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Weak Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of N 2 O 5 in NaCl-Water Solutions
Ist Teil von
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 2023-02, Vol.127 (7), p.1675-1685
Ort / Verlag
United States
Erscheinungsjahr
2023
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
We have measured the temperature dependence of the ClNO
product yield in competition with hydrolysis following N
O
uptake to aqueous NaCl solutions. For NaCl-D
O solutions spanning 0.0054-0.21 M, the ClNO
product yield decreases on average by only 4 ± 3% from 5 to 25 °C. Less reproducible measurements at 0.54-2.4 M NaCl also fall within this range. The ratio of the rate constants for chlorination and hydrolysis of N
O
in D
O is determined on average to be 1150 ± 90 at 25 °C up to 0.21 M NaCl, favoring chlorination. This ratio is observed to decrease significantly at the two highest concentrations. An Arrhenius analysis reveals that the activation energy for hydrolysis is just 3.0 ± 1.5 kJ/mol larger than for chlorination up to 0.21 M, indicating that Cl
and D
O attack on N
O
has similar energetic barriers despite the differences in charge and complexity of these reactants. In combination with the measured preexponential ratio favoring chlorination of 300
, we conclude that the strong preference of N
O
to undergo chlorination over hydrolysis is driven by dynamic and entropic, rather than enthalpic, factors. Molecular dynamics simulations elucidate the distinct solvation between strongly hydrated Cl
and the hydrophobically solvated N
O
. Combining this molecular picture with the Arrhenius analysis implicates the role of water in mediating interactions between such distinctly solvated species and suggests a role for diffusion limitations on the chlorination reaction.