Ozonolysis of 2,3-dimethyl-2-butene

Mixtli Campos-Pineda

Physical Chemistry Seminar

Spring 2015

OutlineMotivation

Ozonolysis

Criegee Intermediates

Products of Ozonolysis

Experimental SetupCRDS

Spectra Analysis

Results2,3-Dimethyl-2-Butene Ozonolysis

Hexafluoroacetone as scavenger

SO2 as scavenger

Summary

Future Work

MotivationOne 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.

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

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

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

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

inFMTME

inFM

CRDS:

Suitable for atmospheric measurements due to:Long sample path (high sensitivity).

Real time measurements.

Portability (in situ measurements).

Spectra analysis:

n

iii N

L

dc

L

dc 0

11

)(11

0

fNNNL

dcacacformformozoz

)(f Contribution from unknown products

fNNNL

dcacacformformozoz

0

11

Results O

OO

+ O3+

n

iiiCOOCHCOOCH NNf

2323

Difference spectrum

Scavenging with HFA

n

iiiCOOCHCOOCH NNf

2323

HFA + sCI SOZ, rearrangement products …

∆[Difference spectra]

n

iiiCOOCHCOOCH NNf

2323

Scavenging with SO2

fNNNNL

dcacacSOSOformformozoz

22

0

11

SO2 + sCI DMDOSO2 + sCI SO3 + AcetoneSO3 + H2O H2SO4

Difference spectrum

n

iii Nf

Unknown contributions from reaction with SO2 increase with pressure

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

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).

SummarySpectral 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.

Future WorkStudy sCI yields for ethene, propene, 2-butane ...

Obtain DMDO spectral information.

Analyze reaction products.

Model kinetics of SO2 scavenging of sCI

AcknowledgementsProf. Jingsong Zhang

Paul Jones

Mike Lucas

Lydia Plett

UCMEXUS Fellowship