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Homogeneous Reduction of CO_2 by Photogenerated Pyridinyl Radicals

Riboni, Francesca and Selli, Elena and Hoffmann, M. R. and Colussi, A. J. (2015) Homogeneous Reduction of CO_2 by Photogenerated Pyridinyl Radicals. Journal of Physical Chemistry A, 119 (19). pp. 4433-4438. ISSN 1089-5639.

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We report that 1-hydropyridinyl radicals (1-PyH^•) photogenerated in solution react with dissolved CO_2 en route to its 2e^– reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H_2O mixtures saturated with 1 atm of CO_2 yields a suite of products, among which we identified Na(HCOO)_2^– (m/z^– = 113), C_5H_6NCOO– (m/z^– = 124), and C_5H_(10)O_2NCOO– (m/z^– = 160) species by electrospray ionization mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO_2 neutrals via collisionally induced dissociation. We infer that 1-PyH^• [from (1) ^3Py^* + 2-PrOH → 1-PyH^• + ^•PrOH] adds to CO_2, in competition with radical–radical reactions, leading to intermediates that are in turn reduced by ^•PrOH into the observed species. The formation of carboxylates in this system, which is shown to require CO_2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e^– reduction of CO_2 by 2-PrOH initiated by Py^*. We evaluate a rate constant (2) k_2(1-PyH^• + CO_2 → •Py-1-COOH) ≈ O (10) M^(–1) s^(–1) and an activation energy E_2 ≥ 9 kcal mol^(–1) that are compatible with thermochemical estimates for this reaction.

Item Type:Article
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Hoffmann, M. R.0000-0001-6495-1946
Colussi, A. J.0000-0002-3400-4101
Alternate Title:Homogeneous Reduction of CO2 by Photogenerated Pyridinyl Radicals
Additional Information:© 2014 American Chemical Society. Special Issue: Mario Molina Festschrift. Received: September 25, 2014. Revised: November 10, 2014. Publication Date (Web): November 11, 2014. M.R.H. and A.J.C. acknowledge financial support from the National Science Foundation (U.S.A.) Grant AC-1238977. F.R. gratefully acknowledges financial support from the Doctorate School in Chemistry of the University of Milan, Italy. We thank Dr. Nathan Dalleska for expert help with the mass spectrometer.
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University of Milan Doctorate School in ChemistryUNSPECIFIED
Issue or Number:19
Record Number:CaltechAUTHORS:20141202-151548793
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Official Citation:Homogeneous Reduction of CO2 by Photogenerated Pyridinyl Radicals Francesca Riboni, Elena Selli, M. R. Hoffmann, and A. J. Colussi The Journal of Physical Chemistry A 2015 119 (19), 4433-4438 DOI: 10.1021/jp509735z
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52293
Deposited By: Ruth Sustaita
Deposited On:02 Dec 2014 23:45
Last Modified:15 Apr 2020 16:33

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