Formaldehyde reaction with oxygen atoms

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

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... 

The hetero-Diels-Alder reaction of formaldehyde with 1,3-butadiene has been investigated with the formaldehyde oxygen atom coordinated to BH3 as a model for a Lewis acid [25 bj. Two transition states were located, one with BH3 exo, and one endo, relative to the diene. The former has the lowest energy and the calculated transition-state structure is much less symmetrical than for the uncatalyzed reaction shown in Fig. 8.12. The C-C bond length is calculated to be 0.42 A longer, while the C-0 bond length is 0.23 A shorter, compared to the uncatalyzed reac-... 

Figure 5. Cartoon models of the reaction of methanol with oxygen on Cu(llO). 1 A methanol molecule arrives from the gas phase onto the surface with islands of p(2xl) CuO (the open circles represent oxygen, cross-hatched are Cu). 2,3 Methanol diffuses on the surface in a weakly bound molecular state and reacts with a terminal oxygen atom, which deprotonates the molecule in 4 to form a terminal hydroxy group and a methoxy group. Another molecule can react with this to produce water, which desorbs (5-7). Panel 8 shows decomposition of the methoxy to produce a hydrogen atom (small filled circle) and formaldehyde (large filled circle), which desorbs in panel 9. The active site lost in panel 6 is proposed to be regenerated by the diffusion of the terminal Cu atom away from the island in panel 7.

First experiments on oxygen atom reactions with hydrocarbons, with the zone of discharge in water vapor, as well as in O2, used as a source of 0 atoms, have shown that the reaction products are formaldehyde, acetaldehyde, acids, alcohols, peroxides, i.e., products of lower degrees of conversion than that yielding H20, CO, and C02. 

Taking into account that the main reaction product is formaldehyde and that the propene molecule is double-bonded (just as ethylene), the leaction of oxygen atoms with propene will proceed as follows ... 

An example of biotoxification is the formation of paraoxon from the insecticide parathion via sulfoxidation. The simple substitution of an oxygen atom for a sulfur atom in the molecule results in a cholinesterase inhibitor with several times more potency. Similarly, the toxic action of methanol in producing blindness is the result of its metabolism to formaldehyde. Examples of bioactivation and biotoxification reactions are shown in Figure 3.2. 

Reactions of Si+ with simple oxygen-containing organic molecules that have been the focus of experimental studies have also been examined computationally40 and related to the analogous reactions by C+. Insertion of Si+ into the C—O bonds of formaldehyde and methanol is found to lead to the most stable products, a result that is accounted for by the stabilization afforded by silyl substitution at the oxygen atom. 

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