Carbonyl oxidation

Oxidative bleaching Oxidative carbonylation Oxidative coupling... 

The 1,3-zwitterion appears to have some diradical as weU as 1,2-zwitterionic (carbonyl oxide) character ... 

Several theories have appeared in the Hterature regarding the mechanism of protection by -PDA antiozonants. The scavenger theory states that the antiozonant diffuses to the surface and preferentially reacts with ozone, with the result that the mbber is not attacked until the antiozonant is exhausted (25,28,29). The protective film theory is similar, except that the ozone—antiozonant reaction products form a film on the surface that prevents attack (28). The relinking theory states that the antiozonant prevents scission of the ozonized mbber or recombines severed double bonds (14). A fourth theory states that the antiozonant reacts with the ozonized mbber or carbonyl oxide (3) in Pig. 1) to give a low molecular weight, inert self-healing film on the surface (3). 

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). 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

Carbonyl oxides (formed by the reaction of diazo compounds with singlet oxygen) may also be used to oxidize sulphoxides74. The corresponding sulphone is formed in reasonable yields and the reaction may be carried out in the presence of the sulphide functionality. The reaction proceeds as shown in equation (21) and involves initial nucleophilic attack by the carbonyl oxide on the sulphoxide sulphur atom followed by the facile departure of the carbonyl compound yielding the required sulphone. 

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]. 

Furans occur widely in nature and many are important commercially. Thus alcohol (29) is used in various insecticides. The carbon atoms. joined to the ring oxygen atom are at the carbonyl oxidation level so that (29) can be made by acid-catalysed cyclisation of (30). Analysis... 

Several procedures that intercept the intermediates have been developed. When ozonolysis is done in alcoholic solvents, the carbonyl oxide fragmentation product can be trapped as an a-hydroperoxy ether.202 Recombination to the ozonide is then prevented, and the carbonyl compound formed in the fragmentation step can also be... 

Especially reactive carbonyl compounds such as methyl pyruvate can trap the carbonyl oxide component. For example, ozonolysis of cyclooctene in the presence of methyl pyruvate leads to 5 when treated with triethylamine 5 is converted to 6, in which the two carbons of the original double bond have been converted to different functionalities.205... 

Scheme 12.22 provides some examples of the oxidation of aromatic alkyl substituents to carboxylic acid groups. Entries 1 to 3 are typical oxidations of aromatic methyl groups to carboxylic acids. Entries 4 and 5 bring the carbon adjacent to the aromatic ring to the carbonyl oxidation level. 

THF-2-phenyl-l-boraadamantane 34 was transformed into l-hydroxy-2-phenyladamantane 56 in 47% overall yield by a carbonylation-oxidation sequence (Scheme 18) <2002IZV1437>. 

Carbonylation-oxidation of the THF complexes (S)-58 and (R)-58 afforded the optically active (3 )-(+)-2-methyl-l-adamantanol (3)-60 and (R)-(—)-2-methyl-l-adamantanol (R)-60, respectively (Scheme 24) <2003MC121, B-2003MI97>. 

The THF complexes of bis(l-boraadamantyl)methane 70, racemic 67a, and a mixture of racemic- and meso-b s( -boraadamantyl)ethane were transformed into the corresponding bis(l-hydroxyadamantyl-2)alkanes 74 and 75 via a standard carbonylation-oxidation procedure (Scheme 30) <2000IZV501, B-2003MI94>. 

RHF-based methods including MP2 fail to reliably reproduce the vibrational spectra of carbonyl oxides,69 and therefore at the time when 7a was synthesized for the first time22 the calculation of its IR spectrum was beyond the computational capabilities. DFT calculations (B3LYP/6-31G(d,p)) now permit the reproduction of the IR spectrum of 7a with high accuracy even on a personal computer, and thus confirm the earlier assignment. 

The dioxirane 8a is much less labile than the carbonyl oxide 7a, and UV irradiation (A > 400 nm) is required to induce the rearrangement to lactone 9a. With 70 kcal/mol this is the most exothermic step in the whole reaction sequence from la to 9a. All of these reaction intermediates were generated in subsequent steps in high yields and characterized by matrix IR spectroscopy. 

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. 

Some of the earliest studies of triplet carbenes in frozen media by epr spectroscopy revealed that these intermediates react rapidly with molecular oxygen (Trozzolo and Gibbons, 1967). This should not come as a surprise since the combination of a triplet carbene with triplet oxygen is a spin-allowed process. Indeed, recent measurements show that this reaction proceeds with a rate that is approximately at the diffusion limit. The product of this reaction (17) is the expected carbonyl oxide (Werstiuk et al., 1984 ... 

Irradiation of DAAN in benzene gives 3AN. This carbene reacts with oxygen very rapidly to give an intermediate believed to be the carbonyl oxide. The triplet carbene reacts with labeled a-methylstyrene to give the cyclopropane with total loss of stereochemistry (Table 6). Direct irradiation in neat isopropyl alcohol gives the ether in low yield (relative to the yields from XA, DMFL, FL, and BFL). The other products are those expected to result from hydrogen-atom abstraction. Triplet-sensitized irradiation of DAAN in the alcohol does not give a detectable amount of the ether. 

The chemical properties of DPM have been probed with each of the procedures identified earlier. This carbene is known to react with alcohols to give ethers (Kirmse, 1963 Bethell et al., 1965), it adds to olefins non-stereospecifically to form cyclopropanes (Skell, 1959 Baron et al., 1973 Gaspar et al., 1980 Tomioka et al., 1984), and it is rapidly converted to a carbonyl oxide with oxygen (Werstiuk et al., 1984 Casal et al., 1984). 

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). 

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