630-13-7Relevant articles and documents
Kinetics of a Criegee intermediate that would survive high humidity and may oxidize atmospheric SO2
Huang, Hao-Li,Chao, Wen,Lin, Jim Jr-Min
, p. 10857 - 10862 (2015/09/15)
Criegee intermediates are thought to play a role in atmospheric chemistry, in particular, the oxidation of SO2, which produces SO3 and subsequently H2SO04, an important constituent of aerosols and acid rain. However, the impact of such oxidation reactions is affected by the reactions of Criegee intermediates with water vapor, because of high water concentrations in the troposphere. In this work, the kinetics of the reactions of dimethyl substituted Criegee intermediate (CH3)2 COO with water vapor and with SO2 were directly measured via UV absorption of (CH3)2COO under near-atmospheric conditions. The results indicate that (i) the water reaction with (CH3)2 COO is not fast enough (kH2O -16 cm3s-1) to consume atmospheric (CH3)2COO significantly and (ii) (CH3)2COO reacts with SO2 at a near-gas-kinetic-limit rate (kSO2 = 1.3 × 10-10 cm3s-1). These observations imply a significant fraction of atmospheric (CH3)2 COO may survive under humid conditions and react with SO2, very different from the case of the simplest Criegee intermediate CH2OO, in which the reaction with water dimer predominates in the CH2OO decay under typical tropospheric conditions. In addition, a significant pressure dependence was observed for the reaction of (CH3)2COO with SO2, suggesting the use of low pressure rate may underestimate the impact of this reaction. This work demonstrates that the reactivity of a Criegee intermediate toward water vapor strongly depends on its structure, which will influence the main decay pathways and steady-state concentrations for various Criegee intermediates in the atmosphere.
Reactions of gaseous, halogenated propene radical cations with ammonia: A study of the mechanism by Fourier transform ion cyclotron resonance
Buechner, Michael,Nixdorf, Andreas,Gruetzmacher, Hans-Friedrich
, p. 1799 - 1809 (2007/10/03)
The gas-phase ion-molecule reactions of the radical cations of 2-chloropropene (1+.), 2-bromopropene (2+.), and 2-iodopropene (3+.), as well as of the corresponding three 3,3,3-trifluoropropenes (4+.- 6+.) with ammonia have been studied by FT-ICR mass spectrometry complemented by ab initio calculations of the reaction thermochemistry. In all cases a deprotonation of the 2-halopropene radical cations by ammonia is distinctly exothermic. In spite of this, the substitution of the halo substituent by NH3 is the main reaction pathway for 1+. and 2+. and is still competing for the slowly reacting iodo derivative 3+.. In the latter case deprotonation generates not only NH(4/+), but also the proton-bridged dimer [H3N·· H+··NH3]. These effects prove that the first addition step of the substitution by an addition-elimination mechanism of the haloalkene radical cations can compete effectively with exothermic deprotonation and occurs without noticeable activation energy. In fact it appears likely that the deprotonation of the unsaturated radical cations proceeds also by an addition-elimination process. The calculation of the reaction enthalpy shows that addition of NH3 to the ionized 3,3,3-trifluoro-2-halopropenes 4+.-6+. is especially exothermic. Experimentally this effect is not only reflected in the increased reaction efficiency of the substitution product, even in the case of the iodo derivative 6+., but also in competing fragmentations of the strongly excited distonic intermediates generated by the addition step. This corroborates the postulate that the variation of the rate constants with the substituents, which is observed for the reactions of ionized haloalkenes with ammonia, is caused by the excess energy released in the initial addition step.
