Solubility of acetic acid and trifluoroacetic acid in low-temperature (207-245 k) sulfuric acid solutions: implications for the upper troposphere and lower stratosphere

The solubility of gas-phase acetic acid (CH(3)COOH, HAc) and trifluoroacetic acid (CF(3)COOH, TFA) in aqueous sulfuric acid solutions was measured in a Knudsen cell reactor over ranges of temperature (207-245 K) and acid composition (40-75 wt %, H(2)SO(4)). For both HAc and TFA, the effective Henry's law coefficient, H*, is inversely dependent on temperature. Measured values of H* for TFA range from 1.7 × 10(3) M atm(-1) in 75.0 wt % H(2)SO(4) at 242.5 K to 3.6 × 10(8) M atm(-1) in 40.7 wt % H(2)SO(4) at 207.8 K. Measured values of H* for HAc range from 2.2 × 10(5) M atm(-1) in 57.8 wt % H(2)SO(4) at 245.0 K to 3.8 × 10(8) M atm(-1) in 74.4 wt % H(2)SO(4) at 219.6 K. The solubility of HAc increases with increasing H(2)SO(4) concentration and is higher in strong sulfuric acid than in water. In contrast, the solubility of TFA decreases with increasing sulfuric acid concentration. The equilibrium concentration of HAc in UT/LS aerosol particles is estimated from our measurements and is found to be up to several orders of magnitude higher than those determined for common alcohols and small carbonyl compounds. On the basis of our measured solubility, we determine that HAc in the upper troposphere undergoes aerosol partitioning, though the role of H(2)SO(4) aerosol particles as a sink for HAc in the upper troposphere and lower stratosphere will only be discernible under high atmospheric sulfate perturbations.     

Adsorption and hydrolysis of alcohols and carbonyls on ice at temperatures of the upper troposphere

The uptake of gaseous ethanol, 1,1,1-trifluoroethanol, acetone, chloral (CCl(3)CHO), and fluoral (CF(3)CHO) on ice films has been investigated using a coated-wall flow tube at temperatures 208-228 K corresponding to the upper troposphere (UT), with a mass spectrometric measurement of gas concentration. The uptake was largely reversible and followed Langmuir-type kinetic behavior, i.e., surface coverage increased with the trace gas concentration approaching a maximum surface coverage at a gas phase concentration of N(max) ～ (2-4) × 10(14) molecules cm(-3), corresponding to a surface coverage of ～30% of a monolayer (ML). The equilibrium partition coefficients, K(LinC), were obtained from the experimental data by analysis using the simple Langmuir model for specific conditions of temperature and concentration. The analysis showed that the K(LinC) depend only weakly on surface coverages. The following expressions described the temperature dependence of the partition coefficients (K(LinC)) in centimeters, at low coverage for ethanol, trifluoroethanol, acetone, chloral, and fluoral: K(LinC) = 1.36 × 10(-11)?exp(5573.5/T), K(LinC) = 3.74 × 10(-12)?exp(6427/T), K(LinC) = 3.04 × 10(-9)?exp(4625/T), K(LinC) = 7.52 × 10(-4)?exp(2069/T), and K(LinC) = 1.06 × 10(-2)?exp(904/T). For acetone and ethanol the enthalpies and entropies of adsorption derived from all available data showed systematic temperature dependence, which is attributed to temperature dependent surface modifications, e.g., QLL formation. For chloral and fluoral, there was an irreversible component of uptake, which was attributed to hydrate formation on the surface. Rate constants for these surface reactions derived using a Langmuir-Hinshelwood mechanism are reported.     

Diffusion of HDO in pure and acid-doped ice films

In these experiments, a few bilayers of D(2)O were vapor-deposited on a pure crystalline H(2)O ice film or an ice film doped with a small amount of HCl. Upon deposition, H/D isotopic exchange quickly converted the D(2)O layer into an HDO-rich mixture layer. Infrared absorption spectroscopy followed the changes of the HDO from the initial HDO mixture layer to HDO isolated in the H(2)O ice film. This was possible because isolated HDO in H(2)O ice has a unique, sharp peak in the O-D stretch region that can be distinguished from the broad peak due to the initial HDO mixture layer. The absorbance of isolated HDO displayed first-order kinetics and was attributed to diffusion of HDO from the HDO-rich mixture layer into the underlying H(2)O ice film. While negligible diffusion was observed for pure ice films and for ice films with HCl concentrations up to 1 x 10(-4) mole fraction, diffusion of HDO occurred for higher concentrations of (2-20) x 10(-4) mole fraction HCl with a concentration-independent rate constant. The diffusion under these conditions followed Arrhenius behavior for T = 135-145 K yielding E(a) = 25 +/- 5 kJ/mol. The mechanism for the HDO diffusion involves either (i) molecular self-diffusion or (ii) long-range H/D diffusion by a series of multiple proton hop and orientational turn steps. While these spectroscopic results compare favorably with recent studies of molecular self-diffusion in low-temperature ice films, the diffusion results from all the ice film studies at low temperatures (ca. T < 170 K) differ from earlier bulk ice studies at higher temperatures (ca. T > 220 K). A comparison and discussion of the various diffusion studies are included in this report.     

Kinetics of ClONO(2) reactive uptake on ice surfaces at temperatures of the upper troposphere

The reactive uptake kinetics of ClONO(2) on pure and doped water-ice surfaces have been studied using a coated wall flow tube reactor coupled to an electron impact mass spectrometer. Experiments have been conducted on frozen film ice surfaces in the temperature range 208-228 K with P((ClONO)(2)) < or = 10(-6) Torr. The uptake coefficient (gamma) of ClONO(2) on pure ice was time dependent with a maximum value of gamma(max) approximately 0.1. On HNO(3)-doped ice at 218 K the gamma(max) was 0.02. HOCl formation was detected in both experiments. On HCl-doped ice, uptake was gas-phase diffusion limited (gamma > 0.1) and gas-phase Cl(2) was formed. The uptake of HCl on ice continuously doped with HNO(3) was reversible such that there was no net uptake of HCl once the equilibrium surface coverage was established. The data were well described by a single site 2-species competitive Langmuir adsorption isotherm. The surface coverage of HCl on HNO(3)-doped ice was an order of magnitude lower than on bare ice for a given temperature and P(HCl). ClONO(2) uptake on this HCl/HNO(3)-doped ice was studied as a function of P(HCl). gamma(max) was no longer gas-phase diffusion limited and was found to be linearly dependent on the surface concentration of HCl. Under conditions of low HCl surface concentration, hydrolysis of ClONO(2) and reaction with HCl were competing such that both Cl(2) and HOCl were formed. A numerical model was used to simulate the experimental results and to aid in the parametrization of ClONO(2) reactivity on cirrus ice clouds in the upper troposphere.     

Thermal evolution of acetic acid nanodeposits over 123-180 K on noncrystalline ice and polycrystalline ice studied by FTIR reflection-absorption spectroscopy: hydrogen-bonding interactions in acetic acid and between acetic acid and ice

Acetic acid vapor-deposited on ultrathin noncrystalline ice (NCI) and polycrystalline ice (PCI) films (less than 6 nm thick) under ultrahigh vacuum conditions has been investigated by using Fourier Transform Infrared Reflection-Absorption Spectroscopy. Pristine acetic acid deposited at 123 K (on a copper support) appears as an amorphous solid, which undergoes an irreversible phase transformation to a more structurally ordered (polycrystalline) form upon annealing to 153 K. Acetic acid is found to adsorb on NCI and PCI films initially through hydrogen bonding between C=O and dangling OH (of ice), followed by the formation of multilayers at 123 K. Thermal evolution studies of a low exposure of acetic acid on the ultrathin NCI and PCI films show that acetic acid undergoes coevaporation with water likely as an acetic acid hydrate at 155 K, which continues until the entire ice film has been exhausted at 165 K. Above 165 K, the remaining acetic acid solid appears to evaporate without undergoing the phase transformation, in contrast to the case of a high acetic acid exposure. Coevaporation of acetic acid with water is also found to proceed at a faster rate than the subsequent evaporation of acetic acid, which is consistent with the weaker interactions observed in the H-bonded acetic acid hydrate than that in acetic acid solid.     

Uptake measurements of ethanol on ice surfaces and on supercooled aqueous solutions doped with nitric acid between 213 and 243 K

Uptake of ethanol either on pure frozen ice surfaces or supercooled solutions doped with HNO3 (0.63 and 2.49 wt %) has been investigated using a coated wall flow tube coupled to a mass spectrometric detection. The experiments were conducted over the temperature range of 213-243 K. Uptake of ethanol on these surfaces was always found to be totally reversible whatever were the experimental conditions. The number of ethanol molecules adsorbed per surface unit was conventionally plotted as a function of ethanol concentration in the gas phase and subsequently analyzed using Langmuir's model. The amount of ethanol molecules taken up on nitric acid doped-ice surfaces was found to increase largely with increasing nitric acid concentrations. For example at 223 K, and for an ethanol gas-phase concentration of 1x10(13) molecules cm3, the number of adsorbed molecules are (in units of molecules cm-2): approximately 1.3x10(14) on pure ice; approximately 1.4x10(15) on ice doped with HNO3 0.63 wt %; approximately 7.5x10(15) on ice doped with HNO3, 2.49 wt %, i.e. 60 times larger than on pure ice. Since, according to the shape of the isotherms, the adsorption did not proceed beyond monolayer coverage, the enormous increase of ethanol uptake was explained by considering its dissolution in either a supercooled liquid layer (T<230 K) or a liquid solution (T>230 K). The formation of both was indeed favored by the presence of the HNO3. Our experimental results suggest that the amount of ethanol dissolved in such supercooled solutions follows Henry's law and that the Henry's law constants at low temperatures, i.e., 223-243 K, can be estimated by extrapolation from higher temperatures. Such supercooled solutions which exist in the troposphere either in deep convective clouds or in mixed clouds for temperature above 233 K, might be responsible for the scavenging of large amounts of soluble species, such as nitric and sulfuric acids, oxygenated VOCs including alcohols, carboxylic acids, and formaldehyde.     

Infrared spectroscopy of acetic acid and formic acid aerosols: pure and compound acid/ice particles

Acetic acid aerosol particles, formic acid aerosol particles and mixed acid/ice particles were generated in a collisional cooling cell at a temperature of 78 K and investigated using in situ rapid scan Fourier transform infrared spectroscopy. The infrared spectra reveal that the internal structure of the particles critically depends on the particle formation conditions and, especially for the mixed particles, on the composition. The acetic acid particles are likely to have only a partially crystalline structure whereas the formic acid particles are likely to have an overall crystalline structure. The existence of acid in the mixed acid/ice particles prevents the ice from crystallization even at low acid concentrations (less than 10%). Mid-infrared refractive index data were derived from the different particle spectra, which can be helpful for remote sensing of such systems.     

Adsorption of acetic acid on ice: experiments and molecular dynamics simulations

Adsorption study of acetic acid on ice surfaces was performed by combining experimental and theoretical approaches. The experiments were conducted between 193 and 223 K using a coated wall flow tube coupled to a mass spectrometric detection. Under our experimental conditions, acetic acid was mainly dimerized in the gas phase. The surface coverage increases with decreasing temperature and with increasing concentrations of acetic acid dimers. The obtained experimental surface coverages were fitted according to the BET theory in order to determine the enthalpy of adsorption deltaH(ads) and the mololayer capacity N(M(dimers)) of the acetic acid dimers on ice: deltaH(ads) = (-33.5 +/- 4.2) kJ mol(-1), N(M(dimers)) = (l1.27 +/- 0.25) x 10(14) dimers cm(-2). The adsorption characteristics of acetic acid on an ideal ice I(n)(0001) surface were also studied by means of classical molecular dynamics simulations in the same temperature range. The monolayer capacity, the configurations of the molecules in their adsorption sites, and the corresponding adsorption energies have been determined for both acetic acid monomers and dimers, and compared to the corresponding data obtained from the experiments. In addition, the theoretical results show that the interaction with the ice surface could be strong enough to break the acetic acid dimers that exist in the gas phase and leads to the stabilization of acetic acid monomers on ice.     

Electrochemical and XPS measurements on thin oxide films on zirconium

The potentiodynamic growth of thin oxide films on zirconium electrodes was investigated by coulometric and simultaneous impedance measurements, as a function of the electrode potential (0 V ⩽ E ⩽ 9 V), the pH (0 ⩽ pH ⩽ 14) and the surface preparation (electropolishing, etching and mechanical polishing). The initial film thickness d₀ is at least 4–6 nm; with increasing potential, the oxide grows irreversibly by 2.6 nm/V (pH 0.3) up to 3.2 nm/V (pH 14). In Cl⁻- and ClO⁻₄-containing solutions the oxide growth is limited by localized corrosion. The oxide behaves like a typical insulator with a donor concentration N_D < 10¹⁹ cm⁻³ and a dielectric constant D = 31. Below −0.5 V (vs. SHE) only, th film behaves like an n-type semiconductor with N_D ≈ 3 × 10¹⁹ cm⁻³. From photoelectrochemical measurements a direct and an indirect transition with band gap energies of E_g = 5 eV and E_g = 2.8 eV could be derived. Anodic electron-transfer reactions (ETRs) are blocked at the homogeneous oxide surface, but cathodic ETRs are possible at larger overvoltages. Near the flatband potential E_fb ≈ −1.3 ± 0.2 V (vs. SHE) hydrogen evolution takes place with a simultaneous increase of the capacity which may be attributed to hydrogen incorporation. With XPS measurements the stoichiometry of the oxide film was determined as ZrO₂ at all the pH values examined, but a thin outer layer contained some hydroxide. Components of the forming electrolyte could not be detected (sulphate, borate and perchlorate < 1%), but etching in HF caused accumulation of F⁻ at the inner boundary.     

Adsorption study of acetone on acid-doped ice surfaces between 203 and 233 K

Adsorption studies of acetone on pure ice surfaces obtained by water freezing or deposition or on frozen ice surfaces doped either with HNO3 or H2SO4 have been performed using a coated wall flow tube coupled to a mass spectrometric detection. The experiments were conducted over the temperature range 203-233 K and freezing solutions containing either H2SO4 (0.2 N) or HNO3 (0.2-3 N). Adsorption of acetone on these ice surfaces was always found to be totally reversible whatever were the experimental conditions. The number of acetone molecules adsorbed per ice surface unit N was conventionally plotted as a function of acetone concentration in the gas phase. For the same conditions, the amount of acetone molecules adsorbed on pure ice obtained by deposition are about 3-4 times higher than those measured on frozen ice films, H2SO4-doped ice surfaces lead to results comparable to those obtained on pure ice. On the contrary, N increases largely with increasing concentrations of nitric acid in ice surfaces, up to about 300 times under our experimental conditions and for temperatures ranging between 213 and 233 K. Finally, the results are discussed and used to reestimate the partitioning of acetone between the ice and gas phases in clouds of the upper troposphere.     

Oxidation of propane to acrylic acid and acetic acid over alkaline earth-doped Mo-V-Sb-Ox catalysts

Alkaline earth metal (Mg, Ca, Sr and Ba)-doped Mo-V-Sb-Ox catalysts, prepared by a dry-up method, have been investigated for their catalytic performance in the oxidation of propane under different reaction conditions. The catalysts have been characterized by N2 adsorption-desorption, temperature-programmed desorption (TPD) of NH3, SEM and XRD. Influence of water vapor on the catalytic performance, particularly on the selectivities to acetic acid and acrylic acid, has also been studied. The selectivity to acrylic acid was improved significantly by the doping of alkaline earth metals to Mo-V-Sb-Ox catalysts. The surface acidic sites of the catalyst decreased with the doping of the catalyst with alkaline earth metals, which ultimately was found to be beneficial for obtaining high selectivity to acrylic acid. The catalytic activity and product selectivities were found to be influenced by the reaction temperature, C3H8/O2 ratio and space velocity. A significant improvement in the selectivity to acrylic acid has also been observed by the addition of water vapor in the feed of propane and oxygen in the oxidation of propane.     

Kinetics of reaction between acetic acid and Ag2+ in nitric acid medium

The reaction kinetics between acetic acid and Ag²⁺ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H⁺, NO^?₃, and temperature on the reaction are investigated. The rate equation has been determined to be –dc(Ag²⁺)/dt = kc(Ag²⁺)c(HAc)c^?1(H⁺), where k = (610 ± 15) (mol/L)^?1 min^?1 with an activation energy of about (48. 8 ± 3.5) kJ mol^?1 when the reaction temperature is 25°C and the ionic strength is 4.0 mol L^?1. The reduction rate of Ag²⁺ increases with the increase in HAc concentration and/or temperature and the decrease in HNO₃ concentration. However, the effect of NO^?₃ concentrations within 0.5–2.5 mol L^?1 on the reaction rate is negligible. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 47–51, 2013     

Kinetic studies on vapor phase carbonylation of methanol to acetic acid over Rh/Ys catalyst

A novel catalyst Rh/Ys for the carbonylation of methanol to acetic acid with CH3I as the promoter shows excellent activity and selectivity.The reaction is kinetically controlled.The reaction rate is in proportion to the concentration of Rh and CH3I but has nothing to do with those of CH3OHH and CO.The surface active energy is Ea ~51.02 kJ/mol.A mechanism is also proposed.     

Ammonia adsorption on and diffusion into thin ice films grown on Pt(111)

Ammonia adsorption on and diffusion into thin ice films grown on a Pt(111) surface were studied using Fourier transform infrared spectroscopy (FTIR) and thermal desorption spectroscopy. After exposing the crystalline ice film to ammonia molecules at 45 K (ammonia/ice film), we have detected an intriguing feature at 1470 cm(-1) in the FTIR spectra, which is derived from the adsorption of ammonia on the ice with a characteristic structure which appears in thin film range. The peak intensity of this feature decreases gradually as the thickness of the substrate ice increases. In addition, we have detected a feature at 1260 cm(-1) which appears after annealing the ammonia/ice film. The feature corresponds to the ammonia molecules which reach the ice/Pt(111) interface through the ice film. Intriguingly, the intensity of this feature decreases with the ice thickness and there is a linear relation of the peak intensity of the features at 1470 and 1260 cm(-1). We propose a model in which the solubility of the ammonia molecules is much higher for the thin ice film than that for the ideal ice.     

Determination of chloride and sulfate in semiconductor-grade etchants comprised of acetic acid,nitric acid and phosphoric acid

The variable-capacity Dionex Cryptand A1 column was used for the determination of low-ppm levels of chloride and sulfate in etchants comprised of acetic acid, nitric acid and phosphoric acid. All possible ratios of the three acids could be analyzed for chloride and sulfate, if the samples were first diluted 1:100. However, a suitable eluent program was found to be needed for each mixture. A proprietary formulation was chosen to undergo this suitability determination. The resulting gradient was 10 mM KOH with a step to 30 mM NaOH at 15 min, flow-rate=0.5 ml/min; column temperature=29 degrees C; sample loop=7.5 microl. Under these conditions, a low-ppm calibration study (using the proprietary mix as the matrix) was performed and the associated prediction intervals were determined. At 50 ppm (in the original etchant), the +/- prediction interval was +/- 7 ppm for chloride and +/- 20 ppm for sulfate, both at the 95% confidence level. This step gradient was found to be a good starting place for separating the five components in all other ratios of these three acids.     

Preparation and photochromism of Keggin-type molybdphosphoric acid/silica mesoporous composite thin films

Using tetraethoxysilane and 3-aminopropyltriethoxysilane as the silica sources, amino-functionalized organic/inorganic hybrid mesoporous silica thin films with 2-dimensional hexagonal structure have been synthesized by evaporation induced self-assembly process in the presence of cetyltrimethyl ammonium bromide templates under acid conditions. The Keggin-type molybdphosphoric acid (PMo) is incorporated into the mesoporous silica thin films with amino-groups by wetness impregnation, and the PMo/silica mesoporous composite thin films are obtained. The results of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared (FTIR) spectra indicate the PMo molecules maintain Keggin structure and are homogeneously distributed inside mesopores. The composite thin films possess excellent reversible photochromic properties, and change from colorless to blue under ultraviolet irradiation. The photochromic mechanism of the composite thin films is studied by ultraviolet-visible (UV-vis), electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) spectra. It is shown that intervalence charge transfer (IVCT) and ligand-to-metal charge transfer (LMCT) are the main reasons of photochromism. PMo anions interact strongly with amino-groups of the mesoporous suface via hydrogen bond and electrostatic force. After ultraviolet irradiation, the charge transfer occurs by reduction of heteropolyanions accompanying the formation of heteropolyblues with multivalence Mo(VI, V), and the bleaching process of composite thin films is closely related to the presence of oxygen.     

Optical band gap and conductivity measurements of polypyrrole-chitosan composite thin films

Electrical conductivity and optical properties of polypyrrole-chitosan（PPy-CHI） conducting polymer composites have been investigated to determine the optical transition characteristics and energy band gap of composite films.The two electrode method and I-V characteristic technique were used to measure the conductivity of the PPy-CHI thin films,and the optical band gap was obtained from their ultraviolet absorption edges.Depending upon experimental parameter,the optical band gap（E_g） was found within 1.30-2.32 eV as estimated from optical absorption data.The band gap of the composite films decreased as the CHI content increased.The room temperature electrical conductivity of PPy-CHI thin films was found in the range of 5.84×10^-7-15.25×10^-7 S·cm^-1 depending on the chitosan content.The thermogravimetry analysis（TGA） showed that the CHI can improve the thermal stability of PPy-CHI composite films.     

Reactive uptake of acetic acid on calcite and nitric acid reacted calcite aerosol in an environmental reaction chamber

The heterogeneous chemistry of gas-phase acetic acid with CaCO(3)(calcite) aerosol was studied under varying conditions of relative humidity (RH) in an environmental reaction chamber. Infrared spectroscopy showed the loss of gas-phase reactant and the appearance of a gaseous product species, CO(2). The acetic acid is observed to adsorb onto the calcite aerosol through both a fast and a slow uptake channel. While the fast channel is relatively independent of RH, the slow channel exhibits enhanced uptake and reaction as the RH is increased. In additional experiments, the calcite aerosol was exposed to both nitric and acetic acids in the presence of water vapor. The rapid conversion of the particulate carbonate to nitrate and subsequent deliquescence significantly enhances the uptake and reaction of acetic acid. These results suggest a possible mechanism for observed correlations between particulate nitrate and organic acids in the atmosphere. Calcium rich mineral dust may be an important sink for simple organic acids.     

New possibilities in nitration with a mixture of nitric acid and acetic anhydride

Summary A mixture of nitric acid and acetic anhydride with a nitric acid content of 80 moles per cent has a considerably more powerful nitrating action than a mixture with 35–50 moles per cent of nitric acid. It is desirable to use this mixture for the nitration of furans with low sensitivity to electrophilic attack.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 103–110, January, 1965