Piperidine-phenols reactions

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

The authors presume that the observed effect is due to acid catalysis by methanol, but no catalysis by phenol was observed. Pietra and Vitali111 have shown earlier that phenol catalyses the reaction of l-fluoro-2,4-dinitrobenzene with piperidine in benzene. 

The low structural specificity of the antihistamines has already been noted. It is perhaps not too surprising, therefore, to find Lhat attachment of the basic side chain directly onto one of the. iromatic rings affords active compounds. In an unusual reaction reminiscent of the Claisen rearrangement, benzyl chloride affords the substituted phenol, 46, on heating with phenol itself. Alkyl-.ition of 46 with 2-dimethylaminoethyl chloride gives phenyltolox-.imine (47).Alkylation of that same intermediate (46) with 1-bromo-2-chloropropane, leads to 48. Use of that halide to alkyl-,ite piperidine gives the antihistamine, pirexyl (49). ... 

As expected, 2-halo-l,3-dithianes react with nucleophiles under Sn conditions. Suitable nucleophiles are enamines <2002TL9517, 2004T6931> and phenols <1997MOL7>. The reaction with EtOC(S)S K, followed by oxidation, provided a xanthate which generated a 1,3-dithiane 1-oxide radical upon treatment with Bu3SnH (Scheme 69) <2004T7781>. An efficient one-carbon radical precursor has also been obtained by addition of 2,2,6,6-tetramethyl-piperidine-l-oxyl (TEMPO) to 2-lithio-l,3-dithiane. The reactivity of this compound has been demonstrated <2005S1389>. 

With Binaphthol/M(OTf)3 Complexes (M = Yb, Sc) A chiral ytterbium triflate, derived from Yb(OTf)3, (R)-binaphthol, and a tertiary amine, has been applied to the enantioselective Diels-Alder reaction of cyclopentadiene with crotonoy 1 oxazolidinones. Among various tertiary amines, c/s-1,2,6-trimethyl piperidine was found to be highly effective [44] (Eq. 8 A.23). The unique structure of such chiral Yb catalysts is characterized by hydrogen bonding between the phenolic hydrogens of (R)-binaphthol and the nitrogens of tertiary amines. 

For the stronger proton acceptors (ammonia, monoethylamine, and piperidine) a relation between the B proton affinities and the spectral shifts of the S3 <- S0 states of phenol(B) or naphthol(B) shows a linear dependence for proton affinities lower than a limit value situated around 10.4 eV (s240 kcal mol-1) for both phenol or naphthol molecules. Above this limit, the spectral shift is much larger and is different for phenol and 1-naphthol (see Figure 4-17). Nevetheless, this limit seems to correspond with the energetical limit of the proton transfer reaction. 

In general, the elastomer must be prereacted (adducted) with the epoxy for the toughening effect to take place. Adducts reduce the likelihood of early phase separation and maintain the solubility of the elastomer in the uncured resin system. For CTBN the reaction is carried out at high temperatures (150 to 160°C) and usually in the presence of a catalyst, such as tris-dimethylamino phenol or piperidine. The resulting epoxy-CTBN adducts are available from several suppliers, and they can be easily formulated into epoxy adhesives. 

Phthalimide-N-sulfenyl chloride, 375 Phthaloylamino acids, 212 Phthaloyl-L-valine, 212 Phytuberin, 197 Phytyl chloride, 499, 500 Picrotoxinin, 265, 430 Pictei-Spengler cyclization, 308 Pinacol-typc reduction, 513 -Pinene, 346, 367 Piperidine acetate, 318 Piperidinium acetate, 375-376 Polonovski reaction, 484 Polyaminolactams, 378-379 Polycyclic phenols, 102 Polyene cyclization, 291-292 Polyethylene glycols, 360, 376 Polyketides, 302 Polyphosphate ester, 376-377 Polyprenylation, 499-500 Potassium-Ammonia, 273, 377 Potassium-t-Butylamine-18-Crown-6, 377-378... 

Attachment of B ansformation Products of Stabilizers. Up-to-date knowledge dealing with the chemistry of transformation products of phenolic [6, 15, 17, 20] and aromatic aminic [16, 43, 230] antioxidants and photoantioxidants based on hindered piperidines [10] indicates the possibility of attaching compounds having structures of quinone imine or quinone methide, or of radical species like cyclohexadienonyl, phenoxyl, aminyl or nitroxide to polymeric backbones. These reactions proceed mostly via reactivity of macroalkyl radicals derived fi-om stabilized polymers. Various compounds modelling this reactivity have been isolated [19, 230]. These results are of importance mainly for the explanation of mechanisms of antioxidant activity [6, 22, 24]. 

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