggested that an active-site tyrosine residue could facilitate the oxidation of some aldehydes that show no detectable hydration. Double alcohol and aldehyde oxidase activities of AAO would contribute to H2O2 supply by the enzyme. The Authors Journal compilation

In natural environments such as atmospheric aerosols, organic compounds coexist with inorganic salts but, until recently, were not thought to interact chemically. We have recently shown that inorganic ammonium ions, NH 4+, act as catalysts for acetal formation from glyoxal, a common atmospheric gas. In this work, we report that inorganic ammonium ions, NH4+, and carbonate ions, CO32-, are also efficient catalysts for the aldol condensation of carbonyl compounds. In the case of NH4+ this was not previously known, and was patented prior to this article. The kinetic results presented in this work show that, for the concentrations of ammonium and carbonate ions present in tropospheric aerosols, the aldol condensation of acetaldehyde and acetone could be as fast as in concentrated sulfuric acid and might compete with their reactions with OH radicals. These catalytic processes could produce significant amounts of polyconjugated, light-absorbing compounds in aerosols, and thus affect their direct forcing on climate. For organic gases with large Henry's law coefficients, these reactions could also result in a significant uptake and in the formation of secondary organic aerosols (SOA). This work reinforces the recent findings that inorganic salts are not inert towards organic compounds in aerosols and shows, in particular, that common ones, such as ammonium and carbonate salts, might even play important roles in their chemical transformations.

Hydrotalcite-supported gold nanoparticles (Au/HT) were found to be a highly efficient heterogeneous catalyst for the aerobic oxidation of alcohols under mild reaction conditions (4O°C, in air). This catalyst system does not require any additives and is applicable to a wide range of alcohols, including less reactive cyclohexanol derivatives. This Au/HT catalyst could also function in the oxidation of 1-phenylethanol under neat conditions; the turnover number (TON) and turnover frequency (TOF) reached 200,000 and 8,300 h -1, respectively. These values are among the highest values compared to those of other reported catalyst systems at high conversion. Moreover, the Au/HT can be recovered by simple filtration and reused without any loss of its activity and selectivity.

Treatment of Pd4phen2(CO)2(OAc)4 with metal nitrates such as Cu(NO3)2 produced monodispersed Pd nanoclusters with a mean diameter and standard deviation (d±σ) of 38±2.1 A (σ/d = 6%). The Pd nanoclusters act as heterogeneous catalysts for the selective oxidation of primary aromatic allylic alcohols using molecular oxygen as an oxidant. This unique catalysis can be ascribed to multiple interactions between the alcohol and specific ensemble sites consisting of Pd0, Pd+, and Pd2+ on the cluster surface.

The photolysis of NaS2O8 aqueous solutions containing Cl- ions is a clean technique for kinetic studies of the species Cl./Cl2.- in the presence and absence of added aromatic substrates. Laser and conventional flash-photolysis methods were used to study the aqueous phase reactions of chlorine atoms and Cl2.- (340 nm) radical ions in the presence and absence of benzene. A mechanism that considers the decay of Cl2.- in aqueous solutions with chloride ion concentrations from 1 x 10-4 to 0.6 M, total radical (Cl. + Cl2.-) concentrations at (0.1-1.5) x 10-5 M, and 2.5-3 pH was proposed. Kinetic computer simulations supported interpretation of the experimental data. The rate constants 6 x 109/M-sec ≤ k ≤ 1.2 x 1010/M-sec and 5/M-sec were determined for the reactions of Cl. and Cl2.-, respectively, in the aqueous phase. The organic radicals produced from these reactions showed an absorption band with maximum at 300 nm that was assigned to a Cl-cyclohexadienyl radical (Cl-CHD). The kinetic analysis of the traces supported a reversible reaction between Cl-CHD and O2. A reaction mechanism leading to the formation of chlorobenzene was proposed.

Oxidation of 1-vinyl-2-cycloalken-1-ols with PDC regiospecifically affords conjugated dienones in moderate to good yields.