Chemistry Of Acetone Research Articles

The chemistry of acetone at extreme conditions by density functional molecular dynamics simulations

Density functional molecular dynamics simulations have been performed in the NVT ensemble (moles (N), volume (V) and temperature (T)) on a system formed by ten acetone molecules at a temperature of 2000 K and density ρ = 1.322 g cm(-3). These conditions resemble closely those realized at the interface of an acetone vapor bubble in the early stages of supercompression experiments and result in an average pressure of 5 GPa. Two relevant reactive events occur during the simulation: the condensation of two acetone molecules to give hexane-2,5-dione and dihydrogen and the isomerization to the enolic propen-2-ol form. The mechanisms of these events are discussed in detail.

Acetone Chemistry on Oxidized and Reduced TiO2(110)

The chemistry of acetone on the oxidized and reduced surfaces of TiO2(110) was examined using temperature-programmed desorption (TPD) and high-resolution electron energy-loss spectroscopy (HREELS). The reduced surface was prepared with about 7% oxygen vacancy sites by annealing in ultrahigh vacuum (UHV) at 850 K, and the oxidized surface was prepared by exposure of the reduced surface to molecular oxygen at 95 K followed by heating the surface to a variety of temperatures between 200 and 500 K. Acetone adsorbs molecularly on the reduced surface with no evidence for either decomposition or preferential binding at vacancy sites. On the basis of HREELS, the majority of acetone molecules adsorbed in an η1 configuration at Ti4+ sites through interaction of lone-pair electrons on the carbonyl oxygen atom. Repulsive acetone−acetone interactions shift the desorption peak from 345 K at low coverage to 175 K as the first layer saturates with a coverage of ∼1 ML. In contrast, about 7% of the acetone adlayer decomposes when the surface is pretreated with molecular oxygen. Acetate is among the detected decomposition products but only comprises about one-third of the amount of decomposed acetone, and its yield depends on the temperature at which the O2-exposed surface was preheated to prior to acetone adsorption. Aside from the small level of irreversible decomposition, about 0.25 ML of acetone is stabilized to 375 K by coadsorbed oxygen. These acetone species exhibit an HREELS spectrum unlike that of η1-acetone or of any other species proposed to exist from the interaction of acetone with TiO2 powders. On the basis of the presence of extensive 16O/18O exchange between acetone and coadsorbed oxygen in the 375 K acetone TPD state, it is proposed that an acetone−oxygen complex forms on the TiO2(110) surface through nucleophilic attack of oxygen on the carbonyl carbon atom of acetone. The reaction between acetone and oxygen is initiated at temperatures as low as 135 K based on HREELS. The major decomposition pathway of the acetone−oxygen complex liberates acetone in the 375 K TPD peak. This species may be a key intermediate in acetone thermal and photolytic chemistry on TiO2 surfaces.

Detection of methyl isocyanate in air with the use of hand-held ion mobility spectrometers

Methyl isocyanate (MIC), CH3NCO, is a relatively simple molecule, but ion mobility spectra derived from studies of this molecule are complex. MIC is known to polymerize, which would lead one to expect that proton-bound monomer, proton-bound dimer, and even larger proton-bound ions could be observed. Indeed, this is the case, and a number of other species can also be observed. In this case headspace above a relatively fresh (i.e., recently purchased) MIC sample was analyzed, and numerous peaks were observed in a single spectrum. Peak identities and intensities were, of course, concentration dependent. Over a range of concentrations, as many as 16 peaks were observed. IMS systems used for these studies included chemical agent monitors (both water and acetone chemistry), a miniaturized hand-held IMS device (Mini-IMS) and an IMS-MS/MS instrument. Although ion mobility spectra are complex, it has been shown that hand-held IMS devices can be useful for detecting or monitoring airborne concentrations of this toxic and hazardous compound. IMS/MS/MS experimentation yielded some mass identifications, and possible ion compositions are proposed. Reduced ion mobility of H+(CH3NCO)(H2O)n was tentatively determined to be 1.91±0.02 cm2 / V s. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 285–294, 1997