The photochemistry of complex ions: photochemical and thermal decomposition of the trioxalatocobaltate III complex

1955 ◽  
Vol 228 (1173) ◽  
pp. 252-263 ◽  
Keyword(s):  
Quantum Efficiency ◽  
Reaction Rate ◽  
Ultra Violet ◽  
Reaction Scheme ◽  
Thermal Reaction ◽  
Water Molecules ◽  
Back Reaction ◽  
Complex Ions ◽  
Excited Complex ◽  
Photochemical Quantum Yield

The photochemistry of the trioxalatocobaltate III complex was studied. It was shown that both the peak in the ultra-violet region (attributed to electron transfer) and that in the blue (attributed to d->d transitions) are photochemically active. Primary quantum efficiencies were found for various lines to be: 313 m μ , 0.365; 365 m μ , 0.345; 405 m μ , 0.085; 435 m μ , 0.06. The quantum efficiency of cobaltous ion formation is twice the primary quantum efficiency. No temperature dependence was detected. Ethyl alcohol (up to 75%) and acetone (up to 60%) did not effect the photochemical quantum yield. The radical C 2 O 4 - is postulated as intermediate capable of reducing mercuric chloride in the course of the reaction. The reaction scheme consists of photo-excitation, primary dark back-reaction, dissociation of excited complex and non-rate-determining oxidation of the C 2 O 4 - ion. The thermal reaction was also studied. It was found that the reaction rate could be presented by -d[Co Ox 3- 3 ]/d t = k 1 [Co Ox 3- 3 ]+ k 2 [H + ][Co Ox 3- 3 ] k 1 and k 2 were evaluated as 1.62 x 10 18 exp ( - 33 600/ RT ) s -1 and 1.77 x 10 19 exp ( - 32500/ RT ) s -1 (mol./l.) -1 respectively. Both the neutral and acid reactions were, however, postulated to proceed through a pseudomonomolecular mechanism involving water molecules with the [H + ] ion effecting the level of the transition state. Activation energies are discussed and finally the suitability of the trioxalatocobaltate III complex for chemical actionometry is analyzed.

scholarly journals Geometrical inversion in light

1930 ◽  
Vol 129 (810) ◽  
pp. 299-313 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Organic Compounds ◽  
Quantum Efficiency ◽  
Ultra Violet ◽  
Light Energy ◽  
Quantitative Investigation ◽  
Trans Form ◽  
Geometrical Isomers ◽  
Ultra Violet Radiation ◽  
Violet Radiation

One of the most interesting types of photochemical change is exhibited by the class of organic compounds known as geometrical isomers. Under the influence of ultra-violet radiation these substances change from the cis-form to the trans-form and vice versa . Although many compounds of this class are known, no quantitative investigation has been made of the relation between the light energy absorbed and the amount of change produced except in the case of maleic and fumaric acids. This pair of geometrical isomers was investigated by Warburg, who found a very low quantum efficiency for the change in both directions. Yolmar, however, stated that maleic-fumaric acids and citraconic-mesaconic acids underwent a decomposition of the same nature as oxalic and malonic acids, where carbon dioxide is one of the products of decomposition.

scholarly journals The Effects of Mixing, Reaction Rates, and Stoichiometry on Yield for Mixing Sensitive Reactions—Part II: Design Protocols

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Syed Imran A. Shah ◽  
Larry W. Kostiuk ◽  
Suzanne M. Kresta
Keyword(s):  
Rate Ratio ◽  
Reaction Rate ◽  
Relative Rate ◽  
Reaction Diffusion ◽  
Reaction Rates ◽  
Reaction Scheme ◽  
Considerable Effect ◽  
Mixing Condition ◽  
Reaction Diffusion Model ◽  
Rate Ratios

Competitive-consecutive and competitive-parallel reactions are both mixing sensitive reactions where the yield of desired product depends on how fast the reactants are brought together. Recent experimental results have suggested that the magnitude of the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model was developed at the micromixing scale, yielding a single general Damköhler number. Dimensionless reaction rate ratios were derived for both reaction schemes. A detailed investigation of the effects of initial mixing condition (striation thickness), dimensionless reaction rate ratio, and reaction stoichiometry on the yield of desired product showed that the stoichiometry has a considerable effect on yield. All three variables were found to interact strongly. Model results for 12 stoichiometries are used to determine the mixing scale and relative rate ratio needed to achieve a specified yield for each reaction scheme. The results show that all three variables need to be considered when specifying reactors for mixing sensitive reactions.

PHOTO-INITIATED FREE RADICAL POLYMERIZATION OF METHYL ACRYLATE IN AQUEOUS SOLUTION

1957 ◽  
Vol 35 (11) ◽  
pp. 1267-1277 ◽  
Author(s):  
C. Chaitanyan Menon ◽  
M. Santappa
Keyword(s):  
Aqueous Solution ◽  
Free Radical ◽  
Radical Polymerization ◽  
Methyl Acrylate ◽  
Free Radical Polymerization ◽  
Reaction Scheme ◽  
Ferrous Ion ◽  
Back Reaction ◽  
Photochemical Process ◽  
Initiation Of Polymerization

Photo-initiated free radical polymerization of methyl acrylate in aqueous solution is described. Using mainly light of wavelength 3650 Å and the ion pairs Fe3+OH− and Fe3+Cl− as photosensitizers the kinetics of polymerization were investigated by studying the effect of the variation of (i) intensity of light, (ii) concentration of monomer, (iii) fraction of light absorbed by the ion pair, and (iv) ferrous ion accumulating in, or initially added to, the system on (a) molecular weight of polymer, (b) the rate of disappearance of monomer, and (c) the rate of production of ferrous ion. The results have been analyzed in the light of a reaction scheme involving (1) a primary photochemical process and a dark back reaction, (2) initiation of polymerization by the primary product Fe2+OH or Fe2+Cl, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation by a free radical, (6) propagation, and (7) termination. Examination of the experimental results in the light of the reaction scheme indicated that the initiation of polymerization was due to OH or Cl free radicals formed by the dissociation of the primary product and that termination occurred by combination of growing polymer chains. Some expressions involving specific rate constants have been evaluated.

Unusually strong emission from an exciplex formed between benzenoid solvents and dibenzoylmethanatoboron difluoride. Formation of a triplex

1995 ◽  
Vol 73 (11) ◽  
pp. 1902-1913 ◽  
Author(s):  
Pierre Valat ◽  
Véronique Wintgens ◽  
Yuan L. Chow ◽  
Jean Kossanyi
Keyword(s):  
Quantum Yield ◽  
Rate Constant ◽  
Fluorescence Quantum Yield ◽  
Equilibrium Constants ◽  
Back Reaction ◽  
Benzene Derivative ◽  
Exciplex Formation ◽  
Excited Complex ◽  
Low Concentrations ◽  
Dibenzoylmethanatoboron Difluoride

Benzene derivatives give, in cyclohexane solution, a strongly emitting (Φf up to 0.8) excited complex with dibenzoylmethanatoboron difluoride (DBMBF2). The rate constant kex for the complex formation varies between 3.5 × 109 and 2.6 × 1010 M−1 s−1 depending on the benzene derivative, and the complex emission can already be detected at very low concentrations of the aromatics. This behaviour is different from that found in acetonitrile where the DBMBF2 emission disappeared completely before the new emission of the complex could be detected. The position of the complex emission and its lifetime depend upon the redox potential of the aromatics: the lower the latter, the longer the lifetime and the more the emission is red-shifted. The monotonous increase of the lifetime and of the fluorescence quantum yield of the emission with the concentration of the aromatics has been interpreted on the basis of an equilibrium between the exciplex and excited DBMBF2. The equilibrium constant varies with the electron-donating property of the aromatics, from 2.7 for benzene to 560 M−1 for isodurene. A decrease in the excited complex lifetime or in its fluorescence quantum yield is observed in some cases when the aromatics concentration is close to that of the pure solvent. Such behaviour is believed to arise from a new equilibrium resulting from the interaction of the exciplex with a second molecule of the aromatics to form triplex species. A detailed kinetic study has been undertaken in case of p-xylene, and the rate constants of all the processes involved in the double equilibrium have been determined. No basic difference is observed in the rate constant for exciplex formation when a single or double equilibrium is assumed; on the other hand, large discrepancies are found in the exciplex deactivation processes, specially for the back reaction from the exciplex to excited DBMBF2. The equilibrium constants between DBMBF2 and the exciplex, on one hand, and between the latter and the triplex are 56.6 and 0.68 M−1, respectively, when the concentration of p-xylene in cyclohexane is 3.3 M. Keywords: fluorescence, exciplex, triplex, dibenzoylmethanatoboron difluoride, kinetics.

scholarly journals Studies in polymerization - III. The polymerization of methyl methacrylate

1949 ◽  
Vol 197 (1050) ◽  
pp. 356-373 ◽  
Keyword(s):  
Methyl Methacrylate ◽  
Ultra Violet ◽  
Vapour Phase ◽  
Thermal Reaction ◽  
Chain Process ◽  
Radical Chain ◽  
Violet Light ◽  
Normal Radical ◽  
Bond Mechanism ◽  
Radical Chain Process

The polymerization of methyl methacrylate has been studied by the viscosity method (part I, 1948). The reaction is shown to be a normal radical chain process with velocity constants at 0°C given in table 3. It has been found that irradiation of methyl methacrylate by ultra-violet light produces a catalyst, while an inhibitor is formed by a thermal reaction. These facts account for the difficulties experienced by other workers. A reinvestigation of the vapour-phase polymerization shows that they also account for the anomalous polymerization observed by Melville (1937), and attributed by him to a ‘bound-bond’ mechanism. Chain termination in the polymerization of styrene and methyl methacrylate is shown to occur by disproportionation.

scholarly journals Aromatization of light naphtha fractions on zeolites 1: Kinetic model

2003 ◽  
Vol 57 (9) ◽  
pp. 399-403 ◽  
Author(s):  
Svetlana Rovenskaja ◽  
Nikolaj Ostrovski
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Scheme ◽  
Activation Energies ◽  
Modeling And Optimization ◽  
Light Naphtha ◽  
Reaction Rate Constants

On the basis of analyzing kinetic experimental data performed in laboratory integral reactors a lumping kinetic model of the "Zeoforming" process was developed. A reaction scheme of the lumped components was proposed, that was adapted to the technological requirements. The reaction rate constants and activation energies were estimated, that are valid for certain feed compositions. The model is intended for further modeling and optimization of the process.

scholarly journals Quantum efficiency of Pd/TiO2 catalyst for photocatalytic reforming of methanol in ultra violet region

2019 ◽  
Vol 73 (11) ◽  
pp. 2707-2714 ◽  
Author(s):  
Hasliza Bahruji ◽  
Hasmerya Maarof ◽  
Norizah Abdul Rahman
Keyword(s):  
Quantum Efficiency ◽  
Ultra Violet ◽  
Tio2 Catalyst

Hexaaquairon(III) perchlorate trihydrate

2006 ◽  
Vol 62 (4) ◽  
pp. i94-i95 ◽  
Author(s):  
Andreas Fischer
Keyword(s):  
Hydrogen Bonds ◽  
Single Crystal ◽  
Crystal Packing ◽  
Water Molecules ◽  
Complex Ions ◽  
Charge Balancing ◽  
Perchlorate Hexahydrate

A single crystal of commercially available `iron(III) perchlorate hexahydrate' has been structurally characterized and shown to be hexaaquairon(III) tris(perchlorate) trihydrate, [Fe(H2O)6](ClO4)3·3H2O. The structure contains [Fe(H2O)6]3+ complex ions, charge-balancing perchlorate ions and three water molecules of crystallization per Fe atom. A network of O—H...O hydrogen bonds helps to stabilize the crystal packing. Fe, Cl and one water O atom occupy special positions with site symmetries \overline{3}, 2, and 2, respectively.

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