Electron transfer from carbanionic salts to linear sequences of conjugated double bonds, 2. Reaction with trans‐β‐carotene

Abstract

The reactions of a set of organoalkaline compounds with trans-p-carotene (Car) were studied in solution (using UV/Vis, ESR, and mass spectroscopy) and compared with the reactions of the same set with insoluble polyacetylene. It was shown that the naphthalene radical ion and the dicarbanionic dimer of 1, I-diphenylethylene, 1,1,4,4-tetraphenyl-l,4-butanediide, react with Car by a simple electron transfer leading to Car radical ion and dianion. This dianion is protonated by methanol mainly at carbon 7 or 7'. On the contrary of diphenylalkyllithium compounds add to Car double bonds. This addition of I mol of diphenylalkyllithium per Car takes place mainly at the central double bond. sec-Butyllithium (sec-BuLi) reacts also by addition to Car. The addition products are in some cases instable and decompose to radical ions through a non-elucidated mechanism. These transfer or addition reactions with Car, as well as the exclusive electron transfer observed with polyacetylene, are rationalized on the basis of the relative redox potentials of reactants. a) Part I : cf.".

Facile Electron Uptake by Carotenoids Under Mild, Non‐Radiative Conditions: Formation of Carotenoid Anions

“…[18] Therefore, the prompt appearance of Car 2-3 suggests either a direct two electron uptake, a rapid, successive one-electron attachment or a single electron uptake followed by an immediate disproportionation reaction 2 Car ·-Ǟ Car 2-+ Car. [14] A probable dimerisation 2 Car ·-Ǟ Car-Car 2-has been excluded. [33] Despite exhaustive investigations the mechanistic evidence for electron transfer reactions in alkaline DMSO remains uncertain: a cryptically formulated multistep addition reaction of DMSO -with dicarbonyl compounds was explicitly presented as "belief ".…”

“…[9] So far, electron uptake by Car has been investigated by quite elaborated methods: chemical reactions with metals (Al-Hg, Na, K, Cs), [10][11][12][13] and metal organic compounds (e.g. sBuLi), [14] electrochemical methods, [15] ionizing rays (pulse radiolysis) [2,16,17] and flash photolysis. [18] Notwithstanding, electron transfer to Car should be possible without relying on particular scrupulous procedures.…”

Thermal aging of tetraalkyl ammonium doped polyacetylenes

“…The commercial /3-carotene was purified and carefully handled as previously described with necessary precautions to avoid any trace of proton donors. 10 The /3-carotene dianion was synthesized in a glass apparatus provided with a glass filter and optical cell, which was flamed and sealed under vacuum, by reacting a THF solution of /3-carotene over a sodium mirror. The resulting solution was filtered through a coarse frit into the quartz cell.…”

“…Figure10. Optical spectral changes observed during the transformation of /3-carotene radical anion Bu4N+ (Amax = 815) to /3-carotene (A",x = 458) and /3-carotene monoanion Bu4N+ (Amax = 760): (a) /3-carotene, (1) t = 0, (2) t = 20 h, (3) t = 50 h, (4) t = 10 days.…”

Key to Xenobiotic Carotenoids

“…Such compounds ought to be included in a forthcoming extended register. Enlarging the selection criteria to <C20 chains, to xenobiotic C,H,O carotenoids, considering heteroatoms outside the carotenoid carbon skeleton sphere and taking into account ionic bounded heteroatoms is desirable for future compilation [36,37]. It would furthermore be valuable to have at hand a complete directory of isotope-substituted carotenoids (D, T, 13 C, 14 C) [38,39,40].…”