Oxygen atom migration

Reaction of S-oxide of 1,4-dimethylthiobenzene 56 with trifluoroacetic acid provides another example of an oxygen atom migration that proceeds through a dication. The dication is in rapid equilibrium with the protonated sulfoxide 57 (Scheme 19).83... 

Bright, Coxon, and Steel697 reported the cyclization of a methallyl carbinol in HSO3F via the intermediacy of a protonated oxetane involving a unique oxygen atom migration [Eq. (5.252)]. 

Dissociative chemisorption of the aldehyde aldehyde oxygen atom migrates to the vacant anion site reduction of the metal formation of OH by H abstraction from the aldehyde. 

Aitken (343) has calculated the heats of transport of oxygen in U02+ , UO2. f, and (U,Pu)02 by theoretical treatment based on irreversible thermodynamics, resulting in the estimated values for solid phase diffusion of 32,100 140 and 120 88 kcal/mol, respectively. It may hence be expected that the oxygen atoms migrate from high toward low terperature by solid phase diffusion in all the cases considered. 

Those including, in addition to the mere extraction of framework aluminum, a second step in which framework vacancies are filled in,e. g.,by intrinsic silicon and oxygen atoms migrating in the zeolite lattice under hydrothermal conditions. 

The mechanism of the Fries reaction is not known with certainty. One mechanism regards it as a true intramolecular rearrangement in which the acyl group migrates directly from the oxygen atom to the carbon atoms of the ring. Another scheme postulates that the ester is cleaved by the reagent... 

The hydroxy oxygen of a peracid has a higher electrophilicity as compared to a carboxylic acid. A peracid 2 can react with an alkene 1 by transfer of that particular oxygen atom to yield an oxirane (an epoxide) 3 and a carboxylic acid 4. The reaction is likely to proceed via a transition state as shown in 5 (butterfly mechanism), where the electrophilic oxygen adds to the carbon-carbon n-hond and the proton simultaneously migrates to the carbonyl oxygen of the acid ... 

We recognize redox reactions by noting whether electrons have migrated from one species to another. The loss or gain of electrons is easy to identify for monatomic ions, because we can monitor the charges of the species. Thus, when Br ions are converted into bromine atoms (which go on to form Br2 molecules), we know that each Br ion must have lost an electron and hence that it has been oxidized. When 02 forms oxide ions, 02-, we know that each oxygen atom must have gained two electrons and therefore that it has been reduced. The difficulty arises when the transfer of electrons is accompanied by the transfer of atoms. For example, is chlorine gas, Cl2, oxidized or reduced when it is converted into hypochlorite ions, CIO" ... 

In this reaction, the C atom of C02, the Lewis acid, accepts an electron pair from the O atom of a water molecule, the Lewis base, and a proton migrates from an H20 oxygen atom to a C02 oxygen atom. The product, an H2C03 molecule, is a Bronsted acid. 

The mechanism involves a simple 1,2 shift. The ion (52, where all four R groups are Me) has been trapped by the addition of tetrahydrothiophene. It may seem odd that a migration takes place when the positive charge is already at a tertiary position, but carbocations stabilized by an oxygen atom are even more stable than tertiary alkyl cations (p. 323). There is also the driving force supplied by the fact that the new carbocation can immediately stabilize itself by losing a proton. 

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

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