Intermolecular Hydrogen Transfer Research Articles

Reactive molecular dynamics simulation in the early stage of naphthalene carbonisation

ABSTRACT Molecular simulation methods were utilised to do research into reactive molecular dynamics in the early stage of naphthalene carbonisation. The structural properties and charge distribution of naphthalene were investigated by the quantum chemistry. The net charge distributed on α-position carbon atom was slightly more than that on β-position carbon atom, and the reaction activity of α-position carbon atom was stronger. Reactive force field ReaxFF was used to simulate reactive molecular dynamics. Condensation, pyrolysis, rearrangement and hydrogen transfer reactions happened during the simulation. And the main reaction route in the early stage of naphthalene coking process was acquired. The formation of free radical was initiated by the intermolecular hydrogen transfer reaction rather than homolytic C−H bond dissociation. The reaction mechanism may provide theoretical guidance for the practical production of needle coke.

Initial Decomposition Mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under Shock Loading: ReaxFF Parameterization and Molecular Dynamic Study

We report a reactive molecular dynamic (ReaxFF-MD) study using the newly parameterized ReaxFF-lg reactive force field to explore the initial decomposition mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under shock loading (shock velocity >6 km/s). The new ReaxFF-lg parameters were trained from massive quantum mechanics data and experimental values, especially including the bond dissociation curves, valence angle bending curves, dihedral angle torsion curves, and unimolecular decomposition paths of 3-Nitro-1,2,4-triazol-5-one (NTO), 1,3,5-Trinitro-1,3,5-triazine (RDX), and 1,1-Diamino-2,2-dinitroethylene (FOX-7). The simulation results were obtained by analyzing the ReaxFF dynamic trajectories, which predicted the most frequent chain reactions that occurred before NTO decomposition was the unimolecular NTO merged into clusters ((C2H2O3N4)n). Then, the NTO dissociated from (C2H2O3N4)n and started to decompose. In addition, the paths of NO2 elimination and skeleton heterocycle cleavage were considered as the dominant initial decomposition mechanisms of NTO. A small amount of NTO dissociation was triggered by the intermolecular hydrogen transfer, instead of the intramolecular one. For α-NTO, the calculated equation of state was in excellent agreement with the experimental data. Moreover, the discontinuity slope of the shock-particle velocity equation was presented at a shock velocity of 4 km/s. However, the slope of the shock-particle velocity equation for β-NTO showed no discontinuity in the shock wave velocity range of 3–11 km/s. These studies showed that MD by using a suitable ReaxFF-lg parameter set, could provided detailed atomistic information to explain the shock-induced complex reaction mechanisms of energetic materials. With the ReaxFF-MD coupling MSST method and a cheap computational cost, one could also obtain the deformation behaviors and equation of states for energetic materials under conditions of extreme pressure.

Study on 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) decomposition using online photoionization mass spectrometry and theoretical simulations

5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) is a representative and insensitive energetic compound mainly used as a component of low vulnerable ammunition, but its decomposition process is not clear up to date. Herein, online photoionization mass spectrometry combined with theoretical simulations was employed to shed light on the thermal decomposition mechanism of NTO. The experimental and calculated results provide evidences for the thermal decomposition of NTO through direct ring rupture and intermolecular hydrogen transfer pathways. The initial decomposition step of NTO single molecule is direct ring rupture, followed by NO2 removal. The remaining structure undergoes C-N bond cleavage leading to HN2 dissociation, the CONCH finally decomposes into CO and HCN. The major products of NTO decomposition include N2, CO2, H2N2, NH3, and the minor products are HN2, H3N3, H2O, which is basically consistent with experiments. The formation mechanism of decomposition products is also discussed in detail and the total decomposition pathways are constructed.

Catalytic C–O bond cleavage in a β-O-4 lignin model through intermolecular hydrogen transfer

A base-free and redox neutral approach for the selective breaking of aryl ether bond (C–O) contained by a lignin model compound mimicking a β-O-4 linkage is reported. A palladium loaded metal-organic framework (MOF) was used as a catalyst for this purpose. The reaction proceeds through dehydrogenation of benzylic alcohol moiety followed by the hydrogenolysis of the ether bonds. Therefore, no external hydrogen source is required for the reaction to take place.

Predicted Reaction Mechanisms, Product Speciation, Kinetics, and Detonation Properties of the Insensitive Explosive 2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105).

2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is a relatively new and promising insensitive high-explosive (IHE) material that remains only partially characterized. IHEs are of interest for a range of applications and from a fundamental science standpoint, as the root causes behind insensitivity are poorly understood. We adopt a multitheory approach based on reactive molecular dynamic simulations performed with density functional theory, density functional tight-binding, and reactive force fields to characterize the reaction pathways, product speciation, reaction kinetics, and detonation performance of LLM-105. We compare and contrast these predictions to 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a prototypical IHE, and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX), a more sensitive and higher performance material. The combination of different predictive models allows access to processes operative on progressively longer timescales while providing benchmarks for assessing uncertainties in the predictions. We find that the early reaction pathways of LLM-105 decomposition are extremely similar to TATB; they involve intra- and intermolecular hydrogen transfer. Additionally, the detonation performance of LLM-105 falls between that of TATB and HMX. We find agreement between predictive models for first-step reaction pathways but significant differences in final product formations. Predictions of detonation performance result in a wide range of values, and one-step kinetic parameters show the similar reaction rates at high temperatures for three out of four models considered.

External electric field reduces the explosive sensitivity: a theoretical investigation into the hydrogen transference kinetics of the NH2NO2∙∙∙H2O complex.

Controlling the selectivity of detonation initiation reaction to reduce the explosive sensitivity has been a Holy Grail in the field of energetic materials. The effects of the external electric fields on the homolysis of the N-NO2 bond and initiation reaction dynamics of NH2NO2∙∙∙H2O (i.e., intermolecular and 1,3-intramolecular hydrogen transfers) were investigated at the MP2/6-311++G(2d,p) and CCSD/6-311++G(2d,p)//MP2/6-311++G(2d,p) levels. The results show that the N-NO2 bond is not the "trigger linkage." The notable transiliences of the activation energy of the intermolecular hydrogen transfer are found with the field strength of - 0.012a.u. along the -x-direction, leading to the conversion of the main reaction between the intermolecular and 1,3-intramolecular hydrogen transference. The activation energies of two kinds of the hydrogen transferences are increased under the external electric fields along the -y-direction. In particular, due to the conversion of the main reaction, the activation energies of the overall reaction are increased significantly along the -x-direction, leading to the significant reduced explosive sensitivities. Therefore, by controlling the field strengths and orientations between the "reaction axis" and external electric field along the y- and x-directions, the selectivity of the initiation reaction could be controlled and the explosive sensitivity could be reduced. Employing AIM (atoms in molecules) and surface electrostatic potentials, the origin of the control of reaction selectivity and the reduction of sensitivity is revealed. This work is of great significance to the improvement of the technology that the external electric fields are added safely into the energetic material system to enhance the explosive performance. Graphical abstract.

Electride-Sponsored Radical-Controlled CO2 Reduction to Organic Acids: A Computational Design.

Converting CO2 into high-value chemicals has been regarded as an important solution for a sustainable low-carbon economy. In this work, we have theoretically designed an innovative strategy for the absorption and activation of CO2 by the electride N3Li, that is, 1,3,5(2,6)-tripyridinacyclohexaphane (N3) intercalated by lithium. DFT computations showed that the interaction of CO2 with N3Li leads to the catalytic complex N3Li(η2 -O2 C), which can initiate the radical-controlled reduction of another CO2 to form organic acids through radical reactions in the gas phase. The CO2 reduction consists of four steps: (1) The formation of N3Li(η2 -O2 C) through the combination of N3Li and CO2 , (2) hydrogen abstraction from RH (R=H, CH3 , and C2 H5 ) by N3Li(η2 -O2 C) to form the radical R. and N3Li(η2 -O2 C)H, (3) the combination of CO2 and the radical R. to form RCOO. , and (4) intermolecular hydrogen transfer from the intermediate N3Li(η2 -O2 C)H to RCOO. . In the whole reaction process, the CO2 moiety in the complex N3Li(η2 -O2 C) maintains a certain radical character at the carbon atom of CO2 and plays a self-catalyzing role. This work represents the first example of electride-sponsored radical-controlled CO2 reduction, and thus provides an alternative strategy for CO2 conversion.

Coupling effects of high temperature and pressure on the decomposition mechanisms of 1,1‐diamino‐2,2‐dinitroehethe crystal: Ab initio molecular dynamics simulations

AbstractRecently, Dreger et al. experimentally investigated the phase diagram and decomposition of 1,1‐diamino‐2,2‐dinitroethene (FOX‐7) single crystal compressed hydrostatically up to 10 GPa and heated over a range of 293–750 K (J. Phys. Chem. C 2016, 120, 11092–11098). As a continuation, we performed ab initio molecular dynamic simulations to study the initiation mechanisms and subsequent decomposition of FOX‐7 at a temperature of 504 K (initial decomposition temperature) coupled with a pressure of 1–5 GPa, 604 K at 5GPa, and 704 K at 5 GPa. However, our two compressing ways are different: the former is static hydrostatical compression, while our way is dynamic compression. Our results indicate that the initial decomposition mechanism was dependent on the temperature but independent of the pressure. The initial decomposition step is the bimolecular intermolecular hydrogen transfer. The subsequent decomposition of FOX‐7 is sensitive to both the temperature and pressure. At 504 K, the decomposition of FOX‐7 was accelerated from 1 to 2 GPa and from 3 to 5 GPa but decelerated from 2 to 3 GPa. The temperature exhibits a positive effect on the decomposition. Overall, the temperature and pressure have great cooperative effects on the decomposition of FOX‐7. Our study may provide new insight into understanding the initial mechanisms and decomposition reactions of energetic materials at relatively low temperatures coupled with different pressures in atomic detail.

Controlling the Ratio of the Reactions of Intermolecular Hydrogen Transfer and Cracking on Setups with Fixed and Recycled Catalyst Beds

The effect of the main parameters (temperature, pressure, and dilution of the reaction medium with an inert gas) of such catalytic processes as the cracking of vacuum gasoil and the hydrogenless refining and cracking of gasoline fractions on the ratio of the selectivity of the cracking and intermolecular hydrogen-transfer reactions is studied. Control over the ratio of these reactions allows products to be obtained according to the requirements for processing feedstocks. An increase in the time of feedstock–catalyst contact, a reduction in the degree of diluting the reaction mixture with an inert gas, and a rise in pressure result in greater selectivity for hydrogen-transfer reactions. Experiments are performed on setups with fixed and recycled beds of zeolite-containing catalysts. The transformation of feedstocks containing deuterated compounds is investigated.

Correction to: Simulated Temperature Programmed Desorption of Acetaldehyde on CeO2(111): Evidence for the Role of Oxygen Vacancy and Hydrogen Transfer

The temperature programmed desorption of acetaldehyde adsorbed on partially reduced CeO2(111) has been studied in detail using microkinetic modeling based on self-consistent, periodic density functional theory calculations at the GGA-PW91+U level. Previous experimental studies (Chen et al. J. Phys. Chem. C 115: 3385, 2011; Calaza et al. J. Am. Chem. Soc. 134: 18034, 2012) have shown that, whereas on fully oxidized CeO2(111) acetaldehyde desorbs molecularly with a peak temperature of 210 K, the polymerization and enolization of acetaldehyde dominate the surface reactivity on partially reduced CeO2(111), resulting in acetaldehyde desorption at higher temperatures. Here we propose a comprehensive reaction mechanism that is consistent with the spectroscopic evidence of the identities of the surface intermediates and with the observed desorption activities, including the formation of ethylene and acetylene. Besides acetaldehyde (CH3CHO) and its enolate (CH2CHO), several other C2H x O species are proposed as key intermediates which are not seen spectroscopically, including ethoxy (CH3CH2O), ethyleneoxy (CH2CH2O), and formylmethylene (CHCHO). Our study suggests that oxygen vacancies play the critical role of activating the carbonyl bond and thereby facilitating β C–H bond scissions in acetaldehyde, leading to enolization, intermolecular hydrogen transfer, deoxygenation, and potentially C–C coupling reactions.

Control of Contribution of Cracking and Intermolecular Hydrogen Transfer in Cracking of Gasoline Fractions in Fixed and Circulating Catalyst Bed Reactors

The studies were focused on the influence of key parameters (temperature, pressure, dilution of the reaction medium with an inert gas) of catalytic processes (cracking of vacuum gasoil, hydrogen-free upgrading and cracking of gasoline fractions) on the ratio of selectivities to cracking and intermolecular hydrogen transfer. Controlling the ratio of these reactions allows the required products to be obtained on the feedstock processing. Lengthening of the feedstock-catalyst contact time, a decrease in the proportion of the diluting inert gas, and the pressure rise provides an increase in the selectivity to hydrogen transfer. Fixed and circulating catalyst bed setups were used for the experiments. Transformations of the feedstock containing deuterated compounds were studied.

First-principles investigation of the coupling-induced dissociation of methane and its transformation to ethane and ethylene

Quantum chemical computations predict that compression of the methane dimer to an inter-nuclear separation lower than 2 Å facilitates a concerted coupling and dissociation of CH bonds of the molecules to form ethane/ethylene. In this bimolecular, concerted mechanism, ethane formation is accompanied by production of H radicals from each methane moiety that may further abstract hydrogen atoms to lead to ethylene formation. Alternatively, transformation to ethane and ethylene proceeds via stepwise molecular hydrogen elimination, with the first eliminated hydrogen molecule originating from one of the methane moieties, accompanied by an intermolecular hydrogen transfer, and the second originating from both methyl groups.

An interactive chemical enhancement of CO2 capture in the MEA/PZ/AMP/DEA binary solutions

Chemical absorption is an effective method for CO2 capture. Due to their high absorption/desorption efficiency, amines have been used in single or blended form. Compared with the single ones, blended solvents usually show better absorption/desorption performance because of their interactive enhancement effect, however the mechanism is still unclear. In this study, the chemical interactive reaction is assumed to be one of the key factors for the enhancement. Based on this, the reactions of CO2 absorption in binary amine solvents (the binary mixtures of monoethanolamine (MEA)/piperazine (PZ)/2-amino-2-methyl-1-propanol (AMP)/diethanolamine (DEA)) have been investigated. The ab initio method with Density Functional Theory (DFT) is adopted in the simulations. Compared with other amines, numerical results showed that PZ presents the lowest forward energy barrier and the second lowest backward energy barrier in zwitterion formation. During the intermolecular hydrogen transfer processes, PZ shows a significant enhancement effect on MEA/DEA/AMP in the interactive reactions. For MEA, it shows an enhancing effect on AMP but hindering effect on PZ and DEA. Moreover, it was found that the MEA+COO− based reactions have good absorption property while the AMP+COO− based ones have good desorption performance. These findings reveal the interactive effect between different amines during the interactive reactions, which may provide theoretical instructions for solvent screening of blended solutions.

Hydrogen Promoted Decomposition of Ammonium Dinitramide: an ab initio Molecular Dynamics Study

Thermal decomposition of a famous high oxidizer ammonium dinitramide (ADN) under high temperatures (2000 and 3000 K) was studied by using the ab initio molecular dynamics method. Two different temperature-dependent initial decomposition mechanisms were observed in the unimolecular decomposition of ADN, which were the intramolecular hydrogen transfer and N—NO2 cleavage in N(NO2)−. They were competitive at 2000 K, whereas the former one was predominant at 3000 K. As for the multimolecular decomposition of ADN, four different initial decomposition reactions that were also temperature-dependent were observed. Apart from the aforementioned mechanisms, another two new reactions were the intermolecular hydrogen transfer and direct N—H cleavage in NH4+. At the temperature of 2000 K, the N—NO2 cleavage competed with the rest three hydrogen-related decomposition reactions, while the direct N—H cleavage in NH4+ was predominant at 3000 K. After the initial decomposition, it was found that the temperature increase could facilitate the decomposition of ADN, and would not change the key decomposition events. ADN decomposed into small molecules by hydrogen-promoted simple, fast and direct chemical bonds cleavage without forming any large intermediates that may impede the decomposition. The main decomposition products at 2000 and 3000 K were the same, which were NH3, NO2, NO, N2O, N2, H2O, and HNO2.

Mechanism of Photoinduced Triplet Intermolecular Hydrogen Transfer between Cycloxydim and Chlorothalonil.

The possible reaction mechanisms for the experimentally observed hydrogen transfer between the herbicide cycloxydim (CD) and the triplet fungicide chlorothalonil (CT) were identified with density functional theory (DFT) and time-dependent density function theory (TDDFT) computations. Excited energy transfer (EET) calculations indicate that reactants for intermolecular hydrogen transfer were formed via energy transfer from triplet CT to ground state CD. Three possible reaction pathways after EET were identified, and hydrogen transfer from the hydroxyl group on the cyclohexane ring of CD to CT exhibited the lowest energy barrier. Natural population analysis (NPA) along the reaction pathways has confirmed that the pathways involved either electron transfer induced proton transfer or coupled electron-proton transfer, leading to different potential energy profiles. Electrostatic potential (ESP) study substantiated the reaction mechanisms in different pathways. This study suggests an explanation for the accelerated photodegradation of CD by CT and provides a pipeline for future studies of photoinduced intermolecular hydrogen transfer.

Effects of non-aqueous solvents on CO2 absorption in monoethanolamine: Ab initio calculations

Monoethanolamine (MEA) is the most typical alkanolamine and its aqueous solutions are widely used for CO2 absorption with mature technology, but the regeneration process is energy consuming. To reduce the energy demand, non-aqueous solvents, such as methanol and ethanol are proposed to substitute water in amine solutions. To understand the influence of the aqueous and non-aqueous solvents on CO2 capture process, the chemical reactions of MEA absorbing CO2 were conducted via ab initio calculations. The non-aqueous solvents discussed in this paper are methanol, ethanol, 1-propanol and 2-propanol. The reaction patterns were investigated and energy barriers were observed. The results show that zwitterion formation and the followed intermolecular hydrogen transfer are proven to be the most possible reaction pattern in both aqueous and non-aqueous solvents. The energy analysis shows that the forward reaction energy barriers increase while the backward barriers decrease as the solvent changes from water to methanol, ethanol, 1-propanol and 2-propanol in turn. The decreases of the energy barriers for backward processes are much higher than the corresponding increases for forward processes. These results indicate that lower energies are required in non-aqueous solvents than in water during the desorption reactions and the non-aqueous solvents are very promising to reduce the regeneration energy consumption in MEA capturing CO2 process. Moreover, the reaction energy gaps between different solvation effects were found to have linear relationship with the logarithm of the dielectric constant difference, which could provide an easy way to theoretically predict the reaction energies of monoethanolamine absorbing CO2 in other solvation effect and can be used to screen appropriate CO2 capture solvent.

Direct observation of stepwise intermolecular proton and hydrogen transfer between alcohols and the triplet state of 4-nitro-1-naphthol.

Solvent assisted excited state intramolecular proton or hydrogen transfer has received much attention in bi-functional molecules with hydrogen donating and hydrogen accepting groups. As a typical photoacid, 1-naphthol exhibits photo-stable behavior in methanol; whether this would be disrupted by a bonded hydrogen accepting group contained in the molecule is still not assured. We present nanosecond transient absorption measurements relating to kinetics and the characteristic absorption of key intermediates upon the excitation of 4-nitro-1-naphthol in alcoholic solutions, and also transient resonance Raman spectroscopy studies combined with theoretical calculations to identify the structures of these intermediates, and we reveal the reaction mechanism to be stepwise deprotonation, hydrogen abstraction and protonation. These results demonstrate that alcohol assisted intramolecular proton or hydrogen transfer cannot occur in this system, but that the solvent cluster plays an important role during such stepwise reactions.

Catalytic Transfer Hydrogenation of Biomass-Derived Carbonyls over Hafnium-Based Metal-Organic Frameworks.

A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor. The results are compared with their zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies using isotopically labeled isopropanol provide evidence that the transfer hydrogenation occurs through a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. The generality of the procedure has been demonstrated by accomplishing the transformation with aldehydes, ketones, and α,β-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Brønsted-acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to γ-valerolactone in good yield of 75 %.

Reversibility of the Hydrogen Transfer in TKX-50 and Its Influence on Impact Sensitivity: An Exceptional Case from Common Energetic Materials

Hydrogen transfer (HT) has been confirmed to possibly serve as a crucial step to initiate and control the decay of common energetic materials (EMs). Nevertheless, the case of currently thriving energetic ionic salts (EISs), as well as the difference in the HT influence on the properties and performances of common EMs and EISs, is poorly known. In this work, we carry out a comparative study of the HTs of dihydroxylammonium-5,5′-bistetrazole-1,1′-diolate (TKX-50) and β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (β-HMX), as the candidates of EISs and common EMs, respectively, by means of ab initio molecular dynamics simulations and climbing image nudged elastic band calculations, as well as powder X-ray diffraction (PXRD) detections. As a result, the HT in TKX-50 is found to be significantly different from that in β-HMX in many respects. The HT in TKX-50 can occur reversibly between the adjacent cations and anions as an intermolecular reaction. The HT is in fact a proton transfer and is energetically preferred as a first-step reaction with a relatively low energy barrier, instead of a rate-determining one for the entire decay of TKX-50. In comparison, with respect to HMX, the intermolecular HT unlikely takes place, while the intramolecular one, with a neutral H atom and a relatively high energy barrier, occurs as one of the possible rate-controlling steps toward the entire decomposition. More importantly, the reversible HT in TKX-50 implies a completely novel impact sensitivity mechanism for EMs; i.e., the external impact energy can partly be converted into the chemical energy stored first (when heating to approaching ignition) and dissipated by the chemical energy release subsequently (when cooling), which contributes to low impact sensitivity. This work provides an exception of a prior reaction favoring high impact safety of EMs, relative to those that mostly result in irreversible and disastrous consequences. Thus, this study hopefully extends the fields of both HT and EMs.

Ab Intio Calculations on Reaction Process of Piperazine Absorbing CO2

The increasing amount of CO2 emitted to the atmosphere has a deep impact on the environment. It is urgent to take effective measures to reduce CO2 emissions from its intensive emission source. Chemical absorption is an effective way to cover the large reduction of CO2, and piperazine (PZ) is one of the amines that have good performance on CO2 capture. To make a deep understanding of the chemical mechanism of PZ absorbing CO2, computational studies on PZ chemically absorbing CO2 are discussed in this work using Density functional theory (DFT).Possible reaction pathways of PZ absorbing CO2 are analyzed. Due to the special chemical structure of PZ, the reaction processes can be divided into two parts, the process of (PZ+CO2)+PZ and (PZ+2CO2)+PZ. To make a good understanding of the reaction process, a comparison of that between PZ and MEA are discussed. The results show that PZ has lower forward and backward energy barriers than MEA in the zwitterion formation, but in the intermolecular hydrogen transfer process, PZ has higher forward and backward barriers than MEA. For the reaction process of PZ+2CO2, it can be stated as a two-step zwitterion formation with two transition states. For the following intermolecular hydrogen transfer of PZ(COO)2+PZ, the atom movements are similar to that of (PZCOO+PZ). All the discussions provide theoretical information of PZ chemical absorbing CO2.