Photochemical oxidation of thio ketones: steric and electronic aspects

Oxidation of diaryl, aryl alkyl, and dialkyl thioketones by singlet oxygen generated via self-sensitization and other independent methods yielded the corresponding ketone and sulfine in varying amounts. A zwitterionic/ diradical intermediate arising out of the primary interaction of singlet oxygen with the thiocarbonyl chromophore is believed to be the common intermediate for the ketone and sulfine. While closure of the zwitterion/diradical to give 1,2,3-dioxathietane would lead to the ketone, competing oxygen elimination is believed to lead to the sulfine. This partitioning is governed by steric and electronic factors operating on the zwitterionic/diradical intermediate.

An experimental study of oxidation of zinc sulphide pellets

Oxidation of zinc sulphide pellets is carried out in the ranges of 600-826°C temperature, 0.3-0.5 porosity and 15-50 minutes of reaction time. An experimental technique is employed to simultaneously determine the rate of weight loss of the solid and conversions of the solid reactant at various levels in the pellet for different reaction times. A structural model is used to explain the experimental results. It is found that the model predicts both the experimental results obtained under various conditions reasonably well.

Kinetics of Chemical Vapor Deposition

A generalized mass transport model is developed for predicting the rate ofdeposition in chemical vapor deposition (CVD) systems. This combines thegeneralized method of obtaining equilibrium composition, with elemental fluxbalance expressions. This procedure avoids the usual problems encountered incalculating the rates in multicomponent systems, like writing overall reactionschemes. The dependence of multicomponent diffusivities on the fluxes is accountedin this model using an iterative procedure. The model developed isapplied to the deposition of titanium carbide on cemented carbide tool bitsfrom a gas mixture of titanium tetrachloride, toluene, and hydrogen. Experimentaldeposition rates were obtained using a thermogravimetric assembly.Mass transport controlled rates give an order of magnitude estimates of theobserved rates.

Styrene Oxidation to Benzaldehyde by Polymer Anchored Wilkinson Complex

Wilkinson complex, insolubilized by anchoring to polymeric Amberlite beads, had been used for the liquid-phase catalytic oxidation of styrene to benzaldehyde and formaldehyde in toluene medium. Styrene conversion was followed by measuring the oxygen volume in contact with the reaction mixture in a specially designed closed batch apparatus. Styrene conversion depended upon catalyst loading and distribution inside the porous beads, while temperature had little effect on it. The internal diffusional effects on the conversion process have been taken into consideration by a mathematical model which allowed calculation of effectiveness factors for various catalyst loadings and corresponding catalyst distributions. The influence of external diffusion was separately determined by plotting initial rate versus catalyst loading. The proposed method can be readily extended to immobilized enzymes in porous matrices.

Styrene Oxidation to Benzaldehyde by Polymer Anchored Wilkinson Complex

Wilkinson complex, insolubilized by anchoring to polymeric Amberlite beads, had been used for the liquid-phase catalytic oxidation of styrene to benzaldehyde and formaldehyde in toluene medium. Styrene conversion was followed by measuring the oxygen volume in contact with the reaction mixture in a specially designed closed batch apparatus. Styrene conversion depended upon catalyst loading and distribution inside the porous beads, while temperature had little effect on it. The internal diffusional effects on the conversion process have been taken into onsideration by a mathematical model which allowed calculation of effectiveness factors for various catalyst loadings and corresponding catalyst distributions. The influence of external diffusion was separately determined by plotting initial rate versus catalyst loading. The proposed method can be readily extended to immobilized enzymes in porous matrices.

Kinetics Of The Aminolysis Reactions Of Chlorocyclotriphosphazenes-Changeover From A Sn2(P) To A Sn1(P) Mechanism

A change-over from SN2(P) to SN1(P) mechanism is established for the chlorine replacement reactions of halogenocyclophosphazenes; this mechanistic change-over helps in rationalising the diverse findings reported for this class of reactions.

Cuprous oxide catalyzed air oxidation of thiosulfate and tetrathionate

Thiosulfate (S2O32−) and tetrathionate (S4O62−)are oxidized to sulfate by air at atmospheric pressure and 50–70°C in the presence of cuprous oxide (Cu2O) as catalyst. Sulfate is produced from S2O32− by series-parallel reaction paths involving S4O62− as an intermediate. The rate data obtained for air oxidation of S2O32− on Cu2O agree well with a pseudo-homogeneous first order kinetic scheme, yielding values of rate constants for series parallel reaction paths which have been used in modelling the catalyzed air oxidation of S2O32−. Air oxidation of S4O62− on Cu2O proceeds at a higher rate in the presence of S2O32− than in its absence. Cu2O is less active than Cu2S for the air oxidation of S2O32−, as shown by the rate constant values which for Cu2O catalyzed oxidation are an order of magnitude smaller than those for the Cu2S catalyzed oxidation.

Estrogen Induction Of Biotin-Binding Protein In Immature Chicks - Kinetics, Hormonal Specificity And Modulation

Employing a specific radioimmunoassay for quantification, the kinetics of estrogen-induced elevation in the plasma concentration of biotin-binding protein (BBP) in immature male chicks was investigated. A single injection of the steroid hormone enhanced the plasma BBP content several-fold at 6 h, reaching peak levels around 48 h and declining thereafter. A 2-fold amplification of the response was evident during secondary stimulation with the hormone. The magnitude of the response was hormonal dose-dependent while the initial lag phase and the time of peak protein accumulation were unaltered within the hormonal doses tested. The circulatory half-life of the specific protein in normal and estrogenized birds was 10 h. Hyperthyroidism markedly decreased the hormonal response while the opposite effect was seen during hypothyroidism. The antiestrogens E- and Z-clomiphene citrate effectively blocked the protein induction whereas progesterone, either alone or in combination with estrogen, was ineffective in modulating the induction. Cycloheximide administration drastically inhibited the inductive response. The above observations clearly suggest that the genes corresponding to the two isofunctional proteins of chicken egg, viz. BBP and avidin, are differentially regulated.

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl4), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 2 at two different temperatures and in different solvents. The square-root dependence of Rp on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

On the kinetics of crystal growth from a supercooled melt

We present a theoretical analysis of the dynamics of crystal growth from a supercooled melt. A molecular theory of crystal growth that pays proper attention to the structure at the liquid-solid interface is discussed.

Surface oxidation of cadmium, indium, tin and antimony by photoelectron and Auger spectroscopy

Surface oxidation of Cd, In, Sn and Sb has been investigated by employing valence bands, metal 4d levels and plasmon bands in X-ray photoelectron spectra. O(KLL), metal M4N45N45, and plasmon transitions in electron-induced Auger spectra as well as Auger transitions due to the metal (metal oxide) and plasmons in X-ray-induced Auger spectra. The surface oxides are In2O4, CdO and a mixture of SnO and SnO2 in the case of In. Cd and Sn respectively. The facility of surface oxidation is found to vary as In>Cd>Sn>Sb. Inter-atomic Auger transitions involving oxygen valence bands have been identified on oxidized surfaces of Cd and In.

Electrode kinetics of a nickel/cadmium cell and failure-mode prediction. Estimation of equivalent resistance of an internal short

A quantitative expression has been obtained for the equivalent resistance of an internal short in rechargeable cells under constant voltage charging.

XPS and XAES studies of surface segregation and oxidation of Cu-Ge alloy

Surface segregation of Ge is seen in the Cu-5at%Ge alloy with an activation enthalpy equal to 17 kJ/mol. Oxidation of the alloy in the temperature range 400 to 600 K shows the formation of Cu2O and GeO which on further heating in vacuum at 650 K converts to GeO2 with the reduction of Cu2O to Cu.

Surface segregation and oxidation studies of Cu-Sn and Cu-Pd alloys by x-ray photoelectron and auger spectroscopy

X-ray photoelectron and Auger spectroscopic techniques have been employed to study surface segregation and oxidation of Cu-1 at%Sn, Cu-9at%Pd and Cu-25at%Pd alloys. Both Cu-Pd(9%) and Cu-Pd(25%) alloys show segregation of Cu when heated above 500 K. The Pd concentration was reduced by 50% at 750 K compared to the bulk composition; the enthalpy of segregation of Cu is around - 6kJ/mol. Sn segregation is seen from 470 to 650 K in the Cu-Sn(1%) alloy, and a saturation plateau of Sn concentration above 650 K is observed. Surface oxidation of Cu-Sn(1%) and Cu-Pd(9%) alloys at 500 K showed the formation of Cu2O on the surface with total suppression of Sn or Pd on the respective alloy surfaces. On vacuum annealing the oxidised Cu-Sn alloy surface at 550 K, a displacement reaction 2Cu2O+Sn→4Cu+SnO2 was observed. However, under similar annealing of the oxidised Cu-Pd(9%) alloy surface at 500 K, oxide oxygen was totally desorbed leaving the Cu-Pd alloy surface clean. In the case of the Cu-Pd(25%) alloy, only dissociatively chemisorbed oxygen was seen at 500 K which desorbed at the same temperature. Oxygen spill-over from copper to palladium is suggested as the mechanism of oxygen desorption from the oxidised Cu-Pd alloy surfaces.

X-ray photoelectron spectra and Auger studies of the surface oxidation of cobalt

Surface oxidation of Co has been investigated at different temperatures in the 300–600 K range at oxygen exposures upto 106 L by XPES and AES techniques. In the XPES, both the valence band and core level bands have been employed to monitor the oxidation while in the AES, metal Auger intensity ratios as well as O(KLL)/Co(L23M45M45) ratios have been examined. Only CoO is formed on the surface at high oxygen exposures at and above 500 K.