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Galvinoxyl radicals: Synthesis of new derivatives, determination of low oxygen contents, and stability studies

Lampp, Lisa, Azarkh, Mykhailo, Drescher, Malte, Imming, Peter
Tetrahedron 2019 v.75 no.18 pp. 2737-2747
byproducts, chemical reactions, chemical structure, electron paramagnetic resonance spectroscopy, free radicals, octanol, oxygen, solvents
Two new derivatives of galvinoxyl (1), a perdeutered (2) and an adamantyl-analog (3) for potential applications as spin probes were synthesized. The synthesis with deuterated educts yielded 2 with 98% D. It exhibited an 18-line EPR spectrum in octanol with narrow peak-to-peak linewidth. The EPR spectrum of 3 was very similar to galvinoxyl, but with differences in the linewidth due to unresolved long-range couplings with adamantyl-protons. Compound 2 showed a higher response to oxygen (4.8 μT/% O2) than 1 (2.8 μT/% O2). The coupling pattern of 2 allowed the determination of oxygen at low levels (0–6%) by a new type of analysis of the EPR pattern. The stability of the radicals strongly depended on the amount of hydrogalvinoxyl, a by-product of the galvinoxyl synthesis, and the solvent type. A molecular mechanism for the stabilization by hydrogalvinoxyl and the influence of solvent type is proposed.