Recent Advances in the Synthesis of High Explosive Materials

Abstract

This review discusses the recent advances in the syntheses of high explosive energetic materials. Syntheses of some relevant modern primary explosives and secondary high explosives, and the sensitivities and properties of these molecules are provided. In addition to the synthesis of such materials, processing improvement and formulating aspects using these ingredients, where applicable, are discussed in detail.

Full text

Review
Recent Advances in the Synthesis of High
Explosive Materials
Jesse J. Sabatini 1, * and Karl D. Oyler 2, *
Received: 31 July 2015; Accepted: 22 December 2015; Published: 29 December 2015
Academic Editor: Thomas M. Klapötke
1US Army Research Laboratory Weapons & Materials Research Directorate (WMRD) Lethality Division,
Energetics Technology Branch, Aberdeen Proving Ground, MD 21005, USA
2US Army Armaments Research, Development & Engineering Center (ARDEC) Energetics, Warheads, &
Manufacturing Directorate Explosives Development Branch, Picatinny Arsenal, NJ 07806-5000, USA
*Correspondence: jesse.j.sabatini.civ@mail.mil (J.J.S.); karl.d.oyler.civ@mail.mil (K.D.O.);
Tel.: +1-410-278-0235 (J.J.S.); +1-973-724-4784 (K.D.O.)
Abstract:
This review discusses the recent advances in the syntheses of high explosive energetic
materials. Syntheses of some relevant modern primary explosives and secondary high explosives,
and the sensitivities and properties of these molecules are provided. In addition to the synthesis of
such materials, processing improvement and formulating aspects using these ingredients, where
applicable, are discussed in detail.
Keywords: energetic materials; explosives; synthesis; organic chemistry; processing
1. Introduction
There is an ever-increasing need for the development of new energetic materials for explosive
applications. This includes, but is not limited to, the area of primary explosives and secondary high
explosives. Primary explosives (or “primaries” as they are colloquially called) are defined as energetic
materials that possess an exceptionally high initiation sensitivity to impact, friction, electrostatic
discharge, heat, and shock. Primaries are known to reach detonation very quickly after such an initiation
event. The large amount of energy released upon initiation of a primary—typically in the form of heat
or a shockwave—is used to initiate less sensitive energetic materials, including secondary explosives,
propellants, and pyrotechnics. Despite their highly sensitive nature, primaries are, in general, less
powerful than secondary explosive materials [
1
]. In other words, primaries typically possess lower
detonation velocities, detonation pressures, and a lower heat of detonation than a given secondary
explosive. Despite the lower energy of a primary, extreme care is urged when handling these materials.
Primaries are ubiquitous in both military munitions and commercial items, where their main
function is to serve as the key ingredient in initiators such as detonators, blasting caps, and pyrotechnic
percussion primer formulations. By far, the most commonly used primary explosives by the U.S. military
are lead azide (used most often in detonators and blasting caps) and lead styphnate (most often
found in percussion primers). There has been significant interest in recent years to develop new
primary explosive materials, as the lead content of these materials is highly objectionable from both
a toxicological and environmental standpoint [2].
Secondary explosives (colloquially known as “secondaries”) differ from primaries in that they
are much less sensitive to impact, friction, electrostatic discharge, heat, and shock. Instead, they are
intended to be initiated by the heat and shockwave generated from a detonating primary explosive
charge. There is a tremendous need for the development of secondary explosives that have higher
performance, lower sensitivity, and lower toxicity than the currently fielded explosive compounds.
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Crystals 2016,6, 5 2 of 22
Higher performing secondaries are classified as those having higher detonation velocities, higher
detonation pressures, higher crystalline densities, and a higher heat of detonation. Secondary explosives
with a higher performance typically correlate to an increase in brisance, which is defined as the
fragmentation ability or shattering effect of an explosive charge within a specific vicinity. As a rule of
thumb, explosives with higher crystal densities and higher enthalpies of formation (
∆f
H
0
) directly
correlate to higher detonation pressures, detonation velocities, and overall greater energy release.
Secondaries possessing a lower sensitivity are crucial for the development of insensitive munitions
(IM). In the IM sub-area, the development of explosive materials with higher thermal stability and
secondary explosive-based formulations that have a low sensitivity to bullet/fragment impact are
critical. Minimizing sympathetic detonation—the unintended detonation of a nearby explosive charge
which has been caused by a deliberate explosion of another explosive charge, as well as fast- and slow
cook-off (the exploding of a munition due to excessive heat in the vicinity)—is key to those interested
in IM-based materials. The ideal secondary explosive will have a low toxicity profile of the explosive
itself, its degradation products via natural degradation pathways, as well as its detonation products.
Although the field of explosives chemistry has existed for well over a century and produced
a wealth of published compounds and their performance data, general literature reviews on explosive
compounds [
3
–
5
] are relatively small in number and infrequently published. To supplement this list,
herein we seek to provide an overview of the more significant recent advances in the area of explosive
molecules. This summary is by no means exhaustive, given the wide scope of the explosives field, and
the topics covered will focus largely on relatively recently developed compounds which are thought to
have the highest likelihood of seeing practical application in the future.
2. Primary Explosives
2.1. Legacy Primary Explosives
While primary explosives have historically consisted of materials that exhibit reasonable explosive
power and a high sensitivity, these legacy materials also possess a high density as a result of the
presence of heavy metals within their respective structures. The structures of some historically used
primary explosives are given in Figure 1. It is commonly agreed that the highly toxic mercury fulminate
(1), adopted for use in some of the first percussion primer formulations in the early 1800s [
6
] and
later by Alfred Nobel for some of the first blasting caps in 1867 [
7
], is the first primary explosive to
see practical application. The high costs associated with mercury, the high sensitivity of mercury
fulminate, and its ability to lose performance under high loading pressures paved the way for lead
azide (2) to replace the compound starting in the early 1900s [
8
]. Today, lead azide (including its
less sensitive dextrin-coated form) finds wide-ranging application in energetic materials as the main
primary explosive ingredient in blasting caps and detonators.
A few years after lead azide began to find applications is the energetics field, the first practical
use of lead styphnate was described in a British patent [
9
]. Lead styphnate comes in two forms;
normal lead styphnate (lead(II) 2,4,6-trinitro-benzene-1,3-diolate hydrate) (3) and basic lead styphnate
(di(lead(II) hydroxide)-2,4,6-trinitro-benzene-1,3-diolate) (4). Although less powerful than lead azide,
lead styphnate is easier to initiate. For this reason, basic lead styphnate is present in some lead
azide-based stab detonator formulations such as NOL-130. The use of basic lead styphnate instead
of normal lead styphnate in stab detonator mixtures assists in preventing the decomposition of lead
azide via a hydrolytic pathway. Normal lead styphnate is commonly encountered as the main primary
explosive ingredient in primer applications.

Crystals 2016,6, 5 3 of 22
Crystals 2016, 6, 5
3
Figure 1. Chemical structure of the primary explosives; mercury fulminate (1), lead azide (2) and
normal lead styphnate (3) and basic lead styphnate (4).
2.2. Why “Green” Primary Explosives?
Over the past two decades, there has been a significant interest amongst the US Department of
Defense (DoD) community, in particular, to address environmental issues associated with military
explosives, propellants, and pyrotechnics. Today, lead azide and lead styphnate comprise the vast
majority of military and civilian primary explosive use. The obvious issue with these two materials
is the presence of lead, which is an established heavy metal toxin. Until the 1960s, these materials
were not believed to significantly impact health [10]. Over the past five decades, however, the view
of lead-based primary explosives has changed significantly. Ingestion and/or inhalation of lead is
now known to affect the central nervous system, the renal system, the blood, and has been a
contributing factor in mental impairment and behavioral issues [11]. Lead has become one of the most
regulated chemical substances on an international scale. It is classified as a toxic pollutant in the USA,
and efforts have been underway for decades to remove lead from Federal facilities, including DoD
facilities [12]. In 2012, the National Research Council recommended that the DoD review its 30 years
old policy on protecting workers from lead exposure in firing ranges [13]. In Europe, the Registration,
Evaluation, Authorization, and Restriction of Chemicals (REACH) program has called for the specific
regulation of lead azide and lead styphnate. Therefore, a clear need exists for the successful
development and replacement of these two aforementioned primary explosives.
Aside from the environmental concerns associated with lead azide, a further complication exists
in that the material is known to slowly decompose under ambient conditions (Scheme 1). Lead azide
reacts with CO2 and H2O to produce basic lead carbonate and highly toxic hydrazoic acid (HN3). HN3
can react with exposed copper metal surface in pipes and wires, thus generating the highly sensitive
and deadly copper azide (Cu(N3)2). Several fatal military accidents over the years have been
associated with the accidental generation of copper azide [14].
Scheme 1. Decomposition reaction of lead azide.
2.3. “Green” Primary Explosive Candidates
2.3.1. Metal-Free Primary Explosives
2.3.1.1. Cyanuric Triazide (CTA)
CTA (6), prepared in a single, efficient, and eco-friendly step by treatment of cyanuric trichloride
(5) with sodium azide (Scheme 2), has more explosive power than lead azide, making it a suitable
replacement for lead azide in large-sized detonators. Unfortunately, there are several complications
with the material, in particular its tendency to undergo sublimation at elevated temperatures [15].
Further, the earlier syntheses of CTA reported an extreme sensitivity of the material to ignition
stimuli [16]. The crystalline material from the earlier syntheses exhibited a needle-like morphology,
which broke easily, thus increasing the risk of accidental detonation.
Figure 1.
Chemical structure of the primary explosives; mercury fulminate (1), lead azide (2) and
normal lead styphnate (3) and basic lead styphnate (4).
2.2. Why “Green” Primary Explosives?
Over the past two decades, there has been a significant interest amongst the US Department of
Defense (DoD) community, in particular, to address environmental issues associated with military
explosives, propellants, and pyrotechnics. Today, lead azide and lead styphnate comprise the vast
majority of military and civilian primary explosive use. The obvious issue with these two materials
is the presence of lead, which is an established heavy metal toxin. Until the 1960s, these materials
were not believed to significantly impact health [
10
]. Over the past five decades, however, the view of
lead-based primary explosives has changed significantly. Ingestion and/or inhalation of lead is now
known to affect the central nervous system, the renal system, the blood, and has been a contributing
factor in mental impairment and behavioral issues [
11
]. Lead has become one of the most regulated
chemical substances on an international scale. It is classified as a toxic pollutant in the USA, and efforts
have been underway for decades to remove lead from Federal facilities, including DoD facilities [
12
].
In 2012, the National Research Council recommended that the DoD review its 30 years old policy on
protecting workers from lead exposure in firing ranges [
13
]. In Europe, the Registration, Evaluation,
Authorization, and Restriction of Chemicals (REACH) program has called for the specific regulation
of lead azide and lead styphnate. Therefore, a clear need exists for the successful development and
replacement of these two aforementioned primary explosives.
Aside from the environmental concerns associated with lead azide, a further complication exists
in that the material is known to slowly decompose under ambient conditions (Scheme 1). Lead azide
reacts with CO
2
and H
2
O to produce basic lead carbonate and highly toxic hydrazoic acid (HN
3
).
HN
3
can react with exposed copper metal surface in pipes and wires, thus generating the highly
sensitive and deadly copper azide (Cu(N
3
)
2
). Several fatal military accidents over the years have been
associated with the accidental generation of copper azide [14].
Crystals 2016, 6, 5
3
Figure 1. Chemical structure of the primary explosives; mercury fulminate (1), lead azide (2) and
normal lead styphnate (3) and basic lead styphnate (4).
2.2. Why “Green” Primary Explosives?
Over the past two decades, there has been a significant interest amongst the US Department of
Defense (DoD) community, in particular, to address environmental issues associated with military
explosives, propellants, and pyrotechnics. Today, lead azide and lead styphnate comprise the vast
majority of military and civilian primary explosive use. The obvious issue with these two materials
is the presence of lead, which is an established heavy metal toxin. Until the 1960s, these materials
were not believed to significantly impact health [10]. Over the past five decades, however, the view
of lead-based primary explosives has changed significantly. Ingestion and/or inhalation of lead is
now known to affect the central nervous system, the renal system, the blood, and has been a
contributing factor in mental impairment and behavioral issues [11]. Lead has become one of the most
regulated chemical substances on an international scale. It is classified as a toxic pollutant in the USA,
and efforts have been underway for decades to remove lead from Federal facilities, including DoD
facilities [12]. In 2012, the National Research Council recommended that the DoD review its 30 years
old policy on protecting workers from lead exposure in firing ranges [13]. In Europe, the Registration,
Evaluation, Authorization, and Restriction of Chemicals (REACH) program has called for the specific
regulation of lead azide and lead styphnate. Therefore, a clear need exists for the successful
development and replacement of these two aforementioned primary explosives.
Aside from the environmental concerns associated with lead azide, a further complication exists
in that the material is known to slowly decompose under ambient conditions (Scheme 1). Lead azide
reacts with CO2 and H2O to produce basic lead carbonate and highly toxic hydrazoic acid (HN3). HN3
can react with exposed copper metal surface in pipes and wires, thus generating the highly sensitive
and deadly copper azide (Cu(N3)2). Several fatal military accidents over the years have been
associated with the accidental generation of copper azide [14].
Scheme 1. Decomposition reaction of lead azide.
2.3. “Green” Primary Explosive Candidates
2.3.1. Metal-Free Primary Explosives
2.3.1.1. Cyanuric Triazide (CTA)
CTA (6), prepared in a single, efficient, and eco-friendly step by treatment of cyanuric trichloride
(5) with sodium azide (Scheme 2), has more explosive power than lead azide, making it a suitable
replacement for lead azide in large-sized detonators. Unfortunately, there are several complications
with the material, in particular its tendency to undergo sublimation at elevated temperatures [15].
Further, the earlier syntheses of CTA reported an extreme sensitivity of the material to ignition
stimuli [16]. The crystalline material from the earlier syntheses exhibited a needle-like morphology,
which broke easily, thus increasing the risk of accidental detonation.
Scheme 1. Decomposition reaction of lead azide.
2.3. “Green” Primary Explosive Candidates
2.3.1. Metal-Free Primary Explosives
2.3.1.1. Cyanuric Triazide (CTA)
CTA (6), prepared in a single, efficient, and eco-friendly step by treatment of cyanuric trichloride
(5) with sodium azide (Scheme 2), has more explosive power than lead azide, making it a suitable
replacement for lead azide in large-sized detonators. Unfortunately, there are several complications
with the material, in particular its tendency to undergo sublimation at elevated temperatures [
15
].
Further, the earlier syntheses of CTA reported an extreme sensitivity of the material to ignition

Crystals 2016,6, 5 4 of 22
stimuli [
16
]. The crystalline material from the earlier syntheses exhibited a needle-like morphology,
which broke easily, thus increasing the risk of accidental detonation.
Crystals 2016, 6, 5
4
Scheme 2. Synthesis of cyanuric triazide (CTA, 6).
Although CTA was first patented in 1921 [17], a newer synthetic procedure for the material
developed by ARDEC in 2009 resulted in a reduced particle size of the material [18]. As a result of
the new synthesis procedure, CTA has been further investigated by researchers at ARDEC, and has
found successful use as a replacement for both lead azide and lead styphnate in the NOL-130 stab
detonator mix, as well as some more recent work as a potential lead styphnate replacement in
percussion primer formulations (NB: The lead-based NOL-130 formulation consists of 40% lead
styphnate, 20% lead azide, 20% barium nitrate, 15% antimony trisulfide, and 5% tetrazene). The
sublimation of CTA, and thus its looming safety issues, however, remains an Achilles heel for this
material if it is to ever gain serious traction in having widespread serious military and civilian
applications.
2.3.1.2. 2-Diazo-4,6-Dinitrophenol (DDNP)
The synthesis of DDNP (9) is described in Scheme 3. Treatment of picric acid (7) with a controlled
simultaneous addition of aqueous sodium sulfide yields sodium picramate (8), which is then
converted to DDNP via the Griess diazotization. DDNP has found explosive use since the early 20th
century [1]. Although old enough to be considered a legacy primary explosive, it tends to fall into a
different category because of its heavy metal-free nature.
Scheme 3. Synthesis of DDNP (9).
At this time, DDNP is generally considered to be an unsuitable candidate for demanding
military primer applications. The material is reputed to suffer from reliability issues in extreme cold
weather climates. DDNP’s low sensitivity to friction, its low flame temperature, and its
incompatibility with lead azide also plague this compound [19]. Due to different requirements
necessary for the production of commercial primer formulations, DDNP has found recent usage and
interest from the civilian sectors as a “green” replacement for lead styphnate in primer applications
[20,21].
2.3.1.3. Peroxide-Based Explosives
Although primary explosives are designed with the intent to be sensitive to various ignition
stimuli, it has always been believed that peroxide-based explosives are too sensitive to garner
practical use for even primary explosive applications. Chemically, the high degree of instability of
the oxygen-oxygen bond is the culprit behind this sensitivity. Two peroxide-based materials that
have been studied extensively are triacetone triperoxide (TATP) and hexamethylenetriperoxide
diamine (HMTD). Their syntheses are remarkably simple and are performed from cheap,
commercially available starting materials, as summarized in Scheme 4. TATP (10) and HMTD (11)
are synthesized from acetone and hexamine, respectively, in the presence of acidic water and
Scheme 2. Synthesis of cyanuric triazide (CTA, 6).
Although CTA was first patented in 1921 [
17
], a newer synthetic procedure for the material
developed by ARDEC in 2009 resulted in a reduced particle size of the material [
18
]. As a result of the
new synthesis procedure, CTA has been further investigated by researchers at ARDEC, and has found
successful use as a replacement for both lead azide and lead styphnate in the NOL-130 stab detonator
mix, as well as some more recent work as a potential lead styphnate replacement in percussion primer
formulations (NB: The lead-based NOL-130 formulation consists of 40% lead styphnate, 20% lead
azide, 20% barium nitrate, 15% antimony trisulfide, and 5% tetrazene). The sublimation of CTA, and
thus its looming safety issues, however, remains an Achilles heel for this material if it is to ever gain
serious traction in having widespread serious military and civilian applications.
2.3.1.2. 2-Diazo-4,6-Dinitrophenol (DDNP)
The synthesis of DDNP (9) is described in Scheme 3. Treatment of picric acid (7) with a controlled
simultaneous addition of aqueous sodium sulfide yields sodium picramate (8), which is then converted
to DDNP via the Griess diazotization. DDNP has found explosive use since the early 20th century [
1
].
Although old enough to be considered a legacy primary explosive, it tends to fall into a different
category because of its heavy metal-free nature.
Crystals 2016, 6, 5
4
Scheme 2. Synthesis of cyanuric triazide (CTA, 6).
Although CTA was first patented in 1921 [17], a newer synthetic procedure for the material
developed by ARDEC in 2009 resulted in a reduced particle size of the material [18]. As a result of
the new synthesis procedure, CTA has been further investigated by researchers at ARDEC, and has
found successful use as a replacement for both lead azide and lead styphnate in the NOL-130 stab
detonator mix, as well as some more recent work as a potential lead styphnate replacement in
percussion primer formulations (NB: The lead-based NOL-130 formulation consists of 40% lead
styphnate, 20% lead azide, 20% barium nitrate, 15% antimony trisulfide, and 5% tetrazene). The
sublimation of CTA, and thus its looming safety issues, however, remains an Achilles heel for this
material if it is to ever gain serious traction in having widespread serious military and civilian
applications.
2.3.1.2. 2-Diazo-4,6-Dinitrophenol (DDNP)
The synthesis of DDNP (9) is described in Scheme 3. Treatment of picric acid (7) with a controlled
simultaneous addition of aqueous sodium sulfide yields sodium picramate (8), which is then
converted to DDNP via the Griess diazotization. DDNP has found explosive use since the early 20th
century [1]. Although old enough to be considered a legacy primary explosive, it tends to fall into a
different category because of its heavy metal-free nature.
Scheme 3. Synthesis of DDNP (9).
At this time, DDNP is generally considered to be an unsuitable candidate for demanding
military primer applications. The material is reputed to suffer from reliability issues in extreme cold
weather climates. DDNP’s low sensitivity to friction, its low flame temperature, and its
incompatibility with lead azide also plague this compound [19]. Due to different requirements
necessary for the production of commercial primer formulations, DDNP has found recent usage and
interest from the civilian sectors as a “green” replacement for lead styphnate in primer applications
[20,21].
2.3.1.3. Peroxide-Based Explosives
Although primary explosives are designed with the intent to be sensitive to various ignition
stimuli, it has always been believed that peroxide-based explosives are too sensitive to garner
practical use for even primary explosive applications. Chemically, the high degree of instability of
the oxygen-oxygen bond is the culprit behind this sensitivity. Two peroxide-based materials that
have been studied extensively are triacetone triperoxide (TATP) and hexamethylenetriperoxide
diamine (HMTD). Their syntheses are remarkably simple and are performed from cheap,
commercially available starting materials, as summarized in Scheme 4. TATP (10) and HMTD (11)
are synthesized from acetone and hexamine, respectively, in the presence of acidic water and
Scheme 3. Synthesis of DDNP (9).
At this time, DDNP is generally considered to be an unsuitable candidate for demanding military
primer applications. The material is reputed to suffer from reliability issues in extreme cold weather
climates. DDNP’s low sensitivity to friction, its low flame temperature, and its incompatibility with
lead azide also plague this compound [
19
]. Due to different requirements necessary for the production
of commercial primer formulations, DDNP has found recent usage and interest from the civilian
sectors as a “green” replacement for lead styphnate in primer applications [20,21].
2.3.1.3. Peroxide-Based Explosives
Although primary explosives are designed with the intent to be sensitive to various ignition
stimuli, it has always been believed that peroxide-based explosives are too sensitive to garner
practical use for even primary explosive applications. Chemically, the high degree of instability
of the oxygen-oxygen bond is the culprit behind this sensitivity. Two peroxide-based materials
that have been studied extensively are triacetone triperoxide (TATP) and hexamethylenetriperoxide
diamine (HMTD). Their syntheses are remarkably simple and are performed from cheap, commercially

Crystals 2016,6, 5 5 of 22
available starting materials, as summarized in Scheme 4. TATP (10) and HMTD (11) are synthesized
from acetone and hexamine, respectively, in the presence of acidic water and hydrogen peroxide.
The historically negative safety profile of peroxide-based primary explosives, coupled with the blatant
terroristic use of materials such as TATP and HMTD have discouraged the investigation and use of
organic peroxides as a viable energetic material for practical use.
Crystals 2016, 6, 5
5
hydrogen peroxide. The historically negative safety profile of peroxide-based primary explosives,
coupled with the blatant terroristic use of materials such as TATP and HMTD have discouraged the
investigation and use of organic peroxides as a viable energetic material for practical use.
Scheme 4. Synthesis of TATP (10) and HMTD (11).
Work spearheaded by Winter in 2015, however, has shown that organic peroxides can be
designed that exhibit high performance, yet reasonable sensitivities [22]. As summarized in Scheme
5, a given diketone or dialdehyde was reacted with hydrogen peroxide in the presence of a catalytic
amount of iodine to afford the bis-geminal hydroperoxy derivatives 12–15. Despite the presence of
normally labile peroxy groups, it is believed that the lability is suppressed due to the presence of
intermolecular O–H…O hydrogen bonds, as well as several O…O and C…H close contacts which
was determined to occur in the crystalline lattice of 15 upon confirmation of the structure by single
crystal X-ray diffraction.
Scheme 5. Synthesis of stable peroxide-based primary explosives.
The sensitivities and performance of geminal peroxides 12–15, compared to TATP, are
summarized in Table 1. Remarkably, geminal peroxy compounds 12–15 are more insensitive to
impact and friction than TATP, with comparable or better ESD sensitivities. This phenomenon occurs
despite the better oxygen balances, higher crystalline densities, higher detonation velocities, and total
energy of detonation values compared to TATP. The Winter approach is unique because it describes
the first known examples of stabilized peroxide-based primary explosives. Although the thermal
stabilities of this class of compounds could use some improvement, the area of peroxide-based
primary explosives, in light of this discovery, ought to be investigated further for possible
application.
Scheme 4. Synthesis of TATP (10) and HMTD (11).
Work spearheaded by Winter in 2015, however, has shown that organic peroxides can be designed
that exhibit high performance, yet reasonable sensitivities [
22
]. As summarized in Scheme 5, a given
diketone or dialdehyde was reacted with hydrogen peroxide in the presence of a catalytic amount of
iodine to afford the bis-geminal hydroperoxy derivatives 12–15. Despite the presence of normally
labile peroxy groups, it is believed that the lability is suppressed due to the presence of intermolecular
O–H . . . O hydrogen bonds, as well as several O . . . O and C . . . H close contacts which was determined
to occur in the crystalline lattice of 15 upon confirmation of the structure by single crystal X-ray diffraction.
Crystals 2016, 6, 5
5
hydrogen peroxide. The historically negative safety profile of peroxide-based primary explosives,
coupled with the blatant terroristic use of materials such as TATP and HMTD have discouraged the
investigation and use of organic peroxides as a viable energetic material for practical use.
Scheme 4. Synthesis of TATP (10) and HMTD (11).
Work spearheaded by Winter in 2015, however, has shown that organic peroxides can be
designed that exhibit high performance, yet reasonable sensitivities [22]. As summarized in Scheme
5, a given diketone or dialdehyde was reacted with hydrogen peroxide in the presence of a catalytic
amount of iodine to afford the bis-geminal hydroperoxy derivatives 12–15. Despite the presence of
normally labile peroxy groups, it is believed that the lability is suppressed due to the presence of
intermolecular O–H…O hydrogen bonds, as well as several O…O and C…H close contacts which
was determined to occur in the crystalline lattice of 15 upon confirmation of the structure by single
crystal X-ray diffraction.
Scheme 5. Synthesis of stable peroxide-based primary explosives.
The sensitivities and performance of geminal peroxides 12–15, compared to TATP, are
summarized in Table 1. Remarkably, geminal peroxy compounds 12–15 are more insensitive to
impact and friction than TATP, with comparable or better ESD sensitivities. This phenomenon occurs
despite the better oxygen balances, higher crystalline densities, higher detonation velocities, and total
energy of detonation values compared to TATP. The Winter approach is unique because it describes
the first known examples of stabilized peroxide-based primary explosives. Although the thermal
stabilities of this class of compounds could use some improvement, the area of peroxide-based
primary explosives, in light of this discovery, ought to be investigated further for possible
application.
Scheme 5. Synthesis of stable peroxide-based primary explosives.
The sensitivities and performance of geminal peroxides 12–15, compared to TATP, are summarized
in Table 1. Remarkably, geminal peroxy compounds 12–15 are more insensitive to impact and
friction than TATP, with comparable or better ESD sensitivities. This phenomenon occurs despite the
better oxygen balances, higher crystalline densities, higher detonation velocities, and total energy of
detonation values compared to TATP. The Winter approach is unique because it describes the first
known examples of stabilized peroxide-based primary explosives. Although the thermal stabilities of
this class of compounds could use some improvement, the area of peroxide-based primary explosives,
in light of this discovery, ought to be investigated further for possible application.

Crystals 2016,6, 5 6 of 22
Table 1. Sensitivities and performance of geminal peroxides 12–15 and TATP.
Data Category 12 13 14 15 TATP
IS [J] a2 1 2 3 0.3
FS [N] b5 5 5 <5 0.1
ESD c[J] c0.2 0.5 0.1 0.25 0.16
Tdec [˝C] d117 98 100 105 150–160
ΩCO2[%] e´126.2 ´114.18 ´100.76 ´88.83 ´151.19
ρ[g/cc] f1.35 1.375 1.6 1.6 1.18
Pcj [kbar] g117 126 195 195 –
Vdet [m/s] h6150 6250 6428 7130 5300
∆f
H
0
[kJ/mol]
i´703.6 ´660.8 ´418.2 ´418.2 ´583.8
∆exU0[kJ/kg] j´4636 ´4875 ´5083 ´5498 ´2745
a
IS = impact sensitivity;
b
FS = friction sensitivity;
c
ESD = electrostatic discharge;
d
T
dec
= Temperature
of decomposition;
eΩCO2
= CO
2
oxygen balance;
fρ
= crystalline density;
g
P
cj
= detonation pressure;
hVdet = detonation velocity; i∆fH0= molar enthalpy of formation; j∆exU0= total energy of detonation.
2.3.1.4. Tetrazene and MTX-1
1-Amino-1-(1H-tetrazol-5-yl)-azo-guanidine hydrate, known colloquially as tetrazene (16), is
a well-known sensitizer in percussion primer compositions (Figure 2) [
8
]. Without its presence in
primers, initiation is known to be dreadfully unreliable, or fails to function altogether. Despite its
reliability and widespread use in primers, tetrazene suffers from a high degree of hydrolytic and
thermal instability. It has been found to rapidly decompose at temperatures of ca. 90
˝
C, and this
temperature is commonly encountered during handling and storage of the material. Addition of
boiling water to tetrazene is also known to rapidly decompose the material.
Crystals 2016, 6, 5
6
Table 1. Sensitivities and performance of geminal peroxides 12–15 and TATP.
Data Category 12 13 14 15 TATP
IS [J] a 2 1 2 3 0.3
FS [N] b 5 5 5 <5 0.1
ESDc [J] c 0.2 0.5 0.1 0.25 0.16
Tdec [°C] d 117 98 100 105 150–160
Ω[%] e −126.2 −114.18 −100.76 −88.83 −151.19
ρ [g/cc] f 1.35 1.375 1.6 1.6 1.18
Pcj [kbar] g 117 126 195 195 –
Vdet [m/s] h 6150 6250 6428 7130 5300
ΔfH0 [kJ/mol] i −703.6 −660.8 −418.2 −418.2 −583.8
ΔexU0 [kJ/kg] j −4636 −4875 −5083 −5498 −2745
a IS = impact sensitivity; b FS = friction sensitivity; c ESD = electrostatic discharge; d Tdec = Temperature
of decomposition; e Ω = CO2 oxygen balance; f ρ = crystalline density; g Pcj = detonation pressure; h
Vdet = detonation velocity; i ΔfH0 = molar enthalpy of formation; j ΔexU0 = total energy of detonation.
2.3.1.4. Tetrazene and MTX-1
1-Amino-1-(1H-tetrazol-5-yl)-azo-guanidine hydrate, known colloquially as tetrazene (16), is a
well-known sensitizer in percussion primer compositions (Figure 2) [8]. Without its presence in
primers, initiation is known to be dreadfully unreliable, or fails to function altogether. Despite its
reliability and widespread use in primers, tetrazene suffers from a high degree of hydrolytic and
thermal instability. It has been found to rapidly decompose at temperatures of ca. 90 °C, and this
temperature is commonly encountered during handling and storage of the material. Addition of
boiling water to tetrazene is also known to rapidly decompose the material.
Figure 2. Molecular structure of tetrazene (16) and MTX-1 (17).
In light of these concerns, Fronabarger and Williams reacted tetrazene in aqueous solution to
produce MTX-1, which has promise for serving as a more thermally stable replacement [23,24]. Initial
studies have shown that while tetrazene decomposes exothermically at 144 °C, MTX-1 undergoes
exothermic decomposition at 214 °C. Holding tetrazene at 90 °C for 120 h results in 36% weight loss,
while MTX-1 experiences just 4% weight loss after the same time periods. Exposure of MTX-1 to water
for 120 days has virtually no effect, as MTX-1 can be re-isolated in nearly quantitative yield. It has
been stated that MTX-1 has comparable impact, friction and ESD sensitivities to tetrazene, thus
adding to its appeal as a potential replacement to this traditionally used organic sensitizing agent in
primer compositions.
2.3.2. Metal-Organic Primary Explosives
2.3.2.1. Potassium 4,6-Dinitrobenzofuroxan (KDNBF)
KDNBF (21) is synthesized in a three-step procedure, as summarized in Scheme 6 [25]. Exposure
of o-nitroaniline to NaOCl and base affords benzofuroxan 19, which is subjected to mixed acid
nitration to yield dinitrobenzofuroxan 20. Treatment of dinitrobenzofuroxan with potassium
bicarbonate furnishes KDNBF.
Figure 2. Molecular structure of tetrazene (16) and MTX-1 (17).
In light of these concerns, Fronabarger and Williams reacted tetrazene in aqueous solution
to produce MTX-1, which has promise for serving as a more thermally stable replacement [
23
,
24
].
Initial studies have shown that while tetrazene decomposes exothermically at 144
˝
C, MTX-1 undergoes
exothermic decomposition at 214
˝
C. Holding tetrazene at 90
˝
C for 120 h results in 36% weight loss,
while MTX-1 experiences just 4% weight loss after the same time periods. Exposure of MTX-1 to
water for 120 days has virtually no effect, as MTX-1 can be re-isolated in nearly quantitative yield.
It has been stated that MTX-1 has comparable impact, friction and ESD sensitivities to tetrazene, thus
adding to its appeal as a potential replacement to this traditionally used organic sensitizing agent in
primer compositions.
2.3.2. Metal-Organic Primary Explosives
2.3.2.1. Potassium 4,6-Dinitrobenzofuroxan (KDNBF)
KDNBF (21) is synthesized in a three-step procedure, as summarized in Scheme 6[
25
]. Exposure of
o-nitroaniline to NaOCl and base affords benzofuroxan 19, which is subjected to mixed acid nitration
to yield dinitrobenzofuroxan 20. Treatment of dinitrobenzofuroxan with potassium bicarbonate
furnishes KDNBF.

Crystals 2016,6, 5 7 of 22
Crystals 2016, 6, 5
7
Scheme 6. Synthesis of KDNBF.
Potassium is generally considered an innocuous and much safer alternative to lead. Thus,
KDNBF, much like DDNP, has found use as a suitable “green” primary explosive alternative to lead
styphnate in civilian primer compositions. While lead styphnate has a decomposition temperature of
280–290 °C, KDNBF’s decomposition temperature is much lower (217 °C). Also like DDNP, KDNBF
has not been adopted for widespread military use; the lower thermal stability of KDNBF may be one
of the reasons as to why this material has not been used as a universal alternative to lead styphnate
in primary explosive compositions.
2.3.2.2. Potassium 4,6-Dinitro-7-Hydroxybenzofuroxan (KDNP)
Scheme 7 details the synthesis of KDNP (25) [26]. Mixed acid nitration of 3-bromoanisole
delivered trinitro derivative 23. This material was treated with potassium azide in refluxing methanol
to effect concomitant substitution at C–3 and cleavage of the methyl ether, thus yielding azide 24.
Treatment of this azide with diethylcarbonate in heat produces KDNP (25). The approach detailed in
Scheme 6 is an improvement over previous syntheses that required the use of water, which was
retained in the product. This led to the formation of needles that were capable of breaking, and thus
dramatically increased the sensitivity of the material. The new synthetic procedure allowed for a free-
flowing powder to be obtained, and particle size could be varied by simple variations in temperature
and the addition rate of the solvent during recrystallization.
Scheme 7. Synthesis of KDNP (25).
Though originally synthesized over 30 years ago, KDNP has drawn renewed interest as a lead
styphnate replacement, due to its comparable explosive performance in military-relevant primers
and its thermal stability, as provided in Table 2 [22,26]. Note the structural similarities that exist
between KDNBF and KDNP; though KDNP possess a single hydrogen atom less than KDNBF, the
absence of this hydrogen allows for the restoration of aromaticity in the benzofuroxan ring system.
This phenomenon likely serves to explain the increased thermal stability of KDNP compared to
KDNBF.
Scheme 6. Synthesis of KDNBF.
Potassium is generally considered an innocuous and much safer alternative to lead. Thus, KDNBF,
much like DDNP, has found use as a suitable “green” primary explosive alternative to lead styphnate
in civilian primer compositions. While lead styphnate has a decomposition temperature of 280–290
˝
C,
KDNBF’s decomposition temperature is much lower (217 ˝C). Also like DDNP, KDNBF has not been
adopted for widespread military use; the lower thermal stability of KDNBF may be one of the reasons
as to why this material has not been used as a universal alternative to lead styphnate in primary
explosive compositions.
2.3.2.2. Potassium 4,6-Dinitro-7-Hydroxybenzofuroxan (KDNP)
Scheme 7details the synthesis of KDNP (25) [
26
]. Mixed acid nitration of 3-bromoanisole delivered
trinitro derivative 23. This material was treated with potassium azide in refluxing methanol to effect
concomitant substitution at C–3 and cleavage of the methyl ether, thus yielding azide 24. Treatment of
this azide with diethylcarbonate in heat produces KDNP (25). The approach detailed in Scheme 6is
an improvement over previous syntheses that required the use of water, which was retained in the
product. This led to the formation of needles that were capable of breaking, and thus dramatically
increased the sensitivity of the material. The new synthetic procedure allowed for a free-flowing
powder to be obtained, and particle size could be varied by simple variations in temperature and the
addition rate of the solvent during recrystallization.
Crystals 2016, 6, 5
7
Scheme 6. Synthesis of KDNBF.
Potassium is generally considered an innocuous and much safer alternative to lead. Thus,
KDNBF, much like DDNP, has found use as a suitable “green” primary explosive alternative to lead
styphnate in civilian primer compositions. While lead styphnate has a decomposition temperature of
280–290 °C, KDNBF’s decomposition temperature is much lower (217 °C). Also like DDNP, KDNBF
has not been adopted for widespread military use; the lower thermal stability of KDNBF may be one
of the reasons as to why this material has not been used as a universal alternative to lead styphnate
in primary explosive compositions.
2.3.2.2. Potassium 4,6-Dinitro-7-Hydroxybenzofuroxan (KDNP)
Scheme 7 details the synthesis of KDNP (25) [26]. Mixed acid nitration of 3-bromoanisole
delivered trinitro derivative 23. This material was treated with potassium azide in refluxing methanol
to effect concomitant substitution at C–3 and cleavage of the methyl ether, thus yielding azide 24.
Treatment of this azide with diethylcarbonate in heat produces KDNP (25). The approach detailed in
Scheme 6 is an improvement over previous syntheses that required the use of water, which was
retained in the product. This led to the formation of needles that were capable of breaking, and thus
dramatically increased the sensitivity of the material. The new synthetic procedure allowed for a free-
flowing powder to be obtained, and particle size could be varied by simple variations in temperature
and the addition rate of the solvent during recrystallization.
Scheme 7. Synthesis of KDNP (25).
Though originally synthesized over 30 years ago, KDNP has drawn renewed interest as a lead
styphnate replacement, due to its comparable explosive performance in military-relevant primers
and its thermal stability, as provided in Table 2 [22,26]. Note the structural similarities that exist
between KDNBF and KDNP; though KDNP possess a single hydrogen atom less than KDNBF, the
absence of this hydrogen allows for the restoration of aromaticity in the benzofuroxan ring system.
This phenomenon likely serves to explain the increased thermal stability of KDNP compared to
KDNBF.
Scheme 7. Synthesis of KDNP (25).
Though originally synthesized over 30 years ago, KDNP has drawn renewed interest as a lead
styphnate replacement, due to its comparable explosive performance in military-relevant primers
and its thermal stability, as provided in Table 2[
22
,
26
]. Note the structural similarities that exist
between KDNBF and KDNP; though KDNP possess a single hydrogen atom less than KDNBF, the
absence of this hydrogen allows for the restoration of aromaticity in the benzofuroxan ring system.
This phenomenon likely serves to explain the increased thermal stability of KDNP compared to KDNBF.

Crystals 2016,6, 5 8 of 22
Table 2. Sensitivities and performance of KDNP (25).
Data Category KDNP (25)
IS [J] a0.047
FS [N] b9.81
ESD c[µJ] c>675
Tdec [˝C] d285
ΩCO2[%] e´34.3
ρ[g/cc] f1.982
∆fH0[kJ/mol] g´197.07
∆exU0[kJ/kg] h3280
a
IS = impact sensitivity;
b
FS = friction sensitivity;
c
ESD = electrostatic discharge;
d
T
dec
= Temperature of
decomposition; eΩCO2= CO2oxygen balance; fρ= crystalline density; g∆fH0= molar enthalpy of formation;
h∆exU0= total energy of detonation.
2.3.2.3. Potassium 1,1'-dinitramino-5,5'-Bis(tetrazolate) (K2DNABT)
In 2014, Klapötke reported the synthesis and performance of K
2
DNABT (31) [
27
]. This material is
prepared in a seven step sequence, starting from dimethyl carbonate (Scheme 8). Desymmetrization of
dimethyl carbonate, followed by condensation with glyoxal afforded bis(hydrazone) 27. Treatment with
N-chlorosuccinimide (NCS), followed by displacement of the chlorines with azide, afforded diazido
bis(hydrazone) intermediate (29). Acid-induced cyclization to give bis(tetrazole) (30), nitration of
this species with dinitrogen pentoxide, and formation of the resultant dipotassium salt afforded K2DNABT.
Crystals 2016, 6, 5
8
Table 2. Sensitivities and performance of KDNP (25).
Data Category KDNP (25)
IS [J] a 0.047
FS [N] b 9.81
ESD c [µJ] c >675
Tdec [°C] d 285
Ω[%] e−34.3
ρ [g/cc] f 1.982
ΔfH0 [kJ/mol] g −197.07
ΔexU0 [kJ/kg] h 3280
a IS = impact sensitivity; b FS = friction sensitivity; c ESD = electrostatic discharge; d Tdec = Temperature
of decomposition; e Ω = CO2 oxygen balance; f ρ = crystalline density; g ΔfH0 = molar enthalpy of
formation; h ΔexU0 = total energy of detonation.
2.3.2.3. Potassium 1,1'-dinitramino-5,5'-Bis(tetrazolate) (K2DNABT)
In 2014, Klapötke reported the synthesis and performance of K2DNABT (31) [27]. This material
is prepared in a seven step sequence, starting from dimethyl carbonate (Scheme 8). Desymmetrization
of dimethyl carbonate, followed by condensation with glyoxal afforded bis(hydrazone) 27. Treatment
with N-chlorosuccinimide (NCS), followed by displacement of the chlorines with azide, afforded
diazido bis(hydrazone) intermediate (29). Acid-induced cyclization to give bis(tetrazole) (30),
nitration of this species with dinitrogen pentoxide, and formation of the resultant dipotassium salt
afforded K2DNABT.
Scheme 8. Synthesis of K2DNABT (31).
K2DNABT was prepared based on the premise that it could serve as a potential replacement for
lead azide in detonator applications; it is particularly intriguing in that it incorporates two 1-
nitraminotetrazole moieties, each consisting of six consecutive nitrogen atoms which contribute
greatly to the high explosive output of the molecule. Compared to lead azide, K2DNABT was found
to have comparable sensitivities to impact, friction and ESD, a significantly larger detonation velocity,
and a similar detonation pressure (Table 3). K2DNABT was subjected to 100 °C for 48 h and was found
to undergo no mass loss or decomposition at this temperature. Undoubtedly, this material holds
promise and should be investigated further as a potential alternative to lead azide. However, its
current synthesis does suffer from a lengthy synthesis route, and low yields were encountered in
some of the synthetic transformations; most notably, the conversion of dichloro bis(hydrazone) (28)
to diazido bis(hydrazone) (29), which proceeded in only 38% yield.
Scheme 8. Synthesis of K2DNABT (31).
K2DNABT was prepared based on the premise that it could serve as a potential replacement for lead
azide in detonator applications; it is particularly intriguing in that it incorporates two 1-nitraminotetrazole
moieties, each consisting of six consecutive nitrogen atoms which contribute greatly to the high
explosive output of the molecule. Compared to lead azide, K
2
DNABT was found to have comparable
sensitivities to impact, friction and ESD, a significantly larger detonation velocity, and a similar
detonation pressure (Table 3). K
2
DNABT was subjected to 100
˝
C for 48 h and was found to undergo
no mass loss or decomposition at this temperature. Undoubtedly, this material holds promise
and should be investigated further as a potential alternative to lead azide. However, its current
synthesis does suffer from a lengthy synthesis route, and low yields were encountered in some of the
synthetic transformations; most notably, the conversion of dichloro bis(hydrazone) (28) to diazido
bis(hydrazone) (29), which proceeded in only 38% yield.

Crystals 2016,6, 5 9 of 22
Table 3. Sensitivities and performance of K2DNABT as compared to Pb(N3)2.
Data Category K2DNABT (31) Pb(N3)2
IS [J] a1 2.5–4
FS [N] bď1 0.1–1
ESD c[J] c0.003 <0.005
Tdec [˝C] d200 315
ΩCO2[%] e´4.8 ´11
ρ[g/cc] f2.11 4.8
Pcj [kbar] g5920 8330
Vdet [m/s] h33.8 31.7
∆fH0[kJ/mol] i326.4 450.1
∆exU0[kJ/kg] j1036.1 1569
a
IS = impact sensitivity;
b
FS = friction sensitivity;
c
ESD = electrostatic discharge;
d
T
dec
= Temperature
of decomposition;
eΩCO2
= CO
2
oxygen balance;
fρ
= crystalline density;
g
P
cj
= detonation pressure;
hVdet = detonation velocity; i∆fH0= molar enthalpy of formation; j∆exU0= total energy of detonation.
2.3.2.4. 1,5-(dinitramino) Tetrazole Dipotassium Salt
In 2015, Klapötke went on to synthesize the similarly structured dipotassium salt of
1,5-dinitramino tetrazole (33), as described in Scheme 9[
24
,
28
]. Treatment of methyl carbazate 26 with
cyanogen azide produced tetrazole (32), which was subjected to nitration, followed by basic conditions
to give the dipotassium salt of 1,5-Dinitramino tetrazole.
Crystals 2016, 6, 5
9
Table 3. Sensitivities and performance of K2DNABT as compared to Pb(N3)2.
Data Category K2DNABT (31) Pb(N3)2
IS [J] a 1 2.5–4
FS [N] b ≤1 0.1–1
ESD c [J] c 0.003 <0.005
Tdec [°C] d 200 315
Ω [%]
e −4.8 −11
ρ [g/cc] f 2.11 4.8
Pcj [kbar] g 5920 8330
Vdet [m/s] h 33.8 31.7
ΔfH0 [kJ/mol] i 326.4 450.1
ΔexU0 [kJ/kg] j 1036.1 1569
a IS = impact sensitivity; b FS = friction sensitivity; c ESD = electrostatic discharge; d Tdec = Temperature
of decomposition; e Ω = CO2 oxygen balance; f ρ = crystalline density; g Pcj = detonation pressure;
h Vdet = detonation velocity; i ΔfH0 = molar enthalpy of formation; j ΔexU0 = total energy of detonation.
2.3.2.4. 1,5-(dinitramino) Tetrazole Dipotassium Salt
In 2015, Klapötke went on to synthesize the similarly structured dipotassium salt of 1,5-
dinitramino tetrazole (33), as described in Scheme 9 [24,28]. Treatment of methyl carbazate 26 with
cyanogen azide produced tetrazole (32), which was subjected to nitration, followed by basic
conditions to give the dipotassium salt of 1,5-Dinitramino tetrazole.
Scheme 9. Synthesis of the dipotassium salt of 1,5-Dinitramino tetrazole (33).
Tetrazene and its organic-based replacement, MTX-1, was discussed in Section 2.3.1.2. Klapötke
has reasoned that given the high density, detonation velocity, detonation pressure, and impact and
friction sensitivity of (33) (Table 4), this compound could also serve as a potential replacement for
tetrazene as a sensitizing agent in primary explosive formulations. The shockwave produced by 50
mg of (33) was found to easily detonate the secondary explosive RDX.
Table 4. Sensitivities and performance of the dipotassium salt of 1,5-Dinitramino tetrazole (33) and
CL-20.
Data Category 33 CL-20
IS [J] a 1 4
FS [N] b ≤5 48
Tdec [°C] c 240 315
Ω [%] d−12.03 −10.95
ρ [g/cc] e 2.177 2.04
Pcj [kbar] f 522 444
Vdet [m/s] g 10011 9730
ΔfH0 [kJ/mol] h −112.4 365.4
ΔexU0 [kJ/kg] i 3938 6168
a IS = impact sensitivity; b FS = friction sensitivity; c Tdec = Temperature of decomposition; d Ω = CO2
oxygen balance; e ρ = crystalline density; f Pcj = detonation pressure; g Vdet = detonation velocity; h ΔfH0
= molar enthalpy of formation; i ΔexU0 = total energy of detonation.
Scheme 9. Synthesis of the dipotassium salt of 1,5-Dinitramino tetrazole (33).
Tetrazene and its organic-based replacement, MTX-1, was discussed in Section 2.3.1. Klapötke has
reasoned that given the high density, detonation velocity, detonation pressure, and impact and friction
sensitivity of (33) (Table 4), this compound could also serve as a potential replacement for tetrazene as
a sensitizing agent in primary explosive formulations. The shockwave produced by 50 mg of (33) was
found to easily detonate the secondary explosive RDX.
Table 4. Sensitivities and performance of the dipotassium salt of 1,5-Dinitramino tetrazole (33) and CL-20.
Data Category 33 CL-20
IS [J] a1 4
FS [N] bď5 48
Tdec [˝C] c240 315
ΩCO2[%] d´12.03 ´10.95
ρ[g/cc] e2.177 2.04
Pcj [kbar] f522 444
Vdet [m/s] g10011 9730
∆fH0[kJ/mol] h´112.4 365.4
∆exU0[kJ/kg] i3938 6168
a
IS = impact sensitivity;
b
FS = friction sensitivity;
c
T
dec
= Temperature of decomposition;
dΩCO2= CO2oxygen balance; eρ
= crystalline density;
f
P
cj
= detonation pressure;
g
V
det
= detonation velocity;
h∆fH0= molar enthalpy of formation; i∆exU0= total energy of detonation.

Crystals 2016,6, 5 10 of 22
2.3.2.5. Copper(I) 5-Nitrotetrazolate (DBX-1)
DBX-1 has been a compound of intense investigation recently, due to its similarities to lead azide
with respect to its initiating ability and impact, friction and ESD sensitivity, as well as high thermal
stability [
29
]. Unlike the blue copper(II) nitrotetrazole octahedral complex reported by Huynh [
30
],
DBX-1 is the copper(I) salt that manifests as orange-red crystals and adopts the dimeric structure (as
determined by single-crystal X-ray) shown in Scheme 10. More importantly, it can easily be synthesized
as a free-flowing powder (essential for practical applications) which was never observed for the Huynh
compounds. Further, DBX-1 has been successfully demonstrated to be a “drop-in” replacement for lead
azide (meaning it can be substituted as a direct, volume-for-volume replacement with no hardware
changes) in some existing detonator designs. It is also being investigated as a replacement for lead
styphnate in certain applications as well. DBX-1 has been shown to be more resistant to oxidation than
lead azide when subjected to thermal cycling conditions (i.e., high temperature and high humidity).
DBX-1 is known to slowly decompose when stored in water, and shows incompatibility when in the
presence of periodate-based oxidizers [
31
]. Nonetheless, due to the aforementioned positive qualities,
DBX-1 is being sought as a replacement for lead-based primary explosives.
The traditional synthetic procedure for making DBX-1 is described in Scheme 10. Exposure of
5-aminotetrazole to a modified Sandmeyer reaction affords copper acid salt 34, which is converted to
the sodium salt of 5-nitrotetrazole (NaNT, 35) upon exposure to NaOH as originally described by von
Herz [
32
] and later modified by Gilligan [
33
]. Subsequently, CuCl
2
is treated with sodium ascorbate to
generate the copper(I) species in situ, which reacts with NaNT to yield DBX-1 (36). The performance
and sensitivities for this compound are detailed in Table 5.
Table 5. Performance and sensitivities of DBX-1 (36).
Data Category DBX-1 (36)
IS [J] a0.036
FS [N] b>0.098
ESD c[µJ] c12
Tdec [˝C] d337
ΩCO2[%] e´9.0
ρ[g/cc] f2.584
∆fH0[kJ/mol] g280.9
∆exU0[kJ/kg] h3816.6
a
IS = impact sensitivity;
b
FS = friction sensitivity;
c
ESD = electrostatic discharge;
d
T
dec
= Temperature of
decomposition; eΩCO2= CO2oxygen balance; fρ= crystalline density; g∆