TME Ozonolysis

1. Ozonolysis of
2,3-dimethyl-2-butene
Mixtli Campos-Pineda
Physical Chemistry Seminar
Spring 2015

2. Outline
Motivation
Ozonolysis
Criegee Intermediates
Products of Ozonolysis
Experimental Setup
CRDS
Spectra Analysis
Results
2,3-Dimethyl-2-Butene Ozonolysis
Hexafluoroacetone as scavenger
SO2 as scavenger
Summary
Future Work

3. Motivation
One of the most important processes of Volatile Organic
Carbons (VOCs) in the atmosphere is oxidation.
One of the main oxidation reactions of VOCs is
ozonolysis.

4. Carbonyl oxides, also know as Criegee Intermediates
(CIs), are produced by ozonolysis through the breaking
of a primary ozonide (POZ).

5. CIs are formed with a energy distribution that results in
only a fraction undergoing reactions or rearrangements.
Resulting in short lifetimes.

6. Rearrangement, decomposition, or reaction of carbonyl
oxides in the atmosphere produces secondary organic
aerosols, OH radicals, peroxy radicals, etc.

7. Experimental Setup
Ozonolysis 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 inFM
SO2/HFA
in
FMTME
in
FM

8. CRDS:
Suitable for atmospheric measurements due to:
Long sample path (high sensitivity).
Real time measurements.
Portability (in situ measurements).

9. Spectra analysis:
   
   






n
i
ii N
L
dc
L
dc

 0
11

10.    
      )(
11
0


fNNN
L
dc
acacformformozoz 






)(f Contribution from
unknown products

11.    
        

fNNN
L
dc
acacformformozoz 






0
11
Results + O3
+

12.          
n
i
iiCOOCHCOOCH NNf  2323
Difference spectrum

13. Scavenging with HFA
         
n
i
iiCOOCHCOOCH NNf  2323
HFA + sCI  SOZ, rearrangement products …

14. ∆[Difference spectra]
         
n
i
iiCOOCHCOOCH NNf  2323

15. Scavenging with SO2
   
          

fNNNN
L
dc
acacSOSOformformozoz 





 22
0
11
SO2 + sCI  DMDO
SO2 + sCI  SO3 + Acetone
SO3 + H2O  H2SO4

16. Difference spectrum
   
n
i
ii Nf 

17. Unknown contributions from reaction with SO2 increase
with pressure

18. Consumption of SO2 reaches a maximum at high initial
SO2 concentrations, which corresponds to the amount of
sCI in the reactor.

19. Yield of sCI increases with pressure and is in agreement
with previous work by Donahue et al.†
†Donahue, NM; Drodz, GT; Epstein, SA; Presto, AA; and JH Kroll, PCCP. 13, 10848 (2011).

20. Summary
Spectral contributions that could not be attributed to measurable
products nor to sCI were found during all ozonolysis experiments.
Spectral contributions increased when the sCI was scavenged either
by HFA or SO2. This can be due to production of SOZ,
rearrangement of the sCI, or aerosol formation.
Measurement of consumed SO2 during scavenging can be used to
indirectly measure the yield of sCI.
The yield of sCI is increases with pressure and is a minimum around
20 torr.

21. Future Work
Study sCI yields for ethene, propene, 2-butane ...
Obtain DMDO spectral information.
Analyze reaction products.
Model kinetics of SO2 scavenging of sCI

22. Acknowledgements
Prof. Jingsong Zhang
Paul Jones
Mike Lucas
Lydia Plett
UCMEXUS Fellowship