Chemistry at and near the surface of liquid sulfuric acid: A kinetic, thermodynamic, and mechanistic analysis of heterogeneous reactions of acetone
- Univ. of Minnesota, MN (United States). Dept. of Chemistry
The interactions of gas-phase acetone with liquid sulfuric acid solutions are described. The solutions were prepared as 0.05--0.10 {micro}m thick films deposited on single-crystal metal substrates. Experiments were carried out over broad ranges of acid composition (70 {minus} >96 wt % H{sub 2}SO{sub 4}), temperature (180--220 K), and acetone pressure (10{sup {minus}7}{minus}10{sup {minus}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 % H{sub 2}SO{sub 4}, protonated acetone undergoes a self-condensation/dehydration reaction to form mesityl oxide. In films that contain 85 wt % or more H{sub 2}SO{sub 4}, a second reaction sequence occurs, ultimately resulting in the formation of tremethylbenzene. The uptake probability measurements are consistent with the infrared data. In 70 wt % H{sub 2}SO{sub 4}, 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 % H{sub 2}SO{sub 4} 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 {minus}66 kJ mol{sup {minus}1} and {minus}249 J mol{sup {minus}1} K{sup {minus}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.
- OSTI ID:
- 696650
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 34; Other Information: PBD: 26 Aug 1999
- Country of Publication:
- United States
- Language:
- English
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