PAPER

CRIMINALISTICS

Mark S. Bali,1 B.Sc. (Hons); David Armitt,2 Ph.D.; Lynne Wallace,1 Ph.D.; and Anthony I. Day,1 Ph.D.

Cyclic Pentanone Peroxide: Sensitiveness andSuitability as a Model for TriacetoneTriperoxide*

ABSTRACT: Research to counter the threat of organic peroxides such as triacetone triperoxide (TATP) is at times hampered by their inher-ent extreme sensitiveness and volatility. This work describes an approach to lowering some risks associated with the handling of TATP in thelaboratory through the use of an analog species, tripentanone triperoxide (TPTP). Sensitiveness has been tested via standard methods. GCMSanalysis has shown that TPTP degrades via similar mechanisms to TATP under a range of conditions. Slight differences in product compositionwere traced to side reactions which may also affect impurities present in homemade TATP synthesis. A pilot field trial was conducted to evalu-ate TPTP as a substitute for TATP in explosive detection dog (EDD) scent training. The degradation studies have yielded insights into the com-plexities of the acidic degradation of cyclic peroxides with potential forensic application, and TPTP’s inadequacy as a TATP pseudoscent is avaluable example of the limitations of such training aids.

KEYWORDS: forensic science, triacetone triperoxide, tripentanone triperoxide, cyclic peroxide, organic peroxide, thermal degradation,acidic degradation, degradation products, pseudoscent, explosive detection dog

Triacetone triperoxide is one of the most easily manufacturedof the organic peroxide explosives and has seen considerableuse in the terrorist community where it is utilized by militantgroups as a ready supply of primary high explosive (1). Its fric-tion sensitiveness of <0.1 N and impact sensitiveness of 0.3 Nmmake it more dangerous to handle than common primary explo-sives such as lead azide (2). The unique threat and detectionissues posed by TATP have lead to a renewed research interestin its characterization (3), detection (4,5), and neutralization(6–8).A notable characteristic of TATP is its high vapor pressure,

which can lead to dangerous redeposition on nearby surfaces,particularly around the caps or lids of storage containers. TATPcrystals formed in closures can detonate when disturbed by thefriction generated when opening. One study has quantified thissublimation, finding that 6.5% (by mass) of a sample can sub-lime within 48 h at 18°C (9). To improve laboratory safety indegradation trials, we sought an analog compound to alleviatethe concerns of sublimation and consequent hazardous deposi-tion of TATP.Tripentanone triperoxide (TPTP) (Fig. 1) was identified as a

suitable candidate for these purposes as previous literature had

suggested TPTP was up to 50 times more “stable” than TATP(10). It should be noted that the cited study did not provide anydefinition or measurement of stability; however, it seems thatthermal stability in solution was used as an approximation. TPTPhas been previously identified as a potential antimalarial drug(14) and as a radical initiator (10) for polymerization; however,no data could be identified in the literature which quantified itsexplosive characteristics. As TPTP possesses the same cyclicperoxide backbone as TATP, it was anticipated to have similarreactivity. The longer ethyl moieties on TPTP were expected toprovide more van der Waals interactions and therefore weexpected TPTP to have a lower vapor pressure than TATP.To test these hypotheses, basic sensitiveness tests were con-

ducted allowing us to compare the susceptibility of TPTP to initi-ating stimuli compared with TATP. TPTP’s suitability as a TATPanalog was examined by quantifying its rate of sublimation, aswell as comparing its degradation products under thermal andacidic conditions. Finally, a pilot field trial was conducted toassess the suitability of TPTP as an explosive detection dog(EDD) training surrogate in lieu of TATP. This was premised on

FIG. 1––Structures of tripentanone triperoxide (TPTP) and dipentanonediperoxide (DPDP) and their acetone homologs.

1School of Physical, Environmental and Mathematical Sciences, UNSWCanberra at the Australian Defence Force Academy, PO Box 7916, CanberraBC, ACT 2610, Australia.

2Weapons Systems Division, Defence Science and Technology Organisa-tion, Edinburgh, Adelaide, SA 5111, Australia.

*Support provided by the Australian Defence Force’s Chief of DefenceForce Scholarship.

Received 16 Nov. 2012; and in revised form 6 May 2013; accepted 1 June2013.

1© 2014 American Academy of Forensic Sciences

J Forensic Sci, 2014doi: 10.1111/1556-4029.12439

Available online at: onlinelibrary.wiley.com

the similar chemistry of the two compounds and sought to estab-lish whether EDDs were able to distinguish between them.

Experimental

CAUTION! The organic peroxides detailed in this study havethe characteristics of primary explosives with extreme levels offriction, heat, and impact sensitiveness. All procedures must becarried out by properly qualified and equipped personnel takingall relevant precautions.

Instruments

A Shimadzu QP 2010 Ultra fitted with a SGE SolGel Wax col-umn (1.0 lm film, I.D. 0.25 mm, 30 m) was used for all reportedGCMS methods. All analyses (except thermal degradation in tolu-ene) of peroxides and degradation products utilized an initial tem-perature of 40°C for 1 min, 20°C/min ramp to 100°C, held for3 min, followed by 30°C/min finishing at 190°C, and held for2 min. Injector temperature was 100°C, interface 200°C, and lin-ear column flow at 2 mL/min of He gas. Split ratio was set at 100.Concentrations were quantified using external standards. Standardconcentration curves used four data points and were not correctedto intersect at the origin. GCMS standards were of analytical qual-ity except ethyl propionate which was synthesized by the acid-cat-alyzed esterification of propanoic acid and ethanol, purified bydistillation, and its purity confirmed by NMR. Aqueous acidicsamples were neutralized over CaCO3. Nonacidic mixtures free ofnonvolatiles were sampled directly.For the thermal degradation of TPTP in toluene, products

were analyzed by GCMS using an initial temperature of 40°Cfor 1 min, 20°C/min ramp to 100°C, held for 3 min, followedby 30°C/min finishing at 278°C, and held for 5 min. Injectortemperature was 285°C, interface 270°C, and linear column flowat 2 mL/min of He gas. Split ratio was set at 100. Bibenzyl,ethyl propionate, and 3-pentanone were purified by publishedprocedures (11) and were calibrated against 0.005 M naphtha-lene in acetonitrile as an internal standard. Concentrations ofother products were estimated qualitatively from their peak areaagainst the internal standard and were identified by matchingagainst the GCMS software’s NIST library (12). Complete deg-radation of TPTP was confirmed by the previously describedlower-temperature method.NMR spectra were recorded on a Varian Unityplus-400 (Agi-

lent, Santa Clara, CA) spectrometer. All NMR experiments wereconducted at 25°C unless otherwise stated. 1H NMR spectrawere referenced to TMS (0 ppm) at 25°C using the residual 1Hsignal of the respective deuterated solvent. 1D spectra wererecorded with between 16 and 1024 transients. T1 experimentswere conducted using the Varian VNMR software (Agilent)using inversion recovery method and relaxation delay of 20 secbetween increments. An initial pulse (calibrated to 180°) wasfollowed by an incremental delay between 1.25 msec and20.48 sec then a 90° observe pulse. T1 was obtained throughexponential data analysis by VNMR software.IR spectra were recorded on a Shimadzu IRPrestige-21 spectro-

meter (Shimadzu, Kyoto, Japan). Samples were prepared in KBrpellets and analyzed between 400 and 3500 per cm with 16 scans.

Sensitiveness Testing

Explosive sensitiveness testing was carried out at Defence Sci-ence and Technology Organisation (DSTO) (Edinburgh, SA,

Australia). The Rotter impact test was utilized for impact sensi-tiveness testing. A 30 mg test sample in a brass cap wasinverted over a steel anvil and connected to a manometer, and a5 kg weight was dropped from varying heights. An initiationwas assumed if gas evolution was >1 mL. The standard BAMfriction test method was used for sensitiveness testing. Electro-static discharge sensitiveness was tested on a custom-madeDSTO apparatus. The sample is placed in five individual holesof a plastic disk over a copper base. A copper disc was placedover each hole, and the electrode lowered to touch the disc. Themachine was armed, and the charge released five times for eachhole. No initiation is defined as 25 shots at a particular chargewithout reaction. Test energies of 0.045, 0.45, and 4.5 J wereused for the test. Temperature of initiation was measured by a200 mg sample placed in a glass tube and heated at 5°C/minuntil reaction was indicated by smoke, flame, or explosion.

Synthesis

Tripentanone triperoxide and dipentanone diperoxide (DPDP)were synthesized using a procedure based on the method ofCerna et al. (10). A typical synthesis was conducted as follows:14 g of 70% (w/w) aqueous H2SO4 was added to 6.34 g (56mmol) of 30% (w/w) aqueous H2O2 and the mixture cooled to-10°C. 4.3 g (50 mmol) of 3-pentanone was added dropwiseover 1 h with continued stirring, and the temperature maintainedfor 3 days. The mixture was extracted with 100 mL of 40°C BPpetroleum ether, and the ether layer washed three times with50 mL saturated aqueous ammonium chloride, three times with50 mL distilled water then dried overnight over Na2SO4. Thesolvent was removed under vacuum to yield a crude mixture ofDPDP, TPTP, and mixed hydroperoxides.Separation of these products was achieved using flash chroma-

tography. A column (2.5 cm dia., 20 cm length) of 200 meshsilica gel was washed with 100 mL of dichloromethane/petro-leum ether (BP 60–70°C) 50:50 solution, followed by 200 mLof pure petroleum ether. The crude product was loaded onto thecolumn and eluted with petroleum ether. TPTP was eluted firstfollowed closely by DPDP (DPDP could only be isolated with aminimum of c. 20% TPTP impurity) and finally the polar,1,1′-(dioxybis [1-ethylpropylidene]) bis-hydroperoxide. The lattercompound was eluted in high purity and was characterized byNMR. 1H NMR (CDCl3): d 0.95 (t, J = 8.2 Hz, 12H), 1.71(m, 8H), 9.60 (s, 2H) 13C NMR: d 8.0 (s), 22.1 (s), 115.4 (s).The NMR assignment including 2D spectra correlates with thestructure described by Milas and Golubovic (13). Repeated flashchromatography of the DPDP-rich fractions via column chroma-tography yielded very small amounts of relatively pure DPDP asa colorless oil M.P. c. �8°C. 1H NMR (CDCl3): d 0.95(t, J = 7.6 Hz, 12H), 1.64 (br, 4H), 2.24 (br, 4H); 13C NMR: d8.0 (s), 22.1 (s), 115.6 (s). IR (cm�1) 1464, 1352, 1275, 1157,1144, 1043, 957, 928, 669, 486.The TPTP fractions were concentrated under vacuum and dis-

solved in minimal warm methanol. A drop of water was added,and overnight refrigeration yielded a white needle-like precipitatewhich was dried in vacuo at room temperature overnight to yieldTPTP (825 mg, 2.7 mmol, 16% yield). Anal. Calcd forC15H30O6 (306.40): C, 58.80; H, 9.87; N, 0.0. Found C, 58.98;H, 9.70; N, 0.00. M.P. 60°C. 1H NMR (CDCl3): d 0.92(t, J = 7.6 Hz, 12H), 1.46 (m, 4H), 1.82 (m, 4H) 13C NMR(CDCl3): d 8.0 (s), 22.3 (s), 111.6 (s). IR (cm�1) 2978, 2947,2878, 1458, 1342, 1273, 1246, 1023, 1157, 1134, 1064, 1041,1010, 972, 926, 748, 594, 555.

2 JOURNAL OF FORENSIC SCIENCES

Degradation Studies

To test the reactivity of TPTP, its reaction under acid-catalyzed conditions was compared with that of TATP. AqueousHCl degradations were conducted in methanol. A 30–40 mgsample of TPTP was dissolved in 10 mL of methanol in a volu-metric flask, and a 100 lL aliquot of 3 M HCl added. A 1 mLsample was taken at 10 min and quenched over solid Na2CO3 orCaCO3. This sample was then analyzed by GCMS. Further sam-ples were taken at 40 and 70 min or as dictated by reactionspeed. Control experiments without HCl were conducted usingknown concentrations of ethyl propionate, 3-pentanone, andTPTP, which confirmed that these compounds were effectivelyextracted using this method.Thermal degradation assays were conducted using the method

reported by Eyler et al. (22). Aliquots of 1 mL 20 mM TPTPsolution in toluene in vacuum-sealed ampoules were heated in aparaffin wax bath at 173°C (�1°C) for 16 h. The solutions werediluted to 10 mL with acetonitrile, then analyzed by GCMS.Sublimation was measured by taking a sample of c. 300 mg

TPTP in a 20 mL Wheaton vial and drying in vacuo overnight,weighing then leaving open to the air for 1 month at c. 18°C.The sample was weighed at weekly intervals.

Explosive Detection Dog Field Trial

Explosive detection dog field trials were carried out at theEDD cell, School of Military Engineering, Moorebank, NewSouth Wales. Three trained Australian army EDD’s and theirhandlers were utilized for this trial. Two of the dogs were newlytrained using conventional military explosives, and one moreexperienced dog had been briefly exposed to a TATP trial anumber of years ago. None of the dogs were considered “cur-rent” in being able to detect peroxide explosives. The tests wereconducted in abandoned buildings in large rooms with remnantfurniture. The University of New South Wales Ethics Secretariatapproved the use of dogs for the purpose of this trial, approvalID 10/146. Eppendorf microcentrifuge tubes with clip-seal topswere oven dried to reduce any trace volatiles for 2 days at 70°C.Five milligrams of TATP or 25 mg TPTP were weighed intoeach tube and sealed (TPTP had been dried in vacuo at roomtemperature overnight to remove other volatiles). The largerTPTP sample was used to compensate somewhat toward itslower vapor pressure, but this was not calculated quantitatively.Samples were stored over dry ice until required. During all seri-als conducted, empty vials which had undergone the same prepa-ration and storage were used as controls. The dogs showed nointerest in these controls.The dogs were “imprinted” on TPTP by cueing them on to a

visible sample (in metal cages) with their reward toy on top ofthe sample. After about three such serials, the reward was onlygiven once the dog “indicated” (sat) near the sample. Once indi-cation was given without verbal or other prompting, the trainingwas reinforced with hidden samples in single-blind tests, withreward only provided on correct indication of TPTP. The hiddensamples did not utilize the metal cages, with the open vialsplaced in inaccessible locations such as behind books or furni-ture, eliminating any possible visual stimulus. The hidden sam-ples were exposed once to each dog (with the order of dogsbeing different each time) before being moved to a fresh room.Experiments to assess the ability for the dogs to distinguish

between TATP and TPTP were carried out by hidden samples ofTATP and observing the EDD’s reaction. Again, the samples

were moved after each dog had a single attempt to locate it. Thehandlers directed the dog around the room, but did not attemptto cue the dog onto the hidden target if it was missed. Usinga larger quantity of TATP (25 mg) in a single hide (equivalentto the TPTP sample mass) did not affect the outcome of thisexperiment.

Results and Discussion

Pentanone Peroxides and their Characterization

Using our described procedure, TPTP was successfully sepa-rated from the crude mixture containing DPDP and a range ofhydroperoxides (only one was isolated but there was NMR evi-dence of other minor products). The ratio of products variedgreatly depending on temperature, reagent concentration, andduration of synthesis; however, this was not studied in detail.Characterization by 1H NMR was consistent with the literaturefor DPDP (14), and the spectrum for TPTP has been fullyassigned (Fig. 2). NMR experiments for TATP and diacetonediperoxide (DADP) were conducted on samples provided byDSTO. It is interesting to note that the TPTP exhibits axial andequatorial methylene signals, as opposed to the equivalent meth-yls of TATP. This indicates that the trimeric peroxide rings ofthe TPTP and TATP have different conformations in solution. Alikely cause for this is that the bulkier ethyl groups of TPTPforce the peroxide ring to adopt a much more rigid conforma-tion, which results in axial and equatorial environments beingvisible on the NMR timescale. The spectra of the dimer and tri-mer of both peroxides are shown in Fig. 2, with assignmentsconfirmed by 1H NOESY and COSY 2D NMR experiments (notshown). The broad methylene peaks in the DPDP spectrumresolve into quartets at temperatures below 15°C, as has beenpreviously described (14). TPTP was further characterized byelemental analysis, and its IR spectrum matches well with pub-lished results (13). Comparison of the IR spectrum of TPTP andDPDP (Fig. 3) reveals a general blueshift as the ring sizeincreases, which mirrors the reported theoretical and experimen-tal behavior of the acetone homologs (15). The blueshift is par-ticularly apparent in the c. 500–600 per cm region which isassigned as ring deformation in the previous reference.Being related cyclic oligomers, DPDP, and TPTP cannot be

conclusively distinguished from one another by their NMR spec-tra alone, as the integral and indeed elemental ratios of the dimerand trimer are identical. To provide confirmation that our spectrawere correctly assigned, a T1 experiment was conducted as acorrelation to molecular size. This follows the well-establishedrelationship between molecule size, tumbling rate, and T1 wheresmaller molecules exhibit longer T1 relaxation under identicalconditions (16). It was found that DPDP had a T1 of c. 1.6 sec(averaged across all protons) while TPTP was significantlyshorter at c. 0.9 sec. The shorter T1 for TPTP is consistent withits larger molecular size confirming that our overall assignmentis correct.

Relative Safety

Having successfully purified and characterized our target ana-log, sensitiveness testing was carried out to identify whetherTPTP was indeed less susceptible to initiating stimuli thanTATP. A combination of industry standard and custom-designedequipment was used to test friction, impact electrostatic, andthermal stability. The results are summarized in Table 1.

BALI ET AL. . CYCLIC PENTANONE PEROXIDE 3

It is important to note that some of the measurements reportedhere are below the sensitivity limitations of the equipment used,so it is not possible to determine whether TPTP is in fact moreor less friction or impact sensitive than TATP. Nevertheless,TPTP is a very sensitive primary explosive in terms of frictionand impact sensitiveness; thus all handling must still be con-ducted with extreme care. This is illustrated by the “violent reac-tion” of 200 mg of TPTP in the ignition temperature experimentwhich resulted in the thick-walled glass test tube being shatteredto a fine dust. The friction and heat risks can be controlled by

synthesizing only small quantities, removing heat sources, use ofTeflon-coated joints and spatulas, and storing samples as solu-tions till required. It is favorable that electrostatic sensitivenessis significantly less than that of TATP as this is a difficult stimu-lus to eliminate during handling without the use of specializedequipment, facilities, and clothing. Another significant factor isthat TPTP exhibits extremely slow sublimation at room tempera-ture (<1% by weight over 30 days at 18°C), which allows it tobe stored without risk of dangerous recrystallization. Sealed sam-ples stored in our laboratory for up to 1 year without refrigera-tion have exhibited no sign of sublimation-related deposition andremain as loose crystalline powders. No significant degradationwas noted in these samples.

Degradation of Cyclic Peroxides

As our wider studies are focused on an evaluation of methodsof safely degrading cyclic peroxides, it was important to confirmthe suitability of TPTP as a model compound in this context.The degradation of TATP by mineral acid is a well-studiedmechanism (7,17–19), providing a suitable benchmark for thispurpose. The reaction of TPTP with acid yielded pentanone asthe primary product with ethyl propionate as the next mostabundant species, particularly in the early stages of the reaction.Figure 4 shows the reaction over time using GCMS to trackreaction progress.The predominance of pentanone as the primary product corre-

lates well with the acidic degradation of TATP. Furuya (19)detected three equivalents of acetone for each mole of TATPwhen degraded by acid. Furuya’s study did not, however, show

5007501000125015001/cm

%T

1464

.03

1454

.39

1380

.13

1351

.19

1335

.76

1300

.08

1275

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1242

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.60

1158

.30

1133

.23

1065

.72

1041

.61

1012

.67

973.

1394

9.02

926.

84

848.

72

769.

6374

6.48

595.

0756

3.24

554.

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1301

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7.76

804.

32

763.

81

669.

30

580.

57

499.

5648

6.06

FIG. 3––The IR spectra of tripentanone triperoxide (TPTP) and dipenta-none diperoxide (DPDP).

TABLE 1––Sensitiveness data for tripentanone triperoxide (TPTP) and triacetone triperoxide (TATP).

Initiating Stimulus (unit) Impact (Figure of Insensitiveness) Friction (N of Pressure) Electrostatic (J) Ignition Temperature (°C)

TPTP <10* <5* Initiation at 4.5 but not 0.45 153 violent reactionTATP <10* <5* <0.045* Sublimes before reaction

*Below sensitivity threshold of instrument.

■a/b c/d

e

a/c b/d

e

a ba

b

OO CH3

CH3

a

a a

▲

TATP

●a b

cd

O

CH3

CH3

HH

H H

Oe

e

OO CH3

CH3DADP

DPDP

a b

cd

O

CH3

CH3

HH

H H

O e

eTPTP

■

▲

2.0 1.0 2.0 1.0

2.02.0 1.0 1.0

FIG. 2––1H NMR of acetone and pentanone peroxides. Spectra and structure of monomer units with peak assignments for the dimers and trimers are shown.▲ = acetone, ● = water in chloroform, ∎ = trace tripentanone triperoxide (TPTP).

4 JOURNAL OF FORENSIC SCIENCES

any existence of ester products. Other work published by Armittet al. (18) also did not report methyl acetate in the acidic degra-dation of TATP. The generation of ester products in the earlystages of TPTP’s acidic degradation may be explained by a dis-tinct side reaction where ketones are subjected to Baeyer–Villig-er oxidations.Conventional Baeyer–Villiger oxidation involves a ketone

being reacted with a strong oxidant such as trifluoroperoxyaceticacid, which inserts an oxygen to yield an ester (20) (Fig. 5,scheme A). In the degradation of cyclic peroxides, dihydroperox-ides (which are likely initial breakdown products of cyclicperoxides [17,18]) could act in a similar role as trifluoroperoxy-acetic acid, oxidizing pentanone to ethyl propionate (Fig. 5,scheme B). This hypothesis is supported by the observation thatthe rate of ester formation is highest early in the reaction, whenhydroperoxides would be at their highest concentration relativeto ketones.Furthermore, it was found that ester formation was reduced or

eliminated when a substrate was added which was more readilysubjected to Baeyer–Villiger rearrangements as an “oxidationtrap” (Table 2), making it evident that ester formation occurs viaan intermolecular mechanism. In this rearrangement, migratoryaptitude is ordered as H>C(R3)>Ph, CH(R2)>CH2R>CH3 (20),in keeping with cationic stability of the migratory group. Methylacetate is not a notable reaction product in the acidic breakdownof TATP due to the known poor migratory properties of methylgroups, making Baeyer–Villiger rearrangement unfavorable. Thisis supported in the observation that 3-methyl-2-butanone yieldedoxygen insertion on the secondary (butyl) side of the ketonerather than at the methyl. Hence, it is apparent that thepredominant breakdown mechanism for TPTP mirrors that pro-

posed for TATP by Armitt et al. (18), while a side reaction ofthe major product (3-pentanone) and intermediate hydroperox-ides leads to the formation of ethyl propionate. We are exploringthis mechanism further as part of our studies on cyclic peroxidedegradation.Our investigations show that while there are some differences

in reaction products between TATP and TPTP, the fundamentalmechanism in acidic conditions appears to be the same, givingthe ketone product in both cases. Not only does this make TPTPa safer substitute for initial degradation experiments, but the pos-sibility of different minor reaction products might also provide auseful insight into the fate of trace impurities in the precursorketone used for the synthesis of homemade cyclic peroxides.Commercial acetone has been found to usually contain traces ofketones such diacetone alcohol (21) which is as susceptible toBaeyer–Villiger rearrangements as the 3-methyl-2-butanone usedin the described experiments as an oxygen trap. Hence, the pres-ence of trace esters in crude cyclic peroxide mixtures could belinked to characteristic ketones during synthesis, potentially pro-viding an indicator of the source of precursor materials.Thermal degradation was also investigated and compared

against previously published studies concerning TATP. It hasbeen shown that the toluene solvent acted as a radical trap whenTATP was thermally degraded via a radical mechanism (22),leading to the radical coupling of two toluene molecules to formbibenzyl. In our work, we found that bibenzyl was also presentafter the degradation of TPTP under identical conditions(Table 3), indicating that a similar radical mechanism is respon-sible for the thermal degradation of TPTP.Interestingly, thermal degradation showed a marked decrease

in the concentration of ketone produced by TPTP compared withthe acetone produced by TATP in the referenced work. This isbalanced in part by the production of the ester ethyl propionate.Another thermal degradation study on TATP (23) has foundmethyl acetate present as a degradation product in ratios of

1

1.5

2

2.5

on w

ith re

spec

t to

TPTP

TPTP

ethyl propionate

3 t

0

0.5

0 50 100 150 200 250 300

Mol

e fr

actio

Time (min)

3-pentanone

FIG. 4––Proportion of key reaction products in the aqueous acidic degra-dation of tripentanone triperoxide (TPTP) tracked by quantitative GCMS.Data presented as mole fraction per mole of TPTP being degraded.

FIG. 5––Scheme A shows the general scheme of a Baeyer–Villiger rear-rangement reaction where ROOR is a strong organic hydroperoxide. SchemeB shows the side reaction where 3-pentanone is oxidized to ethyl propionateby hydroperoxides formed in the acidic degradation of tripentanone triperox-ide (TPTP).

TABLE 2––Ester formation in tripentanone triperoxide (TPTP) acidic degra-dation in the presence of substrate ketones.

Substrate Ketone Present During TPTP AcidicDegradation (% Conc)*

None Added 3-methyl-2-butanone Acetophenone

3-pentanone >86 >94% 100%Ethyl propionate <13 <6% None detected

*Figures are representative across a number of repetitions; percentagesrefer to total 3-pentanone and ethyl propionate concentration at 1 h reactiontime.

TABLE 3––Moles of product per mole of cyclic peroxide in toluene solutionat 173°C.

ProductTripentanoneTriperoxide

TriacetoneTriperoxide

Bibenzyl 1.21 1.54 (22)Ketone (pentanone/acetone) 0.14 0.85 (22)Ester (ethyl propionate/methylacetate)

0.42 c. 0.26 (23)*

Ethyl benzene c. 0.2* 0.072 (22)Propyl benzene/1-ethyl-2-methylbenzene c. 0.3* NR

*Determined qualitatively by GCMS software (NIST 05) librarymatches and comparing peak area with an internal standard. NR, not reported.

BALI ET AL. . CYCLIC PENTANONE PEROXIDE 5

c. 20% of the final acetone concentrations. The larger quantityof ester product present in the degradation of TPTP indicatesthat the intramolecular rearrangements may be more favorablethan for TATP. This mechanism is consistent with the greaterradical stability of the a-methylenes in TPTP, whereas TATPhas methyl groups making such rearrangements less favored. Inthis case, therefore, the variation in the proportions of the differ-ent products appears to reflect the stability of intermediates inthe radical breakdown mechanism, while the fundamental mech-anism is the same. This conclusion is supported by the compara-ble concentrations of bibenzyl, indicating that the reactioninitially proceeds by a broadly similar radical mechanism, suchas that proposed by Eyler et al. (22).

TPTP Scent Characteristics

Noting the potential for a small but significant improvementin safety, we investigated the utility of TPTP as a substitute forTATP in EDD scent training. EDDs have proven very receptiveto imprinting on the scent of TATP (24); however, difficulties inhandling, storing, and disposing of TATP due to its inherent vol-atility and sensitiveness make training too risky for most han-dlers. Attempts to embed TATP in safe matrices to reduce itssensitiveness have largely not met with great success (25), par-ticularly due to concerns in the EDD handler community relatingto altered scent profile. Considering the structural similarityshared by TATP and TPTP, a trial was conducted to investigatewhether EDDs could distinguish between the two compounds. Ifthe two compounds could not be distinguished by the dogs, thenpotentially TPTP could be used as a TATP substitute in EDDtraining.It was found that 1 day of training (6–13 exposures per dog)

was sufficient for the EDDs to recognize and reliably indicatethe presence of hidden TPTP samples. When, however, the sam-ples were substituted with TATP, the dogs did not pay anynoticeable attention to the hides. The trial was controlled for thedogs being cued by patterns, human odors, and container scentswhich when coupled with such a strong negative result gives thefindings a high degree of reliability. The result clearly showedthat the two compounds exhibit different scents to the canineolfactory senses. While disappointing in terms of our initial aim,the ability to distinguish such closely related compounds under-scores the high level of discretion inherent in the EDD’s senseof smell.The result also points to a need for canine scent training to

incorporate as many threat compounds as possible, as usingcompounds that are merely similar or of a particular “class” ofcompound is not effective and may result in false negatives onlive tasks. Of equal importance is that one can expect (althoughnot conclusively) that dogs trained on TATP are unlikely toidentify TPTP, which is still a viable (if unlikely based on pre-cursor availability) explosive material. The result also indicatesthat commercial pseudoscents that are based on “de-sensitising”the energetic components of explosive compositions (26) needextensive analysis to be certain that the original energetic mate-rial is not a significant odiferous component in the authenticexplosive scent picture. Whilst such an approach is plausiblewhere the explosive composition is based on energetic materialswith relatively low vapor pressures such as HMX or RDX (26),TATP’s high volatility makes it a major part of the scent “bou-quet”. Thus, modifying its chemistry is likely to lead to majorchanges in scent. In this instance, while TPTP has in someaspects been “desensitized” compared with TATP, its odor has

been noticeably altered from a canine perspective. While thesmall trial reported here is only one example, it demonstratesthat even minor modifications to the structure of energetic mate-rials with high vapor pressures can change the odor to a pointwhere it is no longer useful as a pseudoscent.This small trial has yielded a useful contribution to the scien-

tific community’s relatively poor understanding of the caninesense of smell in relation to explosive headspace (25).

Conclusion

The presented results show that TPTP has potential as aneffective analog for TATP in degradation experiments. We haveshown that our analog compound (TPTP), while still demonstrat-ing primary explosive sensitiveness, has reduced risk. Two ofthe key hazards involved in handling TATP in laboratory pro-cesses and storage – sublimation (with ensuing hazardous rede-position) and electrostatic discharge susceptibility – are mitigatedby TPTP. It has proved to be an effective model compound bydisplaying very similar reactivity to its acetone homolog duringour investigations. Indications are that the primary mechanismsof TPTP’s acidic and thermal degradation are the same asTATP, but consideration needs to be given to secondary rear-rangement reactions and products facilitated by TPTP’s ethylmoieties. TPTP is also a useful comparative tool in evaluatingthe mechanism at work in TATP’s degradation and has revealednuances in the side reactions of cyclic peroxide degradationwhich has potential application as a forensic tool in tracing thefate of trace impurities in precursor chemicals. Given these find-ings, coupled with the small but significant improvement insafety, TPTP may be considered as an alternative to TATP insome experiments by other groups studying this class of com-pounds, particularly where the primary focus is degradation.While our exploration of TPTP’s suitability as a training aid forEDD detection of TATP did not provide the answer we hadhoped for, it did give an insight into the remarkable ability ofEDDs to distinguish between two closely related compounds andprovided a valuable illustration of the limitations of pseudoscentsin high vapor pressure energetic materials.This is the first time the basic sensitiveness characteristics of

TPTP have been reported, and the extreme friction and impactsensitiveness results are a valuable tempering of previous asser-tions that TPTP is significantly more “stable” than TATP (10).While this may still prove to be the case when tested on moresensitive instrumentation, in a practical sense, both peroxidesdeserve the utmost respect during all handling procedures.

Acknowledgments

We thank Craig Wall and Mark Fitzgerald of the Defence Sci-ence and Technology Organisation for conducting the sensitive-ness testing.

References

1. Steven GCS, Gunaratna R. Counterterrorism: a reference handbook.Santa Barbara, CA: ABC-CLIO, 2004.

2. K€ohler J, Meyer R. Explosives. 4th rev and extended edn. Weinheim,Germany: VCH Verlagsgesellschaft, 1993.

3. Reany O, Kapon M,Botoshansky M, Keinan E. Rich polymorphism intriacetone-triperoxide. Cryst Growth Des 2009;9(8):3661–70.

4. Walter MA, Pfeifer D, Kraus W, Emmerling F, Schneider RJ, Panne U,et al. Triacetone triperoxide (TATP): hapten design and development ofantibodies. Langmuir 2010;26(19):15418–23.

6 JOURNAL OF FORENSIC SCIENCES

5. Burks RM, Hage DS. Current trends in the detection of peroxide-basedexplosives. Anal Bioanal Chem 2009;395(2):301–13.

6. Dubnikova F, Kosloff R, Oxley JC, Smith JL, Zeiri Y. Role of metalions in the destruction of TATP: theoretical considerations. J Phys ChemA 2011;115(38):10565–75.

7. Oxley JC, Smith JL, Huang JR, Luo W. Destruction of peroxide explo-sives. J Forensic Sci 2009;54(5):1029–33.

8. Bellamy AJ. Triacetone triperoxide: its chemical destruction. J ForensicSci 1999;44(3):603–8.

9. Kuzmin VV, Solovev MY, Tuzkov YB, Kozak GD. Forensic investiga-tion of some peroxide explosives. Cent Eur J Energ Mater 2008;5(3–4):9.

10. Cerna J, Bernes S, Canizo A, Eyler N. 3,3,6,6,9,9-Hexaethyl-1,2,4,5,7,8-hexaoxacyclononane at 296 K. Acta Crystallogr C 2009;65:o562–4.

11. Armarego WLF, Chai CLL. Purification of laboratory chemicals, 6thedn. Amsterdam; Oxford: Butterworth-Heinemann, 2009.

12. U.S. Department of Commerce. NIST 05 Mass Spectral Library. NIST05 edn. Gaithersburg, MD: U.S. Department of Commerce, 2005.

13. Milas NA, Golubovic A. Studies in organic peroxides.24. Preparation,separation and identification of peroxides derived from diethyl ketoneand hydrogen peroxide. J Am Chem Soc 1959;81(13):3361–4.

14. Zmitek K, Stavber S, Zupan M, Bonnet-Delpon D, Charneau S, GrellierP, et al. Synthesis and antimalarial activities of novel 3,3,6,6-tetraalkyl-1,2,4,5-tetraoxanes. Bioorg Med Chem 2006;14(23):7790–5.

15. Oxley J, Smith J, Brady J, Dubnikova F, Kosloff R, Zeiri L, et al.Raman and infrared fingerprint spectroscopy of peroxide-based explo-sives. Appl Spectrosc 2008;62(8):906–15.

16. Sanders JKM, Mersh JD. Nuclear magnetic double-resonance – the useof difference spectroscopy. Prog Nucl Magn Reson Spectrosc 1982;15:353–400.

17. Tsaplev YB. Decomposition of cyclic acetone peroxides in acid media.Kinet Catal 2012;53(5):521–4.

18. Armitt D, Zimmermann P, Ellis-Steinborner S. Gas chromatography/massspectrometry analysis of triacetone triperoxide (TATP) degradation prod-ucts. Rapid Commun Mass Spectrom 2008;22(7):950–8.

19. Furuya Y, Ogata Y. Kinetics of the acid-catalyzed decomposition oftrimeric acetone peroxide. Bull Chem Soc Jpn 1963;36(4):419–22.

20. March J. Advanced organic chemistry: reactions, mechanisms, and struc-ture. New York, NY: McGraw-Hill, 1968.

21. Wahl JH, Bolz CD, Wahl KL. Investigating solvent purity using compre-hensive gas chromatography: a study of acetones. Lc Gc Eur 2010;23(4):188–99.

22. Eyler GN, Mateo CM, Alvarez EE, Canizo AI. Thermal decompositionreaction of acetone triperoxide in toluene solution. J Org Chem 2000;65(8):2319–21.

23. Oxley JC, Smith JL, Chen H. Decomposition of a multi-peroxidic com-pound: triacetone triperoxide (TATP). Propell Explos Pyrot 2002;27(4):209–16.

24. Oxley JC, Smith JL, Moran J, Nelson K, Utley WE. Training dogs todetect triacetone triperoxide (TATP). In: Carapezza EM, editor. Sensors,and Command, Control, Communications, and Intelligence (C31) Tech-nologies for Homeland Security and Homeland Defense, 2004. Belling-ham, WA: SPIE Press, 2004; 349–53.

25. Lorenzo N, Wan T, Harper R, Hsu Y-L, Chow M, Rose S, et al. Labora-tory and field experiments used to identify Canis lupus var. familiaris;active odor signature chemicals from drugs, explosives, and humans.Anal Bioanal Chem 2003;376(8):1212–24.

26. Adebimpe DB, Zgol MA, Wright GR, inventors; GMA Industries (Anna-polis, MD, US), assignee. Method of producing energetically-inert pseu-doscents of explosive materials, and compositions thereof. United States.2010.

Additional information and reprints requests:Mark S. Bali, B.Sc.School of Physical, Environmental and Mathematical SciencesUNSW Canberra at the Australian Defence Force AcademyPO Box 7916CANBERRA BCACT 2610AustraliaE-mail: m.bali@unsw.edu.au

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