HR: 0800h
AN: A21E-0798 [Abstracts]
TI: Protonation of Alcohols in Sulfuric Acid Solutions at UT/LS Conditions
AU: * Michelsen, R R
EM: rmichelsen@rmc.edu
AF: Randolph-Macon College
Department of Chemistry, PO Box 5005, Ashland, VA 23005, United States
AU: Vernier, K
EM: kvernier@rmc.edu
AF: Randolph-Macon College
Department of Chemistry, PO Box 5005, Ashland, VA 23005, United States
AU: Axson, J
EM: jaxson@rmc.edu
AF: Randolph-Macon College
Department of Chemistry, PO Box 5005, Ashland, VA 23005, United States
AU: Axson, J
EM: jaxson@rmc.edu
AF: now at University of Colorado at Boulder, Department of Chemistry and Biochemistry
215 UCB, Boulder, CO 80309, United States
AU: Morley, D
EM: danielmorley@rmc.edu
AF: Randolph-Macon College
Department of Chemistry, PO Box 5005, Ashland, VA 23005, United States
AB:
The protonation of several small alcohols (ethanol, 2-propanol, and 1-butanol) in cold sulfuric acid aqueous
solutions was measured using variable temperature 13C nuclear magnetic resonance (NMR) spectroscopy.
The acidity of the sulfuric acid + deuterium oxide solutions ranged from 43 to 81 weight percent (wt %)
H2SO4. The pKBH+ values, which are a measure of the acidity of each alcohol, range
from -2.0 for butanol at room temperature to -2.2 for ethanol at -20°C. The protonation enthalpies of the
three alcohols over the temperature range of 22°C to -35°C were found to be small and negative,
ranging from -1.8 kJ mol-1 for 2-propanol to -2.3 kJ mol-1 for ethanol. A small, negative protonation
enthalpy means that the degree of protonation of the alcohol slightly decreases as temperature decreases. The
pKBH+values and protonation enthalpies are used to predict the form of dissolved alcohols in
sulfate aerosols. For typical upper troposphere/lower stratosphere (UT/LS) conditions (40-70 wt %
H2SO4 and 220 K), all three alcohols increase from approximately 10% protonated in 40 wt %
H2SO4 to over 60% protonated in 70 wt % H2SO4. The percent of protonated alcohol
depends more strongly on m*, the slope factor of the excess acidity treatment, than on pKBH+
values. This relationship may reflect solvation effects. The treatment of strongly acidic, non-ideal solutions as
applied to organic solutes in sulfate aerosol particles will be discussed.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting