Excess Formic Acid Research Articles

Intramolecular interaction induced C-C cleavages in fructose conversion in polar aprotic solvents-origin of the formation of excess formic acid and oligomers.

Understanding the mechanism of excess formic acid formation in the dehydration of fructose to HMF would be beneficial to improve HMF selectivity and carbon efficiency. The production of formic acid from keto-D-fructose in polar aprotic solvents, such as THF, DIO, and MTHF, and MIBK solvents without a catalyst was investigated via DFT calculations. It was found that in THF, DIO and MTHF solvents, fructose tended to generate formic acid directly with the catalysis of the intramolecular hydroxyls, especially C6-OH (terminal hydroxyl), while in MIBK, the solvent molecule could react with the intermediates produced in the process, making the barrier of production of acetic acid lower than that of formic acid. Molecular dynamics simulations showed that the lower dielectric polar aprotic solvents (THF, DIO and MTHF) could not destroy the intramolecular H-bonds of hydroxyls in fructose, which could promote the keto-enol tautomerization and hydration steps, facilitating the formation of six-member-ring transition states, which reduced the ring tension and decreased the activation energy greatly, leading to the overproduction of formic acid and oligomers. ETS-NOCV analysis further indicated that the donated electrons from C-O σ-bonds on the carbon chain of fructose made the intramolecular hydroxyls more basic, which could catalyse keto-enol tautomerization with a lower energy barrier than water molecules. To obtain more target products, such as HMF, suitable reaction environments, such as a higher polar aprotic solvent with a low boiling point or restriction of the activity of hydroxyls of fructose, might be selected to destroy the intramolecular interaction and then reduce the overproduction of formic acid and the formation of oligomers.

Reactivity of Heterobimetallic Ion Pairs in Formic Acid Dehydrogenation

The series of bimetallic complexes (tBuPXCYP)Pd(μ-OC)M(CO)2L (X, Y = CH2, O; M = W, Mo; L = Cp, Tp) catalyzes formic acid decomposition into H2/CO2 in fairly mild conditions (25–50 °C, toluene) without any organic base additives. The catalytic activity of bimetallic complexes increases with CH2-substitution of the O-bridges in the (PXCYP)-frame as well as with the proton-donating ability of the Mo/W hydride. The best result was obtained with (tBuPCP)Pd(μ-OC)Mo(CO)2Cp (3), which gives complete conversion at 2 mol % loading in 30 min at 50 °C (TOF = 100 h–1). During the catalysis, LM(CO)3H and (tBuPXCYP)Pd(OCHO) form as visible intermediates, while the palladium hydride species are also involved in the catalytic cycle. The experimental data show that hydride abstraction/CO2 release from palladium formates (tBuPXCYP)Pd(OCHO) is assisted by −OCHO···H–A hydrogen bonding with excess formic acid or acidic hydride LM(CO)3H. These findings highlight the pivotal role of the formate interaction with Brönsted or Lewis acids at the hydride abstraction/CO2 release step and unify the mechanisms suggested for different catalytic systems.

Effect of formic acid as an accelerator on foam-stability, compressive strength, and pore size distribution of foam concrete

In this study, the formic acid as an accelerator was used to increase the properties of the foamed concrete. The impact of formic acid on the performance of foam concrete was investigated experimentally. The experimental results reveal that using formic acid as an accelerator can significantly increase the rate of yield stress evolution in the matrix. The matrix with the higher yield stress evolution rate tends to increase the stability of the fresh foam concrete. In addition, the –COOH in formic acid can absorb the moisture in the foam, thus increasing foam drainage. The excess formic acid in the base mix can reduce the stability of the fresh foam concrete. The compressive strength of foam concrete can be significantly increased with the addition of 1.0% formic acid. A more homogeneous and finer pore structure of foam concrete can be obtained with the incorporation of 1.0% formic acid, which may result in lower water absorption and higher compressive strength.

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

Effect of formic-acid-to-acetic-acid ratio on the structure and spinnability of aqueous aluminium sol of alumina fibre

The structure and spinnability of sol are essential for obtaining high-performance continuous alumina-based fibres. Herein, the surface electrostatic potential analysis and conventional experimental methods (X-ray diffraction, Fourier-transform infrared spectroscopy, 27Al nuclear magnetic resonance solution spectra and rheological methods) were combined to investigate and discuss the relationship between the structure and spinnability of aluminium carboxylate sols with different formic-acid-to-acetic-acid molar ratios. The results showed that the aluminium carboxylate sol structure changed with the formic-acid-to-acetic-acid molar ratio and greatly affected the sol's spinnability. The tetramer (AlO6 oligomer) products comprising two effective active carboxylate groups in the sol increased with the formic acid content, which helped form linear long-chain polymers. However, excess formic acid content led to a large increase of AlO6 monomer products that were unable to form linear long-chain polymers, which decreased the sol's spinnability. When the formic-acid-to-acetic-acid molar ratio was 1.15:0.85, the sol containing more AlO6 oligomer products had the best spinnability. Furthermore, α-Al2O3 ceramic fibres with good morphology, small grains and uniform diameter distribution were obtained after calcination at 1200 °C.

Additive-Free Formic Acid Dehydrogenation Catalyzed by a Cobalt Complex

The reversible storage of hydrogen through the intermediate formation of formic acid (FA) is a promising solution to its safe transport and distribution. However, the common necessity of using bases or additives in the catalytic dehydrogenation of FA is a limitation. In this context, two new cobalt complexes (1 and 2) were synthesized with a pincer PP(NH)P ligand containing a phosphoramine moiety. Their reaction with an excess FA yields a cobalt(I) hydride complex (3). We report here the unprecedented catalytic activity of 3 in the dehydrogenation of FA, with a turnover frequency (TOF) of 67 min–1 measured in the first minute and a turnover number (TON) of 454, without the need for bases or additives. A mechanistic study reveals the existence of ligand–metal cooperativity with intermolecular hydrogen bonding, also influenced by the concentration of formic acid.

One-step preparation of microporous Pd@cPIM composite catalyst film for triphasic electrocatalysis

Triphasic microporous materials (containing solid, liquid, and gas) are of interest in electrocatalysis. In this exploratory study, a polymer of intrinsic microporosity (PIM-EA-TB) is impregnated with PdCl42− metal precursor and vacuum‑carbonised to give an electrically conductive microporous heterocarbon with embedded Pd nanoparticles of typically 10–30nm diameter. This microporous composite catalyst is formed (via spin-coating) as “flakes” of typically 100nm thickness and 1 to 20μm diameter that are readily re-deposited onto glassy carbon electrode substrates. Due to the triphasic conditions, Pd@cPIM electrocatalytic reactivity is high but only for gases (H2 oxidation or O2 reduction). This selectivity is observed even in the presence of excess formic acid fuel in the aqueous/liquid phase. The potential for application in membrane-less micro-fuel cells is discussed.

Gold Particles Supported on Amino‐Functionalized Silica Catalyze Transfer Hydrogenation of N‐Heterocyclic Compounds

AbstractIn this work we demonstrate that exceptionally small gold particles (d=0.6±0.2 nm) supported on amino‐functionalized mesoporous silicate SBA‐15 are highly active in transfer hydrogenation of structurally diverse unsaturated N‐heterocyclic compounds. The heterocyclic ring is reduced selectively. The gold particles aggregate to a diameter of 4–5 nm in the presence of formic acid/triethylamine (hydrogen donor) during the first catalytic run. In subsequent cycles the nanoparticles maintain their size, yielding a very stable catalytic system that was recycled more than five times. In contrast, analogous SBA catalysts featuring larger (∼5–35 nm) gold particles are not active. Excess formic acid also leads to the formation of formamide derivatives of the products of hydrogenation, which can be deformylated quantitatively. Fifteen structurally different substrates, including the scaffolds of quinoline, isoquinoline, quinoxaline, acridine, phenanthroline, quinazoline, and phenanthridine are hydrogenated and deformylated to give the amine products in >90% overall yield. Deuterium labeling experiments indicate that 1,2‐addition with subsequent disproportionation of the formed intermediate is the preferred reaction path over the 1,4‐addition one, suggesting the participation of a gold hydride species.magnified image

Heterogeneous Catalytic Transfer Partial-Hydrogenation with Formic Acid as Hydrogen Source Over the Schiff-Base Modified Gold Nano-Catalyst

The catalytic hydrogenation transformation with gaseous hydrogen in liquid phase always refers to a harsh condition and over-hydrogenation, and it is highly desired to develop new methods with partial-hydrogenation at mild condition. Herein, a heterogeneous catalytic transfer partial-hydrogenation strategy with formic acid as hydrogen source was developed over the Schiff-base modified gold nano-catalysts. The Au/Schiff-SiO2 catalyst was successfully prepared by one pot aldimine condensation and NaBH4 reduction of a gold precursor. The characterization results indicated that the gold nanoparticles with an average size below 2 nm were highly dispersed over the Schiff-base modified silica support. Such Schiff-based gold nano-catalysts exhibits excellent activity and partial-hydrogenation selectivity, with a high yield (>99%) for phenylacetylene partial-hydrogenation and achieving a 75% chemoselectivity for imines at a relative low temperature and atmospheric pressure. More importantly, the excess of formic acid can be removed by the direct dissociation of formic acid over Au/Schiff-SiO2 catalyst with CO2 emission into atmosphere, which leads to a hydrogen source as clean as hydrogen gaseous, but with a much more high activity and selectivity under mild reaction process.

Template-directed syntheses of two 3D metal oxalates: in situ N-methylation and crystal structures

Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn2(C2O4)3]·4H2O (1), and (dmdabco)[Co2(C2O4)3]·4H2O (2) (C2O42− = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco2+ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes.

The Model [NiFe]-Hydrogenases of Escherichia coli.

In Escherichia coli, hydrogen metabolism plays a prominent role in anaerobic physiology. The genome contains the capability to produce and assemble up to four [NiFe]-hydrogenases, each of which are known, or predicted, to contribute to different aspects of cellular metabolism. In recent years, there have been major advances in the understanding of the structure, function, and roles of the E. coli [NiFe]-hydrogenases. The membrane-bound, periplasmically oriented, respiratory Hyd-1 isoenzyme has become one of the most important paradigm systems for understanding an important class of oxygen-tolerant enzymes, as well as providing key information on the mechanism of hydrogen activation per se. The membrane-bound, periplasmically oriented, Hyd-2 isoenzyme has emerged as an unusual, bidirectional redox valve able to link hydrogen oxidation to quinone reduction during anaerobic respiration, or to allow disposal of excess reducing equivalents as hydrogen gas. The membrane-bound, cytoplasmically oriented, Hyd-3 isoenzyme is part of the formate hydrogenlyase complex, which acts to detoxify excess formic acid under anaerobic fermentative conditions and is geared towards hydrogen production under those conditions. Sequence identity between some Hyd-3 subunits and those of the respiratory NADH dehydrogenases has led to hypotheses that the activity of this isoenzyme may be tightly coupled to the formation of transmembrane ion gradients. Finally, the E. coli genome encodes a homologue of Hyd-3, termed Hyd-4, however strong evidence for a physiological role for E. coli Hyd-4 remains elusive. In this review, the versatile hydrogen metabolism of E. coli will be discussed and the roles and potential applications of the spectrum of different types of [NiFe]-hydrogenases available will be explored.

Mechanism of Brønsted acid-catalyzed glucose dehydration.

We present the first DFT-based microkinetic model for the Brønsted acid-catalyzed conversion of glucose to 5-hydroxylmethylfurfural (HMF), levulinic acid (LA), and formic acid (FA) and perform kinetic and isotopic tracing NMR spectroscopy mainly at low conversions. We reveal that glucose dehydrates through a cyclic path. Our modeling results are in excellent agreement with kinetic data and indicate that the rate-limiting step is the first dehydration of protonated glucose and that the majority of glucose is consumed through the HMF intermediate. We introduce a combination of 1) automatic mechanism generation with isotopic tracing experiments and 2) elementary reaction flux analysis of important paths with NMR spectroscopy and kinetic experiments to assess mechanisms. We find that the excess formic acid, which appears at high temperatures and glucose conversions, originates from retro-aldol chemistry that involves the C6 carbon atom of glucose.

Facile in situ syntheses of new templates and formations of three zinc phosphates

Three new organically templated zinc phosphates, namely, [dmdabco][Zn2(HPO4)3]·(H2O) (1), [tmpip]0.5[Zn2(HPO4)2(H2PO4)] (2) and [tmpip][Zn3(HPO4)4] (3) (dmdabco=N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane, tmpip=N,N,N′,N′-tetramethyl-piperazinium), were successfully synthesized under solvothermal reactions and structurally characterized by single-crystal X-ray diffraction. The dmdabco2+ and tmpip2+ templating agents were derived respectively from simple in situ N-alkylation transformations between the methanol solvent and organic cyclic aliphatic diamines, 1,4-diazabicyclo[2,2,2]octane (dabco) in 1 and 1-methylpiperazine in 2 and 3. Such direct methylation feature is unique, and quite different from conventional Eschweiler–Clarke methylation in which an excess of formic acid and formaldehyde was required. Compound 1 exhibits a 4-connected 2D (4, 4) net with pentameric [Zn2(HPO4)3] clusters as secondary building units (SBUs); 2 possesses a complex double layered structure with 12-ring windows. Compound 3 has a (3, 4)-connected 3D pcu architecture with heptameric [Zn3(HPO4)4] clusters as SBUs, forming intersecting 8- and 12-ring channels.

Synthesis and structural characterization of two open-framework zinc phosphites with (3,4)-connected networks

Two new organically templated zinc phosphites, [H2dmpip][Zn3(HPO3)4] (1) and [HMedmpip][Zn3(HPO3)4] (2), where dmpip=2,6-dimethyl-piperazine and Medmpip=N-methyl-2,6-dimethyl-piperazinium, have been synthesized and structurally characterized. Note that the new Medmpip2+ template in 2 is generated from in situ N-methylation reaction between CH3OH and the dmpip amine precursor, which is used to serve as template in 1. Such direct N-methylation transformation is unique, and quite different from conventional Eschweiler–Clarke methylation in which an excess of formic acid and formaldehyde was required. Both compounds are constructed from strictly alternating ZnO4 and HPO3 units, and possess different (3,4)-connected interrupted frameworks with intersecting 8-, 10- and 12-ring channels (for 1), and 8-, 12-ring channels (for 2), respectively. The occurrence of helical channels in the open structure of 1, and fascinating hydrogen-bonded helices between the host inorganic chains and guest organic templates are also noteworthy.

Series of crystalline beryllium phosphates including new templates generated by in situ N-methylation transformation

Four new organically templated beryllium phosphates, [Hmampy][Be(HPO4)2] (1), [dmdabco][Be3(HPO4)4]·(H2O)1.5 (2), [tmpip][Be(HPO4)(H2PO4)]2 (3) and [tmpip][Be2(HPO4)2(H2PO4)]2 (4), where Hmampy = monoprotonated N-methyl-3-(aminomethyl) pyridinium), dmdabco = N,N′-dimethyl-1,4- diazabicyclo[2,2,2]octane and tmpip = N,N,N′,N′-tetramethyl-piperazinium, were hydrothermally synthesized involving in situ generation of structure-directing agents. The Hmampy2+, dmdabco2+ and tmpip2+ templates were in situ generated by methylation of organic cyclic amines: 3-(aminomethyl)pyridine (ampy) in 1, 1,4-diazabicyclo[2,2,2]octane (dabco) in 2, 1,4-dimethyl-piperazine (dmpip) in 3 and piperazine (pip) in 4. This methylation is different from the conventional Eschweiler–Clarke reaction in which an excess of formic acid and formaldehyde is required. Compound 1 contains infinite inorganic chains which are linked by the organic templates in helical hydrogen-bondings, and 2 and 3 possess different layers with eight- and twelve-membered apertures, respectively. Compound 4 has a three-dimensional interrupted open-framework which is constructed from two-dimensional sheets pillared by phosphate nodes, forming intersecting 8-, 10- and 12-ring channels.

Syntheses and characterizations of zinc phosphites with new templates generated by N-alkylation transformations

Two new organically templated zinc phosphites, [tmpip]0.5[Zn2(HPO3)2(H2PO3)] (1) and [dmdabco][Zn3(HPO3)4]·(H2O) (2), have been synthesized under solvothermal conditions, where tmpip=N,N,N′,N′-tetramethyl-piperazinium and dmdabco=N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane. Note that the templating agents tmpip2+ and dmdabco2+ originated from in situ N-methylation transformations between CH3OH solvent and corresponding cyclic aliphatic amine precursors, i.e. piperazine, 1-methylpiperazine or 1,4-dimethylpiperazine in 1, and 1,4-diazabicyclo[2,2,2]octane in 2. Distinct from conventional Eschweiler–Clarke methylation with excess formic acid and formaldehyde, such direct methylation transformation from methanol molecules is unique. Compound 1 consists of ZnO4 tetrahedra, HPO3 and HPO2(OH) pseudopyramids, exhibiting a complex double layered structure with 12-ring windows. Compound 2 is constructed from strictly alternating ZnO4 tetrahedra and HPO3 pseudopyramids, and possesses a (3,4)-connected interrupted architecture with intersecting 8- and 12-ring channels.

Selective Synthesis of Glyceryl Tris[9,10‐(threo)‐dihydroxyoctadecanoate

AbstractElaborating novel triacylglyceride (TAG) based polyester hyperbranched unimolecular encapsulating agents represents an original and promising approach to the selective delivery of hydrophobic biologically active compounds. However, selective modification of double bonds in unsaturated TAG to obtain corresponding pure polyhydroxy derivatives with high yields is still a big challenge. Two novel approaches to synthesize the glyceryl tris[9,10‐(threo)‐dihydroxyoctadecanoate] were proposed and tested: (1) via the bromination and nucleophilic substitution of secondary halide functions by oxyacetyl groups followed by the hydrolysis of acetyls, and (2) direct transformation of the double bonds by the reaction with peroxoformic acid in an excess of formic acid, and the removal of formyl protective groups. Glycerol trioleate and natural olive oil were used as starting materials. The first synthetic route allowed for successful preparation of the corresponding polyhalide and polyoxyacetyl products; however, a more effective final deacetylation procedure is required. The second proposed approach showed a very good reproducibility in obtaining hydroxy‐oxyformyl derivatives. The optimal conditions of the reaction involve the use of diethyl ether as a cosolvent and stirring at room temperature for 30 min. To remove the formyl groups, three original procedures using organic solvent medium at room temperature were proposed: in the presence of cesium carbonate in chloroform–methanol mixture, and two methods using hydrochloric acid in chloroform–methanol mixture or in acetone. All three methods were efficient to carry out the deformylation; nevertheless, TAG esters remained stable only with 15–17 % hydrochloric acid in acetone. Simple isolation procedures and high overall yields (95.6 and 94.9 % for both triolein and olive oil, respectively) allow considering the second approach as a promising method to obtain threo‐polyhydroxy derivatives from unsaturated TAG.

In situ template generation via N-alkylation in the syntheses of open-framework zinc phosphites and phosphate

In methanol-aqueous solutions, three novel structure-directing agents (SDAs) were generated in situ and presented. These in situ reactions feature N-methylation transformations between CH3OH solvent and organic cyclic aliphatic and aromatic amines, i.e. 2-methylpiperazine, 1,4-diazabicyclo[2,2,2]octane (dabco) and 3-(aminomethyl)pyridine. Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such a direct methylation transformation from methanol molecules is unique. In the presence of new SDAs, three organically templated zinc phosphites/phosphates, [pmpip][Zn3(HPO3)4] I (pmpip = N,N,N',N'-tetramethyl-2-methylpiperazinium), [dmdabco][Zn3(HPO3)4] II (dmdabco = N,N'-dimethyl-1,4-diazabicyclo[2,2,2]octane) and [Hmampy][Zn2(HPO4)3] III (mampy = N-methyl-3-(aminomethyl)pyridine), have been prepared and structurally characterized by elemental analysis, IR, thermogravimetric analysis, powder and single-crystal X-ray diffraction. Compound I exhibits a 2D layer with eight-membered apertures, compounds II and III possess a 3D interrupted framework with intersecting 8-, 10- and 12-ring channels (for II), and 8-, 10-ring channels (for III), respectively.

Towards Mixed Fuels: The Electrochemistry of Hydrazine in the Presence of Methanol and Formic Acid

The electrochemistry of formic acid, carbon monoxide and methanol have been investigated and evaluated in combination with hydrazine. Hydrazine was observed to display the anticipated steady-state oxidation waves at platinum (Pt) microelectrodes by cyclic voltammetry, and upon introduction of carbon monoxide (CO) gas, the Pt surface was fully passivated (prior to CO oxidation). However, the two individual responses of hydrazine and formic acid (HCOOH) are to be additive when combined in solution. No detrimental effects were observed upon the hydrazine voltammetry, even in the presence of excess formic acid, despite formic acid clearly displaying characteristic self-poisoning tendencies (primarily due to the formation of CO) in its own voltammetry. Effects intermediate to those of CO and formic acid were observed when methanol was present. Currents were essentially additive at low methanol content, but hydrazine oxidation current decreased by about 40% when an 100-fold excess of methanol was present, corresponding to poisoning by methanol dehydrogenation intermediates. These results are discussed with relevance to mixed fuels for more flexible or powerful fuel cells, and the possible formation of a random microelectrode array (templated by strongly adsorbed poison) on the microelectrode surface.

Efficient fermentation of xylose to ethanol at high formic acid concentrations by metabolically engineered Saccharomyces cerevisiae

Recombinant yeast strains highly tolerant to formic acid during xylose fermentation were constructed. Microarray analysis of xylose-fermenting Saccharomyces cerevisiae strain overexpressing endogenous xylulokinase in addition to xylose reductase and xylitol dehydrogenase from Pichia stipitis revealed that upregulation of formate dehydrogenase genes (FDH1 and FDH2) was one of the most prominent transcriptional events against excess formic acid. The quantification of formic acid in medium indicated that the innate activity of FDH was too weak to detoxify formic acid. To reinforce the capability for formic acid breakdown, the FDH1 gene was additionally overexpressed in the xylose-metabolizing recombinant yeast. This modification allowed the yeast to rapidly decompose excess formic acid. The yield and final ethanol concentration in the presence of 20 mM formic acid is as essentially same as that of control. The fermentation profile also indicated that the production of xylitol and glycerol, major by-products in xylose fermentation, was not affected by the upregulation of FDH activity.