Photochemical and photocatalytic reactions of carbon tetrachloride with alcohols

The photo-initiated oxidation of alcohols by carbon tetrachloride was studied. The main reaction products formed during the irradiation of CCl₄ solutions in ethanol with light of = 254 nm are chloroform, acetaldehyde, and hexachloroethane. With increase in concentration of CCl₄ in the mixture with ethanol from 0.5 to 5 mole/liter, the quantum yields of the formation of CHCl₃ and CH₃CHO decrease from 9.2 to 4.4 and from 4.3 to 1.4, respectively, while the quantum yield of formation of C₂Cl₆ increases from 0.38 to 0.68. By using semiconductor photocatalysts (TiO₂, TiO₂/Pd, CdS), the oxidation of alcohols can be carried by the action of light of the near-UV and visible regions of the spectrum (320 < < 520 nm). When the reaction is carried out photocatalytically, the maximum quantum yields of the formation of CHCl₃ and CH₃CHO were attained with a palladized TiO₂ (0.77 and 0.36, respectively). The initial stage of the mechanism of the photochemical process involves the cleavage of the C-Cl bond with absorption of a quantum of light by the CCl₄ molecule, and this is followed by reactions of free radicals. When semiconductor photocatalysts are used, the cleavage of the C-Cl bond occurs either by the action of hydroxyethyl radicals, formed by the reaction of ethanol molecules with valence zone holes of the semiconductor (in the case of TiO₂), or electrons of the semiconductor conductivity zone (in the case of CdS).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 682–688, November–December, 1989.     

Photochemical reduction of cytochrome c by a 1,4,5,8-naphthalenediimide radical anion

Steady-state UV irradiation of aqueous solutions containing cytochrome c (cyt c) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (BPNDI), a water-soluble aromatic imide, resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) oxidation state. The reaction kinetics were followed by the increase of the ferrocytochrome c absorbance band at 549 nm. The rate of the photochemical reaction was pH dependent, reaching its maximum values over the pH range 4-7. Addition of electrolyte (NaCl) at pH 5 resulted in a decrease in the reaction rate, as expected for reactions between oppositely charged species. Flash photolysis studies revealed that the actual reductant in the reaction was a photogenerated BPNDI radical anion, which transferred an electron to the cyt c heme iron. The participation of imide radicals in the process was confirmed by the ready reduction of cyt c by BPNDI radicals chemically generated with sodium dithionite.     

Photochemical reduction of furil by pentachlorophenol: Cross relaxation and CIDNP

Photolysis of a solution of furil and pentachlorophenol yields proton spin polarized furil as the major reaction product. Dipolar (cross-) relaxation in the furil three spin system was found to transfer CIDNP between the protons, such that resonances which were emissive initially relax to enhanced absorption, and vice-versa, depending on the spin populations produced by the photochemical process.     

Photochemical reduction of n-tosylsulfilimines with thiolate anion

The reaction between N-tosyldiarylsulfilimines and p-toluenethiolate anion did not take place in the dark even upon heating up to 62° but proceeded smoothly upon irradiation with visible light in DMF at room temperature, affording S-N bond cleavage products.     

Photochemical reduction of uranyl ion with triethylamine

Uranyl ion is photochemically reduced to uranium(IV) in the presence of triethylamine and triethylamine is oxidized to secondary amine and acetaldehyde. On the basis of product analysis, temperature independent quantum yields for uranium(IV) formation and abnormal Stern-Volmer plots rule out the simple collisional photochemical annihilation of excited uranyl ion with triethylamine. Static annihilation has a significant contribution in addition to dynamic annihilation.     

Photochemical reduction of phenosafranine by edta and its use in amperometric titrations

Phenosafranine in the presence of ethylenediaminetetraacetic acid is reduced to the leuco dye form on illumination with white light. The rate of photoreduction is strongly pH-dependent and exhibits a maximum at about pH 6. Variables such as wavelength and intensity of the light and the concentration of reactants have been studied. The photoreduction involves a long-lived excited state of the dye and is retarded by small amounts of p-phenylenediamine and iodide. The dye is used as an amperometric indicator in titrations of Pb(II), Zn(II) and Cu(II) with EDTA; the method is applicable in the range 0.02–0.0005 M. The current is caused by anodic oxidation of the phenosafranine reduced in the photochemical reaction with EDTA.     

Photochemical reduction of graphene oxide in colloidal solution

Stable aqueous colloidal solutions of graphene oxide stabilized with sodium polyphosphate were obtained. During irradiation of the colloids the oxygen-containing groups of the graphene oxide are eliminated, and the aromatic graphite-like regions in its composition are expanded. This is accompanied by decrease in the energy of the electronic transitions E_bg in such sp2-hybridized fragments. Photoreduction of the colloidal particles of graphene oxide leads to changes in their hydrodynamic size, resulting from 𝜋𝜋 interactions between the aromatic fragments in the particles. It was shown that the E_bg value can be varied purposefully in the range of 0.5-1.9 eV by varying the experimental conditions.     

Photochemical reduction of uranyl ion with aromatic alkanes

Uranyl ion is photochemically reduced to uranium(IV) in the presence of diphenylmethane and triphenylmethane. Quantum yields for uranium(IV) formation are accelerated with time suggesting the free radical formation, which triggers off a secondary reaction. Lower quantum yield and higherK _sv value for photochemical reduction of uranyl ion with triphenylmethane relative to the respective values observed with diphenylmethane reveals the competition between photophysical and photochemical deactivation of excited uranyl ion due to the presence of three and two phenyl groups in respective aromatic hydrocarbons for photophysical deactivation.     

Catalytic reduction of dinitrogen to ammonia by molybdenum: theory versus experiment

Molybdenum complexes that contain the triamidoamine ligand [(RNCH(2)CH(2))(3)N](3-) (R = 3,5-(2,4,6-iPr(3)C(6)H(2))(2)C(6)H(3)) catalyze the reduction of dinitrogen to ammonia at 22 degrees C and 1 atm with protons from 2,6-dimethylpyridinium and electrons from decamethylchromocene. Several theoretical studies have been published that bear on the proposed intermediates in the catalytic dinitrogen reduction reaction and their reaction characteristics, including DFT calculations on [(HIPTNCH(2)CH(2))(3)N]Mo species (HIPT =hexaisopropylterphenyl = 3,5-(2,4,6-iPr(3)C(6)H(2))(2)C(6)H(3)), which contain the actual triamidoamine ligand that is present in catalytic intermediates. Recent theoretical findings are compared with experimental findings for each proposed step in the catalytic reaction.     

Photochemical interaction of molybdenum and tungsten phosphine hydride complexes with carbon dioxide

UV, IR, and¹H NMR spectra of photoproducts obtained by irradiation of phosphine hydride complexes MH₄L₄ (M = Mo and W; L = PHPh₂, PMePh₂, PEtPh₂, PEt₂Ph, and PBuPh₂) in an atmosphere of CO₂,¹³CO₂, and C¹⁸O₂ have been studied. The photoproducts can be formed due to the insertion of carbon dioxide both into the M-H bond and M-C and M-Ph bonds.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2324–2326, September, 1996.     

Dynamics of dilute water in carbon tetrachloride

A dilute solution of water in a hydrophobic solvent, such as carbon tetrachloride (CCl4), presents an opportunity to study the rotational properties of water without the complicating effects of hydrogen bonds. We report here the results of theoretical, experimental, and semiempirical studies of a 0.03 mole percent solution of water in CCl4. It is shown that for this solution there are negligible water-water interactions or water-CCl4 interactions; theoretical and experimental values for proton NMR chemical shifts (deltaH) are used to confirm the minimal interactions between water and the CCl4. Calculated ab initio values and semiempirical values for oxygen-17 and deuterium quadrupole coupling constants (chi) of water/CCl4 clusters are reported. Experimental values for the 17O, 2H, and 1H NMR spin-lattice relaxation times, T1, of 0.03 mole percent water in dilute CCl4 solution at 291 K are 94+/-3 ms, 7.0+/-0.2 s, and 12.6+/-0.4 s, respectively. These T1 values for bulk water are also referenced. "Experimental" values for the quadrupole coupling constants and relaxation times are used to obtain accurate, experimental values for the rotational correlation times for two orthogonal vectors in the water molecule. The average correlation time, tauc, for the position vector of 17O (orthogonal to the plane of the molecule) in monomer water, H2(17)O, is 91 fs. The average value for the deuterium correlation time for the deuterium vector in 2H2O is 104 fs; this vector is along the OD bond. These values indicate that the motion of monomer water in CCl4 is anisotropic. At 291 K, the oxygen rotational correlation time in bulk 2H2(17)O is 2.4 ps, the deuterium rotational correlation time in the same molecule is 3.25 ps. (Ropp, J.; Lawrence, C.; Farrar, T. C.; Skinner, J. L. J. Am. Chem. Soc. 2001, 123, 8047.) These values are a factor of about 20 longer than the tauc value for dilute monomer water in CCl4.     

Photochemical reduction of organic electron acceptors in aqueous solutions

Conclusions The formation of OH radicals in the photoreduction of aqueous solutions of anthraquinonesulfonic acid as the result of electron transfer from water (OH^–) to a triplet molecule has been demonstrated.Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2615–2617, November, 1969.     

Magnesiothermic reduction of tungsten and molybdenum oxide compounds

A process of producing tungsten and molybdenum powders by magnesium vapor reduction of WO₃, MoO₃, MgWO₄, MgMoO₄, CaWO₄, CaMoO₄, and Ca₃WO₆ within the temperature range 700–800°C at a residual argon pressure of 5–15 kPa has been studied. The reduction of WO₃, MoO₃, MgWO₄, MgMoO₄, and CaMoO₄ was accompanied by separation of the products in the reaction mixture, namely, by the removal of most of the resulting magnesium oxide from the reaction zone. Using tungsten and molybdenum compounds containing MgO or CaO as precursors, tungsten and molybdenum powders with a mesoporous structure and a specific surface area of 18–20 m²/g have been produced.     

Syntheses of hydrated molybdenum bronzes by reduction of MoO3 with NaBH4

Hydrated molybdenum bronzes have been prepared by reduction reaction of MoO3 with NaBH4 in ethanol and DMSO. The reduction reactions in both solvents occur smoothly; thus, the layered structure of MoO3 is maintained in the product. Divalent cation Ca2+ has been intercalated between the MoO3 layers, which leads to highly reduced molybdenum bronze (Mo5.26+). Solvated molybdenum bronze catalyzes the reduction reaction of DMSO by NaBH4, producing CH3SCH3. The structure model of hydrated sodium molybdenum bronze has also been reinvestigated by using the Rietveld analysis. The hydrated molybdenum bronze crystallizes in an orthorhombic structure, in which the structure of Mo octahedron layers is closely related to that in MoO3. However, the structure refinement reveals that the Mo octahedron in the MoO3 layers is axially distorted, which is different from that in MoO3 but similar to an isoelectron compound H0.33MoO3.     

Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)3N]3- ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)3N]Mo), [Mo=NNH2][BAr'4] (Ar' = 3,5-(CF3)2C6H3), [Mo=NH][BAr'4], and Mo(NH3). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)+, which is formed upon treatment of MoH with [2,6-LutH][B(C6F5)4]. We focus on the synthesis of compounds that have not yet been isolated, which include Mo=NNH2, Mo=NH, and Mo(NH2). Mo=NNH2, formed by reduction of [Mo=NNH2]+, has not been observed. It decomposes to give mixtures that contain two or more of the following: MoN=NH, Mo triple bond N, Mo(NH3)+, Mo(NH3), and ammonia. Mo=NH, which can be prepared by reduction of [Mo=NH]+, is stable for long periods in the presence of a small amount of CrCp*2, but in the absence of CrCp*2, and in the presence of Mo=NH+ as a catalyst, Mo=NH is slowly converted into a mixture of Mo triple bond N and Mo(NH2). Mo(NH2) can be produced independently by deprotonation of Mo(NH3)+ with LiN(SiMe3)2 in THF, but it decomposes to Mo triple bond N upon attempted isolation. Although catalytic reduction of dinitrogen could involve up to 14 intermediates in a "linear" sequence that involves addition of "external" protons and/or electrons, it seems likely now that several of these intermediates, along with ammonia and/or dihydrogen, can be produced in several reactions between intermediates that themselves behave as proton and/or electron sources.     

Chemoselective reduction of azides catalyzed by molybdenum xanthate by using phenylsilane as the hydride source

A chemoselective, neutral, and efficient strategy for the reduction of azides to corresponding amines catalyzed by dioxobis(N,N,-diethyldithiocarbamato) molybdenum complex (1, MoO₂[S₂CNEt₂]₂) in the presence of phenylsilane is discovered. This chemoselective reduction strategy tolerates a variety of reducible functional groups.