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Superacid Chemistry on Mildly Acidic Water

Enami, Shinichi and Stewart, Logan A. and Hoffmann, Michael R. and Colussi, Agustín J. (2010) Superacid Chemistry on Mildly Acidic Water. Journal of Physical Chemistry Letters, 1 (24). pp. 3488-3493. ISSN 1948-7185.

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The mechanism of proton transfer across water−hydrophobic media boundaries is investigated in experiments in which the protonation of gaseous n-hexanoic acid (PCOOH) upon collision with liquid water microjets is monitored by online electrospray mass spectrometry as a function of pH. Although PCOOH(aq) is a very weak base (pK_(BH+) < −3), PCOOH(g) is converted to PC(OH)_2^+ on pH < 4 water via a process that ostensibly retains some of the exoergicity of its gas-phase counterpart, PCOOH + H_3O^+ = PC(OH)_2^+ + H_2O, ΔG < −22 kcal mol^(−1). The large kinetic isotope effects observed on H_2O/D_2O microjets, PC(OH)_2^+/PC(OH)OD^+ = 88 and PC(OH)OD^+/PC(OD)_2^+ = 156 at pD = 2, and their inverse dependences on pH indicate that PCOOH(g) hydronation on water (1) involves tunneling, (2) is faster than H-isotope exchange, and (3) is progressively confined to the outermost layers as water becomes more acidic. Proton transfers across steep water density gradients appear to be promoted by both dynamic and thermodynamic factors.

Item Type:Article
Related URLs:
URLURL TypeDescription
Enami, Shinichi0000-0002-2790-7361
Hoffmann, Michael R.0000-0001-6495-1946
Colussi, Agustín J.0000-0002-3400-4101
Additional Information:© 2010 American Chemical Society. Publication Date (Web): December 3, 2010. S.E. appreciates the Japan Society for the Promotion of Sciences Postdoctoral Fellowships for Research Abroad. This work was supported by the U.S. National Science Foundation, Grant AGS-0964853.
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Subject Keywords:water−hydrophobic media boundry; proton transfer; superacid chemistry; water density gradients
Issue or Number:24
Record Number:CaltechAUTHORS:20110131-093348164
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Official Citation:Superacid Chemistry on Mildly Acidic Water Shinichi Enami, Logan A. Stewart, Michael R. Hoffmann, Agustín J. Colussi The Journal of Physical Chemistry Letters 2010 1 (24), 3488-3493
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21929
Deposited By: Tony Diaz
Deposited On:31 Jan 2011 23:39
Last Modified:03 Mar 2020 13:01

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