Ethers in the Gas Phase

The vapor phase photolysis of ethylene oxide has found more attention than that of its higher homologs. It has first been extensively studied by Corner and Noyes (193) in the long wavelength region. Fleming et al. studied the effect of ring size on the photolysis of cyclic ethers such as ethylene oxide, oxetane, and tetrahydrofuran (90). Roquitte (194) did flash 

TABLE 16. Relative yields of products from the photolysis of ethylene oxide (195). Pressures near 10 torr 

The oxetane photolysis (90,91) in the 190 nm region seems largely to proceed by way of the molecular processes 43 through 45. Owing to photolysis of the carbonyl compounds there was some 

The photolysis of tetrahydrofuran with a medium-pressure Hg arc led to carbon monoxide, hydrogen, methane, ethane, ethylene, propylene, cyclopropane, and formaldehyde as major products (196) Quantum yields or absolute yields are not known. The yields of formaldehyde, ethylene, and propane declined with increasing pressure, those of carbon monoxide and cyclopropane increased starting from near zero at very low pressures. In the absence of a material balance mechanistic conclusions cannot be drawn except that the processes 49 to 51 are very likely important. 

TABLE 17. Products (unfiltered Hg arc, arbitrary units (91) from 25°, the vapor phase photolysis of oxetanes conversion 0.3%). Rates of formation.  

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The reactions of the ground-state oxygen atom 0(3P) with symmetric aliphatic ethers in the gas phase were investigated by Liu et al. (1990) using the flash photolysis resonance fluorescence technique. These reactions were found to be first-order with respect to each reactant. The rate constants for three ethers at several temperatures are as follows ... 

Thus 4-chlorophenyl 2,4,5-trichlorophenyl ether (48, Scheme 7) produced 4% of a mixture of the dibenzofurans 49 and 50. Only in the case of 2,3,4-trichlorophenyl 2,3,4,5,6-pentai hlorophenyl ether was production of dibenzofurans by formal loss of o,o -chlorine detected. Neither product was identified, but one is presumably the expected product, 1,2,3,4,8,9-hexachloro-dibenzofuran, and the other must be due to a rearrangement. Chlorination of diphenyl ether in the gas phase is unusual. At 300°C the major product is 4-chlorophenyl phenyl ether, as in the liquid phase, but as the temperature is increased (400-500°C), the amount of 4-chlorophenyl phenyl ether decreases at the expense of 3-chlorophenyl phenyl ether, and dibenzofuran is also produced. ... 

A previous paper described the inhibiting influence of aliphatic amines on the oxidation of ethyl ether in the gas phase (28). It was suggested that one of the principal methods by which amines can act as negative catalysts is by stabilizing free radicals in the gas phase. However, it is necessary to examine the action of amines on the intermediate products formed during oxidation processes. 

The photolysis of dimethyl and diethyl ethers in the gas phase was first studied by Harrison and Lake (172) using a hydrogen discharge lamp. They reported the formation of formaldehyde from dimethyl ether, and ethylene, acetaldehyde, and formaldehyde from diethyl ether. 

The thermal decomposition of dimethyl ether in the gas phase was studied by Hinshelwood and Askey by measuring the increase in pressure in a constant-volume reaction vessel. At 504°C and an initial pressure of 312 mm Hg the following data were obtained ... 

The kinetics of isomerizations of vinyl allyl ethers have been studied in the gas phase, in solution, and in the neat liquid ether. In the gas phase, isomerization rate is independent of pressure down to about 1 torr, below which the rate diminishes with decreasing pressure in the manner characteristic of uni-molecular reactions . The rate of isomerization is not influenced significantly by glass surfaces, but is faster in solution in either non-polar or moderately polar solvents than in the gas phase. Reactivity is increased by methyl substitution of either the vinyl or the allyl group of the ether. All of the isomerizations thus far studied have negative entropies of activation, with values ranging from —8 to —13eu, Isomerization of vinyl allyl ether (neat liquid) at 130°C exhibits a volume of activation of — 18 cm. mole". Published kinetic data are summarized in Table 3. 

A re-investigation of the isotope effects for the Claisen rearrangements of allyl vinyl ether and allyl phenyl ether has shown that there is disagreement between the predicted and literature experimental heavy-atom kinetic isotope effects for about half of these rearrangements studied. A new strategy for revealing the Claisen rearrangement of aUyl phenyl ether in the gas phase has been developed, and... 

There is a review of selected topics in organometallic ion chemistry and evidence for the hollow cage structure of met-cars is collected together with a discussion of cluster-assisted O-bQnd activation.Metal containing ions, [ML]+ (M = Cr, Mn, La, Pr, Yb, Nd and others L = Ph) react with crown ethers in the gas phase by adduct formation or ligand substitution. s... 

Raman spectra show similar behaviour to IR in terms of shift and band breadth but the intensity increase is not observed. Figure 2 illustrates part of the spectrum of a mixture of deuterium chloride and dimethyl ether in the gas phase. The stretching vibration of unassociated DCl can be seen at 2085 cm" along with rotational side bands, while H-bonded DCl yields a broad absorption underlying the sidebands centred near 1885 cm". ... 

Boulamanti AK, Philippopoulos CJ (2008) Photocatalytic degradation of methyl tert-butyl ether in the gas-phase a kinetic study. J Hazard Mater 160 83-87... 

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