Ultraviolet Absorption Spectroscopy of Explosive Peroxides in Solution

K.J. SmitExplosives and Pyrotechnics Group

WSD, DSTO(E)

Organic Peroxides

Home made explosives

• Triacetone Triperoxide (TATP)

• Diacetone Diperoxide (DADP)

OO

OOO

O

OO O

O

Some Characteristics of TATP and DADPSome Characteristics of TATP and DADP

• High sensitiveness to initiation by friction, impact, heat and electrostatic discharge

Melting Point : TATP about 94-95 ºC DADP about 131.5-133 ºC

• TATP sublimes slowly at room temperature

• White or colourless crystals

Solutions of TATP and DADPSolutions of TATP and DADP

Are a lot safer than the solid material

Application of Ultraviolet (UV)/Visible Spectroscopy

• Can it be used to identify TATP and DADP? • Could it be used to determine concentration?• Is it useful to monitor degradation?

Considerations

• Solubility

• Transparency

• Solvent interaction

• Stability of solutions

TATP in Acetonitrile

• Sufficiently Solubility

• Transparent to 200 nm1cm pathlength cells

• Colourless solution

• No spectral structure

• Aged 10 months, no observed effect.Confirmed by GC/MS

200 nm 320 nm

TATP in Dichloromethane

230 nm 320 nm

• More Soluble

• Transparent to about 230 nm

TATP in Chloroform

• Highly soluble

• Opaque below

240 nm 320 nm

240 nm

TATP Solutions

• Poorly structured absorption spectra, not useful for detection or identification, but may give concentrations

• Acetonitrile has the best tranparency in the UV

• Chloroform provides the best solubility

• No evidence of significant solvent effects

• Stable in acetonitrile solution, but possible stability issues in chlorinated solvent over 8 months

Molar Absorptivities

Absorbance = ε x cell pathlength x concentration

Molar Absorptivity(ε, M-1cm-1)

Wavelength (nm)

Chloroform Dichloromethane Acetonitrile

220 140

230 79

240 51 47

250 28 30 27260 17 18 17270 9 10 10

By comparison H2O2 has ε = 13 M- 1cm-1 at 260 nm, and 76 M- 1cm-1 at 220 nmfrom σ → σ* transition, unstructured absorption down to 200 nm

DADP in Acetonitrile

• No spectral structure

• Some evaporation but no degradation apparent after 8

200 nm 320 nm

months

DADP in Chloroform

240 nm 320 nm

• Some increased absorbance at long wavelengths after 10 months

Wavelength (nm) Molar Absorptivity(ε, M-1cm-1)

Relative absorbance 10 months after initial absorbance (%)

250 42 240 ± 15260 26 300 ± 19270 17 360 ± 30

Benzoyl Peroxide in AcetonitrileUV Photolysis

• Xe Lamp used for 5, 10, and 20 minutes

• Isosbestic points

200 nm 320 nm

0

5

10

20 200

20

0

UV Photolysis of TATP in Acetonitrile

• Overlaid spectra of non-photolysed and 14 min. photolysedsolution

• No observable photodegradation, in particular no acetone absorption at 276 nm

200 nm 320 nm

UV Photolysis of TATP in Chloroform

• Photolysis for 1 and 5 minutes appears to result in degradation, but identity of products not known

240 nm 320 nm

0

5

1

UV Photolysis of DADP in Acetonitrile

Photolysis for 5 and 15 minutes appears to result in degradation, at about 230 nm, possibly H2O2

200 nm 320 nm

0

5

1

50

15

Conclusions

• TATP and DADP have unstructured absorption spectra, that are probably of little use for identification.

• Molar absorptivities are low, but may be useful to determine concentration. Little solvent effect on absorption in the solvents studied

• TATP and DADP appear stable in acetonitrile, but may possible degrade very slowly in chlorinated solvents

• TATP does not readily photodegrade in acetonitrile, but appears to photdegrade in chloroform, although chloroform is less transparent. DADP appears less stable in acetonitrile to photolysis.

• UV absorption not very suitable to monitor degradation, and other techniques are required to observe photodegradation products

Acknowledgements

• Phil Davies and Matthew Smith for TATP and DADP Synthesis

• David Armitt and Simon Ellis-Steinborner for GC/MS

• Raoul Pietrobon and Adrian Turner with lab. facilities