Aluminum Hydride Research Articles

Highly accurate CCSD(T) homolytic Al–H bond dissociation enthalpies – chemical insights and performance of density functional theory

We obtain gas-phase homolytic Al–H bond dissociation enthalpies (BDEs) at the CCSD(T)/CBS level for a set of neutral aluminium hydrides (which we refer to as the AlHBDE dataset). The Al–H BDEs in this dataset differ by as much as 79.2 kJ mol−1, with (H2B)2Al–H having the lowest BDE (288.1 kJ mol−1) and (H2N)2Al–H having the largest (367.3 kJ mol−1). These results show that substitution with at least one –AlH2 or –BH2 substituent exerts by far the greatest effect in modifying the Al–H BDEs compared with the BDE of monomeric H2Al–H (354.3 kJ mol−1). To facilitate quantum chemical investigations of large aluminium hydrides, for which the use of rigorous methods such as W2w may not be computationally feasible, we assess the performance of 53 density functional theory (DFT) functionals. We find that the performance of the DFT methods does not strictly improve along the rungs of Jacob’s Ladder. The best-performing methods from each rung of Jacob’s Ladder are (mean absolute deviations are given in parentheses): the GGA B97-D (6.9), the meta-GGA M06-L (2.3), the global hybrid-GGA SOGGA11-X (3.3), the range-separated hybrid-GGA CAM-B3LYP (2.1), the hybrid-meta-GGA ωB97M-V (2.5) and the double-hybrid methods mPW2-PLYP and B2GP-PLYP (4.1 kJ mol−1).

An ambient pressure, direct hydrogenation of ketones.

We report two bifunctional (pyridyl)carbene-iridium(I) complexes that catalyze ketone and aldehyde hydrogenation at ambient pressure. Aryl, heteroaryl, and alkyl groups are demonstrated, and mechanistic studies reveal an unusual polarization effect in which the rate is dependant of proton, rather than hydride, transfer. This method introduces a convenient, waste-free alternative to traditional borohydride and aluminum hydride reagents.

HYDROGENATION OF SILICON, ALUMINUM AND CHLORINE AS CONSTITUENTS OF TARFAYA OIL SHALE (MOROCCO) AT 550°C AND 750°C

The formation of hydrogen chloride as well as silicon hydrides and aluminum hydrides called silanes and alanes respectively are formed when oil shale are thermally treated with hydrogen. These elements are part of the constituents of this oil shale. This work was carried out by a thermobalance (Red Croft) in the dynamic regime for thermal hydrogenation at 550°C and 750°C. The quantitative identification of the elements was done by X-ray diffraction using a dispersive method, a technique that is coupled to the scanning microscope. This work being the continuation of the one already carried out at a temperature of 550°C (A.Attaoui and M. Hafid: 2022), we have extended this to higher temperatures where we have decompositions in addition to kerogen as well as mineral matter. Studies comparing the thermal decomposition of oil shale and kerogen have shown that the mineral matter in oil shale provides surfaces capable of cracking high molecular weight products by thermal or catalytic mechanisms (A.K. Burnham, A. K and J.A.Happe: 1984). These studies indicate that reactions involving the cleavage of carbon-carbon bonds and carbon-hydrogen bonds on mineral surfaces (R.A.Regtop et al: 1985). These authors demonstrated that the carbonized residue in spent shale can increase the magnitude of secondary reactions.

Synthesis and Structural Comparisons of NHC-Alanes

N-heterocyclic carbenes (NHCs) are widely used in organometallic chemistry. Here, we examine the role of NHCs in the stabilisation of aluminium hydrides, AlH3, also known as alanes. This includes an assessment of the various synthetic strategies, comparisons of structural parameters and theoretical insight. Based on percent buried volume (%Vbur) parameters, we report the largest and smallest NHC alanes to date, with noted differences in their observed stability in both the solution and solid state.

Hydroboration of a Diolate Complex Obtained by Carbon Dioxide Capture with Acenaphthenediimine Aluminum Hydride

The reduction of diolate [{(dpp-bian)Al(μ-O2CH2)}2] (1), bearing a redox-active acenaphthene-1,2-diimine ligand (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]-acenaphthene), by boranes has been studied. The reaction of 1 with HBpin proceeds with reduction of the C–O bonds in the −O–CH2–O– fragments and results in [{(dpp-bian)Al(OCH3)}(μ-O){Al(OBpin)(dpp-bian)}] (2) and pinBOCH3. The reduction of 1 by HBcat leads to the formation of the compound [{(dpp-bian)Al(μ-Cat)}2] (3) and (CH3OBO)3. BH3·SMe2 reduces diolate 1 to form the complex [{(dpp-bian)Al(OCH3)}(μ-O){Al(OCH2OBH2)(dpp-bian)}] (4). Compounds 2–4 have been characterized by electron paramagnetic resonance and infrared spectroscopy, and their molecular structures have been determined by single-crystal X-ray analysis. Density functional theory calculations have been performed to analyze the reaction energies and a possible mechanism of an initial stage as well as to explain the different product types.

Synthesis of (±)‐Physovenine through Electrochemical C−O Bond Formation

AbstractWe investigated an electrochemical C−O bond formation approach to (±)‐physovenine. The reaction conditions are mild compared to canonical routes, which typically utilize strong hydride reagents such as lithium aluminum hydride. This enabled extension of the electrochemical cyclization to a substrate bearing the fully functionalized phenyl ring of the natural product. The electrochemical cyclization is diastereoselective and starting from enantiopure substrate would provide a single enantiomer of physovenine. In the course of an initial formal synthesis, we identified conditions to afford modest enantioselective substrate synthesis that demonstrate the feasibility of an enantioselective synthesis. Among the substrates investigated, acetyl‐, tosyl‐ or Boc‐nitrogen substitution led to an alternative electrochemical C−O bond formation pathway where the hydroxyl nucleophile cyclized onto the aromatic ring vs. the 2‐position of the indoline. This work expands the utility of electrochemical C−O bond formation and provides a foundation for further applications to functionalized cyclic ether construction.

Post-polymerization modification of poly(ethyl sorbate) leading to various alternating copolymers

Eight novel alternating copolymers that are not accessible with general methodologies have been synthesized by the post-polymerization modification of poly(propylene-alt-allyl alcohol)100 (PPAA100). PPAA100 is obtained from a group transfer polymerization (GTP) made poly(ethyl sorbate)100 (PES100) by first hydrogenating its backbone double bonds followed by reducing its pendent esters to hydroxyl groups using lithium aluminum hydride. The post-polymerization modification of PPAA100 includes its condensation reactions with three reactive electrophiles, and its Mitsunobu reactions with five nucleophiles. The chemical transformations of the hydroxyl group to other functionalities have resulted in the eight unique head-to-head alternating copolymers which possess a fixed propylene structural unit and an allyl alcohol derived monomeric unit, such as allyl ester, sulfonate, phosphate, ether, halide, and imide. The chemical structures of the obtained polymers are verified by 1H and 13C NMR and FT-IR spectroscopies. Finally, the thermal properties of the resulting polymers with different side groups are studied.

Formic Acid Dehydrogenation via an Active Ruthenium Pincer Catalyst Immobilized on Tetra-Coordinated Aluminum Hydride Species Supported on Fibrous Silica Nanospheres

Formic Acid Dehydrogenation via an Active Ruthenium Pincer Catalyst Immobilized on Tetra-Coordinated Aluminum Hydride Species Supported on Fibrous Silica Nanospheres

Improved Dehydrogenation Properties of LiAlH4 by Addition of Nanosized CoTiO3.

Despite the application of lithium aluminium hydride (LiAlH4) being hindered by its sluggish desorption kinetics and unfavourable reversibility, LiAlH4 has received special attention as a promising solid-state hydrogen storage material due to its hydrogen storage capacity (10.5 wt.%). In this work, investigated for the first time was the effect of the nanosized cobalt titanate (CoTiO3) which was synthesised via a solid-state method on the desorption behaviour of LiAlH4. Superior desorption behaviour of LiAlH4 was attained with the presence of a CoTiO3 additive. By means of the addition of 5, 10, 15 and 20 wt.% of CoTiO3, the initial desorption temperature of LiAlH4 for the first stage was reduced to around 115-120 °C and the second desorption stage was reduced to around 144-150 °C, much lower than for undoped LiAlH4. The LiAlH4-CoTiO3 sample also presents outstanding desorption kinetics behaviour, desorbing hydrogen 30-35 times faster than undoped LiAlH4. The LiAlH4-CoTiO3 sample could desorb 3.0-3.5 wt.% H2 in 30 min, while the commercial and milled LiAlH4 desorbs <0.1 wt.% H2. The apparent activation energy of the LiAlH4-CoTiO3 sample based on the Kissinger analysis was decreased to 75.2 and 91.8 kJ/mol for the first and second desorption stage, respectively, lower by 28.0 and 24.9 kJ/mol than undoped LiAlH4. The LiAlH4-CoTiO3 sample presents uniform and smaller particle size distribution compared to undoped LiAlH4, which is irregular in shape with some agglomerations. The experimental results suggest that the CoTiO3 additive promoted notable advancements in the desorption performance of LiAlH4 through the in situ-formed AlTi and amorphous Co or Co-containing active species that were generated during the desorption process.

Limonin Derivatives via Hydrogenation: Structural Identification and Anti-Inflammatory Activity Evaluation

Limonin is a natural compound which is rich in the fruit of various plants of the Rutaceae family and demonstrated to have a wide range of biological activities. In this work, seven limonin derivatives were successfully synthesized by hydrogenation of limonin, using different reducing agents (sodium cyanoborohydride, lithium aluminum hydride, and sodium borohydride). The chemical structure of the seven derivatives was characterized and identified by a series of techniques, including HR-ESI-MS, 1H-NMR, 13C-NMR, 2D-NMR, and IR. Among the seven limonin derivatives, six limonin derivatives were found to be new compounds which have not been previously reported. Then, the anti-inflammatory activities of the seven synthesized limonin derivatives, as well as the anti-inflammatory activities of eight known natural limonins, were evaluated and compared. Natural limonins, 30-O-Acetylhainangranatumin E and Xylogranatin A, presented significantly better anti-inflammatory activity. Xylogranatin A could inhibit LPS-induced RAW264.7 cell inflammatory factors, with a 90.0% inhibition ratio of TNF-α and 63.77% inhibition ratio of NO release in LPS-induced BV2 cells at 10 μM. Other natural limonins showed poor anti-inflammatory activity. In comparison, all the synthetic limonin derivatives showed decent anti-inflammatory activities, with the highest inhibition ratio of TNF-α of 37.8% and inhibition ratio of NO release of 12.5% in LPS-induced BV2 cells at 10 μM.

Aluminium‐Catalyzed Selective Reduction of Heteroallenes Through Hydroboration: Amide/Thioamide/Selenoamide Bond Construction and C=X (X=O, S, Se) Bond Activation**

AbstractAn unprecedented conjugated bis‐guanidinate (CBG) stabilized aluminium dihydride, [LAlH2; (L={(ArNH)(ArN)−C=N−C=(NAr)(NHAr)}; Ar=2,6‐Et2‐C6H3)] (I) catalyzed chemoselective hydroboration of heteroallenes such as carbodiimide (CDI)s, isocyanates, isothiocyanates, and isoselenocyanates is reported. A wide range of heteroallenes, including electron‐donating and withdrawing groups, experience hydroboration to obtain selectively N‐boryl amide, N‐borylaminal, and N‐boryl methyl amine products. More importantly, a single sustainable molecular aluminium‐based catalyst effectively catalyzes CDIs, isocyanates, isothiocyanates, and isoselenocyanates into formamidines, formamides, thioformamides, and selenoformamides, respectively. Further, heteroallene substrates undergo hydrodeoxygenation (HDO), hydrodesulfurization (HDS), and hydrodeselenization (HDSe) reactions leading to N‐boryl methyl amines. In addition, a series of control and kinetic experiments indicate that the aluminium hydride species are essential for all partial and complete reduction steps and breaking the C=X (X=O, S, and Se) bonds in heteroallenes.

Synthesis of β,γ‐unsaturated ketones with quaternary centers through regioselective hydroacylation of allenes with acyl chlorides

AbstractThe one‐pot synthesis of β,γ‐unsaturated ketones bearing all‐carbon quaternary centers at the α‐position via a highly regioselective hydroacylation of allenes using acyl chlorides and aluminum hydride is reported. The Cu‐catalyzed hydroalumination of 1,1‐disubstituted and 1,1,3‐trisubstituted allenes with diisobutylaluminum hydride resulted in allylaluminum reagents that underwent regioselective acylation in the presence of acid chlorides. Various derivatives of allenes and acyl chlorides were compatible with this process, and α‐quaternary ketones were obtained in high yields with excellent regioselectivity.

Effects of aluminum and aluminum hydride additives on the performance of hybrid rocket motors based on 95% hydrogen peroxide

This paper aims to study experimentally and numerically the effects of aluminum (Al) and aluminum hydride (AlH3) additives on the performance of HRMs. A steady-state numerical model of HRM is established, which adopts the 95% hydrogen peroxide (HP) as the oxidizer. A firing test is completed for the certification of the numerical simulation model, the results illustrate that the regression rate of addition of 38% AlH3 and 20% Al increases by 55.6% compared with pure hydroxyl-terminated polybutadiene (HTPB). A good agreement exists between the simulation regression rate and the experimental data. The deviations of thrust and pressure are less than 3.3% and 3.7%, respectively. Specifically, the error of the regression rate is only 0.3%, indicating that the accuracy of adopting numerical simulation method to predict the characteristics of the HRM is acceptable. Several steady-state simulations based on the different content of AlH3 and Al are performed to investigate the effects on regression rate and combustion performance of the HRM. Due to the addition of H2, the thermal conductivity increases with the decrease of the mass fraction of AlH3, which leads to the increase of the regression rate. The regression rate of the fuel with 8% AlH3 and 50% Al increases by 35.5% than the fuel with 58% AlH3, demonstrating that the effect of Al on the regression rate enhancement is more than that of AlH3. The theoretical specific impulse increases with the mass fraction of AlH3. However, it is owing that the part of H2 does not participate in the reaction with O2 and the oxidizer to fuel ratio (O/F) is far from the optimal O/F, the specific impulse is lower than the theoretical specific impulse.

Improved hydrogen storage properties and mechanisms of LiAlH4 doped with Ni/C nanoparticles anchored on large-size Ti3C2Tx

Lithium aluminum hydride (LiAlH4) with a high hydrogen capacity of 10.5 wt% has become one of the most promising solid-state hydrogen storage materials for onboard hydrogen fuel cell systems. However, neither dehydrogenation kinetics nor cycling behaviors of LiAlH4 can fulfill the requirements of practical application. Here, we prepared the Ni/C nanoparticles anchored on large-size Ti3C2Tx nanosheets, firstly introduced into LiAlH4 to investigate its catalytic effect. Dehydrogenation experiments demonstrate that LiAlH4 doped with 7 wt% Ni/C@Ti3C2 starts to release hydrogen at 56.9 °C. Also, it can release about 4.3 wt% hydrogen within 50 min at 120 °C. The activation energies of LiAlH4 doped with 7 wt% Ni/C@Ti3C2 for the first and second steps are 34.5% and 53.2% lower than the as-received LiAlH4, respectively. Under 300 °C and 40 bar hydrogen, it can absorb 0.58 wt% hydrogen. It is found that in situ formed intermetallic Al2Ti during ball milling can weaken the Al-H bonds in LiAlH4 through interfacial charge transfer and the dehybridization, benefitting for the breaking of the Al-H bond in LiAlH4. In addition, Al2Ti can promote the adsorption and splitting of H2, contributing to the rehydrogenation of LiAlH4.

Directed Stabilization by Air-Milling and Catalyzed Decomposition by Layered Titanium Carbide Toward Low-Temperature and High-Capacity Hydrogen Storage of Aluminum Hydride.

AlH3 is a metastable hydride with a theoretical hydrogen capacity of 10.01 wt % and is very easy to decompose during ball milling especially in the presence of many catalysts, which will lead to the attenuation of the available hydrogen capacity. In this work, AlH3 was ball milled in air (called "air-milling") with layered Ti3C2 to prepare a Ti3C2-catalyzed AlH3 hydrogen storage material. Such air-milled and Ti3C2-catalyzed AlH3 possesses excellent hydrogen storage performances, with a low initial decomposition temperature of just 61 °C and a high hydrogen release capacity of 8.1 wt %. In addition, 6.9 wt % of hydrogen can be released within 20 min at constantly 100 °C, with a low activation energy as low as 40 kJ mol-1. Air-milling will lead to the formation of an Al2O3 oxide layer on the AlH3 particles, which will prevent continuous decomposition of AlH3 when milling with active layered Ti3C2. The layered Ti3C2 will grip on and intrude into the AlH3 particle oxide layers and then catalyze the decomposition of AlH3 during heating. The strategy employing air-milling as a synthesis method and utilizing layered Ti3C2 as a catalyst in this work can solve the key issue of severe decomposition during ball milling with catalysts economically and conveniently and thus achieve both high-capacity and low-temperature hydrogen storage of AlH3. This air-milling method is also effective for other active catalysts toward both reducing the decomposition temperature and increasing the available hydrogen capacity of AlH3.

Effect of α-AlH3 content on ignition and combustion characteristics of multicomponent mixtures

Aluminum hydride (alane, AlH3) is a promising energetic material that can significantly increase the specific impulse of propellants while lowering the combustion temperature. In this work, a CO2 laser was adopted to investigate the effect of α-AlH3 content on the ignition and combustion characteristics of AlH3–Al, AlH3–ammonium perchlorate (AP), AlH3–Al–AP, and AlH3–Al–AP–hydroxyl-terminated polybutadiene (HTPB) mixtures (namely, samples DAl, DAP, T, and Q, respectively). The DAl samples formed a mushroom flame at the beginning of combustion due to the Kelvin-Helmholtz effect under the heat flow generated by the combustion of H2 released from AlH3. The rapid hydrogen release caused the flame to break away from the sample to form a “dark zone”, whose height gradually shortened. The high AlH3 content promoted the decomposition of HTPB to C4 species, resulting in a “dark zone” for Q samples during ignition. The DAP and T samples combusted intensely with lower ignition delay time (ti) and combustion time (tc) and higher maximum combustion temperature (Tmax) than the other two samples due to the AP. The combustion temperatures of the mixed samples were effectively decreased, while the combustion rates were also accelerated by partially replacing Al with AlH3. As the rate of AlH3:Al was increased from 1:3 to 3:1, the Tmax of the DAl, T, and Q samples decreased by 113, 276, and 128 K, respectively, whereas tc decreased by 16.18 %, 32.11 %, and 8.18 %, respectively. However, the ti of the Q samples increased with increasing AlH3, probably because a large amount of hydrogen release exacerbated the effect of the porous layer, thus hindering the escape of the gas phase products. In addition, only weak Al(g) characteristic emission spectra were observed during combustion, which is due to the HTPB adhesion largely inhibiting the combustion of metallic fuels.

Effect and mechanism of lithium aluminium hydride on the pyrolysis process of RDX

Searching for efficient additives for explosives and propellants is always desirable but challenging. To understand the contribution of lithium aluminium hydride (LiAlH4) to the decomposition process of cyclotrimethylenetrinitramine (RDX), the thermal decomposition behaviours of RDX with various ratios of LiAlH4 addition were investigated by thermogravimetric-differential scanning calorimetry (TG-DSC). The main pyrolysis gas products of RDX, RDX/LiAlH4 (4:1) and RDX/LiAlH4 (1:1) were compared by combining thermogravimetric-Fourier infrared spectroscopy (TG-FTIR) and thermogravimetric-photoionization mass spectrometry (TG-MS) techniques, and the influence of LiAlH4 on the main RDX pyrolysis pathways was analysed. The results show a strong interaction between LiAlH4 and RDX during thermal decomposition, and the decomposition peak temperature of RDX decreases from 239.8 °C to about 166.4 °C coupled with explosive decomposition. In the presence of LiAlH4, the active hydrogen of the melted LiAlH4 interacts with the nitro-oxygen of RDX, significantly decreasing the decomposition temperature of RDX and changing the decomposition pattern. This study contributes to further insight into the pyrolysis properties and decomposition mechanism of nitramine energetic materials in the presence of metal hydrides.

Comparative ballistic efficiency of solid composite propellants: which plasticizer/polymer combination is the energetically preferred binder?

The relative efficacy of real energetic plasticizers and polymers for model solid composite propellants comprising 25% aluminum hydride, 50% dinitramide ammonium salt and 25% binder (20% a plasticizer and 5% a polymer) has been estimated. The quantitative dependence of the efficiency of plasticizers on the value of their enthalpy of formation ΔHt0, the oxygen coefficient α, percentage of hydrogen %H and density d has been revealed. 3,4-Dinitrofurazan tested as a plasticizer for the binder provides effective impulse values at the 3rd stage up to ∼2 s higher than those for other plasticizers.

Enhanced stability and combustion performance of AlH3 in combination with commonly used oxidizers

Aluminum hydride (AlH3), as a promising fuel, has been utilized to improve the energy performance of propellants. Moreover, the inherent compatibility and mutual interaction between AlH3 and the commonly used oxidizers of solid propellants are the basics of propellant formulation design. Herein, the homogenous composites of AlH3/oxidizer have been prepared by the in-situ recrystallization method, and then their thermal stability, compatibility, and ignition performance have been investigated. The initial decomposition temperatures (Ti) of AlH3 in composites are increased by at least 16 °C, whereas the thermal decomposition peak temperatures (Tp) of involved oxidizers are lower than that of their pure state. The compatibility tests showed that AlH3 is compatible with the mentioned oxidizers. In particular, the induction time of the dehydrogenation of AlH3 in presence of these oxidizers is improved by almost 1.2 times that of raw AlH3, which means that the oxidizers have an unexpected strong stabilization effect on AlH3 due to strong hydrogen bonding. Moreover, the optimized contents of AlH3 in AlH3/HMX, AlH3/CL-20, and AlH3/AP composites have been determined to be 45 %, 40 %, and 33 %, which have the maximum flame temperatures of 1275.3, 1440.4, and 1616.8 °C, respectively. Besides, AlH3/CL-20 has the strongest flame radiation intensity (18.5 K) and shortest ignition delay time (32.2 ms) among the involved composites.

Synthesis and characterization of d5 -barbarin for use in barbarin-related research.

Based on structural similarities and equine administration experiments, Barbarin, 5-phenyl-2-oxazolidinethione from Brassicaceae plants, is a possible source of equine urinary identifications of aminorex, (R,S)-5-phenyl-4,5-dihydro-1,3-oxazol-2-amine, an amphetamine-related US Drug Enforcement Administration (DEA) controlled substance considered illegal in sport horses. We now report the synthesis and certification of d5 -barbarin to facilitate research on the relationship between plant barbarin and such aminorex identifications. D5 -barbarin synthesis commenced with production of d5 -2-oxo-2-phenylacetaldehyde oxime (d5 -oxime) from d5 -acetophenone via butylnitrite in an ethoxide/ethanol solution. This d5 -oxime was then reduced with lithium aluminum hydride (LiAlH4 ) to produce the corresponding d5 -2-amino-1-phenylethan-1-ol (d5 -phenylethanolamine). Final ring closure of the d5 -phenylethanolamine was performed by the addition of carbon disulfide (CS2 ) with pyridine. The reaction product was purified by recrystallization and presented as a stable white crystalline powder. Proton NMR spectroscopy revealed a triplet at 5.88 ppm for one proton, a double doublet at 3.71 ppm for one proton, and double doublet at 4.11 ppm for one proton, confirming d5 -barbarin as the product. Further characterization by high resolution mass spectrometry supports the successful synthesis of d5 -barbarin. Purity of the recrystallized product was ascertained by High Performance Liquid Chromatography (HPLC) to be greater than 98%. Together, we have developed the synthesis and full characterization of d5 -barbarin for use as an internal standard in barbarin-related and equine forensic research.