Photooxidation of Azomethane: Iv. The Role of Formaldehyde

Shahin, Majdi M.; Kutschke, K. O.

doi:10.1139/v61-008

Cited by 14 publications

(6 citation statements)

References 5 publications

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“…I t seems entirely possible that methane was the sole gaseous product, as has been demonstrated conclusively for ethane dissociation on rhodium films by Roberts. 16 The over-all composition of the adsorbed residues from ethylene decomposition changed regularly with temperature, as shown by the dotted curve in Fig. 2.…”

Section: Discussionmentioning

confidence: 90%

The Chemisorption and Catalytic Decomposition of Ethylene on Nickel

McKee¹

1962

J. Am. Chem. Soc.

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1109small K . When X is a chloro group interaction between the donor chlorine atom and the iodineappears to occur in addition to interaction with the carbonyl. This interaction is probably best described as London dispersion and dipole-induced dipole interactions. Since the interaction is weak, it has a x ' G\H N (~W I I1 H0 Fig. 4.-Possible isomers in XCH,C-N( CHI), compounds.negligible effect on A H , but ring formation leads to a favorable entropy term enhancing the stability of the complex. The favorable entropy term is in part cancelled by the entropy of rearrangement. Coordination can also occur to a lesser extent with isomer 11. As a result of all of these effects, C1-0 // CH&-N(CH& falls on the u* plot. In the case of DMTCA, a chloro group most probably is always cis to the carbonyl. Fischer-Hirschfelder models indicate a pronounced steric effect between the C1 and -N(CH& groups when they are both in the same plane. This steric effect requires the chloro group to be cis to the carbonyl. This chloro group interacts with the iodine and the equilibrium constant for the iodine complex of DMTCA is larger than that expected from the u* number. Since all molecules have a chloro-group cis to the carbonyl, rearrangement is not necessary aad the absence of the unfavorable entropy term for complexation produces a large deviation from the u*-log K line. The interaction of the chloro group with the iodine is not manifested in the heats of association for this effect is smaller than the experimental error in the AH.The chemisorption and dissociation of ethylene on unsupported nickel catalysts has been studied by a volumetric technique over the temperature range -78 to 200'. The formation of ethane by self-hydrogenation was measureable even at the lowest temperature and the kinetics of the reaction were studied between -78' and 0'. The rate of ethane evolution was found to be proportional to the initial concentration of chemisorbed ethylene and the apparent activation energy for the self-hydrogenation reaction was 3 kcal./mole. Above 60°, methane began to appear in the gas phase and at 200' was the sole gaseous product. The mechanism of catalytic dissociation of ethylene and the nature of the adsorbed residiies on the metal surface are discussed.

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Section: Discussionmentioning

confidence: 90%

The Chemisorption and Catalytic Decomposition of Ethylene on Nickel

McKee¹

1962

J. Am. Chem. Soc.

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“…T h e isotopic coinpositioil of the carbon monoxide ( Table 11) also shows that formaldehyde is an efficient source of carboil monoxide i~z this system. A similar coilclusio~l was reached by an application of the same technique to the photooxidation of azomethane (6 Figure 2 shows that the data are not quite in agreement with this prediction since the function shows a slow but steady rise with conversion. This can be explained if it is assumed that, as it becomes more concentrated in the system, acetone can compete with formaldehyde in a reaction analogous to [7].…”

Section: Discussionmentioning

confidence: 62%

“…The present study was undertaken to extend this work to !ower (<5%) coi~versioi~s and to investigate the effect of conversion on the rates of production of the inajor products. The role of formaldehyde as a hydrogen donor in the photooxidation of azomethaile has been iilvestigated previously in this laboratory (4,5,6). Experiments are reported in which formaldehyde-C13 was added to the reactailts in the present systein to investigate this point further.…”

Section: Introductionmentioning

confidence: 79%

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THE OXIDATION OF DI-tertiary-BUTYL PEROXIDE

Blake¹,

Kutschke²

1961

Can. J. Chem.

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The oxidation of di-t-butyl peroxide has been investigated in a static system a t low conversion a t 124' C with sufficient oxygen present t o suppress completely the formation of methane and ethane. T h e decolllposition of the t-butoxy radical is unaffected by the presence of oxygen. A major product of the oxidation is formaldehyde whose yield rapidly approaches a stationary value. I t is postulated t h a t the major source of formaldehyde is the decomposition of methyl peroxy radicals, which may also abstract hydrogen from formaldehyde to form methyl hydroperoxide, and that this competition leads to the stationary concentration of formaldehyde actually observed. Methyl hydroperoxide was demonstrated t o be unstable in the system and the predominant decomposition product: was methanol, a compound also found in high yields in the oxidation. Experiments with added formaldehyde-C13 showed that formaldehyde can be converted to carbon n~oiloxide in the system and indicated that formaldehyde was a likely precursor to the carbon monoxide found in the oxidation. INTRODUCTIONT h e pyrolysis of di-t-butyl peroxide (DTBP) provides a particularly coilveilient source of methyl radicals because of the high activation energy (I) required for the abstraction of hydrogen from that compound. Raley et al. (2) used this method to study the oxidation of methyl radicals but their reactions were carried t o large conversions. T h e experin~ents reported by Bose (3) were also done a t high conversion. The present study was undertaken to extend this work to !ower (<5%) coi~versioi~s and to investigate the effect of conversion on the rates of production of the inajor products. The role of formaldehyde as a hydrogen donor in the photooxidation of azomethaile has been iilvestigated previously in this laboratory (4, 5, 6). Experiments are reported in which formaldehyde-C13 was added to the reactailts in the present systein to investigate this point further. E X P E R I M E N T A LMost of the apparatus was the same as that described in a previous communication (1). A reactioil was started by expanding a mixture of oxygen and D T B P from a preheater held a t 80" C, where pressures could be measured on a quartz spiral gauge, to the Pyrex reaction vessel (volume, 550 ml) the temperature of which could be held to within 0.1" C.Analyses were made for carbon monoxide, acetone, methanol, and formaldehyde; the yields of methane and ethane were vanishingly small. Formaldehyde, oxygen, and carbon monoxide were separated from the liquid products (acetone, methanol, and unreacted DTBP) by passage through a trap held a t -130" C. Formaldehyde was condensed in a second trap a t -196" C and the permanent gases were transferred to a tube containing a mixture of copper and cupric oxide where the carbon monoxide was oxidized a t 270" C. T h e liquid products were analyzed by gas chromatography on a 10-ft column containing 25% dinonyl phthalate and 5% glycerol on Fisher Columpalc (30-60 mesh). With a hydrogen flow rate of 45 ml/minute a t 29" C appe...

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“…The division of products between reactions f and g should be constant, if reaction g is second order, not dependent on [M]. The ratio i?¡(EtOH)/i?i(Et2Os) = kt/kt (12) is entry 8 in Table III, and it varies only between 10 and 13 for the entire series with an average value of 12. This constancy indicates that / and g are, respectively, the only sources of ethanol and diethyl-peroxide, at initial times.…”

Section: Resultsmentioning

confidence: 99%