Tris methid

Quinone methides are electron-deficient at C7, as readily understood via the resonance forms of QM1 shown in Fig. 12.7. They are therefore susceptible to nucleophilic attack at that position. Although reactions during high-temperature pulping demonstrate that 8-<9-4-aryl ether quinone methides QM1 are rearomatized by attack with hard nucleophiles such as HO- and HS, 81 these reactions do not readily occur at ambient temperatures.41,85 Thus, HO will not add to quinone methide QM1 under any conditions that we have tried (including with cosolvents, and using phase-transfer conditions). Of course water will add to quinone methides under acidic conditions... 

Feldman and Eastman have suggested that the kinamycins may by reductively activated to form reactive vinyl radical (25) and orf/to-quinone methide (26) intermediates (Scheme 3.2c) [16]. The authors provided convincing evidence that the alkenyl radical 25 is generated when the model substrate dimethyl prekinamycin (24) is exposed to reducing conditions (tri-n-butyltin hydride, AIBN). Products that may arise from addition of this radical (25) to aromatic solvents (benzene, anisole, and benzonitrile) were isolated. The ort/io-quinone methide 26 was also formed,... 

In the case of sodium tris-(/>-nitrophenyl)-methide the carboxylation reaction with carbon dioxide to give the acid fails to take place, although less stable carbanions are readily carbonated.410... 

Fluorous biphase catalysis was also applied in Friedel-Crafts acylation with Yb tris(perfluoroalkanesulfonyl)methide catalysts with acid anhydrides.59 Of the aromatics studied, activated compounds and naphthalene (95% conversion) showed satisfactory reactivity. 

Hydroboration of a variety of alkenes and terminal alkynes with catecholborane in the fluorous solvent perfluoromethylcyclohexane was performed using fluorous analogs of the Wilkinson catalyst.135 136 Recycling of a rhodium-based alkene hydrosilylation catalyst was also successful.137 Activated aromatics and naphthalene showed satisfactory reactivity in Friedel-Crafts acylation with acid anhydrides in the presence of Yb tris(perfluoroalkanesulfonyl)methide catalysts.138... 

Based on the evidence obtained from the amount and nature of transformation products formed, a mechanism of melt stabilising action of tocopherol in PP and PE has been proposed, see Scheme 6 [34]. It is well known that, like other hindered phenols, a-tocopherol is rapidly oxidised by alkylperoxyl radicals to the corresponding tocopheroxyl radical (a-Toe, Scheme 6a). Further oxidation of the tocopheroxyl radical in the polymers leads to the formation of coupled and quinonoid-type products, e.g. SPD, TRI, DHD (see Figs. 8 and 9). Dimerisation of the intermediate o-quinone methide (QM) leads to the formation of the quinonoid-type dimeric coupled product, SPD (Scheme 6 reaction d). 

Scheme 6 Mechanism of melt stabilising action of a-tocopherol in polyolefins [34], TRI trimer, SPD spirodimer, DHD dihydroxydimer, QM quinine methide, ALD aldehyde, TQ tocoquinone...

Against this background it is important that—quite fitting in this still new millennium— the first catalytic Friedel-Crafts acylations of (still relatively electron-rich) aromatic compounds were reported (Figure 5.35). Trifluoromethane sulfonates ( triflates ) of rare-earth metals, e. g., scandium(III)triflate, accomplish Friedel-Crafts acylations with amounts of as little as 1 mole percent. Something similar is true of the tris(trifluoromethanesulfonyl)-methides ( triflides ) of rare-earth metals. Unlike conventional Lewis acids, the cited rare-earth metal salts can form 1 1 complexes with the ketone produced, but these are so unstable that the Lewis acid can re-enter the reaction. Whether this works analogously for the third catalytic system of Figure 5.35 is unclear. 

Benzaldehyde (81 mg) and methyl trimethoxysilyl dimethylketene acetal (165 mg) were added to a mixure of 3 ml perfluorooctane and 4 ml toluene. To this mixture was added Imol % (based on benzaldehyde) ytterbium (tris(trisperfluorooctanesulfonyl)methide) and the reaction stirred 15 minutes at 40°C. Mixing and heating were stopped and the mixture separated into upper toluene layer and lower perfluorooctane layer. Each layer was analyzed by gas chromatography 99% of the product was detected in the lower layer. Atomic emission spectrometry indicated that at least 99% of the catalyst was also present in the lower layer. 

Preparation of ytterbium tris(tris(perfluorobutanesulfonyl)-methide)... 

Tris(perfluorobutanesulfonyl)methide (3.0 g) was added to a solution of 15 ml acetonitrile, 15 ml water, and ytterbium carbonate (0.39 g). The mixture was stirred 7 hours at ambient temperature and was then heated to 50 °C one hour. The mixture was filtered and the product isolated by vacuum drying at 50°C at 1-10 mm Hg followed by drying at 90°C at 0.01 mm Hg for 24 hours. Elemental analysis supplied. 

DHD and quinonoid-type products, trimers, TRI, spirodimers, SPD, quinone methides, QM, together with some aldehydes, ALD, see Fig. 3 for structures of these products. All the oxidation products were shown to be more highly colored than tocopherol itself, with the aldehydes being the most colored, and the trimers the least colored. 

Degradation products of Irganox 1330 have been extracted from irradiated PP samples by refluxing with chloroform for at least 2 h followed by particle-beam LC-MS analysis. The compounds with quinone methide structures, e.g. l,3,5-trimethyl-2,4,6-tris(3, 5, di-tert-butyl-4-hydroxybenzyl)ben-zene were quantified [64]. 

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