An experimental study of the reactivity of the hydroxide anion in the gas phase at room temperature, and its perturbation by hydration

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Flowing afterglow measurements of rate constants and ionic products are reported which explore the influence of step-wise hydration on the reactivity of the hydroxide anion in the gas phase at 296 ± 2 K. Rate constants have been measured for the reactions of OH−•(H2O)n and/or OD−•(D2O)n with CO2, SO2, CH3OH, C2H5OH, C2H2, CH3COCH3, CH3NO2, and HCN, in most instances for values of n from 0 to 3. The reactions with CO2 and SO2 involve ligand addition or exchange and the results of their study corroborate earlier measurements. The remaining reactions proceed by proton transfer. For these reactions the results establish trends in reactivity as a function of step-wise hydration when relative acidity is preserved and when a reversal occurs in the relative acidity upon hydration. The fast hydrated acid–base reactions were observed to establish interesting hydrated product ions many of which underwent secondary reactions involving the exchange of H2O or D2O for the reagent molecule.

“…This is in contrast with the observations for reaction [5] between hydrated hydroxide ions, OH-. (H?O),,, and COz in the gas phase which indicate reaction on essentially every collision.…”

Section: -8contrasting

confidence: 96%

Section: Co? So?supporting

confidence: 56%

An experimental study of the influence of hydration on the reactivity of the hydroxide anion in the gas phase at room temperature

Raksit¹,

Böhme²

1983

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“…The rate and equilibrium constants measured in this study for acid-base reactions of types [I] and [2] are summarized in Tables 1 and 2. The sources of uncertainty have been described previously (3, 4).…”

Section: Resultsmentioning

confidence: 99%

“…For example, gas-phase measurements of rate and equilibrium constants for solvent-free acid-base reactions of type [ll [I] B-+ AH e A-+ BH and solvated acid-base reactions of type [2] [2] B-.S, + AH * A-.S, + BH have vrovided both a measure of the absolute intrinsic reactivity and relative intrinsic basicity of anions as well as an indication of their perturbation by step-wise solvation. This has been illustrated by results obtained recently in our laboratory using the flowing afterglow technique for reactions of the hydroxide ion, an important base in solution (l,2).…”

Section: Introductionmentioning

confidence: 99%

An experimental study of the reactivity and relative basicity of the methoxide anion in the gas phase at room temperature, and their perturbation by methanol solvation

Mackay¹,

Rakshit²,

Böhme³

1982

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Flowing afterglow measurements at 296 ± 2 K are reported which explore three aspects of the gas-phase acid–base chemistry of the methoxide anion. Firstly, the intrinsic reactivity of this ion has been determined from measurements of rate constants for solvent-free proton-transfer reactions with molecules more acidic than methanol including CH2=C=CH2, C6H5CH3, C2H5OH, C2H2, CH3CN, CH3COCH3, CH3CHO, CH3NO2, and HCN. Secondly, equilibrium constant measurements have been performed for solvent-free proton-transfer reactions which provide a gas-phase scale of acidities for these molecules relative to the acidity of methanol. Finally, rate constants were measured for the reactions of these acids with methoxide ions solvated with up to three molecules of methanol. The results establish trends in reactivity as a function of step–wise solvation when relative acidity is preserved and when a reversal occurs in the relative acidity upon solvation.

“…OH-+ CH3C2H * C3H3-+ H 2 0 for which these were the only reaction channels observed (6,7), and the rate constants were large, (1.4 + 0.4) x and (1.7 rt 0.3) x lop9 cm3 molecule-I s-I, respectively. In fact, the rate constants for proton transfer reactions are generally found to be well-approximated by the AADO ion-molecule collision theory of Su,Su,and Bowers (8).…”

Section: [6]mentioning

confidence: 94%

Hydrocarbon ions in fuel-rich, CH₄–C₂H₂–O₂ flames as a probe for the initiation of soot: interpretation of the ion chemistry

Goodings¹,

Tanner²,

Böhme³

1982

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. Can. J. Chem. 60,2766Chem. 60, (1982.The ion chemistry is discussed for fuel-rich, nearly sooting, methane-oxygen flames at atmospheric pressure with added acetylene. Different types of ion-molecule reactions, both positive and negative, which can contribute through chemical ionization (CI) processes are summarized including their dependence on temperature, pressure, and equivalence ratio 4. Extensive data were presented previously involving ion concentration profiles measured with a mass spectrometer as afunction of distance along the axis of conical flames. An understanding of the dominant CI processes provides insight into the early chemical stage of soot formation associated with the flame reaction zone. The negative ion profiles show moderately unsaturated hydrocarbon ions upstream formed by proton transfer followed by progressive dehydrogenation; the highly unsaturated, carbonaceous ions observed downstream appear to arise by two-and three-body electron attachment, charge transfer, and H-atom stripping. The negative hydrocarbon ions can all be explained in terms of polyacetylene derivatives. The same build-up of carbonaceous species downstream is evident from the positive ion profiles. A major role is ascribed to proton transfer reactions with lesser contributions from charge transfer and ion-molecule condensation; three-body association is probably insignificant. Experiments with added acetylene indicate extensive fuel pyrolysis early in the reaction zone. There is no evidence that an ionic mechanism is dominant in forming soot precursors compared with neutral condensation reactions. Because of complexities in the positive ion chemistry, the negative ions appear t o provide the more straightforward probe of the underlying neutral chemistry. probablement pas importante. Les experiences conduites avec de I'acCtylkne ajoute indiquent une abondante pyrolyse du carburant se produisant trts tBt dans la zone de reaction. 11 n'y a pas de preuve d'un mecanisme ionique dominant lors de la formation des precurseurs de suie par comparaison avec les reactions neutres de condensation. A cause de la complexite de la chimie de I'ion positif, les ions ntgatifs apparaissent comme les meilleures guides pour Ctudier la chimie neutre sous jacente.[Traduit par le journal] Introduction reaction chemistry. It is hoped that an understandIn a recent article (I), here designated as paper I, ing of the kinetics and energetics of the ionwe reported experimental data on the axial distri-molecule reactions responsible for the observed bution of both positive and negative ions monitored flame-ion distribution will lead t o further insights directly through the reaction zones of fuel-rich into the initial chemistry leading to Soot. CH4-C2H2-O2 flames at atmospheric pressure.The types of reactions commonly thought to The natural hydrocarbon ions c,H,? were studied dominate the ion chemistry of flames have been as a probe of the early chemical stages of soot conveniently classified. Those processes which formation. In that paper, the ph...