Oxygen equation

A more detailed study of the biological oxidation of sulphoxides to sulphones has been reported165. In this study cytochrome P-450 was obtained in a purified form from rabbit cells and was found to promote the oxidation of a series of sulphoxides to sulphones by NADPH and oxygen (equation 56). Kinetic measurements showed that the process proceeds by a one-electron transfer to the activated enzymatic intermediate [an oxenoid represented by (FeO)3+] according to equation (57). 

A mechanism analogous in many ways to that of the acid-catalyzed ring opening reaction was advanced for the reaction of the thiirane oxide with alkyl chloromethyl ethers S . The first step is the displacement of the chloride by the sulfoxy oxygen (equation 24). In view of the above mechanistic interpretation, it is quite surprising that the parent thiirane oxide (16a) was found to be protonated on sulfur and not at oxygen in FSOjH-SbFfi at — 78 °C, according to NMR studies s . 

Photochemical irradiation of dimethyl and diethyl sulphoxides yields the corresponding sulphone in the presence of air and a photosensitizer such as methylene blue in yields up to 99% . Sulphoxides are also oxidized when they act as traps for persulphoxides, the intermediate formed on reaction of a sulphide with photochemically generated singlet oxygen - , equation (9). Isotope studies have shown that such reactions proceed through a linear sulphurane intermediate . Persulphones also react with sulphoxides in a similar manner , equation (10). 

It is generally understood that the reaction proceeds in two stages, the first one generating an intermediate quasiphosphonium ion followed by attack of the associated counteranion on an ester linkage at the atom attached to phosphorus through oxygen (Equation 3.2). 

Primary thioamides undergo photochemical hydrogen sulphide extrusion in the absence of oxygen (equation 118)173. 

The introduction of the kinetics of the formation of CO and CO2 into the model modifies the temperature equation (31) and the oxygen equation (33). The slow and fast coke burning equations are unchanged except for a change in the effectiveness factor tjt of Eq. (29) to tjtc given by Eq. (73). A new equation for the conversion of CO is introduced. 

Exposure of alkyllithium or aryllithium compounds to the atmosphere may cause degradation due to reaction with oxygen (equation 1) or air moisture (equation 2). Certain organolithium compounds are unstable at room temperature in the neat form, and require dilution even then they should best be stored at low temperature. The instability may be the result of reactions such as the eliminations depicted in equations 3 and 4, taking place as the temperature rises . 

Next to TBHP also ferf-pentyl hydroperoxide, cumyl hydroperoxide and cyclohexyl hydroperoxide could be employed as oxidant and 2-hydroxycyclobutanone and 2-hydro xycyclododecanone were prepared by this method as well. In 1985, Vedejs and Larsen reported on a preparative method for the a-hydroxylation of camphor and a variety of other ketones utilizing overstoichiometric amounts of oxodiperoxomolybdenum(pyridine)(hexamethylphosphoric triamide) as source of oxygen (equation 67). Yields of products ranged from 34-81% and in some cases also the a-diketone is formed as by-product (0-26%). 

The peroxyl radicals formed combine via a tetraoxide intermediate, which decomposes generating O2 and the corresponding alcohol and a ketone (equation 38a). Alternatively, the tetraoxide intermediate can also decompose, by generating a triplet ketone in the excited state (LAO, equation 38b), which produces O2 by energy transfer to the ground state oxygen (equation 48). 

Several methods for the asymmetric epoxidation of electron-poor alkenes rely on the use of metal peroxides associated with chiral ligands . Enders and coworkers reported that ( )-a,/ -unsaturated ketones may be epoxidized using stoichiometric quantities of diethylzinc and a chiral alcohol, in the presence of molecular oxygen (equation 33). The best enantioselectivities were found using (/ ,/ )-Af-methylpseudoephedrine 54 as R OH... 

Photolysis of Pt02(PPh3)2 in a nitrogen-saturated chloroform solution results in dissociation of singlet oxygen (equation 452).1548... 

The uncatalyzed attack of water on an ester leads to a transition state in which a positive charge develops on the attacking water molecule, and a negative charge on the carbonyl oxygen (equation 2.8). 

Dicarboxylation reactions of alkenes can be carried out such that predominately 1,2-addition of the two ester functions occurs (equation 61). The reaction takes place under mild conditions (1-3 bar, 25 C) in alcohol. It is stoichiometric in palladium, since the palladium(II) catalyst is reduced to palladium(O) in the process, but by use of an oxidant (stoichiometric copper chloride or catalytic copper chloride plus oxygen equation 62 and 63) the reaction becomes catalytic in palladium. In the reoxidation process, water is generated and the build-up of water increases the water gas shift reaction at the expense of the carboxylation. Thus a water scavenger such as triethyl orthoformate is necessary for a smooth reaction. 

The facile photochemical sigmatropic 1,3-trimethylsilyl shift in polysilylacylsilanes from silicon to oxygen (equation 33) was utilized historically to prepare the first relatively stable silenes3 86 87. Silenes prepared by isomerization of acylpolysilanes bear, due to the synthetic approach, a trimethylsiloxy group at the sp2-hybridized carbon and relatively stable silenes of this type have in addition also at least one trimethylsilyl group at the silicon. These substituents strongly influence the physical properties and the chemical behaviour of these silenes. This is noticeable in many reactions in which these Brook -type silenes behave differently from simple silenes or silenes of the Wiberg type. 

Cyclic siloxanes are important precursors in the silicon industry, being formally dimers or trimers of silanone (R2Si=0), a known intermediate. Cyclic siloxanes have been synthesized by four routes, the conventional methods being the condensation of silanediol or the hydrolysis of species such as halosilanes or aminosilanes (Scheme l)16-20. Alternatively, oxidation of disilene by triplet oxygen (equation l)21-27 or oxidation of oxadisiliranes by singlet oxygen (equation 2)28-31 may be utilized. 

This is a useful route for the preparation of aldehydes and ketones from alkenes, and is covered in this section. Photosensitized oxidative cleavage of alkenes occurs in reasonable yield using p-dimethoxybenzene in the presence of oxygen (equation 31)157. The products are aldehydes or ketones depending upon substrate structure. 

Finally, C—C bond formation occurs through regio- and stereospecific reaction between allyl alcohols and ethyl magnesium chloride, in the presence of complex zirconium catalysts, followed by treatment with oxygen (equation 111)434. In this reaction the alkene functionality is lost. 

Catalytic oxy-palladation is an extremely useful method for the synthesis of functionalized THF and tetrahydropyran moieties. This reaction is brought about simply by treating a 1,4- or 1,5-hydroxy alkene with 0.1 mol-eq of Pd(II) salts and copper(I) chloride in DMF, with oxygen (equation 181)655. If this reaction is carried out in the presence of carbon monoxide in methanol, then an ester moiety is introduced into the product molecule (equation 182)656-658. If an alkene is introduced in place of the CO, then a tandem vinylation reaction also takes place (equation 183)659. 

In addition to the possibilities of electron transfer (Equation 2) and energy transfer (Equation 4), electron transfer to singlet oxygen (Equation 7) and subsequent deprotonation (Equation 3), or hydrogen transfer to singlet oxygen (Equation 8) (J3) are to be taken into consideration and make an attempt of a differentiation between those postulated mechanisms extremely difficult. 

An intermolecular homoallylation of glutaraldehyde with isoprene occurs regioselectively at C-l when promoted by [Ni(acac)2]/triethylborane to afford the tetrahydropyran 383 as a single isomer, the methyl group being 1,3-anti with respect to the tetrahydropyranyl oxygen (Equation 159) <2001AGE3600>. 

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