Atmospheric Degradation Pathways of

Hydrofluoroolefins

Jesse Mojeske, Dr. Stacey A. Stoffregen

Bethel University

Depletion of the Ozone Layer

[1]: U.S. Department of State Website; International Chemicals, Wastes, and Air Pollution Issues.[2]: Mario J. Molina, F.S. Rowland, 1974, Nature 249, 810-812.[3]: NASA Website; NASA Ozone Watch.

• The Montreal Protocol called for the phase out of chlorofluorocarbons (CFCs) and

hydrochlorofluorocarbons (HCFCs) in 1984.1

• CFCs and HCFCs are destroying the ozone layer.2

1979 1999 2009 2018

3

Alternatives to CFCs: Desired Properties

• Short atmospheric

lifetime to limit

transport to the

stratosphere.

• Low global warming

potential (GWP): The

amount of energy

absorbed by 1 ton of a

material over a 100

year period compared

to carbon dioxide.

• Low photochemical

ozone depletion

potential (ODP): No C-

Cl bonds

Class Name

Lifetime

(Years) GWP ODP

CFC 1,2-dichlorotetrafluoroethane 300 5820 1.0

HCFC 1-chloro-1,1-difluoroethane 17.9 2310 0.07

PFC* hexafluoroethane 10000 12200 0.0

HC* methane 12 25 0.0

[4]: Wikipedia, List of Refrigerants, https://en.wikipedia.org/wiki/List_of_refrigerants (Accessed June 19th 2019)

[5]: https://sciencestruck.com/atmosphere-layers-in-order (Accessed June 20th 2019)

HC: simple hydrocarbon PFC: Perflourinated carbons

Alternatives to CFCs: Hydrofluoroolefins

• Hydrofluoroolefins (HFOs) are being used as replacement aerosols and

refrigerants

• HFOs are believed to have very little environmental impact, an atmospheric

lifetime of about 7 days, and a low GWP.6,7

[6]: Sulbaek Andersen, et. al., 2005, J. Photochem. Photobiol. A 176, 124e128.

[7]: T.J. Wallington, et. al., 2015, Chemosphere, 129, 135-141.

HFO-1234yc HFO-1234zc HFO-1234ze(E) (Z)-CHF=CFCF3

Decomposition of HFOs

• HFO degradation primarily occurs via reaction with OH radicals.6

• HFO can subsequently degrade in the presence or absence of O2/NO resulting

in carboxylic acid derivatives and aldehydes

• According to the Norwegian Environmental Protection Agency high

concentrations of fluorinated aldehydes are toxic to aquatic environments8

[6]: T.J. Wallington, et. al., 2015, Chemosphere, 129, 135-141.[8]: Study on environmental and health effects of HFO refrigerants (Publication number:M-917|2017), https://www.miljodirektoratet.no/globalassets/publikasjoner/M917/M917.pdf,(Accessed June 21st 2019)

Terminal Addition Internal Addition

Absence of O2/NO

[9]: Balaganesh M., Rajakumar B., J. Phys. Chem. A 2012, 116, 9832-9842

• Addition of OH internal

• Hydrogen rearrangement

• C-C bond scission, C=O formation

• Radical dissociation

Absence of O2/NO

[9]: Balaganesh M., Rajakumar B., J. Phys. Chem. A 2012, 116, 9832-9842

• Addition of OH internal

• Hydrogen rearrangement

• C-C bond scission, C=O formation

• Radical dissociation

Absence of O2/NO

[9]: Balaganesh M., Rajakumar B., J. Phys. Chem. A 2012, 116, 9832-9842

• Addition of OH internal

• Hydrogen rearrangement

• C-C bond scission, C=O formation

• Radical dissociation

Presence of O2/NO

[10]: Parth et al, 2019, Journal of Fluorine Chemistry, 222-223, 31-45

• Addition of OH terminal

• Addition of OO internal

• Cleavage of OO bond by NO

• C-C bond scission, form C=O

• Hydrogen abstraction, form C=O

Presence of O2/NO

[10]: Parth et al, 2019, Journal of Fluorine Chemistry, 222-223, 31-45

• Addition of OH terminal

• Addition of O2 internal

• Cleavage of OO bond by NO

• C-C bond scission, form C=O

• Hydrogen abstraction, form C=O

Presence of O2/NO

[10]: Parth et al, 2019, Journal of Fluorine Chemistry, 222-223, 31-45

• Addition of OH terminal

• Addition of O2 internal

• Cleavage of O2 bond by NO

• C-C bond scission, form C=O

• Hydrogen abstraction, form C=O

Presence of O2/NO

[10]: Parth et al, 2019, Journal of Fluorine Chemistry, 222-223, 31-45

• Addition of OH terminal

• Addition of O2 internal

• Cleavage of O2 bond by NO

• C-C bond scission, form C=O

• Hydrogen abstraction, form C=O

Presence of O2/NO

[10]: Parth et al, 2019, Journal of Fluorine Chemistry, 222-223, 31-45

• Addition of OH terminal

• Addition of O2 internal

• Cleavage of O2 bond by NO

• C-C bond scission, form C=O

• Hydrogen abstraction, form C=O

Research Goals

• Create a potential energy diagram for HFO-1234ze(E), HFO-1234yc, and

HFO-1234zc

• Compare the pathways in the presence and absence of O2/NO

• Compare results to computational studies of other HFOs

Methods

• Calculations were done using Gaussian 16 Software11

, and the WebMO ver.

18.1.001e interface

• Utilized the MU3C supercomputing cluster at Hope College

• All reactants, products, and intermediates were optimized with

MO6-2x/6-311+G** and confirmed using hessians (vibrational frequencies).12

[11]: Gaussian 16, Gaussian, Inc. 340 Quinnipiac Street, Building 40, Wallingford, CT 06492,

Gaussian

[12]: C. Ramanjaneyulu et al, Journal of Fluorine Chemistry, 2015, 178, 266-278

HFO-1234ze(E), Intermediates, and Products

• Initial reactant set

to 0 kcal/mol

• All pathways are

exothermic

• Addition of O2 is

more favorable,

than hydrogen

rearrangement

• What about the

barriers?

Transition State Searching Method

• Modeled molecules after confirmed transition states from M. Balaganesh et al

• Used coordinate scans to scan potential energy surface for maxima, then used

coordinates as starting point for transition state optimization

• Confirmed geometries with hessians, and intrinsic reaction coordinate calculations

Hessians and Intrinsic Reaction

Coordinates

 

If ∇V = 0, stationary point on

potential energy surface

 

If k > 0, real frequency

If k < 0, imaginary frequency

Potential Energy Diagram of HFO-1234ze(E)

Future Work

• Completed potential energy surface of HFO-1234yc, HFO-1234zc, and

HFO-1234ze(E) in presence and absence of O2/NO

• Calculate excited state structures of the above stated molecules

• Begin searching potential energy surface of the addition of other radicals

Acknowledgments

Edgren Scholars Program

References

• [3]: NASA Website; NASA Ozone Watch (Accessed 26th 2018)

• [4]: Sulbaek Andersen, et. al., 2005, Kinetics of the gas phase reactions of chlorine atoms and OH radicals with

CF3CBrCH2 and CF3CF2CBrCH2, J. Photochem. Photobiol. A 176, 124e128

• [5]: T.J. Wallington, et. al., 2015, Atmospheric chemistry of short-chain haloolefins: Photochemical ozone creation

potentials (POCPs), global warming potentials (GWPs), and ozone depletion potentials (ODPs) ,Chemosphere, 129,

135-141

• [6]: Gupta Parth, Rajakumar B., April 10 th 2019, A Theoretical Insight on the Kinetics for the reaction of (E)-/(Z)-

CHF=CF(CF 2 )x=1,2 CF 3 with OH Radicals under Tropospheric Conditions, Journal of Fluorine Chemistry, 222-223,

31-45

• [7]: Balaganesh M. Rajakumar B., September 17 th 2012, Rate Coefficients and Reaction Mechanism for the Reaction of OH

Radicals with (E)-CF3CH═CHF, (Z)-CF3CH═CHF, (E)-CF3CF═CHF, and (Z)-CF3CF═CHF between 200 and 400 K: Hybrid Density

Functional Theory and Canonical Variational Transition State Theory Calculations, J. Phys. Chem. A2012116409832-9842

• [8]: Li-ling Ai, Jing-yao Liu, March 19 th 2014, Mechanism of OH-initiated Atmospheric Oxidation of E/Z-CF3CF=CFCF3: a

Quantum Mechanical Study, J Mol Model (2014), 20:2179

• [9]: C. Ramanjaneyulu et al, Kinetic parameters for the reaction of OH radical with cis-CHFCHCHF2, trans-CHFCHCHF2,

CF2CHCHF2 and CF2CCHF: Hybrid meta DFT and CVT/SCT/ISPE calculations, Journal of Fluorine Chemistry, 2015, 178, 266-278