Dimethoxybenzene Research Articles

Tuning of Interfacial Charge Transport in Organic Heterostructures via Aryl Electrografting for Efficient Gas Sensors.

Modulation of interfacial conductivity in organic heterostructures is a highly promising strategy to improve the performance of electronic devices. In this endeavor, the present work reports the fabrication of a bilayer heterojunction device, combining octafluoro copper phthalocyanine (CuF8Pc) and lutetium bis-phthalocyanine (LuPc2) and tunes the charge transport at the Cu(F8Pc)-(LuPc2) interface by aryl electrografting on the device electrode to improve the device NH3-sensing properties. Dimethoxybenzene (DMB) and tetrafluoro benzene (TFB) electrografted by an aryldiazonium electroreduction method form a few-nanometer-thick organic film on ITO. The conductivity of the heterojunction devices formed by coating a Cu(F8Pc)/LuPc2 bilayer over the aryl-grafted electrode strongly varies according to the electronic effects of the substituents in the aryl. Accordingly, DMB increases while TFB decreases the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. This is explained by the perfect alignment of the frontier molecular orbitals of DMB and Cu(F8Pc), facilitating charge injection into the Cu(F8Pc) layer. On the contrary, TFB behaves like a strong acceptor and reduces the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. Such interfacial conductivity variation influences the device NH3-sensing properties, which increase because of DMB grafting and decrease in the presence of TFB. DMB-based heterojunction devices contain four times higher active sites for NH3 adsorption and could detect NH3 down to 1 ppm with limited interference from humidity, making them suitable for real environment NH3 detection.

Drosophilin A methyl ether (DAME) and other chlorinated dimethoxybenzenes in fungi and forest litter from Sweden

Fungi and substrates undergoing fungal decomposition were collected from forests in northern and southern Sweden and analyzed for chlorinated dimethoxybenzenes (DMBs). Specimens were fungi fruiting bodies, rotting wood, forest litter and underlying humus. Targeted compounds were DAME (1,2,4,5-tetrachloro-3,6-DMB) and related fungal secondary metabolites. A screening procedure was developed which involved soaking the specimens in ethyl acetate followed by analysis by capillary gas chromatography – mass spectrometry with mass selective detection (GC-MSD). DAME was the most frequently found (62% of 47 specimens) and often the most abundant target compound, with range and mean ± SD concentrations of <0.0017–3.81 and 0.21 ± 0.63 mg kg−1 ww. Based on log-log correlations of partition coefficients of hydrophobic compounds between fungal biomass/water (KD) and octanol/water (KOW), five species of fungi are suggested to produce DAME de novo versus bioaccumulation from forest runoff water. Full-scan mass spectra of some high-concentration specimens indicated the presence of a Cl2DMB and a Cl3DMB, which could not be identified further due to lack of standards, and drosophilin A (DA = 2,3,5,6-tetrachloro-4-methoxyphenol), the precursor to DAME. Tetrachloroveratrole (TeCV = 1,2,3,4-tetrachloro-5,6-DMB) was found in only a few specimens. This study supports our hypothesis of fungi as a source of DAME in terrestrial runoff and indicates that other chlorinated secondary metabolites are present. DAME is widely distributed globally, and it would be good to have a better understanding of its sources and pathways as a marker of terrestrial organochlorines and their availability for bioaccumulation.

Electron Donor, Acceptor, and Concentration-Dependent Quenching of Photoluminescent Carbon Nanodots

Carbon nanodots (CNDs) are 0D-carbon nanomaterials with distinct fluorescence properties. Due to the poor understanding of the fluorescent origin and its connection to the structural complexity of CNDs, the full potential in applications of CNDs is still in a stagnant stage. Herein, we present the photoluminescence properties of two CNDs prepared from di-ammonium citrate and tri-ammonium citrate. Synthesis of CNDs was done by pyrolysis of ammonium citrates at 180 °C and 40 h under ambient conditions. We monitored the pyrolysis process using thermogravimetric analysis (TGA) both under air and inert atmospheres, which allowed for the proposal of reaction stoichiometry and structural analyses of CNDs in combination with spectroscopic means. Both CNDs possess strong photoluminescence (PL) emissions at ∼450 nm upon excitation at 365 nm. Concentration-dependent PL emission kinetics were studied to reveal both nanoparticle-like behaviors of CNDs with the enhancement of PL emission upon dilution and aggregation-induced quenching of PL emission that is common for molecular fluorophores. Quenching of CNDs’ emission with the benzophenone as a triplet sensitizer or an acceptor and the dimethoxy benzene as a donor was also studied to present additional PL emission dynamics of CNDs in support of the proposed structure for CNDs. The extensive aggregation and stacking of the proposed CNDs structure were verified using molecular dynamics simulations.

Attraction of Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) to Host Plant Cucurbita maxima Duchesne (Cucurbitaceae) Volatiles

The volatiles extracted by the dynamic headspace collection system from the undamaged and conspecific damaged Cucurbita maxima were analyzed by Gas chromatography–mass spectrometry (GC-MS). The olfactory responses of antennal chemosensilla by male and female A. foveicollis towards the plant volatiles were studied by electroantennography (EAG), while the behavioral responses were analyzed by olfactometer bioassay under laboratory conditions. Scanning electron microscopic study revealed the predominance of antennal olfactory sensilla of seven different types with four types of mechanosensilla. The antennae are sexually dimorphic, with differences in density of the chemosensillae present in the apical band region of segment IX, called the circumferential band, being higher in the females. Female antennae showed maximum peak amplitudes for 2-methyl phenol (at 10 mg/mL), followed by 1,4, dimethoxybenzene (at 5 mg/mL), while male antennae showed maximum amplitudes for heneicosane (at 5 mg/mL). Y-tube bioassays revealed maximum attractiveness towards 1,4, dimethoxy benzene that decreased progressively across heneicosane, pentacosane, tetradecane, ethyl benzene, D-limonene, nonadecane, eicosane, nonanal, decanal, α-pinene, phytol and benzaldehyde in females. However, male species were more responsive towards heneicosane, followed by 1,4 dimethoxybenzene, while the responses to pentacosane and tetradecane were equal, followed by equal responses to decanal, ethyl benzene and nonadecane, and thereafter, a progressively reducing response was observed towards α-pinene, eicosane, nonanal, D-limonene, phytol and benzaldehyde. The study assists in understanding the role of olfaction by A. foveicollis in the host plant Cucurbita maxima by listing compounds that act as potential kairomones for the beetle, and can be expected to facilitate development of an eco–friendly trap and/or by attracting the natural enemies for control of the pest.

Gas sorption and selectivity study of N,N,N′,N′-tetraphenyl-1,4-phenylenediamine based microporous hyper-crosslinked polymers

One of the most important parameters to design porous polymeric materials for gas storage and separation is to discover appropriate linker. Determining the effect of linker, in fixed core, over the selectivity and adsorption has been great challenge. Here, three different N,N,N′,N′-tetraphenyl-1,4-phenylenediamines (TPPA) based microporous hyper-crosslinked polymers synthesized by the Friedel-Craft reactions. Hypercrosslinked polymer, TPPA-DMM, was obtained from dimethoxymethane (DMM) and hypercrosslinked-covalent polymer, TPPA-DMB, from dimethoxybenzene (DMB) in presence of FeCl3. TPPA-CC, covalent triazine polymer was synthesized from cyanuric chloride (CC) via AlCl3 as the catalyst. After the careful characterization of these microporous structures with different analytical and spectral analyses, the gas uptake (for CO2, CH4, O2, CO, and H2) and selectivity properties (for CO2/N2, CO2/O2, for CO2/CO and CO2/CH4) were comparatively investigated at pipe gas temperatures and up to 1 bar. The high BET specific surface areas ranging from 742 to 883 m2/g with ultramicropore characters (0.53–0.58 nm), high chemical stability in different solvents even in concentrated acid and thermal stability (up to 450 °C) promised that these materials can be used in pipe gas processes. By changing the linkers on the core, materials have high gas uptake properties reaching 12.98 wt% for CO2 uptake, 1.57 wt% for CH4 uptake, 1.06 wt% for CO uptake at 1 bar/273 K and also reaching 1.28 wt% for H2 uptake at 1 bar/77 K. In addition, the unusual N2 phobic character down to 0.2 wt% and O2 phobic character down to 0.3 wt% were observed. The selectivity was calculated by using the ideal adsorbed solution theory (IAST). The selectivities were found reaching 80.4 for CO2/N2, 8.5 for CO2/CH4, 30.1 for CO2/CO and 39.1 for CO2/O2. These calculations show that the obtained polymers can be used in post combustion processes which needs high pressures and temperatures. The selectivities of the synthesized materials for the gas sorptions changed drastically by switching the linkers in all three materials. Interestingly, IAST calculations from single to dual gas, in the different ratios, showed that selectivities were almost the same for each polymer within itself at same temperature. To date, these are the first reported discoveries for the porous organic polymers in the literature.

Mechanism and Origins of Product Selectivity of Au‐Catalyzed Coupling Benzisoxazoles with Ynamides: A Computational Study

AbstractAu(I)‐catalyzed coupling of benzisoxazoles and ynamides was recently reported to synthesize challenging indoloquinoline core structures. In this report, we employed DFT methods to elucidate the mechanistic details of this reaction. The results reveal that the catalytic cycle involves initial coupling of ynamide with benzisoxazole, simultaneous ring opening of the isoxazole unit and attack of the dimethoxybenzene (DMOB) unit to gold carbenoid, proton transfer from the DMOB group to hydroxyl group, thioether migration, ring closure, and proton transfer. The experimentally observed ligand‐controlled product selectivity is reproduced well by the calculations. The product selectivity‐determining step is the ring opening of the isoxazole unit. The flexible P(t‐Bu)2(o‐biphenyl) ligand facilitates the approach of the DMOB group to gold carbenoid, which brings about significant C−H/π interactions in the transition state for ring opening, and thus leads to the indoloquinoline product. The rigid 1,3‐bis(diisopropylphenyl)imidazol‐2‐ylidene ligand prefers keeping the DMOB group away from the gold carbenoid, which can cause strong orbital interaction in the transition state for ring opening, and thus results in indole product.

Enhanced catalytic activity of new di-site onium salt in the kinetics of α-Tolunitrile monoalkylation

In this study, we investigate in detail the catalytic efficiency of 1,4-bis-(ethylmethyleneammounium chloride)-2,5- dimethoxy benzene, BEMACDB (multi-site phase transfer catalyst) by observing the pseudo-first order kinetics of mono-alkylation of α-Tolunitrile (ATN). The formation of product was monitored by GC. The comparative study of catalytic efficiency of the new catalysts with single-site salts reveals higher catalytic activity for new catalysts under varying experimental conditions ([BEMACDB], [Base], [ATN], Stirring Speed and Temperature). By understanding the kinetics of mono-alkyaltion, we further establish the experimental parameters that influence reaction conditions. With the support of kinetic data we establish the suitable mechanism for monoalklation of ATN. The catalyst shows consistent catalytic activity in the C-alkylation of ATN in different experimental conditions.

Programming the Knowledge: A Trial QSAR Study Towards the Stability of Dialkoxy Benzene Based Catholyte Molecules for Nonaqueous Redox Flow Batteries

Programming the knowledge: A trial QSAR study towards the stability of dialkoxy benzene based catholyte molecules for nonaqueous redox flow batteries Lu Zhang1, Jingjing Zhang1, Benjamin Silcox3, Illya A. Shkrob1, Rajeev S. Assary2, Lei Cheng2, Levi Thompson4 1Chemical Sciences and Engineering Division, 2Material Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States 3Chemical Engineering, University of Michigan, 500 S State St, Ann Arbor, MI 48109, United States 4Department of Chemical and Biomolecular Engineering, University of Delaware,Newark, DE 19716, Unite States The stability of redox active molecules is a paramount property that dramatically affects the cycling performance in redox flow batteries. Computationally, it requires huge amount of resource to exhaustively iterate all the possible degradation pathways in order to estimate the stability of active species, such as radical cations.1 QSAR, or quantitative structure–activity relationship, provides an interesting approach to correlate chemical structures and properties based on the idea of property changes are all coming from structure modifications. While this approach simplified the insightful analysis of the detailed mechanism, it becomes particular useful to simulate or even predict complex properties, such as the stability of redox molecules. In this talk, we developed a series of dialkoxy benzene based catholyte molecules that are of potential use to nonaqueous redox flow batteries and systematically changed their substitutions on the alkoxy moieties. Then their electrochemical/chemical properties, including redox potential, charged state stability (reflected by EPR life time), and even cycling numbers, have been characterized and analyzed. Importantly, a number of descriptors have been identified based on our long accumulated knowledge regarding stability of the charged radical cations. Finally, a linear regression model was established using those descriptors to simulate the EPR life time, and even cycling numbers and the resulted fittings delivered quite satisfactory correlation between the selected descriptors and properties. While this is only a trial study based on a small set of molecules, the QSAR approach proves to be useful in understanding complex properties for redox active molecules, which could stimulate further understanding and development of such promising materials. Assary, R. S.; Zhang, L.; Huang, J.; Curtiss, L. A., Molecular Level Understanding of the Factors Affecting the Stability of Dimethoxy Benzene Catholyte Candidates from First-Principles Investigations. The Journal of Physical Chemistry C 2016, 120 (27), 14531-14538.

Combining plant volatiles and pheromones to catch two insect pests in the same trap: Examples from two berry crops

Most horticultural crops are attacked by more than one insect pest. As broad-spectrum chemical control options are becoming increasingly restricted, there is a need to develop novel control methods. Semiochemical attractants are available for three important horticultural pests, strawberry blossom weevil, Anthonomus rubi Herbst (Coleoptera: Curculionidae), European tarnished plant bug, Lygus rugulipennis Poppius (Hemiptera: Miridae) and raspberry beetle, Byturus tomentosus deGeer (Coleoptera: Byturidae). Traps targeting more than one pest species would be more practical and economical for both monitoring and mass trapping than traps for single-species. In this study we aimed to (1) improve the effectiveness of existing traps for insect pests in strawberry and raspberry crops by increasing catches of each species, and (2) test if attractants for two unrelated pest species could be combined to capture both in the same trap without decreasing the total catches. Field tests were carried out in four European countries and different combinations of semiochemicals were compared. A volatile from strawberry flowers, 1,4 dimethoxybenzene (DMB), increased the attractiveness of the aggregation pheromone to both sexes of A. rubi. The host-plant volatile, phenylacetaldehyde (PAA), increased the attraction of female L. rugulipennis to the sex pheromone, and, in strawberry, there was some evidence that adding DMB increased catches further. Traps baited with the aggregation pheromone of A. rubi, DMB, the sex pheromone of L. rugulipennis and PAA attracted both target species to the same trap with no significant difference in catches compared to those single-species traps. In raspberry, catches in traps baited with a combination of A. rubi aggregation pheromone, DMB and the commercially available lure for B. tomentosus, based on raspberry flower volatiles, were similar to those in single-species traps. In both crops the efficiency of the traps still needs improvement, but the multi-species traps are adequate for monitoring and should not lead to confusion for the user as the target species are easy to distinguish from each other.

Molecular Level Understanding of the Factors Affecting the Stability of Dimethoxy Benzene Catholyte Candidates from First-Principles Investigations

First-principles simulations are performed to gain molecular level insights into the factors affecting the stability of seven 1,4-dimethoxybenzene (DMB) derivatives. These molecules are potential catholyte candidates for nonaqueous redox flow battery systems. Computations are performed to predict oxidation potentials in various dielectric mediums, intrinsic-reorganization energies, and structural changes of these representative catholyte molecules during the redox process. In order to understand the stability of the DMB-based radical cations, the thermodynamic feasibility of the following reactions is computed using density functional theory: (a) deprotonation, (b) dimerization, (c) hydrolysis, and (d) demethylation. The computations indicate that radical cations of the 2,3-dimethyl and 2,5-dimethyl derivatives are the most stable among the DMB derivatives considered in this study. In the presence of solvents with high-proton solvating ability (water, DMSO, acetonitrile), degradation of cation radical occ...

(3,4-Dimethoxyphenyl)[2-(thiophen-2-ylcarbonyl)phenyl]methanone

In the title compound, C20H16O4S, the thiophene ring makes dihedral angles of 72.9 (2) and 60.5 (2)°, respectively, with the dimethoxy benzene and phenyl rings. In the crystal, C—H⋯O hydrogen bonds link the mol­ecules into a C(9) chain along the b axis. The S and C atoms of the thio­phene ring are disordered over two sets of sites [site occupancies = 0.675 (3) and 0.325 (3)]. A short inter­molecular S⋯O contact [3.084 (2) Å] is observed in the crystal structure, which also features C—H⋯π inter­actions.

Chemical Compositions of Salix aegyptiaca. L. Obtained by Simultaneous Hydrodistilation and Extraction

Volatile components obtained from Salix aegyptiaca L. from Jiroft area in kerman province, Iran was fractionated by simultaneous hydrodistilation and extraction (SHDE) with xylene as solvent using modified Clevenger apparatus and other two traditional extraction methods such as hydrodistilation liquid-liquid extraction (HD-LLE) and Soxhlet extraction (SE) with different solvents. Then volatile oils were analyzed by capillary gas chromatography using flame ionization and capillary gas chromatography mass spectrometry detection. Simultaneous hydrodistilation and extraction volatile oils of S. aegyptiaca L. and other methods extraction product had very different compositions. The major difference was in the 1,4 -dimethoxy benzene content witch was (58.9 %) in the SHDE product, (53.3 %) in HD-LLE and the range of (1.0 % – 1.6 %) in SE obtained with several solvent.

(1′S)-4-(3,4-Dichlorophenyl)-1′-(3,5-dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalene-2-spiro-2′-pyrrolizidine-3′-spiro-3′′-indoline-1,2′′-dione

In the title compound C37H32Cl2N2O4, the unsubstituted pyrrolidine ring shows a twist conformation whereas the substituted pyrrolidine ring shows an envelope conformation. The dimeth­oxy benzene ring is perpendicular to the tetra­lone ring, making a dihedral angle of 89.94 (5)°. Mol­ecules are linked into centrosymmetric dimers by N—H⋯O hydrogen bonds and the crystal structure is stabilized by C—H⋯π inter­actions and C—H⋯O hydrogen bonds. One meth­oxy group is disordered over two positions with the site occupancy factors of 0.84 (2) and 0.16 (2).

Optimization of alkylidene hydrazide based human glucagon receptor antagonists. Discovery of the highly potent and orally available 3-cyano-4-hydroxybenzoic acid [1-(2,3,5,6-tetramethylbenzyl)-1H-indol-4-ylmethylene]hydrazide.

Highly potent human glucagon receptor (hGluR) antagonists have been prepared employing both medicinal chemistry and targeted libraries based on modification of the core (proximal) dimethoxyphenyl group, the benzyl ether linkage, as well as the (distal) benzylic aryl group of the lead 2, 3-cyano-4-hydroxybenzoic acid (3,5-dimethoxy-4-isopropylbenzyloxybenzylidene)hydrazide. Electron-rich proximal aryl moieties such as mono- and dimethoxy benzenes, naphthalenes, and indoles were found to be active. The SAR was found to be quite insensitive regarding the linkage to the distal aryl group, since long and short as well as polar and apolar linkers gave highly potent compounds. The presence of a distal aryl group was not crucial for obtaining high binding affinity to the hGluR. In many cases, however, the affinity could be further optimized with substituted distal aryl groups. Representative compounds have been tested for in vitro metabolism, and structure-metabolism relationships are described. These efforts lead to the discovery of 74, NNC 25-2504, 3-cyano-4-hydroxybenzoic acid [1-(2,3,5,6-tetramethylbenzyl)-1H-indol-4-ylmethylene]hydrazide, with low in vitro metabolic turnover. 74 was a highly potent noncompetitive antagonist of the human glucagon receptor (IC(50) = 2.3 nM, K(B) = 760 pM) and of the isolated rat receptor (IC(50) = 430 pM, K(B) = 380 pM). Glucagon-stimulated glucose production from isolated primary rat hepatocytes was inhibited competitively by 74 (K(i) = 14 nM). This compound was orally available in dogs (F(po) = 15%) and was active in a glucagon-challenged rat model of hyperglucagonemia and hyperglycemia.

Photophysics of novel donor–{saturated rigid hydrocarbon bridge}–acceptor systems exhibiting efficient excitation energy transfer

Intramolecular singlet–singlet energy transfer is reported in a series of novel donor–{saturated rigid hydrocarbon bridge}–acceptor (D–B–A) molecules containing dimethoxynaphthalene (DMN) or dimethoxybenzene (DMB) as the energy donor chromophore, and a dione group as the acceptor. In the case of the DMN donor, the efficiency of energy transfer has been studied as a function of the bridge length with the number of sigma bonds linking the donor and acceptor groups ranging from 6 to 12. Highly efficient energy transfer is observed in all the D–B–A molecules studied, and the results are discussed with reference to the role of dipole–dipole and through-bond donor–acceptor coupling mechanisms. The energy transfer process facilitates efficient photosensitized decomposition of the dione moiety. These results are compared to data published on related donor–acceptor compounds. The chemical structure of the backbone linking the donor and acceptor is shown to have a marked effect on the photophysics of the molecules.

Spectroscopic and Photochemical Study of Inclusion Complexes of Dimethoxybenzenes with Cyclodextrins

The effect of addition of the cyclodextrins (CDx) α-CDx and β-CDx on the photophysics and photochemistry of the dimethoxybenzenes (DMB) 1,4-DMB and 1,2-DMB in aqueous solution has been investigated by means of absorption, circular dichroism, fluorescence, and nanosecond transient absorption spectroscopies. The experimental results are discussed in the light of model calculations on the structure and the circular dichroism spectra of the DMB−CDx complexes. The association of 1,2-DMB with both CDxs is much weaker than that of 1,4-DMB owing to steric hindrance. With β-CDx, 1,4-DMB forms 1:1 complexes with a high association constant (K = 630 M-1) in spite of incomplete inclusion. Complexation of 1,4-DMB with α-CDx strongly affects the photophysical properties of the guest: fluorescence is enhanced and triplet state decay slowed by a factor of 10 or more, depending on the decay reaction mode. Fluorescence enhancement is mainly due to a reduction of the rate constant for internal conversion. The effect of com...

The GC-MS identification of some aliphatic intermediates from the TIO2 photocatalytic degradation of dimethoxybenzenes in water

In an attempt to answer the as yet unsolved question of the structures of the aliphatic compounds resulting from the ring opening of aromatic pollutants in water during a photocatalytic treatment, we have carried out a GC-MS study (with or without silylation) of aqueous solutions of each of the dimethoxybenzenes (DMBs) UV-irradiated in the presence of powder TiO2. The aliphatic intermediates are esters or acids which were identified either by comparison with authentic compounds (as is indicated by an asterisk in the following list) or by interpretation of the mass spectra (EI and CI). From 1,4-DMB, they are: (E)* and (Z)* H3COOC-CH =CH-COOCH3. From 1,3-DMB, they are: H3COOC-CH=CH-CO-COOH3; H3COOC-CO-CH(OCH3)-CH2OH; H3COOC-CH=CH-CHO; H3COOC-CH=CHOCH3. From 1,2-DMB, they are: (E,E) H3COOC-CH =CH-CH=CH-COOCH3*; HOOC-CH=CH-CH=CH-COOCH3 isomers; H3COOC-CH=CH-CHO; (E) HOOC-CH=CH-COOH*; H3COOC-CHOH-CHO; H3COOC-COOCH3*, In the case of 1,2-DMB, additional analyses showed the presence of CH3OH. Its formation was suggested to result from the cleavage of the methoxy groups of DMBs. These identifications show the complexity of the degradation pathways. The dimethyl esters of (E,E) hexadienedioic acid and of (E) and (Z) butenedioic acids could result from the opening of 1,2- or 1,4-DMB, respectively, before these pollutants are hydroxylated. This suggests that hydroxyl radicals are not the only oxidizing species involved. The fact that all aliphatics contain a number of C atoms ≤ to that in DMBs bears witness to the bond cleavages which lead to the mineralization.

Water treatment: Degradation of dimethoxybenzenes by the titanium dioxide‐UV combination

Abstract Three dimethoxybenzenes (DMBs) have been chosen to further assess the capabilities of the TiO2‐UV system to destroy substituted aromatic pollutants in water. At λ > 290 nm and pH = 3, the disappearance of DMB (0.145 mM) is much more rapid in the presence of TiO2 (Degussa P‐25; 2.5 g/L) than by direct photolysis; the intermediates generated by both processes are different. At λ > 340 nm, which avoids any significant contribution of direct photolysis, the order of disappearance is meta > para > ortho. Possible origins for this order are discussed. The main aromatic intermediates correspond to the hydroxylation of the ring with or without the elimination of one or both methoxy groups, and to the para and ortho orientations. From 1, 4‐DMB, para‐benzoquinone is also formed. The temporal variations of 2, 3‐dimethoxyphenol (2, 3‐DMP), 3, 4‐DMP, 2‐methoxyphenol (2‐MP) and 3‐MP have been recorded. At their maximum concentrations, these intermediates correspond to only a few percents of degraded DMB and th...

Photo-oxidative cyanation of aromatics on semiconductor powder suspensions I: oxidation processes involving radical species

Illumination of platinized WO 3 and TiO 2 suspensions in CH 3CN/H 2O mixed solvents containing dimethoxybenzene (DMB) and cyanide leads to the formation of cyanoanisole together with side products. Laser flash photolysis of the transparent colloidal dispersions shows the formation of DMB +.. The amount of DMB + formed decreases in the presence of CN −, which indicates the competitive oxidation of DMB and Cn − rather than the reaction of DMB + and CN −. Using the electron spin resonance spin trapping technique we report for the first time evidence of CN and CH 2CN radical formation in illuminated semiconductor suspensions. Use of dry CH 3CN, DMB and (Bu) 4 +CN − decreases further the yield of cyanoanisole due to formation of a cyanated derivative of tributylamine which, in turn, originates from (Bu) 4 + after cyanide oxidation to CN .

Electron transfer from methoxybenzenes to the excited state of an iridium(III) complex studied by the pulsed laser technique

A new reversible photochemical electron-transfer system involving the photosensitizer (Ir(bpy){sub 2}(C{sub 3},N'bpy)){sup 2+}, Ir(III){sup 2+}, and its acid form Ir(III){sup 3+} and the neutral methoxybenzenes as electron donors is described. The quenching kinetics and back reactions between the photochemical products have been studied both by steady-state emission measurements of the Ir(III)* excited states and by the pulsed laser technique. The effect of a charged polymer, poly(styrenesulfonate) (PSS), is also reported. The iridium complex is reduced to Ir(II){sup 2+} with high quantum yields. Tetramethoxybenzene (TMB) is more efficiently oxidized as compared with dimethoxybenzene (DMB). The acid-base equilibrium of Ir(III)* (pK = 3.5) has only a small, if any, effect on the yields. PSS affects both product yields and reaction kinetics. The back-electron-transfer reaction in the presence of PSS proceeds in two steps. The major step, accounting for most of the initial absorption, is attributed to a reaction between the electron-transfer products in the same polymer aggregate. The slower process is attributed to DMB{sup +} ion radicals which escaped the initial stage of the back reaction and diffused to other polymer aggregates. The positive DMB{sup +} ions are converted to Br{sub 2}{sup {minus}} in the presence of Br{sup {minus}}. The effect ofmore » PSS in the presence as well as in the absence of Br{sup {minus}} ions is discussed. The results indicate an effect of hydrophobic interactions between PSS and DMB.« less