This document outlines an experiment studying the ozonolysis of two alkenes: 2-methyl 2-butene and 2,3-dimethyl 2-butene. The experiment uses a flow reactor and cavity ring-down spectroscopy to measure reaction products. Initial results show peaks corresponding to expected products like carbonyls and Criegee intermediates. Further analysis and kinetic modeling is needed to constrain parameters and optimize agreement between experimental and simulated product yields. Future work includes improving ozone measurement and analyzing reactions of ozone and acetone byproducts.

1. Ozonolysis of 2-methyl 2-butene
and 2,3-dimethyl 2-butene
Group Meeting
Fall 2014

2. Outline
Motivation
Experimental Setup
Results
2-methyl 2-butene
2,3-dimethyl 2-butene
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. Rearrangement, decomposition, or reaction of carbonyl
oxides in the atmosphere produces secondary organic
aerosols, OH radicals, peroxy radicals, etc.

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

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.

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

9. Spectra analysis:
1 1
   

dc
dc
        


 


n
i
i i N
L
L
   
    0

10. Exp
Synth
318 320 322 324 326
0.45
0.40
0.35
0.30
0.25
0.20
0.15


   
       ( )
1 1
0
oz oz form form ac ac      

      
   
N N N f
dc
L


 



11. Results
2-Methyl-2-Butene
+ O3
+
+

12. 326 328 330 332 334
2.5
2.0
1.5
1.0
0.5
0.0


Exp1
Exp2
Synth
Exp1
Exp2
Synth
318 320 322 324 326
1.0
0.8
0.6
0.4
0.2
0.0


1 1
   
          oz oz form form acetald acetald ac ac N N N N
dc
L
       
   

     


 


0
n
                 
CH COO CH COO CH COO CH COO ac R ac i i f    N   N   N   N , 3 3 3 2 3 2
i

13. Comparison of f(λ).
                 
MB CH COO CH COO CH COO CH COO ac R ac i i f    N   N   N   N 2 , 3 3 3 2 3 2
CH COO CH COO ac R ac i i f    N   N   N , 3 2 3 2
Why?
n
i
n
              
i
  1
2 0.105  f  s MB  
  1 0.121  f  s TME  
N 
N
CH COO CH  COO 3 3 2

14. 2,3-Dimethyl-2-Butene
+ O3
+

15. 1 1
   
326 328 330 332 334
1.4
1.2
1.0
0.8
0.6
0.4
0.2
          
   
oz oz form form ac ac      

N N N f
dc
L

0.45
0.40
0.35
0.30
0.25
0.20

 


0
n
              
CH COO CH COO ac R ac i i f    N   N   N , 3 2 3 2
i
0.0


Exp1
Exp2
Synth
318 320 322 324 326
0.15


Exp1
Exp2
Synth

16. Difference spectrum: First attempt
Nbump ~ 2x1011 molecules/cm3
N(CSTR simulation) = 9.84x1011 molecules/cm3
318 319 320 321 322 323 324 325 326 327
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30



17. Scavenging with HFA
Residual (no HFA)
Residual (with HFA)
318 320 322 324 326
0.2
0.0


Residual (no HFA)
Residual (no HFA)
Residual (with 1.6e15 HFA)
318 320 322 324 326
0.2

0.0


18. The choice of Nac and f(λ) greatly effect the difference
spectrum.
Exp
Synth
318 320 322 324 326
0.45
0.40
0.35
0.30
0.25
0.20
0.15

Exp1
Synth
318 320 322 324 326
Nac values need to be constrained:

Optimization of the ozonolysis reaction using kinetic simulations.
Comparison of product yields with literature values.
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1



19. Simulation of the reaction in a flow reactor.
The system of ODEs is solved using
an approximation method by the
kinetic simulator KINTECUS.

20. Concentration profiles in the reactor.
3.0x1015
2.5x1015
2.0x1015
1.5x1015
1.0x1015
5.0x1014
0 1 2 3 4 5 6 7 8 9 10
3.0x1016
2.5x1016
2.0x1016
1.5x1016
1.0x1016
5.0x1015
0.0
0 1 2 3 4 5 6 7 8 9 10
0.0
2.0x1015
1.5x1015
1.0x1015
5.0x1014
0 1 2 3 4 5 6 7 8 9 10
1.2x1012
1.0x1012
8.0x1011
6.0x1011
4.0x1011
2.0x1011
0.0
0 1 2 3 4 5 6 7 8 9 10
0.0
TME
N molecule/cm3
Acetone
sCI
N molecule/cm3
Segment #
O3
Segment #

21. Product yields for different reaction conditions
Alkene/
Ozone
O3 reacted/
O3 initial
Baseline
f(λ)
O3 meas/
O3 sim
Ac meas/
Ac sim
Ac sim/
O3 sim
Ac meas/
O3 meas
YAc YHCHO
(Exp)
YHCHO
(Ref)
16.5 0.6 0.1285 3.2 2.2 10.5 7.2 5 0.53 ~0.40*
6.45 0.47 0.1620 3.8 0.65 8.6 1.4 1.6 0.65 ~0.41*
10.24 0.43 0.1134 4 1.41 8.9 3.1 4 0.8 ~0.40*
30.9 0.75 0.1712 2.31 2.1 14 12.7 4.3 0.55 ~0.38*
14.56 0.67 0.2612 2.97 1.31 13.2 5.8 2.8 0.48 ~0.40*
19.85 0.78 0.2312 2.02 1.73 13.6 11.6 3.3 0.52 ~0.41*
10.33 1 0.3322 0 2.3 13.6 NA 3.4 0.36 0.38 ± 0.04
12.36 1 0.2922 0 2.26 14 NA 3.4 0.42 0.38 ± 0.04

22. Future Work
Improve the measurement of remaining ozone.
Look into the ozone and acetone reactions:
Re-analyze data of TME with HFA using literature yields
for acetone.
Run TME ozonolysis with HFA under optimized
conditions.