Reactions of N₂O₅ with Salty and Surfactant-Coated Glycerol: Interfacial Conversion of Br^– to Br₂ Mediated by Alkylammonium Cations

Abstract

Gas-liquid scattering and product-yield experiments are used to investigate reactions of NO with glycerol containing Br and surfactant ions. NO oxidizes Br to Br for every solution tested: 2.7 M NaBr, 0.03 M tetrahexylammonium bromide (THABr), 0.03 M THABr + 0.5 M NaBr, 0.03 M THABr + 0.5 M NaCl, 0.03 M THABr + 0.01 M sodium dodecyl sulfate (SDS), and 0.01 M cetyltrimethylammonium bromide (CTABr). NO also reacts with glycerol itself to produce mono- and dinitroglycerin. Surface tension measurements indicate that 0.03 M THABr and 2.7 M NaBr have similar interfacial Br concentrations, though their bulk Br concentrations differ by 90-fold. We find that twice as much Br is produced in the presence of THA, implying that the conversion of Br to Br is initiated at the interface, perhaps mediated by the charged, hydrophobic pocket within the surface THA cation. The addition of 0.5 M NaBr, 0.5 M NaCl, or 0.01 M SDS to 0.03 M THABr lowers the Br production rate by 23%, 63%, and 67% of the THABr value, respectively. When CTA is substituted for THA, Br production drops to 12% of the THABr value. The generation of Br under such different conditions implies that trace amounts of surface-active alkylammonium ions can catalyze interfacial NO reactions, even when salts and other surfactants are present.

Heterogeneous N2O5 Uptake During Winter: Aircraft Measurements During the 2015 WINTER Campaign and Critical Evaluation of Current Parameterizations

“…While one recent study has shown that cationic surfactants can enhance the rate of N 2 O 5 bulk‐phase reaction by facilitating surface reactions (Shaloski et al, ), the majority of previous laboratory studies have found that the presence of organics suppresses γ (N 2 O 5 ) relative to pure inorganic salts. The magnitude of suppression, however, is strongly dependent on the organic composition (e.g., Griffiths et al, ; Gross et al, ), particle phase state (e.g., Thornton et al, ), and the presence of surfactants (e.g., Cosman et al, , and references therein), which are controlled by factors such as RH, temperature, and molecular structure and composition.…”

“…Treating organics as a coating with the other three parameterizations improves the median percent difference but cannot reproduce the full range in WINTER values. Both underprediction and overprediction could result from a number of factors including incorrect estimation of the coating thickness, bulk‐phase diffusion and solubility rates, or an enhancement from organics by facilitating surface reactions (Shaloski et al, ). Similar to WINTER, results from three previous field studies found that the simplified resistor framework generally underpredicted γ (N 2 O 5 ), likely due to an overprediction of the organic suppression effect (Morgan et al, ; Phillips et al, ), but improved agreement relative to the inorganic‐only parameterizations (Chang et al, ).…”

When Liquid Rays Become Gas Rays: Can Evaporation Ever Be Non-Maxwellian?

“…Separate studies provide insights into the mechanism of dissolution and reaction. [39,45,46]. In all three cases, the product DCl or Br 2 evaporates in a Maxwellian distribution at the temperature of the liquid.…”

“…During 30 years of observation, we have monitored the vacuum evaporation of liquids such as glycerol, ethylene glycol, alkanes and aromatics, fluorinated ethers, and water from sulfuric acid and pure and salty water itself [39][40][41][42][43]. [39,40,42,[44][45][46][47][48]. We observed Maxwellian speed distributions in every case (except when the vapor pressure is so high that the gas expands supersonically [41,49]).…”

Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone

“…TBA exhibits also a strong ion-pairing capacity, which makes TBA ions important in various areas of chemistry, e.g., in phase-transfer catalysis, where relatively hydrophobic cations are used for precipitating large anions . Several studies have addressed the interfacial properties of TBA containing iodide solutions (including mixtures with bromide) with VUV photoemission. − Also molecular beam scattering experiments of N 2 O 5 interacting with a liquid jet containing tetraalkylammonium surfactants indicated interactions between the positively charged surfactant and reactants or products, also depending on the solvent. , Overall, the details of how charged surfactant ions affect the halide ions, their reactivity, and potentially also reaction products have remained open.…”