Dark singlet oxygenation of organic substrates in single-phase and multiphase microemulsion systems

The disproportionation of hydrogen peroxide catalyzed by molybdate anions provides an effective non-photochemical source of singlet oxygen ¹O₂, (¹Δ_g). Microemulsions are the preferred media to carry out ‘dark’ singlet oxygenation of labile and hydrophobic substrates. Single-phase and multiphase microemulsion systems have been developed and improved for the last decade and their respective advantages and limitations are shortly reviewed and discussed.     

Collision-free photochemistry of methylazide: observation of unimolecular decomposition of singlet methylnitrene

Methylazide photolysis at 248 nm has been investigated by ionizing photofragments with synchrotron radiation in a photofragmentation translational spectroscopy study. CH3N and N2 were the only observed primary products. The translational energy release suggests a simple bond rupture mechanism forming singlet methylnitrene, 1CH3N, and N2. Thus, these experiments reveal the unimolecular decomposition of this highly unstable species. We explain our observations through a mechanism which is initiated by the isomerization of 1CH3N to a highly internally excited methanimine H2C=NH isomer, which decomposes by 1,1-H2 elimination forming HNC+H2 as well as sequential H-atom loss (N-H followed by C-H bond cleavage), to form HCN. No evidence for dynamics on the triplet manifold of surfaces is found.     

Complications in photochemistry of organic peroxides

In spite of much active work in the photochemistry of organic peroxides particularly as photoinitiators, mechanisms for several processes are still unclear. This article discusses the following mechanistic complications in this area. These include a mechanism leading to the cleavage of the peroxide bond in the excited peroxide molecules, singlet sensitization leading to homolytic cleavage of the peroxide bond in spite of negative free energy change estimated for the sensitization as an electron transfer process, and triplet sensitization.     

Preface: special topic on organic photochemistry

正Catalysis under irradiation by visible light has become a highly dynamic and promising research area in chemical sciences.Such catalysis primarily entails photoinduced electron-and energy-transfer chemistry sensitized by     

Crown ether-type organic composite adsorbents embedded in high-porous silica beads for simultaneous recovery of lithium and uranium in seawater

The syntheses of crown ether-type organic composite adsorbents embedded in high-porous silica beads for simultaneous recovery of lithium and uranium in seawater have been achieved and the adsorption behavior of lithium and uranium on the composite adsorbents has been examined in several types of original seawater in the wide temperature and pH ranges. As a result, the composite adsorbents composed of benzo-15-crown-5 (BC15) and benzo-18-crown-6 (BC18) showed the top-class maximum adsorption capacities for lithium [6.5 mg/g (BC15), 11 mg/g (BC18)] and uranium [12 mg/g (BC15), 4.2 mg/g (BC18)].

     

Supramolecular organic photochemistry of crown-ether-containing styryl dyes

The data on the molecular design, spectral properties, photochemistry and complexation of photochromic crown ethers containing a C=C bond are described systematically and generalized. Prospects for the practical application of these compounds are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp 641–665, April, 1997.     

Crystal lattice photochemistry often proceeds in discrete stages. Mechanistic and exploratory organic photochemistry

[formula: see text] While the solid-state photochemistry of crystals has been assumed to proceed to some critical point beyond which the crystal is destroyed, it has now been found that crystal lattice photochemistry often occurs in stages or regimes. In each regime different chemistry generally results. The reaction in different stages may be followed kinetically.     

Hydrogenation of various organic substrates using polystyrene anchored orthometallated ruthenium (II) complex as catalyst

The catalytic activity of orthometallated complex [Ru(azb)(CO)₂Cl]₂ (Hazb = azobenzene) anchored to macroporous polystyrene beads was investigated towards the reduction of organic nitrocompounds, alkenes, alkynes, nitriles, Schiff bases, ketones and aldehydes under high pressure, high temperature conditions in mild coordinating media. Comparative studies have been done with the corresponding unsupported metal complexes. The polymer catalyst was found to be comparable to its homogeneous counterpart in activity and product selectivity but superior in stability and reusability. A tentative reduction mechanism was proposed on the basis of kinetic studies and the isolation of reactive intermediates.     

Layer-by-layer deposition of bimetallic nanoshells on functionalized polystyrene beads

Bimetallic nanoshells on functionalized polystyrene beads have been fabricated through a layer-by-layer deposition technique exploiting electrostatic interaction. The synthesis has been achieved through the immobilization and successive reduction of the corresponding precursor ions. It has been shown that the thickness of the shell can be controlled by a number of cyclic depositions of respective metals onto the surface of the polystyrene beads.     

Regioselectivity of the tri-pi-methane rearrangement: mechanistic and exploratory organic photochemistry

The di-pi-methane rearrangement with two pi-groups attached to the central "methane carbon" of the reactant and which leads to a pi-substituted cyclopropane has been studied intensively. Our present research had the goal of elucidating the regioselectivity of the tri-pi-methane counterpart. The reactants with three pi groups attached to the central carbon mechanistically are capable of affording both di-pi-methane and tri-pi-methane photoproducts. In common with the di-pi-methane system, bridging of two of the pi-systems affords a cyclopropyldicarbinyl diradical intermediate that opens to an allyl carbinyl diradical. This diradical has the option of closing to a three-membered or a five-membered ring. It was found that the regioselectivity of the initial pi-pi-bridging step and the three-ring opening of the cyclopropyldicarbinyl diradical exhibit regioselectivity parallel to that of the di-pi counterpart. Both three-ring and five-ring photoproducts were formed with the ratio varying with conversion. Since the three-ring (i.e. di-pi-methane) photoproducts were found to ring expand to the five-ring (i.e. tri-pi-methane) products, kinetics were employed to determine to what extent the reaction proceeds in a two-step versus direct formation of the five-ring product. It was found that the direct route was the major one.     

Catalyst- and organic solvent-free synthesis of thioacids in water

Thioacids and thioamino acids were synthesized in excellent yields from readily available acyl benzotriazoles and sodium hydrosulfide in water at room temperature. The new methodology features mild reaction conditions, high yields, short reaction times, and does not involve the use of organic solvents or bases. The reaction is eco-friendly, and the workup procedure is simple and does not require chromatographic separation.     

The aza-type-B photochemical rearrangement: the role of a second carbonyl in heterocyclic photochemistry. Mechanistic and exploratory organic photochemistry

In contrast to the photochemistry of monocyclic aza-cyclohexenones, their counterparts with a second carbonyl group undergo photochemical rearrangements which parallel those of the 4,4-disubstituted cyclohexenones.     

The preconcentration of mercury and methylmercury on dithizone-coated polystyrene beads

The preconcentration of "inorganic" and methyl mercury cations from aqueous solution is described. The procedure involves collection of mercury on dithizone-coated macroreticular resin beads prior to analysis by cold-vapour atomic absorption spectroscopy. The beads are readily prepared before use and give rise to quantitative selective recovery of "inorganic" and methyl mercury from fresh and saline water samples.     

Reactivity of low energy excited states: Mechanistic and exploratory organic photochemistry

The photochemistry of 3 - methyl - 3 - (1' - naphthyl) -1 - butene was investigated. Direct irradiation led to 1,1 dimethyl - 2 - (1' - naphthyl)cyclopropane as a primary photoproduct and 2 - methyl - 4 - (1' - naphthyl) - 1 - butene as -a secoandary product. The quantum yield for the formation of the cyclopropane was 0.037. The corresponding triple reaction was less efficient, with a quantum yield of 0.012, but still afforded the same product. The excited single rearragement rate was determined by single photon counting; this proved to be ¹k_XXX = 5.9 × 10⁵ sec^-1.The total rate of S₁ decay was determined as 1.59 × 10⁷ sec^-1 with a lifetime of 62.9 nsec.Thus, the lifetime of this rearranging system is quite simiar to that of simple 1-alkylnaphthalenes (Ca 65 nsec); and, the rate of di-π-methane rearrangement is the slowest known. Finally, the rate of radiationless decay of the singlet was found to be almost temperature independent between room temperature and 77 K.