Destruction of Organophosphorus Nerve Agent Analogues by Activation of O2 under Aqueous Room Tempera

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Destruction of Organophosphorus Nerve Agent
Analogues by Activation of O2 under Aqueous Room
Temperature and Atmospheric Pressure Conditions

• Christina Noradoun, Ryan Hutcheson, Edmund Wong,
  I. Francis Cheng
• University of Idaho, Department of Chemistry,
  Moscow, ID 83844-2343
• ifcheng_at_uidaho.edu 208-885-6387

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Overall Goal

• The destruction or neutralization of xenobiotics.
• Inexpensive Safe Processes.
• Room Temperature and Pressure Conditions (RTP)
• Common Reagents Long Term Storage
• No Specialized Catalysts
• Yang, Y.-C., Chemical Detoxification of Chemical
  Nerve Agent VX,
• Accounts of Chemical Research, 1999, 32, 109-115.

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Oxidative Pathways
-Most attractive oxidant - O2 from air -CxHyXz
O2 CO2 H2O HX (unbalanced) ?Glt0
-Room temperature oxidations by air are
kinetically slow -enzymatic or enzyme-mimics
-Partially reduced O2 (Reactive Oxygen Species)
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Reactive Oxygen Forms
HO-OH b.o. 1 ? 50 kcal/mol
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Partially Reduced Oxygen
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That Last Step The Fenton Reaction
-Reduction of HO-OH H2O2 FeII FeIII HO-
HO. HO. e- HO- Eo 1.8 volts
-HO. reacts with organics with diffusion limited
kinetics
-Possible Roles for O2.- 2O2.- 2H ? H2O2
O2 O2.- FeIII ? O2 FeII
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The Proposed System
Red reducing agent, consumed MII/III O2
activation redox catalyst MII/III Fentons
Reagent
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Putting the System Together The Reducing Agent
Considerations -Costs -Kinetics -Environmental
Ered0
Zero-valent metals Fe ? Fe2 2e- -0.44
volts Ascorbate Ascorbate ? dehydroxyascorbate
2e- 0.154 volts (pH 4)
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Putting the System Together Oxygen Activation
Agents
RTP O2 activation
Biological Systems -cytochrome p450. Chemical
Systems -non-heme iron complexes (cost?) Que,
L. JACS 2003, 125, 2113-2128 -FeIIEDTA
oxidation by O2 Van Eldik, R. Inorg. Chem,
1997, 36, 4115-4120
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Putting the System Together Fentons Reagent

• H2O2 e- ? HO- HO? Ered0 0.26(pH 6) to
  0.08(pH 3) V
• FeIIIEDTA e- ? FeIIEDTA Ered0 0.1 V
• FeII/IIIEDTA is a classic Fentons Reagent
• Used in DNA footprinting studies
• Can FeII/IIIEDTA do both O2 activation
• and the Fenton reaction?

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Summary of Van Eldik Study
FeIIEDTAH(H2O) O2 ? FeIIEDTAH(O2)
H2O FeIIEDTAH(O2) ? FeIIIEDTAH(O2-) FeIIIEDTAH(O
2-) FeIIEDTAH(H2O) ? FeIIIEDTAH(O22-)FeIIIEDTAH
H2O FeIIIEDTAH(O22-)FeIIIEDTAH H2O
2H ? 2FeIIIEDTAH(H2O) H2O2 2FeIIEDTAH(H2O)
H2O2 ? 2FeIIIEDTAH(H2O) H2O Proposes H2O2 as
intermediate Saw no evidence of H2O2
Van Eldik, R. Inorg. Chem, 1997, 36, 4115-4120
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Our System

• System Consists of Fe(0) 20 mesh, EDTA, Air
  Water
• Proposed dioxygen activation schemes.
• Heterogeneous activation at the Fe(0) surface.
• Homogeneous activation by Fe(EDTA). Reaction
  stoichiometries are not balanced and only
  representative of likely processes.
• Heterogeneous activation producing ferryl.

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Method for Detection of Facile Oxidant from O2
Actiavtion
Thiobarbituric acid-reactive substances (TBARS)
assay Nonselective detection of oxidizing
species.
532 nm
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TBARS Results
Results of HO radical trapping by
deoxyribose/thiobarbituric acid system forming a
chromgen (532 nm). The conditions were 30 minutes
of reaction time with 0.1 g 40-70 mesh Fe(0),
under aerobic conditions. Other conditions stated
below.
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Summary of the New System
Consists of Fe(0), EDTA, Air, and Water Fulfills
Several Requirements Inexpensive Reagents
Long Shelf Life Nontoxic No Precious Metal
Catalysts No Special Reaction
Vessels RTP Possibility for Portability
Field Destruction
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Xenobiotic Oxidation Studies
H2O2
O2 2H

EDTA
Iron particles 0.1-1 mm
FeIIEDTA
Fe2
FeIIIEDTA HO- HO.
Aqueous Xenobiotic
CO2 H2O
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Xenobiotic Oxidation Studies
Chlorophenols recalcitrant and oxidatively
stable Malathion Surrogate for
organophosphorous compounds Kinetics Intermed
iates Final Products -50/50 Ethyl
Acetate/Hexane GC-FID -Direct Aqueous
LC-GC -Ion Chromatography
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Oxidation of Chlorophenols

• 0.5 g of 40-70 mesh Fe(0)
• 10 mL of solution
• 0.32 mM EDTA
• 140 ppm 4-chlorophenol
• 4 hour reaction time
• GC and LC-MS
• RTP

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Reaction Vessel
Air flow
2.0 mL 50/50 hexane/ethyl acetate (extraction
only)
10.0 mL water
pH 5.5 6.5, unbuffered.
0.44mM EDTA
0.44mM Xenobiotic
Stir bar
0.5g Fe 20 or 40-70 mesh
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4-CP Degradation Kinetic Studies
Pseudo first-order rate constant -1.11 /hr.
0.5-g 40-70 mesh Fe(0) 0.72 mM EDTA 0.54 mM
4-chlorophenol Aerobic conditions
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Summary of the degradation of the chlorophenols
in this study
. All runs included 0.5 g of 40-70 mesh Fe(0) in
10 mL of solution.    
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Organophosphorous Agents
Malathion
VX
Sarin, GB
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Control Studies

• Control experiments conducted using
• No EDTA
• No O2
• No Fe0
• showed no malathion degradation.
• Post reaction extractions of the iron solids
  using
• Ethyl acetate
• Toluene
• Butanol
• Hexane
• showed the absence of any organics absorbed to
  the iron surface.

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Summary of Identified Intermediates
DES
malathion
max 4-6 hrs
unknown product max 2-3 hrs
malaoxon
PO43- SO42-
Max 7 hrs
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Kinetics of Malathion Degradation
Malathion
Diethyl Succinate (DES)
GC/FID chromatograph, error bars indicate the
standard deviation between three measurements of
each sample.
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Malaoxon
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Unidentified Intermediate
MW 410 g/mol
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Ion Chromatography of other Ionic Products and
Intermediates
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Summary of Intermediates
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Kinetically stable organic species in the
presence of aqueous Fe(0)/EDTA/O2.
24 hour products for the degradation
of -EDTA -Malathion -4-chlorophenol
-pentachlorophenol -phenol
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pH Control and Possible Role
Self Buffering at pH 5.5 production of organic
acids Optimal pH range 3-6
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Technical Summary

• Ability to degrade organic pollutants
• Under room temperature, atmospheric pressure
  conditions
• Inexpensive Reagents Iron particles, water, air
  EDTA
• Unspecialized reactors
• Process is easily transportable, iron particles
  EDTA
• Strong possibility of scale-up
• Example of a Green Oxidant

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Scientific Summary

• First example of abiotic RTP activation of O2
  able to oxidize destructively organics
• Control experiments indicate process is dependent
  on Fe(0), EDTA, air, and water

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Future Investigations

• Mechanisms Understanding the process, C balance
• Kinetics Speeding up the process
• Homogeneous Systems
• Search for an oxidatively stable iron
  chelate/organic solvent
• Basic organic chemistry oxidizable and
  nonoxidizable functional groups
• Application Scale-up

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Desorption Studies
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Time 0 hrs
EDTA
Malathion
Reaction Conditions 0.44mM Malathion 0.44mM EDTA
0.5g FeO O2
HCO3-
propionic acid
oxalate
Time 13 hrs
Iminodiacetic Acid