Kenzi Hori

Photocatalytic degradation of trichloroethylene in water using TiO2 pellets

A recirculating system of aqueous trichloroethylene (TCE) solutions through the packed bed reactor with TiO2 pellets has been developed in order to mineralize TCE without difficulties for filtration and recovery of catalyst. The TiO2 pellets prepared by sol gel method have photocatalytic activity similar to commercially available PC-101 and PC-102 in the powder form and to ST-B11 pellets. In batch experiments with TiO2 powders, Degussa P-25 is the most active photocatalyst, which indicates that specific surface area is not an important factor controlling the photocatalytic activity in aqueous solutions. The degradation rates of TCE in the recirculating system with TiO2 pellets decreased in the presence of H2O2, while were remarkably accelerated by adding S2O8(2-). The presence of S2O8(2-) ions more than 0.01 mol dm(-3) completely suppressed hole-electron recombination and mineralized 50 ppm TCE with the 2 h irradiation. In a reactor without TiO2 photocatalysts, TCE was photodegraded by SO4- radicals which produced by photodissociation of S2O8(2-). The degradation rates increased with increase of the initial S2O8(2-) concentration. However, TCE was not mineralized but converted to intermediates which were slowly degraded to Cl- by continuing the irradiation.

Chlorinated byproducts from the photoassisted catalytic oxidation of trichloroethylene and tetrachloroethylene in the gas phase using porous TiO2 pellets

The photocatalytic degradation of trichloroethylene and tetrachloroethylene in the gas phase, when porous TiO2 pellets were used, produced such undesirable chlorinated byproducts as chloroform (CHCl3) and carbon tetrachloride (CCl4). The formation of byproducts was reduced by increasing oxygen mole fractions in the feed gas stream and/or using the TiO2 pellets fired at a lower temperature. Theoretical calculations indicate that the Cl-radical-initiated reaction produces these byproducts. On the basis of the experimental and the theoretical results, a method to prevent the formation of the chlorinated byproducts is discussed.

Theoretical Study on the Reactivity of Phenyl Cation with a Propyl Group at Ortho-Position

Abstract Photosolvolysis of 2-chloropropylbenzene in trifluoroethanol (TFE) produces propylbenzene, indane, 2-trifluoroethoxypropylbenzene and other solvolysis products. Propylbenzene clearly comes from 2-propylphenyl radical intermediate while the other products suggest existence of 2-propylphenyl cation as an intermediate. Density functional theory (DFT) calculations at the B3LYP/6-31G∗∗ level of theory were carried out to research reaction paths for the solvolysis products through the cationic intermediate. Three paths investigated in the present study well explain the products obtained in our experiments. The DFT calculations strongly suggest existence of the phenyl cation as an intermediate in the photosolvolysis of 2-chloropropylbenzene in TFE.

Theoretical study on oxygen exchange accompanying alkaline hydrolysis of esters and amides. The role of water for the exchange reaction

Abstract The hydrolysis of esters and amides accompanies a fast reaction, which results in exchange of carbonyl 18O to 16O coming from solvent water. The present study considered two paths as the oxygen exchange mechanism. One, Path 1 called the direct path, is the mechanism that a proton of the OH fragment directly moves from the OH to the 18O fragment in the tetrahedral intermediate. The other, Path 2 called the water-assisted mechanism, is that one water molecule assists transferring a proton to make an 18OH fragment. The MP2/6-31+G* level of theory estimated rather high ΔEgas‡(TD) for the direct path of methylacetate and N-methylacetamide (21.8 and 19.7 kcal mol−1, respectively). The ΔEgas‡(H2O), the activation barrier for the water-assisted mechanism, is very low both for the ester (3.8 kcal mol−1) and for the amide (2.8 kcal mol−1). The ΔG‡(H2O) and ΔG‡(OH), calculated activation free energies including solvent effect, are small in comparison with those observed for the breakdown of TD intermediates to exchange or hydrolysis products. The present MO calculation suggests that one solvent water acts as one of the reactants and facilitates both proton transfer from the OH fragment and proton acceptance from the water to form the new 18OH fragment. It is likely that the oxygen exchange reaction accompanying hydrolysis of esters and amides proceeds via the water-assisted mechanism.

Ab initio molecular orbital study on the mechanism of amide hydrolysis dependent on leaving groups

Abstract The alkaline hydrolysis of amides, N-methyl acetamide 1, acetanilide 2, and N-acetyl imidazole 3, was investigated by use of ab initio molecular orbital calculations. A detailed analysis was performed for two possible mechanisms, Path 1 and 2. Path 1, similar to ester hydrolysis, releases CH3COOH and RNH whereas Path 2 contains the RNH group that extracts the H atom from the OH fragment in the tetrahedral intermediate. In this mechanism, carboxylate ion and an amine directly form. It was ascertained that Path 2 is a better route to decompose the TD intermediate than Path 1 for 1 and 2 in the gas phase. The stability of the leaving group RNH determines which route, Path 1 or 2, is preferred in the gas phase. The solvent effect was estimated for the two mechanisms by using the SCRF calculations of the IPCM model.

Dynamic coupling of electronic motion and molecular vibration

Abstract A general dynamic equation for an electron orbital is formulated for the dynamic study of electronic motion coupled with molecular vibration A remarkable “additive” property of a normal vibration on the dynamic electronic structure is found and is demonstrated for the H2 and cyclic C3H3+ systems.

Theoretical investigation of the molecular and electronic structures and excitation spectra of iron phthalocyanine and its derivatives, FePc and FePcLn (L = Py, CN−; n = 1, 2)

The effects of axial ligands on the ground-state geometries, electronic structures and the characteristic optical properties of iron phthalocyanine and its derivatives, FePc and FePcL(n) (L = pyridine (Py) and cyanide (CN(-)); n = 1, 2), were investigated using the density functional theory (DFT) method. The geometries of FePc with a triplet spin state and of FePc(Py), FePc(Py)(2), FePc(CN(-)) and FePc(CN(-))(2) with singlet spin states were optimized under D(4h), C(2v), D(2h), C(4v), and D(4h) molecular symmetries, respectively. The highest occupied molecular orbitals (HOMOs) of FePc, FePc(Py), FePc(Py)(2), and FePc(CN(-)) are pi-type orbitals, which have no contribution from the p(z) atomic orbitals of all nitrogen atoms, whereas the HOMO of FePc(CN(-))(2) is the 7e(g) orbital, which has contributions from the d(xz) and the d(yz) orbitals of the Fe atom mixing with the pi-orbitals of the axial CN(-) ligands. The time-dependent (TD) DFT method gives many optically allowed excitations for FePc, FePc(Py), FePc(Py)(2), FePc(CN(-)), and FePc(CN(-))(2) in the UV-VIS region. Our calculated bands corresponded well with the experimental results. In FePc(Py)(2), the metal-ligand charge transfer (MLCT) transitions from the metal d to the axial-ligand pi*-type orbitals contributed to the B band region. In FePc(CN(-))(2), the MLCT transitions from the metal d to the Pc-ring pi*-type orbitals contributed mainly to the first B band region, but those from the metal d to the axial-ligand pi*-type orbitals did not appear in the energy regions of the Q and B bands. Thus, the axial ligands caused a spectral change in FePc through orbital mixing.

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines by Z. Liu et al.

A recent paper by Lui et al. [Z. Liu, X. Zhang, Y. Zhang, J. Jiang, Spectrochim. Acta A 67 (2007) 1232] reported on the theoretical investigations of the fully optimized geometries and electronic structures of iron (II) phthalocyanine (FePc) with the singlet spin state carried out with the restricted density functional theory (DFT) method, where the B3LYP functional was adopted for the exchange-correlation term; however, the triplet spin state was experimentally reported, and we also obtained the triplet spin state by the unrestricted DFT calculations.

Dynamic analysis of electron density in the course of the internal motion of molecular system

The general dynamic aspect of electron density of a molecular system is studied on the basis of the general equation of the electron orbital which is formulated for the dynamic study of electronic motion. The newly defined electron orbital incorporates the dynamics of molecular vibration into the electronic structures. In this scheme, the change of electron distribution caused by excitation of vibrational state is defined as the ‘‘dynamic electron transfer.’’ The dynamic electron density is found to have the remarkable ‘‘additive’’ property. The time‐dependent aspect of the dynamic electron redistribution is also analyzed on the basis of the ‘‘coherent state.’’ The new method relates the classical vibrational amplitude to the quantum number of the vibrational state. As a preliminary application of the present treatment, the dynamic electron densities of H2, HD, HT, HF, and HCl molecules are calculated by use of ab initio molecular orbital method.

Theoretical study on the polymerization mechanism of substituted maleimides by using a chiral catalyst with Zn2

Abstract It is possible to synthesize poly(N-substituted maleimide) by using a chiral complex consisting of a zinc and N -diphenylmethyl-1-benzyl-2-pyrrolidinoethanamine (DPhBP). The optical specific rotations [ α ] 435 25 in obtained polymers depend on the chirality of ligands in the catalysts. In the present study, density functional theory (DFT) calculations were adopted to investigate the polymerization mechanism in detail. The bulky diphenylmethyl group in the chiral ligand is effective to enhance the formation of the product in the initiation reaction. The geometry related to the pyrrolidine ring of the chiral ligand in the Zn catalyst is responsible for determining the configuration of polymers. It was also confirmed that the bulky substituent on the N atom of the N-substituted maleimide is another factor for obtaining polymers with high [ α ] 435 25 .