Reaction of o-Quinones in Cyclohexane Solutions with Alkyl Radicals Generated by Solution γ-Irradiation

Abstract

The structures of products formed in reactions of tert-butylated o-quinones with alkyl radicals were determined by 1 H and 13 C NMR and two-dimensional 1 H3 1 H NOESY spectroscopy, and also by gas chromatography3mass spectrometry. The major products formed upon g-irradiation of deaerated solutions of 4-tert-butyl-1,2-benzoquinone and 3,5-di-tert-butyl-1,2-benzoquinone in cyclohexane are monoalkyl ethers and products of addition to the C=C bond. In the case of 4-tert-butyl-1,2-benzoquinone, these are products of mixed O3C and C3C alkylation; the adduct formed by addition of the cyclohexyl radical to the C=C bond in 3,5-di-tert-butyl-1,2-benzoquinone gives an unsymmetrical dimer whose structure was proved by single-crystal X-ray diffraction.Quinone fragments are present in molecules of many natural compounds, e.g., flavonoids, vitamins, and drugs; they participate in such biologically important processes as photosynthesis and electron transfer [13 4]. Quinones are formed by two-electron oxidation of the corresponding dihydroxybenzenes [5], by inhibited oxidation in the presence of phenolic antioxidants as a result of disproportionation of hydroxysubstituted phenoxyl radicals, by decomposition of quinone methide peroxides, and by b-cleavage of phenoxyls containing alkoxy substituents [6,7]. Accumulation of quinones and quinoid compounds is believed to be responsible both for the toxicity of cer-ÄÄÄÄÄÄÄÄÄÄÄÄ tain drugs [8,9] and for enhancement of the performance of certain antioxidants (e.g., 2,6-di-tert-butyl-4-methylphenol) in stabilization of polyolefins and polystyrenes [10 312].

The Semiquinone−Ruthenium Combination as a Remarkably Invariant Feature in the Redox and Substitution Series [Ru(Q)n(acac)3−n]m,n= 1−3;m= (−2), −1, 0, +1, (+2); Q = 4,6-Di-tert-butyl-N-phenyl-o-iminobenzoquinone

“…The precursor complex Ru(acac) 2 (CH 3 CN) 2 and the ligand 2-anilino-4,6-di- tert -butylphenol(H 2 Q) , were prepared according to the reported procedures. Other chemicals and solvents were of reagent grade and used as received.…”

3,5,9,12-Tetra-tert-butyl-10,14-dicyclohexyl-2,8-dioxatetracyclo[5.4.0.21,9.13,7]tetradeca-4,12-diene-6,11-dione

“…The title compound, (I), was formed under irradiation ( 137 Cs source) of a deaerated cyclohexane solution containing 3,5-di-tertbutyl-ortho-quinone. The entire description of the results of theradiolysis experiments will be published elsewhere (Maslovskaya & Savchenko, 2005). The compound was isolated as a minor product by preparative thin-layer chromatography on silica.…”