Phenols singly hindered

The solution oxidation technique allows the study of polyolefin autoxi-dation under conditions where the temperature, concentration of reactants, and rates of radical initiation can be controlled. The results should be considered as a useful prelude to any fundamental understanding of the autoxidation processes which occur in neat polymers where the effects of very high viscosity, partial crystallinity, and oxygen diffusion rates are included. The objective of our work was to determine the kinetics and stoichiometry of the inhibited autoxidation of polypropylene in solution. A relatively detailed study of the oxidation of polypropylene inhibited by 2,6-di-terf-butyl-4-methylphenol [butylated hydroxytoluene (BHT)] has been made for comparison with data obtained in polypropylene oxidations inhibited by a variety of other stabilizers which include commercial polyfunctional antioxidants. Singly hindered phenols appeared to be superior in the inhibited-solution oxidation of polypropylene, and the application of this finding to stabilization technology was investigated briefly. 

Figures 5 and 6 show that two polypropylene peroxy radicals are scavenged by the singly hindered phenols, whereas only one is scavenged by the di-ferf-butylphenols. For most inhibitors acting on the low molecular weight substrate cumene, a stoichiometry of two radicals consumed per inhibitor molecule has been found (15). Apparently for polypropylene substrate, 2-ferf-butyl-4-methylphenol more nearly approaches this ideal. Thus, for BHT-inhibited oxidations Reaction 9 applies, whereas with singly hindered phenols, Reaction 7 is appropriate. Reaction 7 along with 2 1 stoichiometry is commonly assumed for neat polymer systems so that the number of radicals generated during an oxidation can be determined (16,17).

Preussomerin I 697 and ( )-preussomerin G 698 were obtained from 620 with a five- and six-steps sequence in 15% and 12% overall yield, respectively, through modifications of substituents of the dioxocin ring. Thus, attack of lithium methoxide from the less hindered face of the enone 620, followed by protection of the phenolic oxygen as its methyl ether provided the methoxy adduct 692. The ketone 693 was obtained through a benzylic bromination-solvolysis-oxidation protocol, which required only a single purification. The C(2)-C(3) olefin was introduced by selective silylation of the C-l carbonyl of diketone 693 and oxidation of the silyl enol ether with Pd(OAc)2. Enone... 

Mononuclear octahedral complexes have been obtained for carbonyl-bound acetic acid, and five-coordinate complexes of sterically hindered phenoxides of the type [V(py)3(C6H3Ph2-2,6)2]. A more hindered phenol gave a four-coordinate complex, [V (C6H3Pr2-2,6)4 Li(thf) 2] in which two pairs of cfr-phenolates were linked by a single Li(thf)+ unit. A binuclear complex of a substituted acetylacetone has the stmcture shown in(l). 

Removal of the MOM and Boc groups followed by regioselective bromination with Py-HBr in dichloromethane followed by cyclization through an iminium ion intermediate furnished the bicycle 10 as a single isomer. Deprotection of the benzyl ether and reduction of the azide group afforded the amino diol 11, which was treated with BrCH2C02Ph and propylene oxide and subsequent Pb(OAc)4 oxidation of the amine to provide 12 (80%). Intermolecular addition of the phenolic compound 13 to 12 in the presence of TEA occurred at the sterically less hindered convex face to provide the key intermediate 14 (Scheme 2). ... 

ET Screw, Single screw extrusion, blow molding, and injection molding, Barr, Robert, Inc. Ethacure, Liquid aromatic diamine epoxy, and urethane curatives, Albemarle Ethafoam, Polyethylene foam, Dow Plastics Ethanox, Hindered phenolic antioxidants, Albemarle... 

As previously explained, formation of dinuclear species upon oxidation of Cu(I) complexes is a thermodynamic sink. Increasing the bulkiness of the ligand can hinder the coordination sphere sufficiently to prevent dimerization. But in that case, the access to the metal is also locked for the substrate. Embedding the metal site at the bottom of a molecular host can be a way to confine copper in a mononuclear environment, while keeping it accessible to substrates via the cavity of the host. Calix[6]arenes have been intensely used for this purpose. " Despite being highly flexible, they can be constrained into the cone conformation by coordination to a single metal center when three alternate phenolic units out of six are... 

Deviations from Beer s law in CCU solutions are not serious. Mixtures containing hindered and free phenolic hydroxyl could be analyzed. In very favorable cases it was possible to analyze as many as six phenolic components from a single 2.7- to 3.0-/ scan. 

The protonolysis reaction of Sm(AlMe4)3 (generated in situ) with a sterically hindered bis-phenol was reported to yield the dimeric bis(aryloxide) samarium(III) tetramethylaluminate 47 (Fig. 7), found to behave as a single-component ethylene polymerization catalyst for the production of UHMWPE (600 psi ethylene, 70°Q [134]. 

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