Ultrafast Events of Photoexcited Iron(III) Chloride for Activation of Benzylic C-H Bonds.

The usage of rare-earth-metal catalysts in the synthesis of organic compounds is widespread in chemical industries but is limited owing to its environmental and economic costs. However, recent studies indicate that abundant-earth metals like iron(III) chloride can photocatalyze diverse organic transformations using blue-light LEDs. Still, the underlying mechanism behind such activity is debatable and controversial, especially in the absence of ultrafast spectroscopic results. To address this urgent challenge, we performed femtosecond time-resolved electronic absorption spectroscopy experiments of iron(III) chloride in selected organic solvents relevant to its photocatalytic applications. Our results show that the long-lived species [Fe(II) ← Cl•]* is primarily responsible for both oxidizing the organic substrate and reducing molecular oxygen through the diffusion process, leading to the final product and regenerating the photocatalyst rather than the most widely proposed free chloride radical (Cl•). Our study will guide the rational design of efficient earth-abundant photocatalysts.

Novel Environmentally Friendly Nanomaterials for Drag Reduction of the Emulsified Acid System.

Matrix acidizing is a technique that is widely used in the petroleum industry to remove scales and create channels in the rock. Removal of scales and creation of channels (wormhole) enhance productivity. Conventional acidizing fluids, such as hydrochloric acid (HCl) for carbonate and a mixture of hydrofluoric acid (HF) and HCl acid, are used for the matrix acidizing process. However, these fluids have some drawbacks, including strong acid strength, corrosion at high temperatures, and quick reactions with scale and particles. Emulsified acid systems (EASs) are used to address these drawbacks. EASs can create deeper and narrower wormholes by reducing the reaction rate of the acid due to the external oil phase. However, EASs have a much higher viscosity compared to conventional acidizing fluids. The high viscosity of EASs leads to a high drag that restricts pumping rates and consumes energy. This study aims to utilize environmentally friendly and widely available nanomaterials as drag-reducing agents (DRAs) of the EAS. The nanomaterials used in this study are carbon nanodots (CNDs). CNDs have unique properties and are used in diverse applications in different industries. The size of these CNDs is usually smaller than 10 nm. CNDs are characterized by their biocompatibility and chemical stability. This study investigates the use of CNDs as DRAs for EAS. Several experiments have been conducted to investigate the CNDs as a DRA for the EAS. The developed EAS was initially tested for conductivity and drop-test analysis to ensure the formation of an inverted emulsion. Thereafter, the thermal stability for the range of temperatures and the rheological properties of the EAS were evaluated to meet the criteria of field operation. Then flow experiments with EASs were conducted before and after adding the CNDs to investigate the efficacy of drag reduction of EASs. The results revealed that CNDs can be used as viscosity reducers for the EAS, where adding the CNDs to the EAS reduces the viscosity at two different HCl concentrations (15 and 20%). It reduces the viscosity of the EAS in the presence of corrosion inhibitors as well as other additives to the EAS, showing its compatibility with the field formulation. The drag reduction was observed at the range of temperatures investigated in the study. The conductivity, stability, and rheology experiments for the sample taken after the flow experiment are consistent, ensuring CNDs work as a DRA. The developed EAS with CNDs is robust in terms of field mixing procedures and thermally stable. The CNDs can be used as a DRA with EAS, which will reduce drag in pipes, increasing pumping rates and saving energy.

Correction: Atmospheric chemistry of CF3CN: kinetics and products of reaction with OH radicals, Cl atoms and O3.

Correction for 'Atmospheric chemistry of CF3CN: kinetics and products of reaction with OH radicals, Cl atoms and O3' by Mads Peter Sulbaek Andersen et al., Phys. Chem. Chem. Phys., 2022, 24, 2638-2645, https://doi.org/10.1039/D1CP05288H.

Correction: Atmospheric chemistry of (Z)- and (E)-1,2-dichloroethene: kinetics and mechanisms of the reactions with Cl atoms, OH radicals, and O3.

Correction for 'Atmospheric chemistry of (Z)- and (E)-1,2-dichloroethene: kinetics and mechanisms of the reactions with Cl atoms, OH radicals, and O3' by Mads P. Sulbaek Andersen et al., Phys. Chem. Chem. Phys., 2022, 24, 7356-7373, https://doi.org/10.1039/D1CP04877E.

Innovative Applications of Red Mud: Converting an Environmental Challenge to a Drilling Asset.

Red mud is generated from alumina production through bauxite digestion with caustic soda. Ma'aden aluminum production estimated the abundance in a million tons as 2.65:1:2 for bauxite, alumina, and red mud, respectively. The real challenge when it comes to red mud pertains to storage capacity; many solutions have been put forward in different industries, and in this study, the utilization of the red mud waste material is presented as a potential weighting material that could be incorporated into the design of drilling fluid systems. This study provides an assessment of the utilization of red mud as a drilling fluid, and it provides directions for the use of red mud in drilling mud systems as a filtration agent and as a finely divided solid used as a weighting material to increase the density of a given drilling fluid system. This study investigates the viability of red mud as an effective additive to drilling fluid and its effect on rheology and filtration. Different techniques are employed in red mud characterization and performance evaluation. The study assesses red mud as an inert solid in a drilling fluid system by investigating the drilling fluid rheology, apparent viscosity (AV), plastic viscosity (PV), and yield point (YP) before and after hot rolling at 150 °F, in addition to filtration properties under low-pressure, low-temperature and higher-pressure, higher-temperature conditions (at 150 °F and a differential pressure of 250 psi). Also, the study highlights the red mud solid characterization, material preparation, and acid dissolution at 150 °F. This study attempts to view the red mud situation from a practical application angle (primarily in the oil and gas industry). Test results show stable drilling mud fluid properties when utilizing red mud solid additives as weighting agents. The drilling mud exhibits relatively low plastic viscosity, gel strength, excellent sag behavior, and reasonable filtration control, even under HPHT conditions in aqueous-based fluids. The material dissolves in acid. Accordingly, red mud provides a viable option for weighting agents and filtration control.

Atmospheric chemistry of (Z)- and (E)-1,2-dichloroethene: kinetics and mechanisms of the reactions with Cl atoms, OH radicals, and O3.

Smog chambers interfaced with in situ FT-IR detection were used to investigate the kinetics and mechanisms of the Cl atom, OH radical, and O3 initiated oxidation of (Z)- and (E)-1,2-dichloroethene (CHClCHCl) under atmospheric conditions. Relative and absolute rate methods were used to measure k(Cl + (Z)-CHClCHCl) = (8.80 ± 1.75) × 10-11, k(Cl + (E)-CHClCHCl) = (8.51 ± 1.69) × 10-11, k(OH + (Z)-CHClCHCl) = (2.02 ± 0.43) × 10-12, k(OH + (E)-CHClCHCl) = (1.94 ± 0.43) × 10-12, k(O3 + (Z)-CHClCHCl) = (4.50 ± 0.45) × 10-21, and k(O3 + (E)-CHClCHCl) = (1.02 ± 0.10) × 10-19 cm3 molecule-1 s-1 in 700 Torr of N2/air diluent at 298 ± 2 K. Pressure dependencies for the Cl atom reaction kinetics were observed for both isomers, consistent with isomerization occurring via Cl atom elimination from the chemically activated CHCl-CHCl-Cl adduct. The observed products from Cl initiated oxidation were HC(O)Cl (117-133%), CHCl2CHO (29-30%), and the corresponding CHClCHCl isomer (11-20%). OH radical initiated oxidation gives HC(O)Cl as a major product. For reaction of OH with (E)-CHClCHCl, (Z)-CHClCHCl was also observed as a product. A significant chlorine atom elimination channel was observed experimentally (HCl yield) and supported by computational results. Photochemical ozone creation potentials of 12 and 11 were estimated for (Z)- and (E)-CHClCHCl, respectively. Finally, an empirical kinetic relationship is explored for the addition of OH radicals or Cl atoms to small alkenes. The results are discussed in the context of the atmospheric chemistry of (Z)- and (E)-CHClCHCl.

Atmospheric chemistry of CF3CN: kinetics and products of reaction with OH radicals, Cl atoms and O3.

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2, oxygen or air diluent at 296 ± 2 K. Values of k(Cl + CF3CN) = (2.43 ± 0.33) × 10-15 and k(OH + CF3CN) = (4.61 ± 0.34) × 10-15 cm3 molecule-1 s-1 were measured. There was no discernible reaction of CF3CN with O3 and an upper limit of k(O3 + CF3CN) ≤ 7.9 × 10-24 cm3 molecule-1 s-1 was established. The IR spectra of CF3CN and CF3CF2CN are reported. The atmospheric lifetime of CF3CN is determined by the reaction with OH and is approximately 6.9 years. Reaction of CF3CN with Cl atoms in a chamber study gives (Z-) and/or (E-) CF3CClNCl and CF3C(O)Cl as major primary products. Under environmental conditions, the OH radical initiated oxidation gives COF2 in a yield of (96 ± 8)%. The global warming potential for CF3CN is estimated as 1030 for a 100 year time horizon.

Nonstatistical Photoinduced Processes in Gaseous Organic Molecules.

Processes that proceed in femtoseconds are usually referred to as being ultrafast, and they are investigated in experiments that involve laser pulses with femtosecond duration in so-called pump probe schemes, where a light pulse triggers a molecular process and a second light pulse interrogates the temporal evolution of the molecular population. The focus of this review is on the reactivity patterns that arise when energy is not equally distributed on all the available degrees of freedom as a consequence of the very short time scale in play and on how the localization of internal energy in a specific mode can be thought of as directing a process toward (or away from) a certain outcome. The nonstatistical aspects are illustrated with examples from photophysics and photochemistry for a range of organic molecules. The processes are initiated by a variety of nuclear motions that are all governed by the energy gradients in the Franck-Condon region. Essentially, the molecules will start to adapt to the new electronic environment on the excited state to eventually reach the equilibrium structure. It is this structural change that is enabling an ultrafast electronic transition in cases where the nuclear motion leads to a transition point with significant coupling between to electronic states and to ultrafast reaction if there is a coupling to a reactive mode at the transition point between the involved states. With the knowledge of the relation between electronic excitation and equilibrium structure, it is possible to predict how the nuclei move after excitation and often whether an ultrafast (and inherently nonstatistical) electronic transition or even a bond breakage will take place. In addition to the understanding of how nonstatistical photoinduced processes proceed from a given excited state, it has been found that randomization of the energy does not even always take place when the molecule takes part in processes that are normally considered statistical, such as for example nonradiative transitions between excited states. This means that energy can be localized in a specific degree of freedom on a state other than the one that is initially prepared. This is a finding that could kickoff the ultimate dream in applied photochemistry; namely light excitation that leads to the rupture of a specific bond.

Prevention of Hematite Settling in Water-Based Mud at High Pressure and High Temperature.

Hematite was recently introduced as a weighting agent in drilling fluids; however, its use has some problems because of the settlement of solid particles (solid sagging). Particularly when it comes to high-pressure high-temperature (HP/HT) wells, sagging causes inconsistency in the drilling fluid and gives rise to serious drilling operational and technical challenges. This work provides a solution to this challenge via a thorough investigation of hematite sagging in water-based mud for HP/HT applications where ilmenite is combined with hematite. The particles of both hematite and ilmenite were first characterized to address their mineralogical and textural features. Field mud formulation was employed using several ilmenite/hematite contents (i.e., 0/100, 25/75, and 50/50% ilmenite/hematite). Then, laboratory experiments were conducted to study the density, pH, and sag performance of the produced drilling fluids. From the sagging tests, the optimal ilmenite/hematite ratio was determined, and rheology, viscoelastic behavior, and filtration properties of the formulated mud were addressed. The tests were conditioned to 300 psi and 250 °F. The results showed a reduction in mud density and pH with increasing ilmenite content, as the density reduced from15 ppg with base hematite until 14.2 ppg for the 50% ilmenite mixture and the pH reduced from 10.5 to 9.3. The static and dynamic sag tests indicated that the addition of 25% of ilmenite solved the hematite-incorporated sagging issue by well placing the sag tendency within the recommended safe range. The 25/75% combination enhanced the yield point (YP) by 37% with only 1 cP increment in plastic viscosity (PV) and an insignificant effect on the gel strength. The YP/PV ratio was improved by 31% indicating better hole cleaning and solid suspension. The filtration behavior of the 25% ilmenite mixture was superior compared to that of the blank hematite because it resulted in 35, 39, and 35% reduction in the filtrate volume, filter-cake weight, and thickness, respectively. This work contributes to improving and economizing the drilling cost and time by the formulation of a stabilized and distinguished-performance drilling mud using combined weighting agents at HP/HT.

Transient Symmetry Controls Photo Dynamics near Conical Intersections.

Excited-state chemistry lacks generalized symmetry rules. With many femtochemistry studies focused on individual cases, it is hard to build up the same level of chemical intuition for excited states as that for ground states. Here, we unravel the degrees of freedom involved in ultrafast internal conversion (IC) by mapping the vibrational coherence of the initial wavepacket and the dependence on molecular symmetry in various cyclic tertiary amines. Molecular symmetry plays an important role in the preservation of vibrational coherence in the transit from one electronic state to another. We show here that it is sufficient for the molecule to simply have the possibility of a more symmetric structure to achieve the preservation of vibrational coherence. It can be transient and still lead to preservation. This finding provides an additional angle on how symmetry influences electronic transitions and an additional piece to the puzzle of establishing symmetry-based selection rules for excited-state processes.

Deducing the Relation between Viscosity and Oil-Induced Structural Changes of Viscoelastic Surfactants Using a Kinetic Approach.

The present study relates viscosity reduction with time of a wormlike micellar solution to the micellar transitions that occur with time in the presence of three n-alkanes, namely, n-decane, n-dodecane, and n-hexadecane. Steady-shear rheology and small-angle X-ray scattering were used to deduce the relationship. The effect of n-alkane concentration was tested only with n-decane. There were at most three stages of viscosity reduction, which appeared in the following order: (i) the rising viscosity stage, (ii) the fast viscosity reduction stage, and (iii) the low-viscosity stage. The stages and rates of viscosity transition depended on the type of micelles present and the degree of micelle entanglement. Moreover, the rate of transition increased when the n-alkane concentration was increased and when the n-alkane molecular mass was reduced. n-Hexadecane induced only the first two stages of transition at a slower rate compared to the other oils.

Design of Green-Emitting Salts from Substituted Pyridines: Understanding the Solid-State Photodimerization of trans-1,2-bis(4-pyridyl)ethylene.

Polymorphic salts of trans-1,2-bis(4-pyridyl)ethylene (bpe), 2[bpeH2 ] ⋅ (SO4 )(2HSO4 ) (1) and [bpeH2 ] ⋅ 2HSO4 (2) have been synthesized and their structures determined by X-ray crystallography. The Schmidt postulate predicts that neither of the salts will give rise to photodimerization so they can both potentially be applied as green light emitters. Despite the predictions, 1 undergoes a stereospecific solid-state photodimerization reaction with 100 % yield. This is due to UV induced combination of sliding and pedal-like movement of the pyridyl ring system that influences the alignment of C=C bonds. The sliding motion is restricted in 2. Consequently, the green emission from 1 is completely quenched after photodimerization. It is evident that counter ions play a dominant role in dis- and enabling photodimerization; their degree of protonization and lattice placement are important solvent controlled design parameters towards crystal structures that can act as future light emitters.

Theoretical study of hydroxyl radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE).

We have characterized the various pathways for OH radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE) and found an oxidative pathway that leads to complete degradation under the prerequisite that OH radicals are present in excess. A simple polarizable continuum model is used to predict the behavior in an aqueous medium and the behavior is unchanged compared to that in the gas phase. The computational study has also revealed some of the fundamental aspects of hydrogen transfer from asymmetric ethers; the ˙OH assisted hydrogen abstraction has a barrier when the reaction takes place at a distance from the heteroatom, that is, at the tert-butyl group, whereas hydrogen abstraction from the methyl group proceeds without a barrier. The addition of ˙OH to (CH3)3COCH2˙ also proceeds without a barrier, and so does hydrogen abstraction from the resulting adduct ((CH3)3COCH2OH) to form (CH3)3COCH(OH)˙. However, a barrier is yet again found in the hydrogen abstraction from the latter to form (CH3)3COCH[double bond, length as m-dash]O and yet again in the formation of the formyl radical (CH3)3COC[double bond, length as m-dash]O˙ by hydrogen abstraction. The latter is the last step before the final stage of complete oxidation of MTBE to form CO2.

Electronic Predissociation in the Dichloromethane Cation CH2Cl2+ Electronic State 2A1.

The loss of a Cl atom from metastable CH2Cl2+ in the mass-analyzed ion kinetic energy experiment is characterized by a borderline zero kinetic energy release and large kinetic isotope effects on chlorine and hydrogen. Ab initio calculations are employed to assist the interpretation in terms of a nonadiabatic reaction involving electronic predissociation of the electronically excited state 2A1 and two-dimensional reaction dynamics. Strong curvature in the reaction coordinate leads to a bobsled effect that accounts for the low kinetic energy release. The kinetic isotope effects enter via the predissociation rate and are interpreted in terms of vibrational overlap integrals.

Vacuum ultraviolet excited state dynamics of small amides.

Time-resolved photoelectron spectroscopy in combination with ab initio quantum chemistry calculations was used to study ultrafast excited state dynamics in formamide (FOR), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) following 160 nm excitation. The particular focus was on internal conversion processes within the excited state Rydberg manifold and on how this behavior in amides compared with previous observations in small amines. All three amides exhibited extremely rapid (<100 fs) evolution from the Franck-Condon region. We argue that this is then followed by dissociation. Our calculations indicate subtle differences in how the excited state dynamics are mediated in DMA/DMF as compared to FOR. We suggest that future studies employing longer pump laser wavelengths will be useful for discerning these differences.

Symmetry controlled excited state dynamics.

Symmetry effects in internal conversion are studied by means of two isomeric cyclic tertiary aliphatic amines in a velocity map imaging (VMI) experiment on the femtosecond timescale. It is demonstrated that there is a delicate structural dependence on when coherence is preserved after the transition between the 3p and 3s Rydberg states. N-Methyl morpholine (NMM) shows unambiguous preserved coherence, consistent with previous work, which is decidedly switched off by the repositioning of oxygen within the ring. From the differences in these dynamics, and an examination of the potential energy surface following the normal modes of vibration, it becomes clear that there is a striking dependence on atom substitution, which manifests itself in the permitted modes of vibration that take the system out of the Franck-Condon region through to the 3s minimum. It is shown that the non Fermi-like behaviour of NMM is due to a conical intersection (CI) between the 3px and 3s states lying directly along the symmetry allowed path of steepest descent out of the Franck-Condon region. NMI, where the symmetry has been changed, is shown to undergo internal conversion in a more Fermi-like manner as the energy spreads through the available modes ergodically.

Atmospheric chemistry of (Z)-CF3CH[double bond, length as m-dash]CHCl: products and mechanisms of the Cl atom, OH radical and O3 reactions, and role of (E)-(Z) isomerization.

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH[double bond, length as m-dash]CHCl were studied at 296 ± 1 K in 10-700 Torr air of N2/O2 diluent. Cl atoms add to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH[double bond, length as m-dash]CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl-Cl adduct. The rate constant for (Z)-CF3CH[double bond, length as m-dash]CHCl + Cl was measured at low pressure (10-15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH[double bond, length as m-dash]CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol-1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH[double bond, length as m-dash]CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH[double bond, length as m-dash]CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH[double bond, length as m-dash]CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl.

Determining Orientations of Optical Transition Dipole Moments Using Ultrafast X-ray Scattering.

Identification of the initially prepared, optically active state remains a challenging problem in many studies of ultrafast photoinduced processes. We show that the initially excited electronic state can be determined using the anisotropic component of ultrafast time-resolved X-ray scattering signals. The concept is demonstrated using the time-dependent X-ray scattering of N-methyl morpholine in the gas phase upon excitation by a 200 nm linearly polarized optical pulse. Analysis of the angular dependence of the scattering signal near time zero renders the orientation of the transition dipole moment in the molecular frame and identifies the initially excited state as the 3p z Rydberg state, thus bypassing the need for further experimental studies to determine the starting point of the photoinduced dynamics and clarifying inconsistent computational results.

Vacuum ultraviolet excited state dynamics of the smallest ring, cyclopropane. II. Time-resolved photoelectron spectroscopy and ab initio dynamics.

The vacuum-ultraviolet photoinduced dynamics of cyclopropane (C3H6) were studied using time-resolved photoelectron spectroscopy (TRPES) in conjunction with ab initio quantum dynamics simulations. Following excitation at 160.8 nm, and subsequent probing via photoionization at 266.45 nm, the initially prepared wave packet is found to exhibit a fast decay (<100 fs) that is attributed to the rapid dissociation of C3H6 to ethylene (C2H4) and methylene (CH2). The photodissociation process proceeds via concerted ring opening and C-C bond cleavage in the excited state. Ab initio multiple spawning simulations indicate that ring-opening occurs prior to dissociation. The dynamics simulations were subsequently employed to simulate a TRPES spectrum, which was found to be in excellent agreement with the experimental result. On the basis of this agreement, the fitted time constants of 35 ± 20 and 57 ± 35 fs were assigned to prompt (i) dissociation on the lowest-lying excited state, prepared directly by the pump pulse, and (ii) non-adiabatic relaxation from higher-lying excited states that lead to delayed dissociation, respectively.

Benzylic Thio and Seleno Newman-Kwart Rearrangements.

The thermally induced OBn → SBn and OBn → SeBn migration reactions facilitate the rearrangement of O-benzyl thio- and selenocarbamates [BnOC(═X)NMe2] (X = S or Se) into their corresponding S-benzyl thio- and Se-benzyl selenocarbamates [BnXC(═O)NMe2] (X = S or Se). A series of substituted O-benzyl thio- and selenocarbamates were synthesized and rearranged in good yields of 33-88%. The reaction rates are higher for substrates with electron-donating groups in the 2 or 4 position of the aromatic ring, but the rearrangement also proceeds with electron-withdrawing substituents. The rearrangement follows first-order reaction kinetics and proceeds via a tight ion pair intermediate consisting of the benzylic carbocation and the thio- or selenocarbamate moiety. Computational studies support these findings.