A Method for the Synthesis of Tetranitroglycoluril from

Imidazo-[4,5-d]-imidazoles with Loss of Dinitrogen Oxide

by William M Sherrill, Eric C Johnson, and Joseph E Banning

ARL-RP-0515 December 2014

A reprint from Propellants, Explosives, Pyrotechnics. 2014;39:670–676.

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Army Research Laboratory

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ARL-RP-0515 December 2014

A Method for the Synthesis of Tetranitroglycoluril from

Imidazo-[4,5-d]-imidazoles with Loss of Dinitrogen Oxide

William M Sherril and Joseph E Banning

Weapons and Materials Research Directorate, ARL

Eric C Johnson

Bowhead Science and Technology

A reprint from Propellants, Explosives, Pyrotechnics. 2014:39670–676.

Approved for public release; distribution is unlimited.
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A Method for the Synthesis of Tetranitroglycoluril from

Imidazo-[4,5-d]-imidazoles with Loss of Dinitrogen Oxide

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A reprint from Propellants, Explosives, Pyrotechnics. 2014:39:670–676.

14. ABSTRACT

A new method for the preparation of tetranitroglycoluril (TNGU, Sorguyl) is described, in which imidazo-[4,5-d]-imidazoles 

are nitrated with the elimination of N2O to generate TNGU. This method of TNGU synthesis results in material that is less 

sensitive than material produced with alternative routes. Additionally, a new spherical morphology of TNGU is disclosed. This 

morphology exhibits an even higher resistance to external insult even than material synthesized with the new method.

15. SUBJECT TERMS

tetranitroglycoluril, sorguyl, TNGU

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William M Sherrill

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DOI: 10.1002/prep.201400041

A Method for the Synthesis of Tetranitroglycoluril from

Imidazo-[4,5-d]-imidazoles with Loss of Dinitrogen Oxide

William M. Sherrill,*[a] Eric C. Johnson,[b] and Joseph E. Banning[a]

1 Introduction

Tetranitroglycoluril (TNGU, Sorguyl) (1) is a powerful high

explosive first described in the 1970’s by Boileau et al. [1].

This material, with a density of 2.01 g cm3 and heat of formation (DHf

) of 50 kJmol1 has a predicted performance

comparable to that of the standard military explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (2), while

approaching the performance of 2,4,6,8,10,12-hexanitro2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) (3) [2]. (Figure 1)

Compound 1 has several characteristics that have prevented its adoption into military formulations to date. It is

hydrolytically unstable even under normal atmospheric

conditions [3], and is significantly more sensitive to external

insult than HMX. If prepared using literature procedures [4],

it exhibits a 50% initiation (H50) value for impact sensitivity

of 10.4 cm, whereas HMX is 24.4 cm on the same apparatus. Additionally, 1 has a friction measurement of 54 N,

whereas HMX is typically 120 N. Taken together, these numbers place TNGU in a category of material that is usually

deemed too sensitive for secondary explosive applications.

Recent attempts to rectify both the hydrolytic instability

and the sensitivity of 1 through substitution of the bridgehead hydrogen atoms resulted in material that was energetically less powerful and still comparably sensitive and

unstable [5]. This led to the idea of using substitution of

the oxygen from the carbonyl position in the dinitrourea

moiety as an additional means of potentially tuning both

the sensitivity and the hydrolytic instability of the molecule.

(Figure 2) To this end, several different imidazo imidazoles

5–7 were prepared using known literature procedures [6]

and attempts were made to further nitrate them in an

effort to produce a novel material 8 (Figure 3).

2 Results and Discussion

2.1 Computational Analysis

The target 8 is predicted by quantum mechanical models

developed by Rice et al. [7] to have a density of

Abstract: A new method for the preparation of tetranitroglycoluril (TNGU, Sorguyl) is described, in which imidazo-

[4,5-d]-imidazoles are nitrated with the elimination of N2O

to generate TNGU. This method of TNGU synthesis results

in material that is less sensitive than material produced

with alternative routes. Additionally, a new spherical morphology of TNGU is disclosed. This morphology exhibits an

even higher resistance to external insult even than material

synthesized with the new method.

Keywords: Tetranitroglycoluril · Sorguyl · TNGU

Figure 1. Structures of high explosives TNGU, RDX, and CL-20.

Figure 2. Structure of compound 1 showing location of bridgehead and carbonyl positions.

[a] W. M. Sherrill, J. E. Banning

US Army Research Laboratory (ARL)

Weapons and Materials Research Directorate

Bldg 1119B Spesutie Island Rd

Aberdeen Proving Ground, MD 21005, USA

*e-mail: william.m.sherrill.civ@mail.mil

[b] E. C. Johnson

Bowhead Science and Technology

103 Bata Boulevard, Suite K

Belcamp, MD 21017, USA

670 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Propellants Explos. Pyrotech. 2014, 39, 670 – 676

Full Paper
2.032 g cm3 and a DHf value of +617.01 kJmol1

. From

these numbers, the predicted performance of this material

exceeds HMX by almost 30% making it a highly desirable

target (Table 1).

2.2 Synthesis

With the predicted performance numbers in hand, attempts were made to synthesize 8 from all three starting

materials 5, 6, and 7. None of the standard suite of acidic

nitration conditions: 100% nitric acid (HNO3), mixed sulfuric

acid (H2SO4)/ <98% HNO3, and acetic anhydride (Ac2O)/

100% HNO3 were found to be strong enough to convert

the lesser nitrated materials to the desired target. When

subjecting materials 6 and 7 to >98% HNO3, no reaction is

observed; however, when using 5, the material is recovered

as the nitrate salt, 6. All three materials exhibit decomposition in mixed H2SO4/HNO3 conditions and no products from

these reactions were successfully recovered. 5 and 6 are

both converted into the dinitro compound 7 when subjected to Ac2O/HNO3 conditions, but were unable to be nitrated further even with extended reaction times and heating.

It was discovered that all three starting materials can be

further nitrated by employing a nitration mixture using trifluoroacetic anhydride (TFAA) in conjunction with nitric

acid. In this case, when 5–7 were dissolved in <98% HNO3

and TFAA was added slowly, a white powder slowly precipitated over time with the evolution of gas bubbles. After

several hours, the powder was isolated and analyzed to

find the material was not 8 as anticipated, but rather TNGU

(1). This was further confirmed by obtaining a nuclear magnetic resonance (NMR) spectrum showing perfect overlap

of signals from a mixture of 1 prepared via the nitration of

5–7 and of 1 prepared via the literature method [4]. All

three starting materials 5–7 yield 1 as the product under

the TFAA/HNO3 conditions with reasonable yields although

using 6 gives the best results with yields typically between

70 to 80%.

2.3 Mechanistic Discussions

Of the myriad of possible scenarios, it is postulated that

two are the most likely. The first being the a-carbon of 8 is

so electronincally withdrawn that the molecule is rapidly

and completely hydrolyzed to 1 on exposure to moisture.

This theory was quickly dismissed by repeating the experiments ensuring anhydrous conditions. Analysis of the material obtained showed it to be identical to material isolated in the original experiments indicating that hydrolysis of

8 is not responsible for the formation of 1 under the reaction conditions or under workup.

The second scenario employs intra- or intermolecular

degradation with elimination of dinitrogen oxide (N2O) as

the driving force behind the formation of 1. Once the material is subjected to the nitration conditions, it is plausible

that each of the materials 5–7, proceed through an intermediate resembling 9 (Figure 4) The a-carbon of this species is severely electron deficient making it highly susceptible to nucleophilic attack.

This type of reactivity with the elimination of N2O has

been documented previously by Wright and McKay [8] in

their attempt to completely nitrate 10, while only recovering 13. (Figure 5) They proposed an intermediate 11, which

could easily rearrange under the nitration conditions with

elimination of N2O to form 12. This was subsequently nitrated under their conditions to form 13. Additionally, this

type of reactivity has been used in the synthesis of 2,6-

dioxo-1,3,4,5,7,8-hexanitrodecahydro-1H,5H-diimidazo[4,5-

b:4’,5’-e]pyrazine (HHTDD) (15) starting from 14 [3].

The intramolecular decomposition mechanism is envisioned to employ the oxygen of the nitrimino moiety of 9

Figure 3. Structure of starting material imidazo imidazoles 5–7

and target 8.

Table 1. Performance predictions from Cheetah 7.0 [2].

8 TNGUb) HMXb) CL-20b)

1 2.03a) 2.01 1.90 2.044

DHf [kJmol1

] 617.01a) 50.0 75.02 386.0

Hcj [GPa] 42.51 41.77 37.19 47.09

Dv [km s1

] 9.621 9.566 9.246 9.970

Dd [kJmL1

] 12.17 11.78 11.00 12.60

OB [%] +11.70 +4.97 21.61 10.95

a) Predicted using the methods of Rice [7]. b) Heat of formation

and density numbers obtained from Cheetah 7.0 database.

Figure 4. Postulated intermediate in the formation of 1.

Propellants Explos. Pyrotech. 2014, 39, 670 – 676 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.pep.wiley-vch.de 671

Synthesis of Tetranitroglycoluril from Imidazo-[4,5-d]-imidazoles
as the nucleophile and then proceed through a four-membered intermediate 16 (Scheme 1) The subsequent re-arrangement of the four-membered cycle results in the liberation of N2O and a nitrourea type species 17. This mechanism is plausible whether the starting intermediate is a dinitro- or trinitroimidazo imidazole.

Alternatively, the intermolecular mechanism starts from

the same intermediate 9. However, it uses an additional

molecule of 9 as the nucleophilic oxygen source and proceeds through an intermediate resembling 18 before collapsing to release two molecules of 17 and two molecules

of N2O. (Scheme 2)

There are two possible ways to test the plausibility of

the degradation theory. The first is utilizing 18O labeled

nitric acid to pinpoint the source of the oxygen nucleophile. The second is to monitor the headspace of the nitration mixture for the appearance of a higher than baseline

concentration of N2O. The latter of these methods was

chosen as the preferable experimental method for this

analysis. Dinitrogen oxide gas exhibits a very specific doublet in the infrared (IR) at ca. 2235 cm1

. Using infrared

spectroscopy it was possible to monitor the concentration

of N2O in the headspace of a nitration mixture with or without a substrate present.

Using a gas flow cell and injecting samples of the reaction headspace at 3 min intervals, the highest concentration of N2O measured for the baseline nitration mixture

never exceeded 0.05 absorbance units (AU). This value was

used as the baseline for the subsequent nitration experiments. When glycoluril is nitrated under the baseline nitration conditions, the measured concentration of N2O increases slightly; however the maximum concentration observed at <0.20 AU was still quite low. When 5, 6, or 7, are

subjected to the nitration conditions, the maximum

amount of N2O observed is more than five times higher

than was observed from the nitration of glycoluril under

the same conditions. (Figure 6) The fact that 1 is the only

product recovered from the nitration of 5–7 together with

the nitration of these compounds exhibiting a marked increase in the concentration of N2O in the headspace of the

reaction relative to both glycoluril and the baseline are

strong indicators that a reaction mechanism similar to what

is depicted in Scheme 1 and Scheme 2 is in operation.

Figure 5. Literature examples of substrates believed to extrude

N2O.

Scheme 1. Proposed mechanism for the intramolecular decomposition and extrusion of N2O.

Scheme 2. Proposed mechanism for the intermolecular decomposition and extrusion on N2O.

Figure 6. Concentration of N2O in headspace of reactions over

time.

672 www.pep.wiley-vch.de 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Propellants Explos. Pyrotech. 2014, 39, 670 – 676

Full Paper W. M. Sherrill, E. C. Johnson, J. E. Banning
2.4 Morphological Discussions

TNGU as obtained from the nitration of glycoluril according

to literature procedures [4] is recovered as small significantly porous clumps of fine needles (Figure 7).

When 1 is synthesized from 5–7 (Figure 8), a different

morphology than that of the literature method is observed

(Figure 7). While still composed of needles, the needles

from 5–7 are significantly longer and thicker than what is

observed from the literature material (Figure 8). This

change in morphology is presumed to be partially responsible for the observed decrease in sensitivity of material obtained from 5–7.

In efforts to obtain various other morphologies of

1 through recrystallization of the material a spherical morphology, which exhibits much improved sensitivity over

even the material synthesized from the imidazo imidazoles,

was discovered (Figure 9).

While many other morphologies of 1 have been described, this appears to be the first time a spherical morphology of the material has been documented. This morphology is easily obtained through solvent/anti-solvent interactions by first dissolving the material in 100% HNO3

and precipitating it by introducing it below the surface of

DCM. The size and quality of the spheres appears to be determined by the rate of addition of the TNGU solution as

well as the ratio of HNO3 to DCM.

2.5 Sensitivity

It is interesting to note that the sensitivity of 1 produced

via the nitration of 5–7 with TFAA/HNO3 is markedly improved over 1 produced using the literature Ac2O/HNO3 nitration of glycoluril [4]. TNGU produced via the literature

method has a drop height of 10.4 cm on ARL’s impact testing apparatus, while that produced via the TFAA method

has a drop height of 28.1 cm. The friction and electrostatic

discharge (ESD) measurement between both samples

remain comparable.

Sphericalized TNGU obtained from treating TNGU prepared via the literature method and from TNGU prepared

Figure 7. Compound 1 as isolated from literature method.

Figure 8. Compound 1 as isolated from imidazo imidazoles.

Figure 9. Compound 1 after sphericalization treatment.

Table 2. Sensitivity data.

Substance Impacta) [cm] Frictionb) [N] ESDc) [J]

1d) 28.1 70 3.25

1e) 10.4 54 3.25

HMX 24.4 120 0.025

1f) 33.2 72 3.25

1g) 39.1 94 3.25

a) H50 impact height determined on an apparatus using a 2 kg

weight by the Langlie one shot method [9]. b) Friction determined

on a Julius Peter’s BAM friction apparatus. c) ESD determined

using an ABL Laboratories ESD Apparatus. d) 1 prepared from 5–7.

e) 1 prepared according to literature procedure [4]. f) Sphericalized

1, which was synthesized according to literature procedure [4]. g)

Sphericalized 1, which was synthesized from the nitrate salt 6.

Propellants Explos. Pyrotech. 2014, 39, 670 – 676 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.pep.wiley-vch.de 673

Synthesis of Tetranitroglycoluril from Imidazo-[4,5-d]-imidazoles
from imidazo imidazoles was subjected to the standard

suite of safety tests, impact, friction, and ESD. It was found

the material prepared from the literature method had an

H50 drop height value of 33.2 cm and material prepared

from the imidazo imidazole had a drop height value of

39.1 cm (Table 2).

3 Experimental Section

Note: While these compounds were prepared without incident according the following procedures, these materials

are energetic and should be prepared and handled cautiously by trained personnel.

3.1 General Considerations

Nuclear magnetic resonance (NMR) spectra were recorded

with a Bruker 600 MHz instrument. All NMR chemical shifts

are reported in ppm relative to TMSCl. FTIR spectra were

recorded with a Bruker Alpha-T fitted with a diamond attenuated total reflectance (DATR) attachment. Density was

measured using gas pycnometry with a Micromeritics AccuPyc 1330 using nitrogen as the analysis gas. Elemental analysis was conducted with a PerkinElmer 2400 Series II CHNS/O

combustion elemental analyzer using helium as the carrier

gas. Differential scanning calorimetry (DSC) was performed

with a TA instruments Q10 or Q20 calorimeter calibrated to

the melting point of indium with a heating rate of 108C

min1 in an aluminum pan with a pin hole. All deuterated

solvents were obtained from Cambridge Isotope Laboratories, Andover, MA, USA. All other materials used were obtained from Sigma Aldrich Corp. St. Louis, MO, USA and

were used as received unless otherwise noted.

3.2 Synthetic Procedures

3.2.1 Synthesis of 5–7

The syntheses of these compounds were carried out according to the methods detailed by Kony [6]. His procedures were quickly and accurately reproduced to yield 5–7

and analysis of the resulting products matched the data

given in his publication.

3.2.2 Alternate Preparation of 6

Compound 6 was originally prepared by the action of

100% HNO3 on the purified hydrochloride salt 5 [6]. It was

discovered 6 is most easily prepared by taking the crude 5

obtained from the procedures described in the paper and

dissolving it in 70% HNO3. Once all the material was dissolved, it could be crash precipitated by pouring over ice

followed by purification from dilute HNO3 as in literature

[6].

3.2.3 Synthesis of 1 from 5–7

Representative Procedure from 5: Compound 5 (100 mg,

0.45 mmol) was dissolved in HNO3 (2 mL, 100%) at 08C in

an inert nitrogen atmosphere. To this solution was added

TFAA (2 mL) dropwise at such a rate as to keep the temperature of the solution below 108C. After the addition was

completed, the reaction was allowed to warm to room

temperature and stirred for 2 h at which point stirring was

stopped and the precipitant was allowed to settle. The

mother liquor was decanted, and the residual solid was

washed with anhydrous DCM (5–7  5 mL). Afterwards, the

solid 1 was dried under vacuum (1333.22 Pa) at ambient

temperature for 2 h. The total amount of 1 recovered from

this process was 70.1 mg (0.22 mmol, 49%) Peak decomposition was observed to be 217–2208C in the DSC. 1

H NMR

(600.182 MHz, [D6]acetone): d=7.78 (s, 2 H). 13C NMR

(150.046 MHz, [D6]acetone): d=141.8, 65.3. FT-IR (DATR):

n ̃ =2997, 2894, 1798, 1652, 1617, 1594, 1255, 1144, 1090,

768, 730, 698 cm1

. C4H2N4O10 : calcd. C 14.92; H 0.63; N

34.79%; found: C 14.89; H 0.63; N 34.72%.

From 6: 1 was prepared from 6 according to the above

representative procedure. The total amount of 1 recovered

from 100 mg (0.40 mmol) of 5 was 104 mg (0.32 mmol,

80%).

From 7: 1 was prepared from 7 according to the representative procedure. The total amount of 1 recovered from

100 mg (0.43 mmol) of 6 was 89.2 mg (0.28 mmol, 65%).

3.2.4 Scale up to 2 g of 1 from 6

The nitrate salt 6 (2.027 g, 8.16 mmol) was dissolved into

HNO3 (40 mL, 100%) at 0 8C in an nitrogen atmosphere. To

this solution was added dropwise TFAA (40 mL) at a rate to

keep the temperature under 108C. Upon completion of the

addition, the material was allowed to warm to ambient

temperature and stirring was continued for 2 h. After the

time had elapsed, the suspension was cooled to 08C, stirring was stopped, and the suspended solid was allowed to

settle. The mother liquor was decanted, and the remaining

solid was washed with DCM (5  20 mL). The material was

vacuum dried (1333.22 Pa, 208C) for 2 h. The total amount

of 1 recovered from this process was 1.89 g (5.86 mmol,

72%).

3.2.5 Procedure for Headspace Analysis

The Bruker Alpha-T was fitted with the transmission

module and in it was placed a 5-cm long gas flow cell

fitted with ZnSe windows. A sample injection port covered

with a septum was fitted in the gas supply line on the gas

supply side of the gas cell approximately 15 cm prior to

the cell. The exhaust of the cell was vented into the fume

hood. Nitrogen carrier gas at 12 mLmin1 was flowed

through the cell at all times, while measuring the concentration of N2O in the headspace. A background of pure ni674 www.pep.wiley-vch.de 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Propellants Explos. Pyrotech. 2014, 39, 670 – 676

Full Paper W. M. Sherrill, E. C. Johnson, J. E. Banning
trogen was used, and a sample of pure N2O was injected

into the cell to confirm the setup was functioning correctly.

A 6 mL sample of the headspace gases from a 100 mg

scale reaction was injected and analyzed at 3 min intervals.

The amount of N2O present in the sample was determined

by measuring the absorbance unit values for the N2O peak

of the doublet at ca. 2235 cm1

.

3.2.6 Sphericalization Procedure

A Typical Procedure at the 2 mmol Scale: TNGU (640 mg,

2 mmol) prepared via literature methods, was dissolved in

HNO3 (6.4 mL, 98%) at 20–25 8C. This homogeneous solution was introduced below the surface to a stirring beaker

of DCM containing ca. 100 mL at a rate approx. 1 mLmin1

.

Once addition is completed, stirring was stopped, and the

TNGU settled to the bottom of the beaker. The supernatant

was decanted and the TNGU was resuspended in ca. 25 mL

of DCM then allowed to settle. This washing procedure was

repeated 4–6 times until no HNO3 remained. The TNGU was

vacuum dried to remove the residual DCM and stored in

a desiccator over Drierite

. The amount of spherical TNGU

recovered from this process was 462 mg (1.43 mmol, 72%).

Scanning electron microscopy of the material from this process stirred at a rate of 250 RPM yielded spheres ca. 3 mM

in diameter.

A Typical Procedure at the 7 mmol Scale: TNGU (2.27 g,

7 mmol) prepared via the literature methods was dissolved

in HNO3 822.7 mL, 98%) at 20–25 8C. This homogeneous

solution was introduced below the surface to a stirring

beaker of DCM containing ca. 200 mL at a rate of approx.

1 mLmin1. Once addition was completed, stirring was

stopped, and the TNGU settled to the bottom of the

beaker. The supernatant was decanted, the TNGU was resuspended in ca. 50 mL of DCM, and then allowed to settle.

This washing procedure was repeated 4–6 times until no

HNO3 remained. The TNGU was vacuum dried to remove

the residual DCM and stored in a desiccator over Drierite

.

The amount of spherical TNGU recovered from this process

was 1.66 g (5.15 mmol, 73%). Scanning electron microscopy

of the material from this process stirred at a rate of 250

RPM yielded spheres ca. 3 mM in diameter.

4 Conclusions

During the attempted synthesis of target compound 8,

a new method for the synthesis of 1 from imidazo imidazoles was discovered. These imidazo imidazoles, 5–7, are

susceptible to the loss of N2O under the nitration conditions, and 1 obtained with this new route is more than

twice more stable to external insult than 1 produced according to traditional literature methods. TNGU isolated

from the nitration of 5–7 still exhibits analytics matching

that of 1 synthesized by literature methods. Furthermore,

a new morphology of TNGU was discovered from solvent/

anti-solvent interactions of HNO3 and DCM. This new,

spherical morphology shows remarkably improved sensitivity over other morphologies previously reported. Additionally, sphericalized 1 as well as TNGU isolated from the nitration of 5–7 appears to exhibit similar hydrolytic stability to

TNGU prepared with alternative methods. Both of these

materials were observed to decompose if left exposed to

a moist atmosphere or upon dissolution in wet solvents.

Acknowledgments

The authors wish to thank Mr. Roy Maulbetsch, Mr. Terry Piatt, and

Ms. Lori Pridgeon for general equipment assistance and supply

management. The authors also wish to thank Drs. Eric Bukowski,

Brian Roos, Thuvan Piehler, and Mr. Stephen Aubert for procedural

input and technical review. The authors also wish to express their

gratitude to Drs. Edward Byrd and Betsy Rice for making available

their computer codes and related scripts. The authors are also indebted to Dr. Kevin McNesby for assistance with FTIR related questions.

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Received: February 14, 2014

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Published online: May 26, 2014

676 www.pep.wiley-vch.de 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Propellants Explos. Pyrotech. 2014, 39, 670 – 676

Full Paper W. M. Sherrill, E. C. Johnson, J. E. Banning
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