Toluene Research Articles

Approaching the free rotor limit: extremely low methyl torsional barrier observed in the microwave spectrum of 2,4-dimethylfluorobenzene.

The microwave spectrum of 2,4-dimethylfluorobenzene was recorded using a molecular jet Fourier transform microwave spectrometer in the frequency range from 2.0 to 26.5 GHz. The spectral assignment and modeling were challenging due to the large tunnelling splittings resulting from the very low barrier to internal rotation of the p-methyl group that approaches the free rotor limit. Internal rotation splittings arising from two inequivalent o- and p-methyl groups were observed, analysed and modelled using the modified version of the XIAM code and the BELGI-Cs-2Tops code, giving a root-mean-square deviation of 549.1 kHz and 4.5 kHz, respectively, for a data set of 885 rotational lines. The torsional barriers of the o- and p-methyl groups were determined to be 227.039(51) cm-1 and 3.23(40) cm-1, respectively. The V3 barrier observed for the p-methyl group is lower than in any other para-methyl substituted toluene derivatives with coupled internal rotations, becoming the lowest value ever observed to date. The barrier to internal rotation of the o-methyl group next to a fluorine atom is consistently around 220 cm-1, as confirmed by comparing it to barriers observed in other toluene derivatives. The experimental rotational constants were compared to those obtained by quantum chemical calculations.

Photocatalytic selective oxidation of toluene under encapsulated air conditions.

Benzaldehydes are indispensable building blocks in chemistry. However, the selective oxidation of toluene to benzaldehyde remains an ongoing challenge due to the low oxidation potential of benzaldehyde compared to toluene. We report herein a mild protocol that combines hydrogen atom transfer (HAT) with encapsulated air conditions and suitable catalyst loading for selective oxidation of toluene with high selectivity as well as good functional-group tolerance and a broad substrate scope for the synthesis of various high-value aromatic aldehydes. Moreover, the compatibility of this reaction with toluene derivatives of bioactive molecules further demonstrated the practicality of this approach. Mechanism studies have demonstrated that the collaboration between the oxygen quantity and the HAT catalytic system has a major impact on the high selectivity of the reaction. This study not only showcases the effectiveness of HAT strategies toward selective oxidation of toluene to benzaldehyde, but also provides an approach to controlling the selectivity of HAT reactions.

Effect of the charge-separated state on the 3MLCT state: Synthesis and study of the photophysics of electron donor-acceptor dyads based on Pt(II)-Schiff base coordination framework and naphthalenediimide chromophore

We prepared Pt(II)-Salen Schiff base complexes with a naphthalenediimide (NDI) unit attached on the coordination framework, to study the intersystem crossing (ISC), the charge separation, and the possible formation of a long-lived triplet charge separated (CS) state. The Pt(II)-Schiff base coordination framework acts as electron donor and it shows ultrafast ISC (<1 ps) and small Stokes shift. NDI acts as electron acceptor. The two units are attached either via a phenyl linker (Pt-NDI) or phenyl ethynyl linker (Pt-CC-NDI). Negligible electronic interaction between the Pt(II)-Schiff base coordination framework and the NDI unit at ground state was observed for both dyads, whereas the phosphorescence of the Pt(II)-Schiff base coordinated framework was quenched to large extent in the dyads, as compared to the reference complexes containing no NDI unit, especially in polar solvents. Electrochemical and optical spectral data show that the CS state energy is 1.93 eV, 1.82 eV, 1.54 eV, 1.43 eV in n-hexane (HEX), toluene (TOL), tetrahydrofuran (THF), acetonitrile (ACN), respectively. In comparison, the 3MLCT state and 3NDI state energy are 1.97 and 2.04 eV, respectively. Nanosecond transient absorption spectra show the formation of the 3MLCT state for Pt-CC-NDI, whose lifetimes is shortened in polar solvents (τT = 3.5 µs, 2.1 µs, 22 ns, and 19 ns in HEX, TOL, THF and ACN, respectively), similar trend was observed for Pt-NDI. Femtosecond transient absorption spectra show that the charge separation takes less than 1 ps both in toluene and acetonitrile. Quenching of the otherwise long-lived triplet excited state (3.5 µs) by a short lived CS state may be developed as a photo-protection mechanism similar to that found in natural photosynthetic apparatus.

Biomonitoring of Exposures to Solvents and Metals in Electronics Manufacturing Facilities in Batam, Indonesia.

Concerns about chemical exposure in the electronics manufacturing industry have long been recognized, but data are lacking in Southeast Asia. We conducted a study in Batam, Indonesia, to evaluate chemical exposures in electronics facilities, using participatory research and biological monitoring approaches. A convenience sample of 36 workers (28 exposed, 8 controls) was recruited, and urine samples were collected before and after shifts. Five solvents (acetone, methyl ethyl ketone, toluene, benzene, and xylenes) were found in 46%-97% of samples, and seven metals (arsenic, cadmium, cobalt, tin, antimony, lead, and vanadium) were detected in 60%-100% of samples. Biological monitoring and participatory research appeared to be useful in assessing workers' exposure when workplace air monitoring is not feasible due to a lack of cooperation from the employer. Several logistical challenges need to be addressed in future biomonitoring studies of electronics workers in Asia in factories where employers are reluctant to track workers' exposure and health.

Acoustical Studies on Binary Mixtures of Methyl Acrylate with Benzene and Mono-Substituted Benzenes at 313.15 K

Ultrasonic velocities and Densities of binary mixtures of Methyl Acrylate (MA) with Benzene and mono-substituted Benzenes like Benzene (B), Methyl benzene (MB), and Ethyl benzene (EB) have been measured at 313.15 K, by using these data, various acoustical parameters like Isentropic compressibility (KS), Intermolecular free length (Lf), acoustic impedance (Z) and relative association (RA) were calculated, further by using these acoustical parameters, excess properties like excess ultrasonic velocities (uE), excess acoustic impedance (ZE), excess isentropic compressibility (KSE) and excess inter-molecular free-length (LfE) were calculated and fitted to Redlich-Kister equation. The existence of inter-molecular interactions between the components in the liquid mixtures was discussed.

Jamming of Miscible Liquids via Electrostatic Repulsion Between Polystyrene-Modified Gold Nanorods and Toluene.

Structured liquids in miscible fluids, due to ineffective resistance to withstand particle self-diffusion, differ from that in immiscible liquids because of interfacial interactions. Here, a kind of structured liquid, jammed by thiol-terminated polystyrene-modified gold nanorods (GNRs) within tetrahydrofuran and toluene (TOL), is developed by introducing electrostatic repulsion to counterbalance the self-diffusion of GNRs. First-principle calculations reveal charge transfer between the GNRs and TOL, resulting in the electrostatic repulsion. The structured liquids can be regarded as mimic "loading vehicles" to controllably carry and transport matter under electric or magnetic fields, where release rate can be adjusted by changing the concentration of the soluble matter for slow release and using the photothermal effect of the assembled GNRs for fast release. This work has developed a new assembly mechanism to form structured liquids, allowing the construction of a flexible and robust droplet platform with possible applications in microreactors, biomimetic permeable membranes, and functional liquid robots.

Repeated toluene and cyclohexane inhalation produces differential effects on HPA and HPT axes in adolescent male rats

Misused volatile solvents typically contain toluene (TOL) as the main psychoactive ingredient. Cyclohexane (CHX) can also be present and is considered a safer alternative. Solvent misuse often occurs at early stages of life, leading to permanent neurobehavioral impairment and growth retardation. However, a comprehensive examination of the effects of TOL and CHX on stress regulation and energy balance is lacking. Here, we compared the effect of a binge-pattern exposure to TOL or CHX (4,000 or 8,000 ppm) on body weight, food intake, the hypothalamus-pituitary-adrenal (HPA) and hypothalamus-pituitary-thyroid (HPT) axes in male adolescent Wistar rats. At 8,000 ppm, TOL decreased body weight gain without affecting food intake. In addition, TOL and CHX altered the HPA and HPT axes’ function in a solvent- and concentration-dependent manner. The highest TOL concentration produced HPA axis hyperactivation in animals not subjected to stress, which was evidenced by increased corticotropin-releasing-factor (CRF) release from the median eminence (ME), elevated adrenocorticotropin hormone (ACTH) and corticosterone serum levels, and decreased CRF mRNA levels in the hypothalamic paraventricular nucleus (PVN). TOL (8,000 ppm) also increased triiodothyronine (T3) serum levels, decreased pro-thyrotropin-releasing-hormone (pro-TRH) mRNA transcription in the PVN, pro-TRH content in the ME, and serum thyroid stimulating hormone (TSH) levels. CHX did not affect the HPA axis. We propose that the increased HPT axis activity induced by TOL can be related to the impaired body weight gain associated with inhalant misuse. These findings may contribute to a better understanding of the effects of the misused solvents TOL and CHX.

A comparative study of the oxidation of toluene and the three isomers of xylene

This paper presents an experimental and modeling study of the oxidation of toluene, ortho-xylene, meta-xylene, and para-xylene in a jet-stirred reactor. In order to facilitate comparisons, the same experimental conditions were used for the four reactants, i.e. temperatures from 600 to 1100 K, a pressure of 1.07 bar, a residence time of 2 s, an initial fuel mole fraction of 0.005, and equivalence ratios of 0.5, 1 and 2. Compared to literature studies using the same type of reactor, due to higher residence time and initial fuel mole fraction, a higher number of oxygenated aromatic products was quantified and some reactivity was observed at lower temperatures, especially for ortho-xylene, which started to react from 700 K. For this fuel, the formation of phthalan, an aromatic compound including an oxetane ring and indicating low-temperature oxidation chemistry, was confirmed. A new detailed kinetic model combining literature mechanisms was proposed and allowed well predicting the reactivity of the four methylated benzenes of interest with an acceptable simulation of most of the quantified products. Flowrate and sensitivity analyses were made to highlight the similarities and to explain the difference of reactivity between the four investigated reactants.

Monitoring of Volatile Additives from Plant Protection Products in Tomatoes Using HS-SPME-GC-HRMS: Targeted and Suspect Approaches.

Additives present in plant protection products (PPPs) are normally not monitored after sample treatments. In this study, the fate of additives detected by targeted and nontargeted analysis in tomato samples treated with two PPPs was carried out. The study was carried out in a greenhouse for 12 days, in which two applications with each PPP were made. Compounds were extracted by applying a headspace solid phase microextraction (HS-SPME) and analyzed by gas chromatography coupled to high resolution mass spectrometry (GC-HRMS), performing targeted and suspect approaches. Three targeted and 15 nontargeted compounds were identified at concentration levels of up to 150 μg/kg. Compounds detected encompassed benzene, toluene, indene, and naphthalene derivatives, as well as conservatives and flavouring compounds. Most of them degraded in less than 7 days after the second application, following first-order kinetic. This study aims to reduce knowledge gaps regarding additives and their fate under real climatic conditions of greenhouses cultivations.

Effect of thermal treatment on zeolite for real-time gas sensing of oxygenated volatile organic compounds

The breathable air is severally polluted due to the emission of various pollutants like volatile organic compounds (VOCs) and dust particles of submicron sizes. These pollutants have several adverse health hazards, which can cause fatal accidents and mortalities. In the current study, we have modified the FAU type of Zeolite (ZE) with the Si/Al to 1 and treated at different temperatures (300–600 °C) in a 10% H2 + 90% N2 mixture to achieve different distributions of oxygen vacancies. The presence of oxygen vacancy and electrons in the lattice is confirmed by EDAX, XPS and ESR techniques. The charge irregularities generated due to trapped electrons are exploited for detection of different VOCs like acetone, ethyl methyl ketone, isopropyl alcohol, ethanol, n-hexane, and benzene using the scanning kelvin probe (SKP) technique. The oxygen vacancies raise the distribution of Lewis and Brønsted basic sites, which impacts the interaction of VOCs with the sample surface and the amount of VOCs uptake. The untreated ZE and treated at 600 °C (ZE600) exhibited n-type behavior with 13.8% oxygen deficient sites with ∼1.9 μmol/g of total basic sites and 3 μmol/g of total acidic sites. The thermal treatment for ZE600 leads to ∼280 folds enhancement in surface photovoltage towards acetone with ∼ 67% of recovery concerning untreated ZE.

Excited-state tris(pentafluorophenyl)borane as a strong single-electron oxidant: Photophysical properties and catalysis

The photophysical properties and photocatalysis of tris(pentafluorophenyl)borane [B(C6F5)3], known as a strong Lewis acid, were revealed. The excited-state B(C6F5)3 exerts single-electron oxidation capability with an oxidation potential (Ered* = 2.02 V vs SCE) close to those of electronically unbiased toluene derivatives (Eox = 2.01 to 2.29 V). This property was experimentally proven by the direct observation of the radical cation of the toluene dimer by the transient absorption spectroscopy of a mixture of B(C6F5)3 and toluene. In cooperation with a suitable Brønsted base catalyst, B(C6F5)3 catalytically generated benzylic radicals from toluene derivatives under photoirradiation for subsequent carbon-carbon bond-forming reactions.

Diels-Alder conversion of biomass-derived furans and ethylene to renewable aromatics over mesoporous titanium phosphate

Metal phosphates such as P-Beta, Zr-P and Sn-P have drawn lots of attention as emerging catalysts for biomass conversion due to its mild acidity which results in high selectivity to the targeted products while minimizing the unwanted side reactions such as coking that are prevalent in reactive biomass-derived compounds. In this study, we have investigated the production of sustainable aromatics such as p-xylene (PX) and toluene (TOL) via Diels-Alder cycloaddition (DAC) of biomass-derived 2,5-dimethylfuran (DMF) and 2-methylfuran (MF) with ethylene over titanium phosphate catalysts. Specifically, the effects of synthesis method (e.g., sol-gel vs hydrothermal), activation method and P/Ti molar ratio on the structural and acid properties of titanium phosphate catalysts were systematically studied to understand the catalytic consequences of the titanium phosphate materials for the DAC of furans. In addition, amphiphilic surfactant was applied to all catalysts for the formation of mesoporous structure. The characterization studies of the prepared catalysts using XRD, BET, FT-IR, XPS, NMR spectroscopy and TPD of ammonia indicated that the degree of Ti-O-P bond formation, catalysts surface area and surface acidity are largely affected by the catalysts synthesis conditions. Overall, the mesoporous titanium phosphate catalyst, synthesized by hydrothermal method at 180 ℃ for 12 h followed by ethanol refluxing at 60 ℃ for 24 h at a molar P/Ti ratio of 1 showed the highest surface area and the highest acid site density which arise from its distinct ordered Ti-O-P bonding structure as evidenced by XPS and NMR. The catalyst demonstrated the remarkably high PX selectivity of > 90 % at the high DMF conversion of > 90 % and the reusability after two successive reaction-regeneration cycles, showing high phosphorus leaching tolerance.

Long-Lived Charge-Separated State in Naphthalimide-Phenothiazine Compact Electron Donor-Acceptor Dyads: Effect of Molecular Conformation Restriction and Solvent Polarity.

To study the charge separation (CS) and long-lived CS state, we prepared a series of dyads based on naphthalimide (NI, electron acceptor) and phenothiazine (PTZ, electron donor), with an intervening phenyl linker attached on the N-position of both moieties. The purpose is to exploit the electron spin control effect to prolong the CS-state lifetime by formation of the 3CS state, instead of the ordinary 1CS state, the spin-correlated radical pair (SCRP), or the free ion pairs. The electronic coupling magnitude is tuned by conformational restriction exerted by the methyl groups on the phenyl linker. Differently from the previously reported NI-PTZ analogues containing long and flexible linkers, we observed a significant CS emission band centered at ca. 600 nm and thermally activated delayed fluorescence (TADF) with a lifetime of 13.8 ns (population ratio: 42%)/321.6 μs (56%). Nanosecond transient absorption spectroscopy indicates that in cyclohexane (CHX), only the 3NI* state was observed (lifetime τ = 274.7 μs), in acetonitrile (ACN), only the CS state was observed (τ = 1.4 μs), whereas in a solvent with intermediate polarity, such as toluene (TOL), both the 3NI* (shorter-lived) and the CS states were observed. Observation of the long-lived CS state in ACN, yet lack of TADF, confirms the spin-vibronic coupling theoretical model of TADF. Femtosecond transient absorption spectroscopy indicates that charge separation occurs in both nonpolar and polar solvents, with time constants ranging from less than 1 ps in ACN to ca. 60 ps in CHX. Time-resolved electron paramagnetic resonance (TREPR) spectra indicate the existence of the 3NI* and CS states for the dyads upon photoexcitation. The electron spin-spin dipole interaction magnitude of the radical anion and cation of the CS state is intermediate between that of a typical SCRP and a 3CS state, suggesting that the long CS-state lifetime is partially due to the electron spin control effect.

Efficient and stable energy conversion using 2D/3D mixed Sn-perovskite photovoltaics with antisolvent engineering

Sn-based organic-inorganic perovskite is a promising light harvesting material to replace toxic problematic Pb-based perovskite. However, surface morphology of 3-dimensional (3D) or 2D/3D mixed Sn-based perovskite structure is difficult to control owing to its very fast crystal growth. Thus, it is necessary to control Sn-based perovskite crystal growth for an efficient photovoltaic performance. In this regard, this work mainly focused on highly oriented crystal growth of 2D/3D mixed Sn-based perovskite structure using antisolvent engineering approach. The various antisolvents including anisole (AS), chlorobenzene (CB), toluene (TL), and diethyl ether (DE) were employed for formation of 2D/3D Sn-based perovskite film. The evaporation rate of antisolvents plays a key role to control the morphology of 2D/3D Sn-based perovskite by altering the nucleation and crystal growth. As a result, TL assisted perovskite film having compact morphology that exhibited best PCE of 8.78%. However, in case of DE, CB, and AS assisted perovskite films exhibited poor morphology due to faster or slower the evaporation rate of these antisolvents compared to TL. Therefore, the introduced approach provides an interesting insight on development of high quality 2D/3D mixed Sn-based perovskite film.

Na+ binding by benzyl halides: A DFT study

The ability of a benzyl halide to bind Na+ is examined computationally using the ω B97X-D functional. The aug-cc-PVTZ basis set was used except X = I for which aug-cc-PVTZ-PP was used instead. Three stable complexes are found in accord with three possible sites for Na+ binding revealed by the electrostatic potential of the benzyl halide. The free energy barriers for the transition to the most stable complex from the other two complexes are small in all cases. In the most stable complex, Na+ binding exhibits simultaneous interactions between the metal ion with both the benzene ring and the halogen atom. The binding energies for the most stable complex are similar across the various benzyl halides with a calculated average value of 31.43 kcal/mol. The average binding energies for the other two complexes are 19.55 kcal/mol and 22.66 kcal/mol. Comparison with Na+ binding by the methyl halides or benzene is made.

Catalytic upgrading of pyrolytic bio-oil from Salicornia bigelovii seeds for use as jet fuels: Exploring the ex-situ deoxygenation capabilities of Ni/Ze catalyst

With the depleting resources of conventional biomass, there is a rising and imminent need to exploit halophytes. Ni catalyst supported by the highly acidic nanocrystalline Hβ-zeolite was used to explore its hydrodeoxygenation capabilities on the pyrolytic bio-oil from Salicornia bigelovii (SB) at temperatures between 200 and 500 °C. The fatty acid and lignin composition of SB seeds was utilized by virtue of ex-situ catalysis which resulted in the yield of iso- and straight-chain alkanes in the jet fuel-hydrocarbon-range and succeeded in meeting the oxygen limits for both civilian and military aviation fuel specifications. Moreover, the catalytically upgraded product consisted of sufficient mono-aromatics such as toluene, xylene and benzene derivatives falling within the optimal aromatic jet-fuel-specifications. Lastly, it was also recommended that this study could be extended to other halophytes as well for contributing to the global vision of sustainability, which aims to utilize biomass in producing ‘drop-in’ transportation fuels.

Alternatives to classic solvents for the isolation of bioactive compounds from Chrysochromulina rotalis

This paper demonstrates a sequential partitioning method for isolating bioactive compounds from Chrysochromulina rotalis using a polarity gradient, replacing classic and hazardous solvents with greener alternatives. Seventeen solvents were evaluated based on their Hansen solubility parameters and for having a similar polarity to the solvents they would replace, four of which were selected as substitutes in the classic fractionation process. Considering the fatty acid and carotenoid recovery yields obtained for each of the solvents, it has been proposed to replace hexane (HEX), toluene (TOL), dichloromethane (DCM) and n-butanol (BUT) with cyclohexane, chlorobenzene, isobutyl acetate and isoamyl alcohol, respectively. In addition, cytotoxic activity was observed when the TOL and DCM solvent extracts were tested against tumour cell lines, demonstrating the antiproliferative potential of compounds containing, for example, fucoxanthin, fatty acids, peptides, isoflavonoids or terpenes, among others.

Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation

Toluene (TL)-methylcyclohexane (MCH) organic hydride is one of the most promising carrier candidates for the large-scale transport and storage of hydrogen. TL Direct electrohydrogenation electrolyzers based on solid polymer electrolyte membrane technology exhibit significant advantages in terms of energy efficiency compared with the conventional TL hydrogenation method. Mass transfer in the catalyst layer is a crucial aspect of the performance of these electrochemical devices. In this study, experiments were conducted using catalyst-coated membranes with various thicknesses to control the catalyst loading (carbon-supported platinum/ruthenium alloy) and investigate its influence on the mass transfer properties and electrolytic performance of a TL direct electrohydrogenation electrolyzers. The current efficiency was also evaluated for TL concentrations between 1% and 100% in the cathode reactant. The results indicated than an optimum thickness of the cathode catalyst layer corresponding to catalyst loadings of 1.4–1.6 mg cm−2 could maximize the current efficiency of the electrolyzer. The presence of hydrogen gas generated as a side reaction in the high-TL concentration range and high MCH concentrations in the low-TL concentration range are the main factors contributing to a decrease in current efficiency.

Experimental studies on combustion and atomization characteristics of aliphatic and aromatic hydrocarbons droplets

This study focused on how the properties of alcohols (ethanol, methanol, n-butanol), ketones (acetone), alkanes (hexane), esters (ethyl acetate), methyl benzenes (toluene), and ethers (diethyl ether) shape individual combustion and atomization behaviors. The experimentation conducted at the droplet scale involved suspending fuel droplets on a ceramic wire and subsequently igniting them for analysis. Experiments were recorded with a high-speed camera and a thermal camera with a spectral range of 7.5–14 μm. The results showed that the flame of the oxygenated fuel droplets, unlike non-oxygenated fuels, has a high non-luminous region seen throughout the combustion process. The diameter reduction of the fuel droplets during combustion tended to obey the D2-law. Single and multicomponent fuel droplets are hemispherical for preheating (Stage I) and hemispherical in droplet disruption mode for combustion and droplet diameter decrease (Stage II). Hexane, diethyl ether, and ethyl acetate were the fuels that were extinguished in the shortest time among the fuels studied here with extinction times of 1.021 s, 0.925 s, and 0.885 s, respectively. Hexane, diethyl ether, acetone, and diesel droplets had the minimum ignition delay times according to the experimental conditions in this study. In terms of maximum flame temperature, ethyl acetate exhibited the highest value among oxygenated fuel droplets, reaching 155 °C, while toluene demonstrated the highest maximum flame temperature of 244 °C among all fuel types, including non-oxygenated fuels.

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A third component (guest) BTO was employed to optimize the miscibility and enhance the crystallinity of PM6/PY2Se‐F host film processed from green solvent toluene (TL), which can effectively suppress the excessive aggregation of PY2Se‐F. As a result, TL‐processed all‐polymer hosted solar cells (all‐PHSCs) exhibited an impressive PCE of 17.01%. Moreover, the strong molecular interaction between the host and guest molecules also enhances the thermal stability of the devices. More details are discussed in the article by Li et al. on page 1066—1074.image