Abstract
The solvated electron in CH3CN is scavenged by CO2 with a rate constant of 3.2 × 1010 M-1 s-1 to produce the carbon dioxide radical anion (CO2 -), a strong and versatile reductant. Using pulse radiolysis with time-resolved IR detection, this radical is unambiguously identified by its absorption band at 1650 cm-1 corresponding to the antisymmetric CO2 - stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH3CN, CO2 - decays on a ∼10 μs time scale via recombination with solvent-derived radicals (R) and solvated protons. Upon addition of formate (HCO2 -), the radiation yield of CO2 - is substantially increased due to H-atom abstraction by R from HCO2 - (R + HCO2 - → RH + CO2 -), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN, CH3, and possibly, H primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH2CN. The removal of solvent radicals by HCO2 - also results in over a hundredfold increase in the CO2 - lifetime. CO2 - scavenging experiments suggest that at 50 mM HCO2 -, about 60% of the solvent-derived radicals are engaged in CO2 - generation. Even under CO2 saturation, no formation of the radical adduct, (CO2)2 -, could be detected on the microsecond time scale.
| Original language | English |
|---|---|
| Pages (from-to) | 10011-10017 |
| Number of pages | 7 |
| Journal | Physical Chemistry Chemical Physics |
| Volume | 20 |
| Issue number | 15 |
| DOIs | |
| Publication status | Published - Jan 1 2018 |
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ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry
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Radiolytic formation of the carbon dioxide radical anion in acetonitrile revealed by transient IR spectroscopy. / Grills, David; Lymar, Sergei V.
In: Physical Chemistry Chemical Physics, Vol. 20, No. 15, 01.01.2018, p. 10011-10017.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Radiolytic formation of the carbon dioxide radical anion in acetonitrile revealed by transient IR spectroscopy
AU - Grills, David
AU - Lymar, Sergei V.
PY - 2018/1/1
Y1 - 2018/1/1
N2 - The solvated electron in CH3CN is scavenged by CO2 with a rate constant of 3.2 × 1010 M-1 s-1 to produce the carbon dioxide radical anion (CO2 -), a strong and versatile reductant. Using pulse radiolysis with time-resolved IR detection, this radical is unambiguously identified by its absorption band at 1650 cm-1 corresponding to the antisymmetric CO2 - stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH3CN, CO2 - decays on a ∼10 μs time scale via recombination with solvent-derived radicals (R) and solvated protons. Upon addition of formate (HCO2 -), the radiation yield of CO2 - is substantially increased due to H-atom abstraction by R from HCO2 - (R + HCO2 - → RH + CO2 -), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN, CH3, and possibly, H primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH2CN. The removal of solvent radicals by HCO2 - also results in over a hundredfold increase in the CO2 - lifetime. CO2 - scavenging experiments suggest that at 50 mM HCO2 -, about 60% of the solvent-derived radicals are engaged in CO2 - generation. Even under CO2 saturation, no formation of the radical adduct, (CO2)2 -, could be detected on the microsecond time scale.
AB - The solvated electron in CH3CN is scavenged by CO2 with a rate constant of 3.2 × 1010 M-1 s-1 to produce the carbon dioxide radical anion (CO2 -), a strong and versatile reductant. Using pulse radiolysis with time-resolved IR detection, this radical is unambiguously identified by its absorption band at 1650 cm-1 corresponding to the antisymmetric CO2 - stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH3CN, CO2 - decays on a ∼10 μs time scale via recombination with solvent-derived radicals (R) and solvated protons. Upon addition of formate (HCO2 -), the radiation yield of CO2 - is substantially increased due to H-atom abstraction by R from HCO2 - (R + HCO2 - → RH + CO2 -), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN, CH3, and possibly, H primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH2CN. The removal of solvent radicals by HCO2 - also results in over a hundredfold increase in the CO2 - lifetime. CO2 - scavenging experiments suggest that at 50 mM HCO2 -, about 60% of the solvent-derived radicals are engaged in CO2 - generation. Even under CO2 saturation, no formation of the radical adduct, (CO2)2 -, could be detected on the microsecond time scale.
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U2 - 10.1039/c8cp00977e
DO - 10.1039/c8cp00977e
M3 - Article
VL - 20
SP - 10011
EP - 10017
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
SN - 1463-9076
IS - 15
ER -