Reactions of oxygen atoms

Lipscomb et al. flash-photolyzed OCIO in the presence of a large excess of inert gas. They found that O2 excited to the eighth vibrational level and CIO3 were produced. Their analysis utilized the reactions 

Reaction (56) did not require a third body under their conditions. From the rate of CIO disappearance, ksg (see below) was found to be 6.2 x 10 l.mole sec at 293 K. 

Clyne and Coxon also measured the rate of removal of CIO. They did this by passing OCIO diluted in Ar into a stream of 2 % chlorine atoms (produced in an Rf. discharge) in Ar at 1 torr and 298 °K. The reaction sequence was 

The absolute concentration of CIO was determined by titration with either O or NO, the respective reactions being 

More recently, Clyne and Coxon have prepared CIO radicals from three different reactions in a flow system viz. 

Harteck and Kopsch68 found that CC14 reacted slightly more rapidly than CH4 with oxygen atoms. The reaction proceeded with a pale red flame to produce CC120 and CI2 in a 1 1 ratio. The overall reaction was 

More recently, Ung and Schiff168 prepared oxygen atoms from the glow discharge of 02 or by the reaction of N atoms with NO. In both cases CQ4 was injected into either the 0-02 or 0-N2 stream. The only products of the reaction were CC120, CO, Cl2, and C02. The product ratios were not markedly affected by changes in temperature (4-100°C) or by the presence of 02. Furthermore, it appeared that CC120, Cl2, and CO were initial products whereas C02 was a secondary product. 

The rate of CC14 removal was monitored and found to follow the rate law 

In order to account for the CO formation, Ung and Schiff postulated the reactions 

The only objection to this sequence is that reaction (4-2) must proceed through an excited CC120 intermediate, so that [C0]/[CC120] should decrease with an increase in pressure, whereas the reverse was observed. 

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Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

Numerous oxidation reactions of sulfur compounds have been described in which S2O or its precursor SO are formed as intermediates but most of these reactions are not suitable to investigate the properties of S2O because of the low yield or the interference from by-products [1]. A relatively clean process is the reaction of oxygen atoms with COS producing SO and CO. The formation of S2O from gaseous SO is a stepwise process according to the following equations (M is a collision partner) [21] ... 

The associative reaction of oxygen atoms with nitric oxide produces the yellow-green chemiluminescence in the air afterglow, easily seen by the naked eye. The reaction has long been used to measure the concentrations of O atoms in kinetics experiments [49-51] and is so bright that it has been used to visualize... 

Slagle, I. R., F. J. Pruss, Jr., and D. Gutman. Kinetics into the steady state. I. Study of the reaction of oxygen atoms with methyl radicals. Int. J. Chem. Kinetics 6 111-123, 1974. 

Boocock, G., and R. J. Cvetanovic. Reaction of oxygen atoms with benzene. Can. 

Also to be mentioned are the reactions of oxygen atom radical anions with organic substrates. These reactions were reviewed by Gronert (2001). For the reactivity of the atomic oxygen anion-radical, see Section 1.7.2. The atomic oxygen anion-radical reacts with benzene, tetramethylene ethane, or cyclopentadienylidene trimethylenemethane. The reactions consist in abstraction of H2 with the formation of H2O and the corresponding distonic anion-radicals as products. 

The absence of hydroxyl absorption in the reaction of oxygen atoms with hydrocarbons is evidence that oxygen atom reactions did not interfere with studying free-hydroxyl reactions, even if oxygen atoms were pumped out from the discharge zone in water vapor. 

The values Bf, C/t Dy, Fy were plotted vs. A0 for various rate constants involved in equations for By, Cf, etc. The final concentrations of By, D/, and Fr products as a function of A0 are shown in Figure 3 for a possible ratio of rate constants h/k = 10 (the reaction of oxygen atoms with the initial substance proceeds less readily than with the primary product) k3/k = 0.5 ko" /k = 0.05 AW" = 6.5 X 10is fc = k, i.e.,acase is taken when the initial substance gives one primary product. 

Fig. 4. The rates of formaldehyde and COt accumulation as a function of the ethane flow rate in reactions of oxygen atoms with etiiane.

Contrary to the C2II6 reaction, the amounts of CH20 and CO appeared to be different, especially at low temperatures. At 60°C. the amount of CO was three times, and at 250°C. one and a half times that of CH20. A conclusion may be drawn that the reaction of oxygen atoms with CH4 proceeds by two parallel steps resulting in CH20 and CO formation. 

It may be seen from Table III that in reactions of oxygen atoms with ethylene, formaldehyde and CO are obtained practically in equal amounts, as in the reaction involving ethane. It will be taken into account that the amount of formaldehyde obtained is practically equal to that of oxygen atoms (Table II). This is indication that CH20 is formed by a nonchain mechanism. On the basis of these facts it should be considered that the main reaction between oxygen atoms and ethylene is... 

In investigating the reaction of oxygen atoms with isobutene, analysis for propene was carried along with that for carbonyl compounds and CO. Propene was separated from isobutene at —112° to about — 115°C., which was possible due to the sufficient difference in vapor pressures (Table III). Experimental results have shown that the amounts of for-... 

Cvetanovic67 was concerned with oxygen atom reactions with unsaturated hydrocarbons. The oxygen atoms were obtained in his experiments by mercury-photosensitized decomposition of N20. Cvetanovi6 came to the conclusion that the reaction of oxygen atoms with ethylene proceeded essentially with scission of the hydrocarbon bond, while with higher olefins this was not observed. Corresponding oxides (epoxides) and carbonyl compounds were formed in the course of the reaction. 

The first difficulty was that a polymer was deposited on the vessel wall in a reaction of oxygen atoms with CHjCHO. This was seen from the appearance of a brown coating at temperatures above 100 °C. 

In studying the reaction of oxygen atoms with CH3CHO by using the photochemical method, at a pressure of 100 mm. Hg and with sensitization by mercury, Cvetanovi664 came to another conclusion, namely, that the reaction of oxygen atoms with acetaldehyde yielded mainly hydroxyl and the CH3CO radical. The hydroxyl formed reacted with an acetaldehyde molecule to form water, and acetyl yields diacetyl. The main reaction products were found to be water and biacetyl. 

The results of determining absolute rate constants for reactions of oxygen atoms with various molecules are summarized in Table IV, A determination of every constant was made at various temperatures, it was possible to determine the activation energies, and the pre-exponential factors as well. The rate constants of some reactions given in Table IV were reported in the literature. 

Rate Constants for Reactions of Oxygen Atoms with Various Molecules... 

Elias and Sohiff68 determined the rate constant for a reaction of oxygen atoms with n-butane. The activation energy value was found to be E = 4.2 0.2 keal., and the pre-exponential factor was Zp = (5 1.6) X 10- . 

Elias and Schiff also determined the rate constant for the reaction of oxygen atoms with ethylene. The activation energy was found to be 1600 cal., and this was consistent with our value of 1360 cal. But the pre-expenonetial factor found by Elias and Schiff was higher than that obtained in our experiments by two powers of ten. 

If hydroxyl were to react by H atom abstraction in the case of ethane, and by addition with ethylene, an inverse dependence would be observed for the activation energy, namely, a decrease from ethane to ethylene, as is the case for hydrogen atom reactions. The activation energies for reactions of oxygen atoms with ethane and ethylene decrease from ethane... 

The C02 was formed from the reaction of oxygen atoms with CC120, as was shown by Ung and Schiff in separate experiments. They found a rate constant of about 6 x 10 M 1 sec-1 which can be attributed to the reaction... 

Fig. 2. Log-log plot of (c-C3F ) vs. [C2F4] in the reaction of oxygen atoms with C2F4 at 22°C. (O, 0)h 5 x 10"9 einstein/min-cc ( )/ 0.8 x 10"9 einstein/min-cc ( )/ 0.1 x 10 9 einstein/min-cc. From Cohen and Heicklen40 with permission of the American Chemical Society.

Fig. 4. Log-log plots of [1 + o] (CF20) and [1 + a] (CaF40) vs. (C2F in the reaction of oxygen atoms with C2F4 in the presence of Oa for [C2F4]/[02] > 0.3 at 23°C. From Heicklen and Knight82 with permission of the American Chemical Society.

Fig. 5. Log-log plot of (CF20)-l-y vs. [02]//al i in the reaction of oxygen atoms with CaF4 in the presence of 02 at 25°C. From Johnston and Heicklen92 with permission of the American Institute of Physics.

The reactions of oxygen atoms with C3Fe have been examined 78,146,150 at room temperature and 125°C in the presence and absence of 02 in a series of studies similar to that for C2F4. The products of the reaction are... 

The reaction of oxygen atoms with C4Fe-2 has been examined at room temperature by Johnston and Heicklen.93 Contrary to the reaction with the smaller perfluoroolefins, the important reaction is not cleavage of the double bond. The principal product of the reaction for C4F6-2 pressures between 10 and 100 torr was z-C3F7CFO. Other products were CF3CFO,... 

The reaction of oxygen atoms with l,3-C4Fe leads predominantly to CF20 and c-C3F4.159 The indicated reaction is... 

Reaction of Oxygen Atoms with Hydrogen. The possible reactions of O atom with H2 are... 

The reaction was reinvestigated by Cvetanovic (21) who found that within a small analytical uncertainty the exclusive primary step was reaction (11). Formation in this reaction of oxygen atoms in their triplet ground state (OIP) is required by the spin conservation rule and there is now ample chemical evidence that this is indeed so. A primary formar tion of an electronically excited N20 molecule, ruled out in the early work on spectroscopic grounds, is also incompatible with the lack of a pressure dependence of the rate of decomposition. 

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