Carbonyl oxides, formation

L oss of Catalyst by Vapor Transport. The direct volatilisation of catalytic metals is generally not a factor in catalytic processes, but catalytic metal can be lost through formation of metal carbonyl oxides, sulfides, and hahdes in environments containing CO, NO, O2 and H2S, and halogens (24). 

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

KMn04 impregnated alumina oxidizes arenes to ketones within 10-30 min under solvent-free conditions using focused microwaves [111]. /i,/i-Disubstituted enamines have been successfully oxidized into carbonyl compounds with KMn04-Al203 in domestic (255 W, 82 °C) and in focused microwave ovens (330 W, 140 °C) under sol-vent-free conditions by Hamelin et al. [112]. The yields are better in the latter case. When the same reactions are conducted in an oil bath at 140 °C, no carbonyl compound formation is observed (Scheme 6.36). 

An a-hydroxy aldehyde will be oxidized relatively rapidly if another hydroxyl group in a position 7 or 5 to the carbonyl permits formation of a pseudoglycol structure by cyclic hemiacetalization. ... 

The carboxylic acid derivatives li-lm can only be matrix-isolated if the corresponding quinone diazides 2i-2m are irradiated with monochromatic blue light (k = 436 nm).81 91 92 UV or broad-band visible irradiation rapidly results in the decarboxylation of the carbenes. As expected, the IR and UV/vis spectra of the carbenes are very similar to that of la. Oxygen trapping results in the formation of the photolabile carbonyl oxides 7. Thus, the carbenes li-lm were identified both spectroscopically and by their characteristic reaction with molecular oxygen. 

The matrix photochemistry of 2v proved to be fairly complicated.108 The primary product of the photolysis of 2v is carbene lv, which was identified by ESR spectroscopy. Under the conditions of matrix isolation the carbene showed the expected reactivity towards molecular oxygen (formation of carbonyl oxide 7v) and carbon monoxide (formation of ketene lOv) (Scheme 22). In contrast to the oxocyclohexadienylidenes (la and derivatives) carbene lv slowly reacted with CO2 to give an a-lactone with the characteristic C=0 stretching vibration at 1896 cm-1. The latter reaction indicates that lv is — as expected — more nucleophilic than la. 

Addition of carbonyl oxide (169) to oximes (168) results in the formation of ( )-Ar-(hydroperoxyalkyl) keto nitrones (170) the reaction involves a one-pot step synthesis (Scheme 2.60) (325, 326). 

Ozonolysis in the presence of NaOH or NaOCH3 in methanol with CH2CI2 as a cosolvent leads to formation of esters. This transformation proceeds by trapping both the carbonyl oxide and aldehyde products of the fragmentation step.149... 

The ozonolyses of enol ethers has been reviewed <91MI 4l6-0l>. The relative dipolarophilicity of certain species to attack by carbonyl oxides has been investigated and, in general, the order of reactivity is aldehydes > enol ethers > esters ss ketones. It is apparent that enol ethers are very reactive towards carbonyl oxides, so much so that 1,2-dioxolane formation can be a major reaction pathway (especially for formaldehyde-O-oxide) <85JOC3365>. 

Dialkyl-l,2,4-oxadithiolane-2-5 -oxides (160) have been synthesized from the dihydro thia-diazole (161) via nitrogen extrusion and 1,3-dipolar cycloaddition of the intermediate ylide with sulfur dioxide (Scheme 45) <90BSB265>. The formation and trapping of carbonyl oxides is described... 

Another route to the formation of carbonyl oxides is the reaction of methylene (CH2) with dioxygen. This oxidative process involving methylene with O2 is one of the most important reactions in the combustion of unsaturated hydrocarbons. The reaction between CH2 (X Bi) 4- O2 has been studied by Anglada and BofilP in the gas phase by carrying out CASSCF and CASPT2 calculations with the 6-31G(d,p) and 6-31H-G(3df,2p) basis... 

Schindler and coworkers verified the formation of hydroxyl radicals kinetically and further RRKM calculations by Cremer and coworkers placed the overall concept on a more quantitative basis by verifying the measured amount of OH radical. An extensive series of calculations on substituted alkenes placed this overall decomposition mechanism and the involvement of carbonyl oxides in the ozonolysis of alkenes on a firm theoretical basis. The prodnction of OH radicals in solution phase was also snggested on the basis of a series of DFT calculations . Interestingly, both experiment and theory support a concerted [4 4- 2] cycloaddition for the ozone-acetylene reaction rather than a nonconcerted reaction involving biradical intermediates . 

Cremer, D., J. Gauss, E. Kraka, J. F. Stanton, and R. J. Bartlett, A CCSEHT) Investigation of Carbonyl Oxide and Dioxirane. Equilibrium Geometries, Dipole Moments, Infrared Spectra, Heats of Formation, and Isomerization Energies, Chem. Phys. Lett., 209, 547-556 (1993). 

Gutbrod, R., R. N. Schindler, E. Kraka, and D. Cremer, "Formation of OH Radicals in the Gas Phase Ozonolysis of Alkenes The Unexpected Role of Carbonyl Oxides, Chem. Phys. Lett., 252, 221-229 (1996). 

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