Chemistry at and near the Surface of Liquid Sulfuric Acid:  A Kinetic, Thermodynamic, and Mechanistic Analysis of Heterogeneous Reactions of Acetone

Abstract

The interactions of gas-phase acetone with liquid sulfuric acid solutions are described. The solutions were prepared as 0.05−0.10 μm thick films deposited on single-crystal metal substrates. Experiments were carried out over broad ranges of acid composition (70 − >96 wt % H2SO4), temperature (180−220 K), and acetone pressure (10-7−10-3 Pa). Two types of measurements are reported: the time-dependent acetone uptake probability, and the infrared spectra of absorbed acetone and its reaction products. From the infrared measurements, a reaction scheme is identified in which gas-phase acetone is taken up by sulfuric acid to form protonated acetone. In solutions containing more than 70 wt % H2SO4, protonated acetone undergoes a self-condensation/dehydration reaction to form mesityl oxide. In films that contain 85 wt % or more H2SO4, a second reaction sequence occurs, ultimately resulting in the formation of trimethylbenzene. The uptake probability measurements are consistent with the infrared data. In 70 wt % H2SO4, the acetone uptake probability rapidly decreases from an initial value near unity to a steady-state value of zero, due to the formation of a saturated acetone + sulfuric acid solution. The Henry's law solubility constants of acetone in 70 wt % H2SO4 were obtained from the integrated uptake measurements. The temperature dependence of the measurements implies that the standard-state enthalpy and entropy changes of acetone solution in 70 wt % sulfuric acid are −66 kJ mol-1 and −249 J mol-1 K-1, respectively. In the more concentrated films, the steady-state uptake probability is never measured to be zero, since absorbed acetone goes on to form the condensation/dehydration products. A two-step kinetic scheme is proposed to account for the reactions of acetone in sulfuric acid. By fitting the data to the model predictions, the Henry's law solubility constants and the reaction rate constants may be estimated.

Seasonal cycles of biogenic volatile organic compound fluxes and concentrations in a California citrus orchard

“…The good correlation of acetaldehyde vs. acetone concentrations (slope = 1.1, R 2 = 0.8) confirms a similar origin of these compounds, as previously observed (Karl et al, 2003;Schade and Goldstein, 2002). The physicochemical properties of these two organic compounds differ in terms of the reactivity in the liquid phase thus affecting their solubilities and Henry's law constants (Noziere and Riemer, 2003), with acetone being less reactive than acetaldeyde (Duncan et al, 1999). Acetaldehyde and acetone were also measured in concentrations up to 15 ppb during the flowering period (Fig.…”

Dissolution, speciation, and reaction of acetaldehyde in cold sulfuric acid

“…Second, with the exception of the most concentrated acid, acetaldehyde is considerably less soluble in mildly acidic solutions than in pure water (extrapolated from measurements made between 0 and 25°C [ Benkelberg et al , 1995]). This result is in direct contrast to other compounds, e.g., acetone [ Duncan et al , 1999; Imamura and Akiyoshi , 2000; Kane et al , 1999; Klassen et al , 1999] and methanol [ Iraci et al , 2002; Kane and Leu , 2001], which exhibit increased solubility in cold acid solutions relative to water, even at <50 wt% H 2 SO 4 . However, decreased solubility in mildly acidic solutions versus water has been observed for some organic compounds (e.g., cyclohexane, isobutane, 2,5‐pentanedione) at room temperature.…”

Products and Mechanisms of Ozone Reactions with Oleic Acid for Aerosol Particles Having Core−Shell Morphologies

“…We speculate that long-chain multifunctional organic molecules result and that these high molecular weight products have low vapor pressures and therefore remain in the condensed phase. Although the formation of high molecular weight compounds such as humic acids 52 has been suggested for reactions of organic molecules in acidic medium, 53 our suggestion of these molecules in the ozonolysis reactions of organic aerosol particles is new.…”