Palladium-catalyzed transfer hydrogenolysis of benzyl acetate with ammonium formate
TL;DR: In this article, the authors showed that the rate of transfer hydrogenolysis was independent of the substrate (benzyl acetate) concentration and first order dependence was exhibited by both hydrogen donor (HCOONH4) and catalyst (10% Pd C ).
Abstract: Transfer hydrogenolysis of benzyl acetate, a model reaction for CO hydrogenolysis, was achieved by ammonium formate and Pd C at 20°C. Hydrogen-donating abilities of various formate salts were found to depend on the counter-ion: K+ > NH4+ > Na+ > NHEt3+ > Li+ > H+. Kinetic studies using HCOONH4 revealed that the rate of transfer hydrogenolysis was independent of the substrate (benzyl acetate) concentration. First order dependence was exhibited by both hydrogen donor (HCOONH4) and the catalyst (10% Pd C ). The initial reaction rate dropped from 46.9 × 10−3 mol L−1 min−1 to 26.8 × 10−3 mol L−1 min−1 when HCOONH4 was replaced with DCOOND4 giving a calculated primary kinetic isotope effect of 1.75. From the kinetic and isotope effect data, a mechanism has been proposed involving abstraction of formyl hydrogen by the catalyst as the rate-limiting step. The rate law derived was R = k′ [HCOONH4] [ Pd C ]. Hydrogen isotope labeling studies using DCOOND4 as hydrogen donor disclosed that the expected monodeuterated toluene (C6H5CH2D) was not formed exclusively. Instead, a mixture of deuterated toluenes (C6H5CHxD3−x) was obtained, demonstrating that benzylic hydrogens are highly labile on the catalyst surface and exchange with the solvent.
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TL;DR: In this paper, a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation, is presented.
Abstract: Reducing oxygen content in biomass-derived feedstocks via hydrodeoxygenation (HDO) is a key step in their upgrading to fuels and valuable chemicals. Organic molecules, e.g., alcohols and formic acid, can donate hydrogen to reduce the substrate in a process called catalytic transfer hydrogenation (CTH). Although it is practiced far less frequently than molecular-hydrogen-based HDO processes, CTH has been proven to be an efficient and selective strategy in biomass upgrading in the last two decades. In this paper, we present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation. Hydrogenation and cleavage of C═O and C–O bonds, respectively, are the two main categories of reactions discussed, owing to their importance in the HDO of biomass-derived feedstocks. On acid–base catalysts, Lewis acid–base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcohols...
539 citations
TL;DR: In this article, the authors have analyzed several novel approaches, including catalytic transfer hydrogenation (CTH), combined reforming and hydrodeoxygenation, metal hydrolysis and subsequent hydrogenation along with non-thermal nitrogen tetramer (NTP) in order to avoid the supply of external H2.
Abstract: Catalytic hydrodeoxygenation (HDO) is a fundamental
process for bio-resources upgrading to produce transportation
fuels or added value chemicals. The bottleneck of this technology
to be implemented at commercial scale is its dependence on high
pressure hydrogen, an expensive resource which utilization also
poses safety concerns. In this scenario, the development of
hydrogen-free alternatives to facilitate oxygen removal in biomass
derived compounds is a major challenge for catalysis science but
at the same time it could revolutionize biomass processing
technologies. In this review we have analyzed several novel
approaches, including catalytic transfer hydrogenation (CTH),
combined reforming and hydrodeoxygenation, metal hydrolysis
and subsequent hydrodeoxygenation along with non-thermal
plasma (NTP) in order to avoid the supply of external H2. The
knowledge accumulated from traditional HDO sets the grounds
for catalysts and processes development among the hydrogen
alternatives. In this sense, mechanistic aspects for HDO and the
proposed alternatives are carefully analyzed in this work.
Biomass model compounds are selected aiming to provide an indepth
description of the different processes and stablish solid
correlations catalysts composition-catalytic performance which
can be further extrapolated to more complex biomass feedstocks.
Moreover, the current challenges and research trends of novel
hydrodeoxygenation strategies are also presented aiming to
spark inspiration among the broad community of scientists
working towards a low carbon society where bio-resources will
play a major role.
145 citations
TL;DR: In this article, a Palladium-catalyzed transfer-hydrogenolysis of primary, secondary, and tertiary benzylic alcohols by formic acid has been studied.
Abstract: A palladium-catalyzed transfer hydrogenolysis of primary, secondary, and tertiary benzylic alcohols by formic acid has been developed and studied. The product hydrocarbons were obtained in excellen ...
90 citations
TL;DR: A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined, and the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic Acid.
Abstract: The inner surface of a metallic tube (i.d. 0.5 mm) was coated with a palladium (Pd)-based thin metallic layer by flow electroless plating. Simultaneous plating of Pd and silver (Ag) from their electroless-plating solution produced a mixed distributed bimetallic layer. Preferential acid leaching of Ag from the Pd–Ag layer produced a porous Pd surface. Hydrogenation of p-nitrophenol was examined in the presence of formic acid simply by passing the reaction solution through the catalytic tubular reactors. p-Aminophenol was the sole product of hydrogenation. No side reaction occurred. Reaction conversion with respect to p-nitrophenol was dependent on the catalyst layer type, the temperature, pH, amount of formic acid, and the residence time. A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined. p-Nitrophenol was converted quantitatively to p-aminophenol within 15 s of residence time in the porous PdO reactor at 40 °C. Evolution of carbon dioxide (CO2) was observed during the reaction, although hydrogen (H2) was not found in the gas phase. Dehydrogenation of formic acid did not occur to any practical degree in the absence of p-nitrophenol. Consequently, the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid.
52 citations
TL;DR: In this paper, the authors investigated the adaption and dehydrogenation of formic acid, hydrazine and isopropanol using periodic density functional theory (DFT).
Abstract: Adsorption and dehydrogenation of formic acid, hydrazine and isopropanol have been investigated using periodic density functional theory (DFT). All the intermediates and transition states have been optimized and the preferred reaction pathways have been found. The adsorption energies for the most stable mode of formic acid, hydrazine and isopropanol are 38.6 kJ/mol, 63.9 kJ/mol and 46.1 kJ/mol, respectively. The dehydrogenation mechanisms of formic acid, hydrazine and isopropanol on Pd(111) surface are proposed and calculated. According to the calculation results, dehydrogenation of formate is more favorable than those of other molecules/groups, and that can be an explanation for the high reactivity of formats in Pd catalyzed transfer hydrogenation.
43 citations
References
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TL;DR: In this paper, a review of transfer reduction using hydrogen donors is presented, focusing mainly on those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen.
Abstract: Reduction of organic compounds is important synthetically both in the laboratory and in industry. There are many methods of effecting reduction which may or may not lead to hydrogenation, but in this review only processes leading to the addition of hydrogen or replacement of a functional group by hydrogen will be considered. Further, this review will be concerned mostly with those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen. Reduction of organic functional groups can be categorized into (i) addition of hydrogen to unsaturated groups as, for example, in the reduction of ketones to alcohols and (ii) addition of hydrogen across single bonds leading to cleavage of functional groups (hydrogenolysis). Removal of oxygen as a reductive process, as in the deoxygenation of oxiranes to alkenes, will not be discussed. Of all the methods available for addition of hydrogen to organic compounds, heterogeneous catalytic transfer reactions have been relatively underutilized. This lack of popularity can be traced to the relatively meager success of much of the earlier research which suggested that the technique was of only limited scope and could provide only modest yields of products. The early pioneering work by Braude' was largely ignored because of poor yields and long reaction times, but the situation has changed considerably following the appearance4 of a stimulating review and the introduction of greater catalyst loadings and different hydrogen donors.2 Another reason for the underutilization of transfer reduction has been the very successful exploitation of molecular hydrogen and hydrides for reduction of organic compounds. In comparison with catalytic reduction using molecular hydrogen, transfer reduction using hydrogen donors has real and potential advantages. Molecular hydrogen, a gas of low molecular weight and therefore high diffusibility, is easily ignited and presents considerable hazards, particularly on the large scale; the use of hydrogen donors obviates these difficulties in that no gas
824 citations
TL;DR: A review of the literature on Peptides, Structure and Biology from 1975 to 1977 by F A .
Abstract: (6) H. Hagenmaier and M. Mutter, Tetrahedron Lett., 767-770 (1974). (7) W. Gohring and G. Jung, Justus Liebigs Ann. Chern., 1765-1789 (1975). (8) M. Mutter, R. Uhmann, and E. Bayer, Justus Liebigs Ann. Chern., 901-915 ( 1975). (9) G. Jung, G. Bovermann, W. Gohring, and G. Heusel in "Peptides: Chemistry, Structure and Biology," R. Walter and J. Meienhofer, Ed., Ann Arbor Sci. Publ., Ann Arbor, Mich., 1975, pp 433-437. (10) F A . Tjoeng, W Staines, S. St-Pierre, and R. S. Hodges, Biochirn. Biophys. Acta, 490, 489-496 (1977). (1975). (1 1) L. B. Smillie, PAABS Revista, 5, 183-263 (1976). (12) R. S. Hodges, J. Sodek, L. B. Smillie, and L. Jurasek, ColdSpring Harbor
192 citations