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