PHOTOOXIDATION OF PROPIONALDEHYDE AT LOW PARTIAL PRESSURES OF ALDEHYDE

1966 ◽  
Vol 44 (24) ◽  
pp. 2973-2979 ◽  
Author(s):  
A. P. Altshuller ◽  
I. R. Cohen ◽  
T. C. Purcell
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Oxygen Molecule ◽  
Radical Mechanism ◽  
Alternative Mechanism ◽  
Alkyl Hydroperoxides ◽  
Free Radical Mechanism ◽  
Partial Pressures ◽  
Peroxy Acids ◽  
Radical Disproportionation

Propionaldehyde at partial pressures of from 0.0006 to 0.04 mm was photooxidized at 3 100 Å in the presence of 150 mm of oxygen. The major products were ethyl hydroperoxide and carbon monoxide. Acetaldehyde was formed at intermediate concentrations and formaldehyde, ethanol, methanol, hydrogen peroxide, and ethane were minor products. No ozone, peroxy acids, or diacyl peroxides could be detected.The results can be explained on the basis of a free-radical mechanism. Certain radical disproportionation reactions which are often postulated are unimportant because of the low partial pressures of propionaldehyde. An alternative mechanism involving direct chemical reaction of an oxygen molecule with the triplet state of the propionaldehyde may be of some significance, but cannot account for all of the products obtained. The present results indicate the importance of alkyl hydroperoxides as products in photooxidations at low partial pressures of aldehyde in the presence of large excesses of oxygen.

Molecular rearrangements. Part XVI. Thermolysis and photolysis of N-benzyldiphenylamine and N-phenylacetyldiphenylamine

1980 ◽  
Vol 58 (12) ◽  
pp. 1229-1232 ◽  
Author(s):  
M. Z. A. Badr ◽  
M. M. Aly ◽  
A. M. Fahmy
Keyword(s):  
Carbon Monoxide ◽  
Free Radical ◽  
Radical Mechanism ◽  
Molecular Rearrangements ◽  
Free Radical Mechanism

Heating N-phenylacetyldiphenylamine in a sealed tube at 360 °C gave rise to carbon monoxide, bibenzyl, toluene, stilbene, diphenylmethane, aniline, carbazole, N-benzylcarbazole, acridine, 9-phenylacridine, 4-aminotriphenylmethane, diphenylamine, p-benzyldiphenylamine, and o-aminodiphenylmethane. A similar result was also obtained on heating N-benzyldiphenylamine, with the exception of carbon monoxide. Such results in addition to those obtained from photolysis of N-phenylacetyldiphenylamine are interpreted in terms of a free-radical mechanism.

Methylene II. Gas phase reactions with ethyl chloride

1968 ◽  
Vol 306 (1485) ◽  
pp. 135-158 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Energy Content ◽  
Incident Light ◽  
Hydrogen Abstraction ◽  
Relative Concentration ◽  
Radical Mechanism ◽  
Gas Phase Reactions ◽  
Free Radical Mechanism ◽  
Singlet Methylene

In this work methylene was prepared by the photolysis of ketene, and the experiments include observations of the effects of changing the wavelength of the photolysing light and of introducing foreign gases. Results are consistent with a free-radical mechanism in which CH 2 abstracts a chlorine or a hydrogen atom from C 2 H 5 Cl: CH 2 +CH 3 CH 2 Cl→ k cl ĊH 2 Cl+CH 3 ĊH 2 , CH 2 +CH 3 CH 2 Cl→ k h1 ĊH 3 +ĊH 3 CH 3 Cl, } CH 2 +CH 3 CH 2 Cl→ k H2 ĊH 3 +CH 3 ċHCl. } ( k H ) All the fourteen products of the radical recombinations have been identified. Disproportionation of radicals and decomposition of excited molecules formed by recombinations yield additional products. Methylene insertion does not appear to play a significant role. When the incident light contains wavelengths in the region 2450 to 4000Å we find that k Cl / k H =1·62, k H1 / k H2 =0·098. If shorter wavelengths are excluded, or if nitrogen is added, lower values of k Cl / k H are obtained. On the other hand, in the presence of carbon monoxide the value of k Cl / k H may be greatly increased. It is suggested that these findings are attributable to differences in reactivity between singlet and triplet methylene. At longer wavelengths, or when nitrogen is present, the relative concentration of the singlet is reduced, but in the presence of carbon monoxide the triplet is removed preferentially (De Graff & Kistiakowsky 1967). Singlet methylene appears to be highly discriminating in its reactions, abstracting chlorine preferentially, while the triplet discriminates in favour of hydrogen abstraction. A kinetic analysis based on these ideas and consistent with the experimental observations shows that k S Cl / k S H >16·3, k T Cl / k T H <0·14. The selectivities shown by the two species of methylene are thought to be a result of differences in electronic structure rather than energy content.

Activated hydrogen peroxide decolorization of a model azo dye-colored pulp

Holzforschung ◽  
2015 ◽  
Vol 69 (6) ◽  
pp. 677-683 ◽  
Author(s):  
Elsa Walger ◽  
Camille Rivollier ◽  
Nathalie Marlin ◽  
Gérard Mortha
Keyword(s):  
Hydrogen Peroxide ◽  
Azo Dye ◽  
Kraft Pulp ◽  
Dye Removal ◽  
Cellulose Degradation ◽  
Degree Of Polymerization ◽  
Radical Mechanism ◽  
Bleached Kraft Pulp ◽  
Free Radical Mechanism ◽  
Alkaline Conditions

Abstract Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H2O2) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H2O2 on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H2O2. A bleached kraft pulp was dyed with a model azo dye and submitted to activated H2O2 bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H2O2 color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH)2 would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH)2 as an activating species.

Molecular rearrangements. Part XX. Thermolysis of carboxylic acid esters

1983 ◽  
Vol 61 (7) ◽  
pp. 1532-1535 ◽  
Author(s):  
M. M. Aly ◽  
M. Z. A. Badr ◽  
A. M. Fahmy ◽  
S. A. Mahgoub
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Nitrogen Atmosphere ◽  
Radical Mechanism ◽  
Benzyl Benzoate ◽  
Phenyl Benzoate ◽  
Free Radical Mechanism ◽  
Homolytic Fission ◽  
Subsequent Decomposition ◽  
Acid Esters

Thermolysis of phenyl benzoate on heating under reflux for ca. 10 days in a nitrogen atmosphere gives phenol, o- and p-hydroxy biphenyl, biphenyl, and carbon monoxide. Phenyl phenylacetate under the same conditions gives toluene, bibenzyl, stilbene, phenol, o- and p-benzylphenol, 9-phenylxanthene, water, and carbon monoxide. Thermolysis of benzyl benzoate is accompanied by decarboxylation and the formation of toluene, diphenylmethane, bibenzyl, stilbene, and biphenyl. Thermolysis of benzyl phenylacetate proceeds smoothly, affording carbon dioxide, toluene, bibenzyl, and stilbene. It was concluded that thermolyses of esters proceeds through a free radical mechanism involving homolytic fission of either the O—CO or O–alkyl bond with subsequent decomposition of the radicals so formed.

scholarly journals Polyoxometalates catalysts in the oxidation of cyclooctane by hydrogen peroxide

2012 ◽  
Vol 77 (11) ◽  
pp. 1599-1607 ◽  
Author(s):  
Wimonrat Trakarnpruk ◽  
Apiwat Wannatem ◽  
Jutatip Kongpeth
Keyword(s):  
Hydrogen Peroxide ◽  
Free Radical ◽  
Reaction Time ◽  
High Selectivity ◽  
Experimental Results ◽  
Molar Ratio ◽  
Radical Mechanism ◽  
Tetrabutylammonium Salt ◽  
Free Radical Mechanism ◽  
Radical Traps

A Keggin-type tungstocobaltate, [Co(2,2'- bipy)3]2H2[CoW12O40]?9.5H2O ([Co]CoW) and tetrabutylammonium salt of vanadium-substituted tungstophosphates [(n-C4H9)4N]4[PVW11O40], [(n-C4H9)4N]5[PV2W10O40] (PVW, PV2W) were used as catalyst for oxidation of cyclooctane with H2O2 as oxidant in acetonitrile. The activity of [(n-C4H9)4N4H[PCo(H2O)W11O39]?2H2O (PCoW) was also compared. The products of the reaction were cyclooctanone, cyclooctanol and cyclooctyl hydroperoxide. The experimental results showed that at H2O2/cyclooctane molar ratio = 3 at 80?C, in 9 h the [Co]CoW yielded higher conversion and selectivity to cyclooctanone. The V-based catalysts are more active than the Co-based tungstophosphate. The PV2W gave rise to high selectivity to cyclooctyl hydroperoxide. Cyclooctane conversion was increased by increasing reaction time or H2O2/cyclooctane molar ratio. In the presence of tungstocobaltate catalyst, 88% cyclooctane conversion and 82% selectivity of cyclooctanone were obtained after 12 h using H2O2/cyclooctane molar ratio of 9. This catalyst is stable upon treatment with H2O2. Experiments with radical traps suggest the involvement of a free-radical mechanism.

Comparative QSAR evidence for a free-radical mechanism of phenol-induced toxicity

2000 ◽  
Vol 127 (1) ◽  
pp. 61-72 ◽  
Author(s):  
Corwin Hansch ◽  
Susan C. McKarns ◽  
Carr J. Smith ◽  
David J. Doolittle
Keyword(s):  
Free Radical ◽  
Radical Mechanism ◽  
Free Radical Mechanism

Dirhodium(II)-Catalyzed Diamination Reaction via a Free Radical Pathway

2021 ◽  
Author(s):  
Zhiying Fan ◽  
Zhifan Wang ◽  
Ruoyi Shi ◽  
Yuanhua Wang
Keyword(s):  
Free Radical ◽  
Bond Formation ◽  
Mechanistic Study ◽  
Radical Mechanism ◽  
Free Radical Mechanism

Unlike C-N bond formation with classical dirhodium(II)-nitrenoids as the key intermediate, dirhodium(II)-catalyzed 1,2-and 1,3-diamination reactions are realized by a free radical mechanism. A mechanistic study revealed that the reactions undergo...

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