Photoöxidation of Butene-1 and Isobutene by Nitrogen Dioxide

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The relative rates of reactions of oxygen atoms with a n~~r n b c r of olefins in the vapor phase deter~nined in previous nrorl; are s~ummarized and supplenlented by some additional results. The uncertainty in the values of the relative rate constants is no\\; believed to be reduced to only a few per cent. A n~~m b e r of simple correlations observed previously have been re-exa~~~inecl on the basis of the more complete and more accurate list of values available a t present. These correlations show a distinct electrophilic character of oxygen atoms in their reactions with olefins and their potential significance for the understanding of the finer details of these addition processes is discussed. INTRODUCTIONPossibilities of finding simple correlations between reaction rates and physical properties of the reactants have been extensively explored a t various times in the past wit11 the object of establishing the factors which contribute to chemical reactivity. Thus, for example, considerations of the lilcely potential energy changes when two molecules interact have suggested linear dependeilce of activation energies on such quantities as heats of reaction or singlet-triplet excitation energies (1-6). In the case of metathetical reactions such views have found little experimental support. Some additioil reactions, o n the other hand, a t least those involving a number of aromatic hydrocarbons (5, 6) and a somewhat restricted group of olefns (T), appear to show simple relations of this kind.Reactions of atoms v~ith serias of structurally related c o m p o u~~d s are particularly attractive for this type of investigation, especially if they can be studied under conditions where complications from solvei~t effects of variable magnitude can be eliminated. Solvent effects are of course absent in vapor phase reactions, but until very recentl~; there were essentially no rate clata for series of adclitioil reactions in the vapor phase. A11 exception to this represented the reactions of H-atom adclitio~ls to olefins, i~lvestigated by Robb and i\/Ielville (8). However, the work now in progress in this laboratory oil these reactions a t higher pressures and with the use of a clifferent technique (9) reveals some differences in the values of the rate constaiits from those obtaiiled by these authors. A discussion of the trends in reactivity in this reaction series has, therefore, to be delajwl until the current ivork is completecl.Although free atoins as a rule possess unpaired electroils and thus have free radical character, they nlay be expected to react in particular reactions as either electrophilic, nucleophilic, or radical reagents. ' he type of the reactant character exhibited mill be largely cleternlined by the relative values of the electron affinities ancl ioi~ization potentials of the atoins ancl their reaction partners.In the past several years extensive information on the vapor phase reactions of oxygen atoms with olefins has been accumulated in this laboratory. Both the mechanisn~ (10, 11) and the relative rates (1...

Section: Methodsmentioning

confidence: 58%

Electrophilic Character of Oxygen Atoms

Cvetanović¹

1960

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“…The photochemical NO2 reactions with olefins play a very important role in the formation of "photochemical smog" and have received considerable attention in recent years (1,(6)(7)(8). There can be little doubt that this process has much in common with the corresponding ozone reactions, although both processes are complex and their full understanding will require considerable further work.…”

mentioning

confidence: 99%

A Study of the Vapor Phase Reaction of Ozone With Olefins in the Presence and Absence of Molecular Oxygen

Wei¹,

Cvetanović²

1963

Relative rates of reaction of ozone with a number of olefins in the vapor phase have been determined a t room temperature in the presence and absence of molecular oxygen. In the absence of oxygen the rates appear t o follow more closely a n electrophilic trend, although some of the deviations observed previously in the presence of oxygen still persist t o some extent. The ratio of olefin t o ozone consunled is unity in the absence of oxygen and varies from about 1.4 to 2 in its presence. In the presence of molecular oxygen, therefore, a secondary attack on the olefins takes place a s well. The yields of products are similarly affected.

“…The reaction of butene-1 with oxygen atoms produced by microwave discharge was found to be more complex than the corresponding reaction with oxygen atoms formecl by mercury-photosensitized decomposition of nitrous oxide (2) or by photolysis of nitrogen dioxide (6). In the last two reactions n-butyraldehyde, or-butylene oside, ancl small amounts of methyl ethyl ketone, acetaldehyde, and propionaldehyde are formed.…”

Section: Resultsmentioning

confidence: 93%

“…T h e same reaction with oxygen atoms from photolysis of NO2 gives large amounts of CHnNOn and CH3N02 instead ( l l ) , because of the presence of excess NO?. In the reaction of butene-1 with oxygen atoms from NO* photolysis some CzHSN03 has indeed been identified, suggesting the presence of free C2H5 radicals (the elution time of C2HjN02 is considerably larger than that of C2HsN03 and C,H5N02 would, therefore, not be observed in small amounts a t the GLC column temperature used) (6). Similarly in the isobutene reaction very small anlounts of CHnN03 and CH3N02 are found, suggesting formation of some free CH3 radicals, as would be expected in this case.…”

Section: Discussionmentioning

confidence: 99%

Reactions of Oxygen Activated by Electrical Discharge With Butene-1

Jarvie¹,

Cvetanović²

1959

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Reactions of oxygell activated by electrical discharge with butene-1 have beer1 studied in a "spherical diffusion" reaction zone. When snlall concentratiorls of oxygen are passed through the discharge tube in helium as the carrier gas, and the concentration of butene-1 in the reaction zone is sufficiently high, the observed products are entirely explainable by an interaction of the ground-state oxygen atoms with butene-1. With large deviations from these conditions considerable complexities arise, and under some conditions a-butylene ozonide and its decomposition products become important and the products are then explainable without any significant participation of oxygen atoms in the process.