Three-dimensional mesoporous titanosilicates prepared by modified sol-gel method: Ideal gold catalyst supports for enhanced propene epoxidation

Mesoporous titanosilicates with 1-12 mol % Ti content and with three-dimensional wormhole-like mesoporosity are prepared by a modified sol-gel technique. Sorption analysis shows that there is little change in the surface properties with increasing Ti concentration in the samples, implying that Ti atoms either are well-dispersed on the walls of the silica matrix or are present inside the framework with no pore blocking effect. Spectroscopic analysis shows that the Ti atoms are atomically dispersed in the silica matrix even at very high Ti concentration and there is no observable Ti aggregate (anatase) present in the samples. These titanosilicate samples after Au deposition followed by trimethylsilylation (for enhanced hydrophobicity) are highly efficient catalysts for vapor-phase propene epoxidation using O2 and H2. It was possible to achieve commercially desirable performance with about 7% propene conversion, >90% propene oxide selectivity, and about 40% hydrogen efficiency.     

Preparation and spectroscopic properties of 2-benzothiazolyl araldehyde hydrazones

Notwithstanding its tendency toward air oxidation in solution, 2-hydrazinobenzothiazole I reacted with aromatic aldehydes in ethanol to give the corresponding hydrazones III-XV in high yields and analytical purity. In related examples, acylation took place under similar conditions to produce hydrazides XVI-XX . The near-infrared bands of the absorption spectra of the araldehyde hydrazones have been associated with charge transfer and appeared to correlate with structural elements of the compounds in a way suggesting that the charge transfer was intermolecular.     

Equilibrium theory of two-dimensional simple liquids

Using the Wigner-Kirkwood expansion and bare Lennard-Jones (LJ) (12-6) potential, an effectiveLJ potential is derived, which includes the quantum effects through the expressions of the effective diameter∂(T, λ) and well-depth (T, λ). We use theWCA perturbation theory to calculate the free energy and pressure for theLJ and effectiveLJ potentials. Simple analytic expressions are given for the reference system and the first order correction calculated. The results are quite good at high density. The quantum effects on the free energy and pressure are also discussed.     

Chemistry of azoimidazoles. Synthesis,spectral characterization and redox studies of N(1)-benzyl-2-(arylazo)imidazolepalladium(II)chloride

Arylazoimidazoles (2) are N,N-chelating ligands. The polymerization trend of the azolate system is restricted via N(1)-benzylation. The parent molecules (2), N(1)-benzylated products (3) and palladium complexes (4) were made by standard methods. The ligands (3) and complexes (4) are new. They have been characterized by elemental analysis, i.r., u.v.-vis. and high resolution 1H-n.m.r. spectral data. Redox studies were carried out by cyclic voltammetry. On complexation, azo reduction is shifted anodically.     

Origins of the differences in solvation by alkanes and perfluoroalkanes Evidence from the S2-S0 spectra of jet-cooled van der Waals complexes of xanthione and azulene

The S₂-S₀ fluorescence excitation spectra ofxanthione (XT) and azulene (AZ) complexed with 1 or 2 molecules of the C₁ to C₁₀ n-alkanes and the C₁ to C₆ perfluoro-n-alkanes have been measured. The 1:1 complexes exhibit microscopic solvent shifts, Δ gn, which are larger for the alkanes than the corresponding perfluoroalkanes, despite the larger molecular polarizability of the latter. The values of Δ gn increase monotonically with carbon number of the adduct to C₁₀ in 1:1 n-alkane complexes with XT and to C₅ in 1:1 n-alkane complexes with AZ. However, Δ gn exhibits no further increase beyond C₂ in 1:1 perfluoro-n-alkane complexes with XT and beyond C₃ in 1:1 perfluoro-n-alkane complexes with AZ. The results are interpreted in terms of a model in which the n-alkanes stretch out along the long axis of the chromophore and ‘wet’ its surface whereas the perfluoro-n-alkanes with carbon numbers 3 away from the surface of the chromophore and are ‘non-wetting’.     

Retroaldol-aldol isomerization of perhydroazulenic hydroxyketones

The retroaldol-aldol isomerization of the epimeric hydroxyketones $\text{3}$ and $\text{5}$ was found to yield predominantly $\text{4}$ and $\text{6}$, respectively, under kinetic conditions in the presence of chelating lithium cations. In hydroxylic medium $\text{4}$ is the preferred kinetic product. Under equilibration conditions $\text{4}$ and $\text{5}$ predominate.     

Fluctuating boundary layers in combined convection flows along a vertical surface

The effect of buoyancy force on laminar boundary layer in two dimensional flow and heat transfer along a semi-infinite vertical surface, when the velocity of the on-coming stream oscillates in magnitude about a steady mean, is analysed. Two separate solutions valid for low and high frequency ranges are developed. It is found that for low frequency oscillations the phase angles of oscillatory components of skin friction and the rate of heat transfer increase as the Grashof number increases. For very high frequencies, the velocity field is of shear-wave type unaffected by the mean flow; the phase lead in the skin friction is, then, /4 and the rate of heat transfer fluctuation indicates a phase lag of /2 over that of the free stream oscillations.The authors are thankful to referee for many useful suggestions.     

The reactivity of the cis-RuCl2 fragment in Ru(P)2(TaiMe)Cl2 with N,O; O,O and S,S-chelators (P = PPh3; TaiMe = 1-methyl-2-(p-tolylazo)imidazole)

Ru(P)₂(TaiMe)Cl₂ [P = PPh₃; TaiMe = 1-methyl-2-(p-tolylazo)imidazole] possesses a cis-RuCl₂ configuration. Dechlorination was carried out in acetone solution by Ag⁺ and the solvated species reacted with N,O-[oxinate (ox), -picolinate (pic)], O,O-[salicylate (sa), 3-formylsalicylate (3-fsa), 5-formylsalicylate (5-fsa)] and S,S-[xanthate (xan), dithiocarbamate (dtc)] chelators to yield [Ru(P)₂(TaiMe)(N,O/O,O/S,S)] (ClO₄) _n (n = 1 for N,O- and S,S-chelators; n = 0 for O,O-chelators). The complexes were characterised by microanalysis, molar conductance, i.r., u.v.–vis. and ¹H-n.m.r. data. Isomeric structures in some complexes were identified by ¹H-n.m.r. spectra. The electronic spectra show a high intensity ( 10⁴) m.l.c.t. transition in the visible region together with a weak shoulder ( 10³) at longer wavelength. Redox studies exhibit a Ru^III/Ru^II couple and quasireversible azo reduction.     

A mild conversion of phenylpropropnoid into rare phenylbutanoids: (E)-4-(2,4,5-trimethoxyphenyl)but-1,3-diene and (E)-4-(2,4,5-trimethozypheny)but-1-ene occuring in Zingiber cassumunar

(E)-4-(2',4',5'-trimethoxyphenyl)but-1,3-diene (4) and (E)-4-(2',4',5'-trimethoxyphenyl)but-1-ene (6), bioactive phenylbutanoids of Zingiber cassumunar, were synthesized exclusively with trans geometry. Treatment of methylmagnesium iodide with (E)-2',4',5'-trimethoxycinnamaldehyde (2), an oxidized product of abundantly available toxic (Z)-phenylpropanoid (1) of Acorus calamus, gave (E)-4-(2',4',5'-trimethoxyphenyl)but-3-en-2-ol (3) which upon dehydration with copper sulphate/silica gel under microwave irradiation for 3 min afforded 4 in 58% yield. Further, catalytic hydrogenation of 4 with 10% Pd/C afforded 4-(2',4',5'-trimethoxyphenyl)butane (5) which upon dehydrogenation with DDQ/SiO2 afforded hypolipidemic 6 in 54% yield.