Separation of Cr(III) and Cr(VI) using melamine-formaldehyde resin and determination of both species in water by FAAS

A method is described for the determination of Cr(VI) and total chromium by FAAS. Cr(VI) is separated from Cr(III) by adsorption on melamine-formaldehyde resin. After elution of Cr(VI) with 0.1 mol/l NaAc solution, it is analysed by FAAS. Total chromium is determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with hydrogen peroxide, total Cr(VI) is concentrated as above. If the total concentration of chromium is sufficient, the determination can be directly made by FAAS. Cr(III) can then be calculated by subtracting Cr(VI) from the total Cr. This method was successfully applied to the determination of chromium in lake water.     

A new organic-inorganic hybrid oxyfluorotitanate [Hgua]2·(Ti5O5F12) as a transparent UV filter

A new generation UV absorber is obtained by microwave-heating-assisted hydrothermal synthesis: [Hgua](2)·(Ti(5)O(5)F(12)). The structure of this hybrid titanium(IV) oxyfluoride is ab initio determined from powder X-ray data by combining a direct space method, Rietveld refinement [orthorhombic, Cmm2, a = 22.410(1) ?, b = 11.191(1) ?, c = 3.802(1) ?], and density functional theory geometry optimization. The three-dimensional network is built up from infinite inorganic layers (∞)(Ti(5)O(5)F(12)) separated by guanidinium cations. The theoretical optical gap (3.2 eV) estimated from density of state calculations is in good agreement with the experimental gap (3.3 eV) obtained by UV-vis diffuse reflectivity. The optical absorption is mainly due to O(2p) → Ti(3d) and F(2p) → Ti(3d) transitions at higher energies. The refraction index is low in the visible range (n ≈ 1.9) compared to that of TiO(2) and, consequently, [Hgua](2)·(Ti(5)O(5)F(12)) shows a good transparency adapted to UV shielding. Under UV irradiation at 254 nm for 40 h, the white microcrystalline powder turns to light purple-gray. This color change is caused by the reduction of Ti(IV) to Ti(III), confirmed by magnetic measurements.     

Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N

The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.     

Photometric measurement of trace As(III) and As(V) in drinking water

A simple, fast and sensitive light-emitting diode (LED)-based photometric method for the differential determination of ppb-ppm levels of As(III) and As(V) in potable water in the presence of ppm levels of phosphate was developed. The detection chemistry is based on the well-known formation of arsenomolybdate, followed by reduction to heteropoly blue. The front-end of the measurement system is configured to selectively retain P(V) and As(V), based on the considerable difference of the pK(a) of the corresponding acids relative to As(III). Thus, it is As(III) that is injected into the medium, oxidized in-line with KBrO(3) to As(V) and forms Mo-blue that is detected by an LED-based detector. Only As(III) is measured if the sample is injected as such; if all As in the sample is prereduced to As(III) (by the addition of cysteine, in a provided in-line arrangement), the system measures As(V)+As(III). In the present form, limit of detection (LOD) (S/N=3) is less than 8 mug l(-1) As, and the linear range extends to 2.4 mg l(-1). Potential interference from dissolved silica and Fe(III) is eliminated by the addition of NaF to the sample.     

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.     

Synthesis, structure, and thermochemistry of the formation of the metal-metal bonded dimers [Mo(mu-TeAr)(CO)3(PiP3)]2 (Ar = phenyl, naphthyl) by phosphine elimination from *Mo(TePh)(CO)3(PiPr3)2

The complexes (*TeAr)Mo(CO)3(PiPr3)2 (Ar = phenyl, naphthyl; iPr = isopropyl) slowly eliminate PiPr3 at room temperature in a toluene solution to quantitatively form the dinuclear complexes [Mo(mu-TeAr)(CO)3(PiPr3)]2. The crystal structure of [Mo(mu-Te-naphthyl)(CO)3(PiPr3)]2 is reported and has a Mo-Mo distance of 3.2130 A. The enthalpy of dimerization has been measured and is used to estimate a Mo-Mo bond strength on the order of 30 kcal mol-1. Kinetic studies show the rate of formation of the dimeric chalcogen bridged complex is best fit by a rate law first order in (*TeAr)Mo(CO)3(PiPr3)2 and inhibited by added PiPr3. The reaction is proposed to occur by initial dissociation of a phosphine ligand and not by radical recombination of 2 mol of (*TeAr)Mo(CO)3(PiPr3)2. Reaction of (*TePh)Mo(CO)3(PiPr3)2, with L = pyridine (py) or CO, is rapid and quantitative at room temperature to form PhTeTePh and Mo(L)(CO)3(PiPr3)2, in keeping with thermochemical predictions. The rate of reaction of (*TeAr)W(CO)3(PiPr3)2 and CO is first-order in the metal complex and is proposed to proceed by the associative formation of the 19 e- radical complex (*TePh)W(CO)4(PiPr3)2 which extrudes a *TePh radical.     

稀土胺羧酸配合物的研究 I. {[MnGd(DTPA)(H2O)5]2·H2O}n配合物的合成和晶体结构

本文首次合成了{MnLn(DTPA)(H2O)5]·H2O}n异核链式配合物(Ln=Gd, Er, Y)单晶,测定了{[MnGd(DTPA)(H2O)5]2·H2O]n的单晶结构。     

Fluorine for hydrogen exchange in the hydrofluorobenzene derivatives C6H(x)F(6-x), where x = 2, 3, 4 and 5 by monomeric [1,2,4-(Me3C)3C5H2]2CeH: the solid state isomerization of [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,5-C6HF4) to [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,6-C6HF4)

The reaction between monomeric bis(1,2,4-tri-tert-butylcyclopentadienyl)cerium hydride, Cp'2CeH, and several hydrofluorobenzene derivatives is described. The aryl derivatives that are the primary products, Cp'2Ce(C6H(5-x)F(x)) where x = 1,2,3,4, are thermally stable enough to be isolated in only two cases, since all of them decompose at different rates to Cp'2CeF and a fluorobenzyne; the latter is trapped by either solvent when C6D6 is used or by a Cp'H ring when C6D12 is the solvent. The trapped products are identified by GC/MS analysis after hydrolysis. The aryl derivatives are generated cleanly by reaction of the metallacycle, Cp'((Me3C)2C5H2C(Me2)CH2)Ce, with a hydrofluorobenzene, and the resulting arylcerium products, in each case, are identified by their (1)H and (19)F NMR spectra at 20 degrees C. The stereochemical principle that evolves from these studies is that the thermodynamic isomer is the one in which the CeC bond is flanked by two ortho-CF bonds. This orientation is suggested to arise from the negative charge that is localized on the ipso-carbon atom due to C(o)(delta+)F(o)(delta-) polarization. The preferred regioisomer is determined by thermodynamic rather than kinetic effects; this is illustrated by the quantitative, irreversible solid-state conversion at 25 degrees C over two months of Cp'2Ce(2,3,4,5-C6HF4) to Cp'2Ce(2,3,4,6-C6HF4), an isomerization that involves a CeC(ipso) for C(ortho)F site exchange.     

Gas-phase electrophilic addition promoted by CH(3)S(+)=CH(2) ions on aromatic systems

The gas-phase methylenation reaction between CH(3)S(+)=CH(2) and alkylbenzenes, aniline, phenol and alkyl phenyl ethers, which yields [M + CH](+) and CH(3)SH, has been studied by Fourier transform ion cyclotron resonance (FT-ICR) techniques and computational chemistry at the DFT level. The methylthiomethyl cation is less reactive than methoxymethyl and, unlike the latter, is unreactive toward benzene. The calculations suggest that reaction with toluene should proceed primarily by addition at the para and ortho positions resulting in a benzyl-type ion. Reaction with aniline-2,3,4,5,6-d(5) reveals that elimination of CH(3)SD is kinetically favored by a factor of 5 over elimination of CH(3)SH. Experiments with C(6)H(6)ND(2) and theoretical calculations suggest that methylenation at the nitrogen atom is energetically favorable and likely, but the observed results may reflect some H/D scrambling, which occurs after attack at a ring position. By comparison, reaction with phenol-2,3,4,5,6-d(5) reveals that methylenation followed by elimination of CH(3)SD is kinetically favored by a factor of 3.8 over elimination of CH(3)SH. For phenol, the theoretical calculations suggest that attack by CH(3)S(+)=CH(2) at the para or ortho position is the only low-energy pathway for methylenation. However, a low-energy pathway for hydrogen scrambling is predicted by the calculations originating from the exit complex, [CH(3)SH(...) CH(2)=C(6)H(4)=OH](+), of reaction at a ring position.     

PHOTOREGULATION OF α-CHYMOTRYPSIN ACTIVITY IN ORGANIC MEDIA: EFFECTS OF BIOIMPRINTING

Abstract α-Chymotrypsin exhibits photoswitchable activities in an organic solvent after covalent modification of the protein backbone with thiophenefulgide active ester (2). The thiophenefulgide-modified α-chymotrypsin exhibits reversible photoisomerizable properties between states (3)-E and (3)-C. The modified α-chymotrypsin, where nine lysine residues are substituted by thiophenefulgide units, retains 60% of the activity of the native enzyme. The activities of thiophenefulgide-modified α-chymotrypsin toward esterification of N -acetyl-L-phenylalanine (4) by ethanol in cyclohexane are controlled by the configuration of the attached photoisomerizable component and by prior bioimprinting of the protein backbone with the reaction substrate (4). The esterification of (4) in cyclohexane using bioimprinted (3)-C is two-fold faster than in the presence of (3)-E. In the presence of a nonbioimprinted enzyme, esterification of (4) by (3)-C is five-fold faster than with (3)-E. The activity of bioimprinted (3)-E toward esterification of (4) is 4.5-fold higher than that of nonbioimprinted (3)-E. Switchable cyclic esterification of (4) is accomplished by sequential photoisomerization of the thiophenefulgide-modified α-chymotrypsin between states (3)-C and (3)-E.     

超临界干燥方法对甲烷燃烧催化剂LaMnAl11O19结构及活性的影响

 摘要：用水热合成法制备了锰取代的六铝酸盐催化剂，并比较了超临界干燥法和普通烘箱干燥法对催化剂结构及甲烷燃烧反应活性的影响．DTA－MS结果表明，超临界干燥过程中，催化剂前驱物中的表面铝羟基部分被乙氧基取代．这种表面修饰作用可保持铝分散的均匀性，使催化剂前驱物中碳酸锰和碳酸镧的分解温度明显降低，且氢氧化铝的脱水温度维持在较适宜的范围内；焙烧后，易形成六铝酸盐相．甲烷燃烧反应结果表明，用超临界干燥方法制得的催化剂对甲烷燃烧反应的催化活性明显高于用普通烘箱干燥方法制得的催化剂．     

A homogeneous catalyst for selective O(2) oxidation at ambient temperature. diversity-based discovery and mechanistic investigation of thioether oxidation by the Au(III)Cl(2)NO(3)(thioether)/O(2) system.

A library of inorganic complexes with reversible redox chemistry and/or the ability to catalyze homogeneous oxidations by peroxides, including but not limited to combinations of polyoxometalate anions and redox-active cations, was constructed. Evaluation of library members for the ability to catalyze aerobic sulfoxidation (O(2) oxidation of the thioether, 2-chloroethyl ethyl sulfide, CEES) led to the discovery that a combination of HAuCl(4) and AgNO(3) forms a catalyst that is orders of magnitude faster than the previously most reactive such catalysts (Ru(II) and Ce(IV) complexes) and one effective at ambient temperature and 1 atm air or O(2). If no O(2) but high concentrations of thioether are present, the catalyst is inactivated by an irreversible formation of colloidal Au(0). However, this inactivation is minimal in the presence of O(2). The stoichiometry is R(2)S + (1)/(2)O(2) --> R(2)S(O), a 100% atom efficient oxygenation, and not oxidative dehydrogenation. However, isotope labeling studies with H(2)(18)O indicate that H(2)O and not O(2) or H(2)O(2) is the source of oxygen in the sulfoxide product; H(2)O is consumed and subsequently regenerated in the mechanism. The rate law evaluated for every species present in solution, including the products, and other kinetics data, indicate that the dominant active catalyst is Au(III)Cl(2)NO(3)(thioether) (1); the rate-limiting step involves oxidation of the substrate thioether (CEES) by Au(III); reoxidation of the resulting Au(I) to Au(III) by O(2) is a fast subsequent step. The rate of sulfoxidation as Cl is replaced by Br, the solvent kinetic isotope effect (k(H)(2)(O)/k(D)(2)(O) = 1.0), and multiparameter fitting of the kinetic data establish that the mechanism of the rate-limiting step involves a bimolecular attack of CEES on a Au(III)-bound halide and it does not involve H(2)O. The reaction is mildly inhibited by H(2)O and the CEESO product because these molecules compete with those needed for turnover (Cl(-), NO(3)(-)) as ligands for the active Au(III). Kinetic studies using DMSO as a model for CEESO enabled inhibition by CEESO to be assessed.     

Reaction of vinyl chloride with group 4 metal olefin polymerization catalysts

The reactions of three types of group 4 metal olefin polymerization catalysts, (C(5)R(5))(2)ZrX(2)/activator, (C(5)Me(5))TiX(3)/MAO (MAO = methylalumoxane), and (C(5)Me(4)SiMe(2)N(t)Bu)MX(2)/activator (M = Ti, Zr), with vinyl chloride (VC) and VC/propylene mixtures have been investigated. Two general pathways are observed: (i) radical polymerization of VC initiated by radicals derived from the catalyst and (ii) net 1,2 VC insertion into L(n)MR(+) species followed by beta-Cl elimination. rac-(EBI)ZrMe(mu-Me)B(C(6)F(5))(3) (EBI = 1,2-ethylenebis(indenyl)) reacts with 2 equiv of VC to yield oligopropylene, rac-(EBI)ZrCl(2), and B(C(6)F(5))(3). This reaction proceeds by net 1,2 VC insertion into rac-(EBI)ZrMe(+) followed by fast beta-Cl elimination to yield [rac-(EBI)ZrCl][MeB(C(6)F(5))(3)] and propylene. Methylation of rac-(EBI)ZrCl(+) by MeB(C(6)F(5))(3)(-) enables a second VC insertion/beta-Cl elimination to occur. The evolved propylene is oligomerized by rac-(EBI)ZrR(+) as it is formed. At high Al/Zr ratios, rac-(EBI)ZrMe(2)/MAO catalytically converts VC to oligopropylene by 1,2 VC insertion into rac-(EBI)ZrMe(+), beta-Cl elimination, and realkylation of rac-(EBI)ZrCl(+) by MAO; this process is stoichiometric in Al-Me groups. The evolved propylene is oligomerized by rac-(EBI)ZrR(+). Oligopropylene end group analysis shows that the predominant chain transfer mechanism is VC insertion/beta-Cl elimination/realkylation. In the presence of trace levels of O(2), rac-(EBI)ZrMe(2)/MAO polymerizes VC to poly(vinyl chloride) (PVC) by a radical mechanism initiated by radicals generated by autoxidation of Zr-R and/or Al-R species. CpTiX(3)/MAO (Cp = C(5)Me(5); X = OMe, Cl) initiates radical polymerization of VC in CH(2)Cl(2) solvent at low Al/Ti ratios under anaerobic conditions; in this case, the source of initiating radicals is unknown. Radical VC polymerization can be identified by the presence of terminal and internal allylic chloride units and other "radical defects" in the PVC which arise from the characteristic chemistry of PCH(2)CHCl(*) macroradicals. However, this test must be used with caution, since the defect units can be consumed by postpolymerization reactions with MAO. (C(5)Me(4)SiMe(2)N(t)Bu)MMe(2)/[Ph(3)C]][B(C(6)F(5))(4)] catalysts (M = Ti, Zr) react with VC by net 1,2 insertion/beta-Cl elimination, yielding [(C(5)Me(4)SiMe(2)N(t)Bu)MCl][B(C(6)F(5))(4)] species which can be trapped as (C(5)Me(4)SiMe(2)N(t)Bu)MCl(2) by addition of a chloride source. The reaction of rac-(EBI)ZrMe(2)/MAO or [(C(5)Me(4)SiMe(2)N(t)Bu)ZrMe][B(C(6)F(5))(4)] with propylene/VC mixtures yields polypropylene containing both allylic and vinylidene unsaturated chain ends rather than strictly vinylidene chain ends, as observed in propylene homopolymerization. These results show that the VC insertion of L(n)M(CH(2)CHMe)(n)R(+) species is also followed by beta-Cl elimination, which terminates chain growth and precludes propylene/VC copolymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization/copolymerization of VC.     

Synthesis and structural characterization of unprecedented bis-asymmetric heteroscorpionate U(III) complexes: [U(kappa3-H2B(pztBu,Me)(pzMe,tBu))2I] and [U(kappa3-H2B(pztBu,Me)(pzMe2))2I

[UI(3)(THF)(4)] reacts at room temperature with 2 equiv of KBp(tBu,Me), in toluene, yielding [U(kappa(3)-H(mu-H)B(pz(tBu,Me))(pz(Me,tBu)))(2)I] (1). This unprecedented complex, stabilized by two asymmetric heteroscorpionate ligands, is formed due to an isomerization process promoted in situ by the metal center. To find a general method for preparing this type of compound, we synthesized the novel asymmetric K[H(2)B(pz(tBu,Me))(pz(Me2))], and by a straightforward salt metathesis with [UI(3)(THF)(4)] the novel bis-asymmetric complex [U(kappa(3)-H(mu-H)B(pz(tBu,Me))(pz(Me2)))(2)I] (2) was isolated and characterized in the solid state and in solution. As indicated by X-ray crystallographic analysis, the U(III) in 1 and 2 is seven-coordinated by two tridentate asymmetric dihydrobis(pyrazoly)borates and by an iodide. In both cases, the coordination geometry around the metal is very distorted, the pentagonal bipyramid being the one which better describes the arrangement of the atoms around the U(III). An approximate C(2) axis can be defined in the solid state, and is maintained in solution as indicated by the (1)H NMR spectrum of 1 and 2. In the course of attempting to crystallize some of the compounds, monocrystals of the dimer [U(kappa(3)-Bp(tBu,Me))(Hpz(tBu,Me))I(mu-I)](2) (3) were isolated. In this compound each U(III) atom is seven-coordinated by one kappa(3)-Bp(tBu,Me), by one terminal and by two bridging iodide ligands, and by a monodentate Hpz(tBu,Me), exhibiting a distorted 4:3 tetragonal base-trigonal geometry.     

Time-resolved electron spin resonance of gallium and germanium porphyrins in the excited triplet state

Gallium and germanium porphyrin complexes in the lowest excited triplet (T1) state have been studied by time-resolved electron spin resonance (TRESR). It is found that for Ge(TPP)(OH)2 (TPP = dianion of tetraphenylporphyrin) intersystem crossing (ISC) from the lowest excited singlet (S1) state to the T1x and T1y sublevels is faster than that to the T1z sublevel (T1x, T1y, and T1z are sublevels of the T1 state), while the ISC of ZnTPP and Ga(TPP)(OH) is selective to the T1z sublevel. This is interpreted by a weak interaction between the dpi orbital of germanium and LUMO (eg) of the porphyrin ligand, resulting in small spin-orbit coupling (SOC). The interpretation is supported by molecular orbital calculations. The ISC of Ge(OEP)(OH)2 (OEP = dianion of octaethylporphyrin) and Ge(Pc)(OH)2 (Pc = dianion of tetra-tert-butylphthalocyanine) is found to be selective to the T1z sublevel in contrast to Ge(TPP)(OH)2. This dependence on the porphyrin ligand is reasonably explained by a difference between the 3(a(1u)eg) (the OEP and Pc complexes) and 3(a(2u)eg) (the TPP complex) configurations. This is the first observation of a difference in selective ISC between the 3(a(1u)eg) and 3(a(2u)eg) configurations. The TRESR spectrum of Ge(TPP)Br2 is different from those of Ge(TPP)Cl2 and Ge(TPP)(OH)2, and is interpreted by SOC between the T1 and T2 states. From ESR parameters the square of the coefficient of the eg orbital on bromine is evaluated as 0.018 in the T1 state.     

Photocatalytic Oxidation of Aromatic Hydrocarbons

In acidic aqueous solutions UO(2)(2+) serves as a photocatalyst (lambda(irr) >/= 425 nm) for the oxidation of benzene by H(2)O(2). Under conditions where 50% of the excited state UO(2)(2+) is quenched by H(2)O(2) (k = 5.4 x 10(6) M(-)(1) s(-)(1)) and 50% by benzene (k = 2.9 x 10(8) M(-)(1) s(-)(1)), the quantum yield for the formation of phenol is 0.70. The yield does not change when benzene is replaced by benzene-d(6), but decreases by a factor of approximately 4 upon the change of solvent from H(2)O to D(2)O. Photocatalytic oxidation of toluene by UO(2)(2+)/H(2)O(2) produces PhCHO, PhCH(2)OH, and a mixture of cresols with a total quantum yield of 0.28 under conditions where 50% of UO(2)(2+) is quenched by H(2)O(2). The quenching of UO(2)(2+) by benzene and substituted benzenes takes place with k > 10(8) M(-)(1) s(-)(1). The system UO(2)(2+)/t-BuOOH/C(6)H(6)/hnu does not result in the oxidation of benzene, but instead yields methane and ethane.     

Solution study of a structurally characterized monoalkoxo-bound monooxo-vanadium(V) complex: spontaneous generation of the corresponding oxobridged divanadium(V,V) complex and its electroreduction to a mixed-valence species in solution

An interesting transformation of a structurally characterized monooxoalkoxovanadium(V) complex [VO(OEt)L] (LH 2 = a dibasic tridentate ONO donor ligand) in solution leading to the formation of the corresponding monooxobridged divanadium(V,V) complex (VOL) 2O is reported. This binuclear species in solution is adequately characterized by elemental analysis, measurement of conductance (in solution), various spectroscopic (UV-vis, IR, NMR, and mass spectrometry) techiniques and by cyclic voltammetry. The corresponding mixed-valence vanadium(IV,V) species has been generated in CH 3CN solution by controlled potential electrolysis of (VOL) 2O. This mixed-valence species is identified and studied by EPR technique (at room temperature and at liquid nitrogen temperature) and also by UV-vis spectroscopy. This study may be regarded as a general method of obtaining monooxo-bridged binuclear vanadium(V,V) species from the corresponding mononuclear monooxoalkoxovanadium(V) complexes of some selected dibasic tridentate ONO chelating ligands, which can be utilized as the precursor of monooxobridged divanadium(IV,V) mixed-valence species in solution obtainable by controlled potential electrolysis.     

Theoretical study of oxidation of cyclohexane diol to adipic anhydride by [Ru(IV)(O)(tpa)(H2O)]2+ complex (tpa ═ tris(2-pyridylmethyl)amine)

The catalytic conversion of 1,2-cyclohexanediol to adipic anhydride by Ru(IV)O(tpa) (tpa ═ tris(2-pyridylmethyl)amine) is discussed using density functional theory calculations. The whole reaction is divided into three steps: (1) formation of α-hydroxy cyclohexanone by dehydrogenation of cyclohexanediol, (2) formation of 1,2-cyclohexanedione by dehydrogenation of α-hydroxy cyclohexanone, and (3) formation of adipic anhydride by oxygenation of cyclohexanedione. In each step the two-electron oxidation is performed by Ru(IV)O(tpa) active species, which is reduced to bis-aqua Ru(II)(tpa) complex. The Ru(II) complex is reactivated using Ce(IV) and water as an oxygen source. There are two different pathways of the first two steps of the conversion depending on whether the direct H-atom abstraction occurs on a C-H bond or on its adjacent oxygen O-H. In the first step, the C-H (O-H) bond dissociation occurs in TS1 (TS2-1) with an activation barrier of 21.4 (21.6) kcal/mol, which is followed by abstraction of another hydrogen with the spin transition in both pathways. The second process also bifurcates into two reaction pathways. TS3 (TS4-1) is leading to dissociation of the C-H (O-H) bond, and the activation barrier of TS3 (TS4-1) is 20.2 (20.7) kcal/mol. In the third step, oxo ligand attack on the carbonyl carbon and hydrogen migration from the water ligand occur via TS5 with an activation barrier of 17.4 kcal/mol leading to a stable tetrahedral intermediate in a triplet state. However, the slightly higher energy singlet state of this tetrahedral intermediate is unstable; therefore, a spin crossover spontaneously transforms the tetrahedral intermediate into a dione complex by a hydrogen rebound and a C-C bond cleavage. Kinetic isotope effects (k(H)/k(D)) for the electronic processes of the C-H bond dissociations calculated to be 4.9-7.4 at 300 K are in good agreement with experiment values of 2.8-9.0.     

Alternative Syntheses of L-(-)-Oleandrose from L-Rhamnose1 Preparation of Glycals

L-Rhamnal (2) is prepared from L-rhamnose (3) by use of an improved generalized Fischer-Zach reaction. L-Rhamnal (2) is then converted to L-(-)-oleandrose (1) by stannylene mediated selective methylation and effective hydration. Benzyl α-L-oleandrose (12) is prepared by selective methylation and deoxygenation of L-rhamnose (3).     

Properties of chloroformyl peroxynitrate, ClC(O)OONO(2)

The synthesis of ClC(O)OONO(2) is accomplished by photolysis of a mixture of Cl(2), NO(2), and CO in large excess of O(2) at about -70 degrees C. The product is isolated after repeated trap-to-trap condensation. The solid compound melts at -84 degrees C, and the extrapolated boiling point is 80 degrees C. ClC(O)OONO(2) is characterized by IR, Raman, (13)C NMR, and UV spectroscopy. According to the IR matrix spectra, the compound exists at room temperature only as a single conformer. The molecular structure of ClC(O)OONO(2) is determined by gas electron diffraction. The molecule possesses a gauche structure with a dihedral angle of phi(COON) = 86.7(19) degrees , and the C=O bond is oriented syn with respect to the O-O bond. The short O-O bond (1.418(6) A) and the long N-O bond (1.511(8) A) are consistent with the facile dissociation of ClC(O)OONO(2) into the radicals ClC(O)OO and NO(2). The experimental geometry of ClC(O)OONO(2) is reproduced reasonably well by B3LYP/6-311+G(2df) calculations, whereas the MP2 approximation predicts the N-O bond considerably too long and the dihedral angle too small.