Yields of stabilized Crieege Intermediates
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Transcript of Yields of stabilized Crieege Intermediates
Low pressure yields of stabilized Criegee intermediates
produced from ozonolysis of trans-2-butene and
2,3-dimethyl-2-butene
Mixtli Campos-Pineda, Jingsong ZhangPHYS 174
ACS, Fall 2016
OutlineMotivation
OzonolysisCriegee intermediates (CIs)Measuring the yields of CIs
Experimental SetupCRDSAnalysis of spectra
ResultsScavenging with SO2
trans-2-butene ozonolysis: CH3CHOO2,3-dimethyl-2-butene ozonolysis: (CH3)2COO
Summary
Motivation
One of the most important reaction pathways of Volatile Organic Carbons (VOCs) in the atmosphere is oxidation.
One of the main oxidation reactions of unsaturated VOCs is ozonolysis.
O 2
R, alkyl radical
RH, hydrocarbon
HONO +hn OH
OH NO
RO 2
RO
HO 2NO 2
ROONO 2
RONO 2
RO 2carbonyl+
alcohol
ROOH
NO 2
O3
O2
hn
OH Alkenes
OH productionmechanism inalkene + O3 reactions
Carbonyl oxides, also know as Criegee Intermediates (CIs), are produced by ozonolysis through the breaking of a primary ozonide (POZ).
The ozonolysis reaction is highly exothermic. The primary ozonide is formed with high internal energy.
Olzmann, M., Kraka, E., Cremer, D., Gutbrod, R. & Andersson, S. The Journal of Physical Chemistry A 101, 9421–9429 (1997).
CIs are formed with a broad energy distribution.
Olzmann, M., Kraka, E., Cremer, D., Gutbrod, R. & Andersson, S. The Journal of Physical Chemistry A 101, 9421–9429 (1997).
“hot” CI
“stabilized” CI
CIs with high internal energy (“hot” CIs), isomerize and decompose rapidly, forming atmospherically relevant products.
“vinoxy” radicalVinyl hydroperoxide (VHP)
CIs with low internal energy, “stabilized” CIs (sCIs), can competitively undergo unimolecular dissociation and bimolecular reactions:
Vereecken, L., H. Harder, and A. Novelli. PCCP 16, no. 9 (2014).
Recent developments in direct measurement of sCIs produced from CH2I2 photolysis (CH2I + O2) allowed experimental measurement of rate constants of CI reactions.
Welz, O. et al. Science 335, 204–207 (2012).
Measuring yields of sCIs
Scavenging
(e.g. w/ SO2)
Dimethyl dioxiraneSO3 + AcetoneH2SO4
y??
(1-y)??R1R2CO + CI “hot” CI decomposition
isomerization
“stabilized” CI
collisionalstabilization/excitation
bimolecular reactions
Alk + O3
(excess)
(∆O3)
(∆SO2) (∆H2SO4)or
Previous work on measuring sCI yields: Hatakeyama et al.
Hatakeyama, Shiro, Hiroshi Kobayashi, Zi Yu Lin, Hiroo Takagi, and Hajime Akimoto. JPC 90, no. 17 (August 1986): 4131–35. doi:10.1021/j100408a059.
Hatakeyama, Shiro, Hiroshi Kobayashi, and Hajime Akimoto. JPC 88, no. 20 (September 1984): 4736–39. doi:10.1021/j150664a058.
trans-2-butene
ethene
• High pressure to low pressure
• Measurement of ∆H2SO4
Previous work on measuring sCI yields: Drozd et al.
2,3-dimethyl-2-butene
• High pressure to low pressure
• Measurement of ∆HFA - ∆SOZ
Drozd, G. T., Kroll, J. & Donahue, N. M. JPCA 115, 161–166 (2011).
Hexafluoroacetone
Secondary ozonide
More recently: Hakala et al.
• High pressure to low pressure
• Measurement of ∆H2SO4
Hakala, J. P. & Donahue, N. M. JPCA 120, 2173–2178 (2016).
Experimental SetupOzonolysis of alkenes is done using a flow reactor:
Reaction products are measured using cavity ring-down spectroscopy (CRDS).Spectra of the main products is subtracted in order to look for CI features.
Dye Laser PMT
To pump
Purge Purge
03 gen
FM
N2 inFMSO2/HFA in
FMTME in
FM
CRDS:
Suitable for atmospheric measurements due to:Long sample path (high sensitivity).Real time measurements.Portability (in situ measurements).
)(11
0
fNNNLdc
acacformformozoz
)(f Contribution from unknown products
Spectra analysis:
n
iii N
Ldc
Ldc
0
11
Scavenging with SO2
Results
Scavenging
(e.g. w/ SO2)
Dimethyl dioxiraneSO3 + AcetoneH2SO4
y??
(1-y)??R1R2CO + CI “hot” CI decomposition
isomerization
“stabilized” CI
collisionalstabilization/excitation
bimolecular reactions
Alk + O3
(excess)
(∆O3)
(∆SO2)
Completely consumed in the reaction:∆O3 = [O3]i
fNNNNLdc
acacSOSOformformozoz
22
0
11
SO2 + sCI DMDOSO2 + sCI SO3 + AcetoneSO3 + H2O H2SO4
∆SO2 can be measured directly in the reaction:
3 absorption features of SO2 between 320 – 325 nm
Determination of the yield of sCI by titration with SO2
𝑌 𝑠𝐶𝐼=∆𝑆𝑂2
∆𝑂3
trans-2-butene ozonolysis
Hatakeyama, Shiro, Hiroshi Kobayashi, and Hajime Akimoto. The Journal of Physical Chemistry 88, no. 20 (September 1984): 4736–39. doi:10.1021/j150664a058.
2,3-dimethyl-2-butene ozonolysis
Drozd, Greg T., Jesse Kroll, and Neil M. Donahue.The Journal of Physical Chemistry A 115, no. 2 (January 20, 2011): 161–66. doi:10.1021/jp108773d.
Mechanistic implications
Copeland, Grant, Mariana V. Ghosh, Dudley E. Shallcross, Carl J. Percival, and John M. Dyke. Physical Chemistry Chemical Physics 13, no. 39 (2011): 17461. doi:10.1039/c1cp21922g.
Mechanistic implications
C6H12 + O3 (CH3)2CO + y(P)[(CH3)2COO]* + [1-y(P)] (CH3)2COO
“hot” CI unimolecular decomposition and isomerization
“stabilized” CI bimolecular reactions
Summary
SO2 consumption measured by CRDS can be used to determine yields of sCIs in ozonolysis reactions of alkenes.
Measurements of low pressure sCI yields were found for trans-2-butene and 2,3-dimethyl-2-butene. The nascent yields of sCIs were found by extrapolation to be 0 for trans-2-butene, and 0.15 for 2,3-dimethyl-2-butene
Mechanism of secondary ozonolysis products needs to incorpórate pressure-dependent sCI yield information.
AcknowledgementsProf. Jingsong ZhangPaul JonesMike LucasGe SunJian Chen
UCMEXUS Fellowship