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)