Hans-Rudolf Meier

Some aspects of a new class of sulfur containing phenolic antioxidants

Abstract The commercial sulfur containing antioxidant AO2 (Irganox 1520) is compared with other classical phenolic antioxidants, and its special autosynergistic profile, particularly under dynamic test conditions (Brabender, 160 °C), in commercial polybutadiene rubber is investigated. AO2 outperforms all other tested phenolic stabilizers. A tentative mechanistic explanation for the action of AO2 is given, consisting of either a concerted reaction or a ‘tandem reaction’ of the antioxidant with macroalkylperoxy radicals. Other mechanistic pathways, for instance the role of the phenoxy radical 8 or its C,Orecombination products with oxygen centered radicals (such as macroalkylperoxy radicals) and of the recently synthesized stable quinone methide 10 are discussed. CIDNP experiments, generating the radical 8 from AO2 , demonstrate that the main reaction between phenoxy radicals 8 is regioselective C,O-recombination, giving rise to the dimers 9a and 9b and no direct formation of quinone methide 10 and C,C-coupling products is observed.

Reactions of Sulfur Containing Phenolic Antioxidants for Elastomers

Alkyl-hydroxybenzylthioethers are efficient storage and processing stabilizers for elastomers and adhesives. Especially alkyl-(2-hydroxybenzyl)thioethers represent an intramolecular combination of a primary and secondary antioxidant, i.e. a phenolic and a thioether moiety in an optimized spatial arrangement. The mechanism of their intramolecular synergism was investigated. The best overall stabilizers are 2,4-bis(alkylthiomethyl)-6-methylphenols, e.g. AOl, in contrast to 2,6-dialkyl-4-alkylthiomethylphenols(B), 4-alkyl-2,6-bis(alkylthiomethyl)phenols C.

STABLE QUINONE METHIDES II: ADDITION OF THIOLS TO QUINONE METHIDES, SYNTHESIS OF BISALKYLTHIOSUBSTITUTED QUINONE METHIDES AND TRITHIO-ORTHOBENZOATES

Abstract Regioselective oxidation of the p-alkylthiomethylphenols 1 with K3[Fe(CN)6] to the monosubstituted p-quinone methides 2 followed by addition of thiols R3SH gives rise to the dithioacetals 3.1 This reaction sequence can be extended to introduce a third RS substituent by repeating the above mentioned reactions. Spectroscopic data, especially 1H-NMR and 13C-NMR data of the quinone methides 4 and the new trithioorthoesters 5 are discussed. The same regioselectivity as for the oxidation of la 1 is observed when compounds with two different activated benzylic positions e.g. 3a and 3b are oxidized with K1[Fe(CN)6]. The sequence 1 → 2 → 3 → 4 → 5 constitutes a new approach to trithio-orthoesters.

Spiro[1,3-benzoxathiepin-4(5H),1′-cyclohexa[2,4]dien]-2,2′-dione, a Novel Heterocyclic Ring System

Abstract Besides the common cyclisation reactions between divalent electrophiles such as Soc12, SC12, etc. and 2,2′-alkylidene-bisphenols 1 with selective attack by the two oxygens yielding dibenzo[d,g][1,3,2]dioxathiocines [1] we observed previously an unusual cyclisation of 1 with S2CI2 with a nucleophilic attack by the ortho- and para-carbon atoms (C(2) and C(4)) of bisphenol 1 [2]. We now report a new type of cyclocondensation reaction of 4,4′,6,6′-tetrasubstituted 2,2′-alkylidene-bisphenols 1 with ClSCOCl affording spiro[1,3-benzoxathiepin-4(5H),1′-cyclohexa[2,4]dien]-2,2′-diones 2 together with the cyclic carbonates 3. The structures of the products were elucidated mainly by l3C-NMR- and 1H-NMR-spectroscopy. The mode of formation of the novel spiro thiocarbonates 2 resp. the known carbonates 3 [3] is discussed.