Dimers oxidation

Thermal degradation of Irganox 1076 in air was studied by means of HPLC-UV/VIS and by preparative HPLC-NMR. At 180 °C cinnamate and dimeric oxidation products are formed, and at 250 °C de-alkylation products are observed [660], On-line LC-NMR hardly covers a real need in polymer/additive analysis, as the off-line option is mostly perfectly adequate for that purpose. 

Chiral 2-imidazoline dianions undergo one-electron oxidation in the presence of TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy) to form a radical anion that is either trapped stereoselectively by TEMPO or undergoes dimerization. Oxidation of bis-diazene oxides leads to novel (9-stabilized 4N/3e radical cations and 4N/2e dications. These were detected by ESR spectroscopy and cyclic voltammetry. B3LYR/6-31G calculations confirmed the nature of the 4N/3e and 4N/2e systems. ... 

It is not surprising that the proton relay for sulfide oxidation (Figure 34) can be extended to the involvement of both HO—OH and RO—OH dimers in the oxidation of amines ". The dimeric forms of the hydroperoxides can reduce the activation barriers as evidenced by the HO—OH and CH3O—OH dimeric oxidation of TMA (Figure 35). The activation barrier for TMA oxidation with dimeric HO—OH is effectively reduced by 12.1 kcalmoU relative to the same oxidation of TMA with monomeric HO—OH (25.8 kcalmoU, Figure 30). 

Figure 1. Alcohol structures obtained after isoprene dianionic dimer oxidation hydrogen transfer position (O).

The CS2 and COS-based ligands are all dealt with in Section 16.4.3. Dimeric oxidation products of the heteroallyls and other ligands in which a CS2 or COS fragment is found are treated briefly in Section 16.4.4. No further attention is paid to ligands like S—S—Me and methanedithiolate or dithioacetal, which occurs for example in the reaction of two moles of (4) with one mole of CS2 in a two-step hydrogen migration.6... 

M. Shamma and H. Guinaudeau, Tetrahedron 40, 479S (1984). Biosynthesis of aporphinoid alkaloids. In addition to monomeric alkaloids, discusses proaporphine- and aporphine-benzyliso-quinoline dimers, dimeric oxidized aporphines, and types derived by catabolism of benzyliso-quinoline-derived dimers. 

Oxygen transfer to the metal site of several organometallics is also possible in some instances this occurred under ultrasonic conditions. In this way its polymeric oxide was obtained from triphenylbismuthine, whereas triphenylstibine afforded its crystalline dimeric oxide [57], Several metalloporphyrins are also oxygenated at the metal site by IOB. Some of the oxo species formed have been isolated but normally they are non-isolable. These systems have been used in some catalytic oxidations. 

Dist, tet., dimeric oxidation product of [Co(N2)(PMe3)3] bridging PMe2, PMe2CH2... 

Photochemical dimerization of the diene (160) has been carried out in the solid state. The styry1isoxazoles (161) are also photoreactive and yield (2+2)-dimers. Oxidation of these affords the a-truxillic acids derivatives (162). The photochemical dimerization of (163) has been reported to afford a cyclobutane derivative when irradiated in the solid phase. A detailed review has surveyed the conformation effects influencing photochemical solid state reactions. ... 

Hydrogenation H ydrof orm ylation Double-bond migration Dimerization Oxidation... 

Naphthol can successfully be dimerized oxidatively, selectively through the o-site to give (22) using copper(II)-amine complexes (70%) or manganese(III) acetylacetonate (69%), and o-o coupling is the major paAway (90%) on ferricyanide oxidation of the trisubstituted phenol (23) to the orthodiphenoqui-none (24). In this context it is of interest that a compound obtained (74%) on ferricyanide oxidation of... 

A 2-amino-1-phenol with a free position para to the hydroxyl group affords a dimeric oxidation product in high yield. Thus Butenandt and co-workers oxidized... 

Properties Slightly yellow liquid or crystals (dimer), oxidizes gradually to diacetyl on exposure to air. D 1.016, bp 140-148C, mp 15C. Soluble in alcohol miscible with water slightly soluble in ether. Combustible. 

FIGURE 15.12 Lignin model dimers oxidation catalyzed by laccase and HBT. (From Bourbonnais, R., Paice, M.G., Freiermuth, B., Bodie, E., Borneman, S., Applied and Environmental Microbiology, 63(12), 4627-4632, 1997. With permission.)... 

Dimerization, oxidative Naphthalene-Lithium. Palladium acetate. Periodic acid. 

Figure 7 shows the structures of commonly found resin acids. It is to be noted that these materials have two major sites for chemical reactions the carboxylic group and the double bonds. It can be expected that the positions of double bond would play an important role in certain reactions. A benzenenoid structure in dehydroabietic acid would Indicate inertness of this molecule toward reactions such as dimerization, oxidation, Diels-Alder, and free radical chain transfer or termination, while resin acids containing conjugated double bonds would undergo these reactions with ease. 

With the model systems used in these investigations, dimer splitting can be induced both by reduction and by oxidation, depending on the sensitizer. While it was inferred from the existence of dimer radical anions D that splitting via the former route occurs in two steps, it has been debated for some time whether this also holds for the latter route, that is, whether dimer oxidation and cleavage are concerted or successive. CIDNP spectroscopy is particularly well suited to answer such questions because the intermediates leave their EPR spectrum (their polarization pattern) in the products. Thus, not only can the intermediates be identified by this signature, even if they are rather short lived, but the occurrence of their polarizations in a product... 

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