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Determining Reaction R ates of N itroaromatic Reduction Reactions . Hayley Johnston Mentor: Ali Salter-Blanc Tratnyek Lab Summer 2013. Background . Release of energetic munitions compounds into the environment leads to contamination Water Soil Sediments - PowerPoint PPT Presentation
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DETERMINING REACTION RATES OF NITROAROMATIC REDUCTION REACTIONS
Hayley JohnstonMentor: Ali Salter-Blanc Tratnyek LabSummer 2013
Background
• Release of energetic munitions compounds into the environment leads to contamination • Water• Soil • Sediments
• Selection of new energetic compounds• Less shock sensitive (safer)• Toxicity• Environmental persistance
Objectives• Determine the reaction rate of various nitroaromatic
compounds in reducing conditions• Formulate quantitative structure activity relationships
(QSARs) • Predict the behavior of current and future ammunitions
contaminants in the environment
2,4,6-trinitrotoluene
2,4-dinitroanisole nitrobenzene
2,4-dinitrotoluene
4-chloro-1-nitrobenzene1,3-dinitrobenzene
Bulk Donor (ox)
Bulk Donor (red)
Electron Carrier (ox)
Electron Carrier (red) Contaminant (red)
Contaminant (ox)
Reduction of Nitroaromatic Compounds (NACs)• Reduction: an electron transfer reaction where the product
gains electrons• Overall Reaction
• 1st Step
• Reduction by electron shuttle (mediator)
ArNO2
2e-+2H+
ArNO2e-+2H+
ArNHOH2e-+2H+
ArNH2
ArNO22e-+2H+
ArNO2-
High rate Moderate rate
Kinetics• Generally assumed to be pseudo-first-order
• Reaction is second order in [Fe(II)P] and [NAC] rate= kFeP[Fe(II)P][NAC]
• [Fe(II)P] is constant so it can combine with the kFeP to get the kobs rate= kobs [NAC]
567
10
2
3
4567
log(
NA
C)
4321
Time (h)
• Obtain second order rate constant (kFeP) from kobs = kFeP [FeP]
3.0
2.0
1.0
0.0
k obs
35x10-6302520151050
[FeP]
Methods
• 60mL Reaction Vial containing:• 25-400μL of 4.29mM iron(III) porphine (FeP)• 1mL of 0.25M cysteine (to generate Fe (II))• 49mL Sodium Phosphate Buffer pH 7.0• 50μL 0.1M nitroaromatic compound (NAC)
• 25O water bath• HPLC detection @ 254nm or
220nm• Sampling frequency based on half
life of NAC
cysteine (ox)
cysteine (red)
Fe(III)P (ox)
Fe(II)P (red) NAC-
NAC
910
2
3
4
5
6
7
8
9100
log(
Con
cent
ratio
n of
DN
T (u
M))
1086420Time (h)
4.29uM FeP 8.58uM FeP 12.87uM FeP 17.16uM FeP 25.74uM FeP 34.32uM FeP
Slope values are the observed reaction rate (kobs)for each reaction
The kobs values are plotted against the concentration of FeP to obtain the kFeP value of each NAC
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
k obs
(1/h
)
35x10-6302520151050
[FeP] M
kFeP=49,135
Reduction Rates of 2,4-dinitrotoluene (DNT) by increasing concentrations of FeP
910
2
3
4
5
6789
100
log(
Con
cent
ratio
n D
NA
N)
1.41.21.00.80.60.40.20.0Time (h)
25.74uM FeP Trial 1 Trial 2 Trial 3 Trial 4
0.1
1
10
log(
Con
cent
ratio
n D
NA
NuM
)
2.52.01.51.00.50.0Time (h)
NP
25.74uM FeP
Trial 1 Trial 3 Trial 5
0.1
1
10
100
log(
Con
cent
ratio
n D
NA
NuM
)
2.52.01.51.00.50.0Time (h)
NP
25.74uM FeP
Trial 1 Trial 3 Trial 5
0.1
1
10
100
log(
Con
cent
ratio
n D
NA
NuM
)
2.52.01.51.00.50.0Time (h)
NP
25.74uM FeP
Trial 1 Trial 3 Trial 5
Complications• New fit parameters• Autocatalytic reaction? A→B A+B→C
Results • First order fit is good up until ≈10μM NAC• This enables me to obtain second order rate constants for
each compound
NB
4-ClNB
2,4-DNT
DNAN
1,3-DNB
TNT
NA
Cs
2.01.51.00.5
log(kFeP)
Acknowledgements
I would like to extend many thanks to:
Ali Salter-BlancPaul Tratnyek
Vanessa Green Oregon Health and Science University (OHSU)