Reaction under atmospheric conditions

Adeniji, S.A., Kerr, J.A., Williams, M.R. (1981) Rate constants for ozone-alkene reactions under atmospheric conditions. Int. J. Chem. Kinet. 13, 209-217. 

In equation (C), A() (or A 111 as used earlier) is the low-pressure limiting rate constant and Ay is the high-pressure limiting rate constant. Fc is known as the broadening factor of the falloff curve its actual value depends on the particular reaction and can be calculated theoretically. Troe (1979) suggests that for reactions under atmospheric conditions, the value of Aft will be 0.7-0.9, independent of temperature. However, values as low as 0.4 are often observed. The NASA evaluations of stratospheric reactions (DeMore et al., 1997) take Aft = 0.6 for all reactions. The IUPAC evaluation (Atkinson et al., 1997a,b) does not restrict Fc to 0.6. However, it is important to note that the values of A0 and Ay will depend on the value of Fc used to match the experimental data. For example, for reaction (11)... 

Barnes, I., V. Bastian, and K. H. Becker, FTIR Spectroscopic Studies of the C H, S + N02 Reaction under Atmospheric Conditions, Chem. Phys. Lett., 140, 451-457 (1987). 

Direct Kinetic and Mechanistic Study of the OH-Dimethyl Sulfide Reaction Under Atmospheric Conditions... 

The purpose of this research was to obtain kinetic data for the reaction of ozone with cycloalkenes and to determine the formation yields of hydroxyl radicals in these reactions under atmospheric conditions. 

Sealed tube reactions are sometimes used when safer reactions under atmospheric conditions failed, and as you can guess from the name, basically a set of reactants are sealed in a tube and heated to drive the reaction to the desired products. However, any chemical heated in a closed system will build up pressure that can make the tube the source of a possible explosion (see Incident 7.3.7.1). 

The mechanisms of the reactions of HO radical with esters (Me formate, Et formate, Et acetate, and Pr acetate) have been explored through quantum chemical and computational kinetics calculations. These reactions, under atmospheric conditions, occur via a complex mechanism, whereby reversible formation of a reactant complex is followed by irreversible H abstraction from C atoms in the a position to alkoxy oxygen. Activation of this position is a consequence of the donor ability of such oxygen and the formation of hydrogen bonds in the transition stmcture. The order of site reactivities for H abstraction was found to be -OCHj- > -CCHj- > HC(0)0- > -OCH3 > CH3C(0)0-. ... 

Shielding and Stabilization. Inclusion compounds may be used as sources and reservoirs of unstable species. The inner phases of inclusion compounds uniquely constrain guest movements, provide a medium for reactions, and shelter molecules that self-destmct in the bulk phase or transform and react under atmospheric conditions. Clathrate hosts have been shown to stabiLhe molecules in unusual conformations that can only be obtained in the host lattice (138) and to stabiLhe free radicals (139) and other reactive species (1) similar to the use of matrix isolation techniques. Inclusion compounds do, however, have the great advantage that they can be used over a relatively wide temperature range. Cyclobutadiene, pursued for over a century has been generated photochemicaHy inside a carcerand container (see (17) Fig. 5) where it is protected from dimerization and from reactants by its surrounding shell (140). 

Several examples of [5C+1S] cycloaddition reactions have been described involving in all cases a 1,3,5-metalahexatriene carbene complex as the C5-syn-thon and a CO or an isocyanide as the Cl-synthon. Thus,Merlic et al. described the photochemically driven benzannulation of dienylcarbene complexes to produce ortho alkoxyphenol derivatives when the reaction is performed under an atmosphere of CO, or ortho alkoxyanilines when the reaction is thermally performed in the presence of an isonitrile [111] (Scheme 63). In related works, Barluenga et al. carried out analogous reactions under thermal conditions [36a, c, 47a]. Interestingly, the dienylcarbene complexes are obtained in a first step by a [2+2] or a [3S+2C] process (see Sects. 2.3 and 2.5.1). Further reaction of these complexes with CO or an isonitrile leads to highly functionalised aromatic compounds (Scheme 63). 

Atkinson R. 1985. Kinetics and mechanisms of the gas-phase reactions of hydroxyl radical with organic compounds under atmospheric conditions. Chem Rev 85 69-201. 

Figure 3.6. Example of the type of kinetic information available for the catalytic reduction of NO on rhodium single-crystal surfaces under atmospheric conditions. The data in this figure correspond to specific rates for C02, N20, and N2 formation over Rh(l 11) as a function of inverse temperature for two NO + CO mixtures PNO = 0.6 mbar and Pco — 3 mbar (A), and Pno — Pco = 4 mbar (B) [55]. The selectivity of the reaction in this case proved to be approximately constant independent of surface temperature at high NO pressures, but to change significantly below Pno 1 mbar. This highlights the dangers of extrapolating data from experiments under vacuum to more realistic pressure conditions. (Reproduced with permission from the American Chemical Society, Copyright 1995).

The results are comparable to those of homogeneous reaction conditions (Table 41.10), and recycling of the catalyst was successful with constant ee-values over five cycles, even though conversion decreased. Amazingly, the catalyst was still active, despite being stored under atmospheric conditions for 24 h (Table 41.10, entry 7). 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

Chemical/Physical. Products identified from the reaction of toluene with nitric oxide and OH radicals include benzaldehyde, benzyl alcohol, 3-nitrotoluene, p-methylbenzoquinone, and o, m, and p-cresol (Kenley et ah, 1978). Gaseous toluene reacted with nitrate radicals in purified air forming the following products benzaldehyde, benzyl alcohol, benzyl nitrate, and 2-, 3-, and 4-nitro-toluene (Chiodini et al., 1993). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of benzaldehyde, benzyl nitrate, 3-nitrotoluene, and o-, m-, and p-cresol (Finlayson-Pitts and Pitts, 1986 Atkinson, 1990). 

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