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理學博士學位 請求論文

Synthesis and Characterization of High Energetic

Tetrazole and Furoxan Derivatives

고에너지 물질로서 테트라졸과 퓨록산 유도체의

합성과 특성

2010 年 2 月

仁荷大學校 大學院

化學科 (化學專攻) 林 忠 煥

理學博士學位 請求論文

Synthesis and Characterization of High Energetic

Tetrazole and Furoxan Derivatives

고에너지 물질로서 테트라졸과 푸록산 유도체의

합성과 특성

2010 年 2 月

指導敎授 조 형 진

이 論文을 博士 學位 論文으로 提出함

仁荷大學校 大學院

化學科 (化學專攻) 林 忠 煥

이 論文을 林 忠 煥의 博士學位論文으로 認定함.

2010 年 2 月

主 審

副 審

委 員

委 員

委 員

Table of Contents

List of Figures ····································································································· iii

List of Schemes ································································································· v

List of Tables ······································································································ v

Abstract (English) ······························································································ vi

Abstract (Korean) ······························································································ viii

I. Introduction

1. High energetic materials and explosives ····································· 1

1.1. Classification of high explosives ··············································· 3

1.1.1. Primary and secondary explosives ··································· 3

1.1.2. Secondary explosives ····························································· 5

1.1.2.1. Aromatic C-nitro compounds ········································· 5

1.1.2.2. N-nitro compounds ···························································· 7

1.1.2.3. Nitrate ester compounds ················································· 9

1.2. Insensitive explosives ····································································· 11

2. Tetrazole derivatives as high explosives ······································· 13

2.1. Tetrazoles ···························································································· 13

2.2. High energetic tetrazole derivatives ······································· 15

2.3. N2FOX-7 ······························································································ 19

3. 3,4-Bis(3-nitrofurazano)furoxan (BNFF) ········································· 20

3.1. Furazans ······························································································· 20

3.2. High energetic furazan derivatives ·········································· 22

3.3. Furoxans ······························································································ 23

3.4. High energetic furoxan derivatives ········································· 25

II. Results and Discussion

1. High energetic tetrazole : N2FOX-7 ··············································· 30

i

1.1. Retrosynthetic analysis of N2FOX-7 ······································· 30

1.2. Nitration of 5-methyltetrazole) ················································· 32

1.3. Nucleophilic substitution of tetrazole ···································· 33

1.4. Synthesis of ETDNA ········································································ 35

1.5. Synthesis of TDNM and it’s salts ············································· 38

1.6. Tautomerism of Tetrazole ··························································· 40

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF) ········································· 47

2.1. Synthesis of AAOF ·········································································· 48

2.2. Synthesis of ACOF ·········································································· 49

2.3. Dimerization of ACOF ··································································· 50

2.4. Synthesis of BNFF by oxidation of BAFF ······························ 52

III. Conclusion

1. High energetic tetrazole ······································································ 55

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF) ········································· 56

IV. Experimental Section

1. High energetic tetrazole ······································································ 57

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF) ········································· 64

V. Reference ········································································································ 69

VI. Appendices

1. Definitions of abbreviations ······························································· 80

2. Spectral data ····························································································· 82

ii

List of Figures

Figure 1. Primary and secondary explosives ······································ 4

Figure 2. Several explosives; Aromatic C-nitro compounds ···· 7

Figure 3. Several explosives; N-nitro compounds ··························· 9

Figure 4. Several explosives; Nitrate ester compounds ············· 11

Figure 5. Insensitive explosives ··························································· 13

Figure 6. Synthesis of 5-picrylamino-1,2,3,4-tetrazole ············· 16

Figure 7. Energetic tetrazole derivatives ········································· 16

Figure 8. Synthesis of bis-nitraminotetrazole ································· 17

Figure 9. Synthesis of energetic tetrazole derivatives ················ 18

Figure 10. Synthesis of tetrazole ammonium salt ························ 18

Figure 11. 5-Dinitromethylenetetrazole ·········································· 19

Figure 12. Predicted properties of N2FOX-7 ································ 20

Figure 13. Furazan and furoxan ···························································· 21

Figure 14. Synthesis of DAF ···································································· 22

Figure 15. Several furazano compounds ·········································· 23

Figure 16. Synthesis of ANF···································································· 23

Figure 17. Synthesis of 4-amino-4'-nitro-3,3'-azofurazan········· 24

Figure 18. DNAzBF and DNABF ···························································· 24

Figure 19. Principle sources of nitrile oxides ·································· 25

Figure 20. DNFX ··························································································· 26

Figure 21. Synthesis of 3,4-disubstituted furoxan ························ 27

Figure 22. Synthesis of DDF ··································································· 27

iii

Figure 23. BAFF and BNFF ······································································· 28

Figure 24. UV spectra of conjugated dinitro compounds ········ 42

Figure 25. UV spectra of the intermediates ···································· 43

Figure 26. Tautomerism of tetrazole ·················································· 44

Figure 27. Structure of N2FOX-7 ·························································· 45

iv

List of Schemes

Scheme 1. Retrosynthetic analysis of N2FOX-7 ··························· 32

Scheme 2. Nitration of 5-methyltetrazole (2) ······························ 33

Scheme 3. Nucleophilic substitution of 5-chloro tetrazole 13

·································································································· 35

Scheme 4. Nucleophilic substitution of triazene 17 ················· 36

Scheme 5. Synthesis of ETDNA from ECA (I) ································ 37

Scheme 6. Synthesis of ETDNA from ECA (II) ······························· 38

Scheme 7. Synthesis of ETDNA from ETA ······································ 39

Scheme 8. The synthesis of TDNM and it's salts ························ 41

Scheme 9. Synthesis of BNFF ································································· 47

Scheme 10. Synthesis of AAOF (24) ··················································· 49

Scheme 11. Synthesis of ACOF (25) ··················································· 50

Scheme 12. Synthesis of BAFF (26) and 31 via nitrile oxide ··· 51

Scheme 13. Synthesis of BNFF by oxidation reaction ················ 53

Table 1. Dimerization of 3-amino-4-chloroximidofurazan (25)

···································································································· 52

v

Abstract

The development of novel high performance explosives and

propellants is required due to the demands for smaller, lighter, and

higher-performance warhead and munitions in modern army

technology. In addition, the development of insensitive munitions and

explosive is also required to prevent explosion by unwanted stimuli,

storage and mechanical shock. 5-Dinitromethylene-5H-tetrazole

(N2FOX-7) was considered as a promising candidate for a novel high

energetic material based on a computer modeling study. In this study

on N2FOX-7, efficient methods were developed to synthesize ethyl 5-

tetazolyldinitroacetate (ETDNA), new intermediate compound,

tetrazolyldinitromethane (TDNM) and it's salts. The spectral data and

the molecular orbital calculation were analyzed and compared for

N2FOX-7 and TDNM. 5-Dinitromethyltetrazole existed in a mixture of

tetrazole and tetrazoline forms depending on the state such as in

solution or in solid. According to the thermal analysis of TDNM salts,

they could be the alternative high energetic compounds.

The development on the synthesis and the characterization of 3,4-

bis(3-nitrofurazano)furoxan (BNFF), an insensitive high explosive

compound, was also studied. BNFF has larger density, higher

detonation velocity, and detonation pressure than 1,3,5,7-tetranitro-

1,3,5,7-tetraazacyclo-octane (HMX). For the synthesis of BNFF,

vi

several intermediates was synthesized efficiently, and the oxidation

reaction of 3,4-bis(amino-furazano)furoxan (BAFF) was examined in

detail.

vii

viii

요 약 문

최근 들어 군 무기체계의 현대화 필요성에 따라 탄두와 탄약의

소형화 및 경량화를 추구하고 고성능화를 이룰 수 있는 보다

우수한 고성능 화약과 추진제 등의 개발이 요구되고 있으며, 뿐만

아니라 저장 및 운반도중의 충격 등 사소한 개시에 의해 야기되는

불필요한 폭발을 방지할 수 있는 둔감화약의 개발이 필요하다.

5-Dinitromethylene-5H-tetrazole (N2FOX-7)은 모델링 연구에 의해서

고에너지 물질로 선정되었다. N2FOX-7 의 합성연구를 통해서

새로운 중간체 화합물인 ethyl 5-tetazolyldinitroacetate (ETDNA)를

효율적으로 합성하였고, tetrazolyldinitromethane (TDNM)와 그의

염들을 합성하였다. 최종화합물인 N2FOX-7 과 TDNM 의 구조분석과

분자궤도계산을 통해 비교 분석하였다. 5-Dinitromethyltetrazole 은

용액이나 고체상에 따라서 테트라졸과 테트라졸린 혼합물 형태로

존재하였다. TDNM 염들의 열적 분석에 따르면 대안적인 고에너지

물질로 사용되어질 수 있다.

둔감성 고에너지 물질로 최근에 알려진 3,4-bis(3-

nitrofurazano)furoxan (BNFF)의 합성 및 특성연구를 진행하였다.

BNFF 는 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclo-octane (HMX)보다

고밀도, 고폭속 그리고 고폭압의 성질을 가진다. 합성연구를 통해서

각 중간체를 효율적으로 합성하였고, 전구체인 3,4-bis(amino-

furazano)furoxan (BAFF)에서 여러 가지 조건에서 산화반응을

진행하여 BNFF 를 합성하였다.

Synthesis and Characterization of High Energetic

Tetrazole and Furoxan Derivatives

Ⅰ. Introduction

1. High energetic materials and explosives

Explosives have been around since Chinese gunpowder was

discovered in the 9th century by Chinese alchemists. However, until

the past 15 years, development of explosives has been characterized

by an approach based largely on intuition and trial and error. For the

development of advanced explosives, high-explosive scientists are

imposing more rigorous chemical structure and scientific techniques

upon all aspects of their work. Researchers are combining

breakthrough computer simulation codes, state-of-the-art experimental

diagnostics, and a culture in which theoretical, synthesis, and

experimental chemists and physicists work alongside each other. The

continuing demand is driving a search for better theoretical models of

the behavior of energetic materials and an improved diagnostic

capability to measure the complex chemical and hydrodynamic

processes during detonation.

High energetic materials and explosives have been classified in

many ways, according to different criteria. All explosives can be

- 1 -

classified as either low or high explosives. Low explosives, also known

as propellant, contain the oxygen needed for their combustion and,

therefore, most combustible materials undergoing deflagration by a

surface burning mechanism. Low explosives can still explode under

confinement but this is a consequence of the increase in pressure

caused by the release of gaseous products. Some low explosives can

also detonate under confinement if initiated by the shock of another

explosive. Low explosives include substances like gunpowder,

smokeless powder and gun propellants. High explosives, on the other

hand, need no confinement for explosion, because their chemical

reactions are far more rapid and undergo the physical phenomenon of

detonation. In these materials the chemical reaction follows a high-

pressure shock wave which propagates the reaction as it moves

through the explosive substance. High explosives typically detonate at

a rate between 5500-9500 m/s and this velocity of detonation (VOD) is

used to compare the performance of different explosives. High

explosives include 2,4,6-trinitro toluene (TNT), nitroglycerine (NG),

1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-

1,3,5,7-tetra-azacyclooctane (HMX).

- 2 -

1.1. Classification of high explosives

High explosives are classified as primary or secondary based on

their susceptibility to initiation.

1.1.1. Primary and secondary explosives

Primary explosives, which include lead azide , silver azide, and lead

styphnate, are highly susceptible to initiation (Figure 1). Primary

explosives often are referred to as initiating explosives because they

can be used to ignite secondary explosives. Initiators are used in

military detonators, industrial blasting caps and stab and shock primers.

Mercury fulminate, which commercially is in the form of a gray powder,

is thermally unstable and very sensitive to impact and friction. Lead

azide, another very important primary explosive, is less sensitive to

impact than mercury fulminate, but more sensitive to friction. Because

it is not easily ignited lead zide is often mixed with lead styphnate,

which is particularly easy to ignite. Diazodinitrophenol (DDNP) is

sparingly soluble in water, non-hygroscopic and less sensitive than

other primary explosives to impact, friction or electrostatic energy.

Lead styphnate is thermally stable, non-corrosive and non-hygroscopic.

- 3 -

It is very sensitive to flame and to electrostatic discharge. Secondary

explosives, which include nitroaromatics and nitramines, are much

more prevalent at military sites than are primary explosives. Because

they are formulated to detonate only under specific circumstances,

secondary explosives often are used as main charge or bolstering

explosives. Secondary explosives can be loosely categorized into

melt-pour explosives, which are based on nitroaromatics such as TNT,

and plastic-bonded explosives which are based on a binder and

crystalline explosive such as RDX.

Figure 1. Primary and secondary explosives

- 4 -

1.1.2. Secondary explosives

Explosives have also been classified by their chemical structure.

The most important class includes organic compounds which contain

the nitro(NO2) group. They are subdivided according to the atom to

which the NO2 group attached. Nitro compounds contain a C-NO2

group, nitramines a C-N-NO2 group, and nitrate esters a C-O-NO2

group.

1.1.2.1. Aromatic C-nitro compounds

Aromatic C-nitro compounds as explosives are shown in Figure 2.

2,4,6-Trinitrotoluene (TNT), typical aromatic C-nitro compound, was

first prepared in 1863. TNT is the most widely used military explosive,

and its main features include low melting point, stability, low sensitivity

to impact, friction, and high temperature. Especially TNT is

synthesized from readily available and cheap raw materials. 1,3,5-

Trinitrobenzene (TNB) is a more powerful explosive than TNT.

However, the synthesis of TNB from benzene is not practical and too

expensive to indirect route for its synthesis. 2,4,6-Trinitrophenol,

commonly known as picric acid was used as a military explosive

- 5 -

although its highly acidic nature enable it to readily corrode metals.

Many highly nitrated polynitroarylenes, such as 2,2',4,4',6,6'-

hexanitrodiphenylamine (hexyl), are powerful explosives but are

prevented from being practical explosives because of their poor

chemical stability. Later interest in polynitroarylenes has resumed over

the past few decades as the demand for thermally stable explosives

with a low sensitivity to impact has increased. Such low sensitive

explosives are 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 1,3-

diamino-2,4,6-trinitro-benzene (DATB), 2,2',4,4',6,6'-hexanitrostilbene

(HNS), etc.

Figure 2. Several explosives; Aromatic C-nitro compounds

- 6 -

1.1.2.2. N-nitro compounds

N-Nitro-based explosives are some of the most powerful explosives

(Figure 3). 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-

tetranitro-1,3,5,7-tetra-azacyclooctane (HMX) are the most important

of the secondary nitramine explosives. RDX exhibits both high

brisance (VOD ∼ 8440 m/s, d = 1.70 g/cm3) and stability, finding

extensive use as a military explosive in the form of compressed or cast

mixtures with other explosives, or in the form of PBXs (plastic bonded

explosives). HMX was discovered during World War II as a

contaminant in a batch of another explosive material, RDX, and the

highest-energy solid explosive produced on a large scale in the United

States. HMX (VOD ∼ 9110 m/s, d = 1.90 g/cm3) exhibits higher

performance than RDX due to its higher density, but this is offset by its

higher cost of production compare to RDX. Consequently, HMX is

restricted to military use, finding use in high performance propellant

and explosive formulations.

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)

and TNAZ are new insensitive nitramine explosives. CL-20 was a

- 7 -

breakthrough in energetic material with higher performance (VOD ∼

9380 m/s, d = 2.04 g/cm3), minimum signature, and reduced-hazard

characteristics. CL-20 has numerous military and commercial

applications. TNAZ is a potential melt-cast explosive (m.p. 101 ℃).

Some compounds are containing the secondary nitramide group such

as NENO [N,N'-dinitro-N,N'-bis(2-hydroxyethyl)oxamide dinitrate].

NENO is powerful secondary high explosives, having low melting point.

Its physical properties allows the melt casting of charges.

1,4-Dinitroglycouril (DINGU) is one of the compounds possessing N-

nitrourea, and it is classified an insensitive high explosive (IHE) and

exhibits good performance (VOD ∼ 7580 m/s, d = 1.99 g/cm3).

- 8 -

Figure 3. Several explosives; N-nitro compounds

1.1.2.3. Nitrate ester compounds

Nitrate esters are an important class of explosives for both

commercial and military use (Figure 4). Glyceryl trinitrate (GTN),

commonly known as nitroglycerine, shows an unacceptably high

sensitivity to impact and mechanical stimuli. Despite nitroglycerine

having many unfavorable properties synonymous with nitrate esters, it

is a powerful high explosive of high brisance (VOD ∼ 7750 m/s, d =

1.59 g/cm3). Ethylene glycol dinitrate (EGDN) is very similar to

nitroglycerine in physical appearance, and it is considered more stable

and less sensitive to impact but more volatile. Pentaerythritol

- 9 -

tetranitrate (PETN) is also a powerful explosive which exhibits

considerable brisance on detonation (VOD ∼ 8310 m/s, d = 1.77

g/cm3), and the most stable and least reactive of the common nitrate

ester explosives. Nitrocellulose, the product from nitrating cellulose in

its various forms, is of vast importance in the explosives industry as

the main component of many modern gun and rocket propellants, and

as a binder for explosive compositions.

Nitrate esters explosives are the most powerful explosives known.

However, their use for some applications is limited, because they are

generally much more sensitive to mechanical stimuli and readily

hydrolyzed in the presence of acid or base.

Figure 4. Several explosives; Nitrate ester compounds

- 10 -

1.2. Insensitive explosives

To improve munitions on the basis of survivability and safety, it is

requiring all new munitions be capable of withstanding accidents, fires,

or enemy attack. One method of addressing this requirement, the use

of 'insensitive munitions' (IM), including propellants and explosives,

was mandated. Thus a new class of IM explosives has been

developed over the past decade.

Some insensitive explosives are shown in Figure 5. TATB is the

benchmark for thermal and impact insensitive explosives and finds

wide use for military, space and nuclear applications. 1,1,3-

Trinitroazetidine (TNAZ) is a material that is more powerful, but less-

sensitive than HMX. The advent of the new high-energy explosive CL-

20 and TNAZ present the possibility of increased performance high

explosives with reduced sensitivity. A nitrogen-rich compound, TNAZ,

can itself be melted and molded. But money was an issue. It costs just

a few tens of dollars to produce a kilogram of HMX or RDX, but about

$200 to create the same amount of TNAZ. Most of the effort for

producing the next generation of energetic materials is currently

- 11 -

centered around the production of TNAZ. TNAZ is one of the few new

energetic materials found to be thermally stable above its melting point.

However, in formulations studies, it has been found that TNAZ has

high volatility that will severely inhibit its utility in military explosive and

propellant applications.

3-Nitro-1,2,4-triazol-5-one (NTO) is also insensitive high explosive

(IHE), and it is much less sensitive to impact than both the widely used

military explosives RDX and HMX. NTO is now widely used alone or in

combination with HMX or RDX for use as a filling for insensitive

munitions. 4,10-Dinitro-4,10-diaza-2,6,8,12-tetraoxaisowurtzitane (TEX;

TOIW) is also an insensitive high performance explosive (VOD ∼

8665 m/s, d = 1.99 g/cm3). 1,1-Diamino-2,2-dinitroethylene (FOX-7),

was first synthesized in 1998 by Latypov and co-workers, have

recently attracted interest as energetic explosives. FOX-7 is a high

energetic material with a lower impact sensitivity than HMX and well

suited for use in high explosive formulations.

- 12 -

Figure 5. Insensitive explosives

2. Tetrazole derivatives as high explosives

2.1. Tetrazoles

Tetrazole (CN4H2) and its derivatives are compounds that have

drawn the attention of many people, due to their practical applications.1

Therefore an amount of publications devoted to the molecular structure,

synthetic methods, chemical and physicochemical properties of

tetrazoles constantly increases. Among the stable structures, this

heteroaromatic system contains the greatest number of nitrogen atoms,

which is the reason why tetrazoles exhibit the extreme values of acidity,

- 13 -

basicity, and complex formation constants. They have specific

thermochemical properties and exhibit multiple reactivity.2-5

The practical importance of these heterocycles results from a

combination of the above-mentioned properties. The tetrazole ring is

the key scaffold of a few of modern drugs (antibacterial, anti-allergic,

anti-inflammatory, angiotensine II antagonists, etc.).6-9 The tetrazolic

acid fragment, -CN4H, has similar acidity to the carboxylic acid group, -

CO2H, and is almost isosteric with it. but this fragment is metabolically

more stable than the carboxylic acid.10 Hence, replacement of -CO2H

groups by -CN4H groups in biologically active molecules has been

widely applied in research areas of major interest.11

Tetrazoles found also application as highly effective explosives,

rocket fuel and gas generating compositions were developed.12-16 As

mention it above, nitrogen-rich substances on the basis of tetrazole

and tetrazine structure are receiving as components for energetic

applications. So they and their metal salts (complexes) have been

investigated.17-19 Compounds such as 1-H tetrazole and 5-

aminotetrazole can be used as nucleophilies to incorporate the

tetrazole ring into other molecules. 5-Aminotetrazole is synthesized

- 14 -

from the reaction of dicyandiamide with sodium azide in hydrochloric

acid.

2.2. High energetic tetrazole derivatives

Agrawal and co-workers reported the synthesis of two tetrazole-

based explosives, namely, 5-picrylamino-1,2,3,4-tetrazole (PAT)20 and

5,5'-styphnylamino-1,2,3,4-tetrazole (SAT)21 from the reaction of 5-

amino-1,2,3,4-tetrazole with picryl chloride and styphnyl chloride

respectively (Figure 6 and 7). These explosives have been studied for

their thermal and explosive properties. The thermal stability of SAT

(exothermic peak at 123℃) is lower than PAT (exothermic peak at

185℃), which is possibly attributed to the decreased electron-

withdrawing power of the picryl group by being attached to two

tetrazole units. PAT and SAT have calculated VODs of 9126 m/s and

8602 m/s respectively.21

- 15 -

Figure 6. Synthesis of 5-picrylamino-1,2,3,4-tetrazole

The reaction of 5-aminotetrazole with 3,5-diamino-2,4,6-

trinitrofluoro-benzen generates the energetic tetrazole (Figure 7).22

Figure 7. Energetic tetrazole derivatives

The bis-nitramine has been prepared in the reaction of 1,5-

diaminotetrazole with glyoxal, followed by reduction of the resulting

fused heterocycle with sodium borohydride and subsequent N-nitration

of the piperazine nitrogens (Figure 8).23

- 16 -

Figure 8. Synthesis of bis-nitraminotetrazole

The tetrazole ring can be synthesized from the 1,3-dipolar

cycloaddition of an azide with a cyanide group or a similar nitrogen

dipolarophile. Tri-n-butyltin azide and trimethylsilyl azide have been

used as organic alternatives to the azide anion. Ammonium azide is

frequently used and is generated in situ from sodium azide and

ammonium chloride in DMF. 6-Ammino-1,2,4-triazolo[4,3-b][1,2,4,5]-

tetrazine (ATTz), the fused heterocycle, has been synthesized from the

reaction of 3,6-diaminotetrazine with nitrous acid and then sodium

azide.24 The heterocycle, incorporating both a tetrazole and furoxan

group, has been prepared from the reaction of 3-nitro-2,6-

dichloropyridine with two equivalents of azide anion followed by

heating of the product under reflux in benzene (Figure 9).25

- 17 -

Figure 9. Synthesis of energetic tetrazole derivatives

5-(Trinitrometyl)tetrazole and 5-(dinitrofluoromethyl)tetrazole have

been synthesized and isolated as their ammonium salts in the

reactions of trimethylsilyl azide with the corresponding nitriles followed

by reaction with ammonia in diethyl ether (Figure 10).26

Figure 10. Synthesis of tetrazole ammonium salt

5-Nitrotetrazole is readily prepared from the diazotization of 5-

aminotetrazole in the presence of excess sodium nitrite and is best

- 18 -

isolated as the copper salt complex with ethylenediamine.27 The salts

of 5-nitrotetrazole have attracted interest for their initiating properties.

The mercury salt is a detonating primary explosive.27 The amine salts

of 5-nitrotetrazole are reported to form useful eutectics with ammonium

nitrate.28

2.3. N2FOX-7

As mentioned before, FOX-7 has attracted interest as an insensitive

high energetic explosive. Since it was developed, many researchers

tried to synthesize molecules based on FOX-7 skeleton. We designed

5-dinitrometylenetetrazole (N2FOX-7) which is comprised of tetrazole

and dinitromethylene moieties (Figure 11). N2FOX-7 was theoretically

calculated and considered by state-of-the-art experimental diagnostics

and computer simulation.

Figure 11. 5-Dinitromethylenetetrazole

- 19 -

According to the predicted data, 5-dinitrometylenetetrazole would be

high performance (typically defined by the detonation velocity, D, and

the detonation pressure, P) and insensitive material (Figure 12).

Figure 12. Predicted properties of N2FOX-7

3. 3,4-Bis(3-nitrofurazano)furoxan (BNFF)

3.1. Furazans

The synthesis of new derivatives of 1,2,5-oxadiazole 2-oxide

(furoxan, Figure 13) has attracted considerable attention in recent

years. This interest stems largely from the fact that many furoxan

derivatives exhibit biological activities and, particularly, from the ability

- 20 -

of some of these derivatives to serve as donors of nitrogen oxide.29-33

In addition, N and O containing derivatives of this heterocycle are

potential components of gas generating compositions.34,35

Figure 13. Furazan and furoxan

Most compounds containing a furazan ring have common

characteristics such as high standard enthalpy of formation (ΔHf°), high

nitrogen content, high energy density, good thermal stability, and low

melting point. Nitro and amino derivatives of the furazan ring (1,2,5-

oxadiazole, Figure 13) are nitrogen-rich energetic materials with

potential use in both propellant and explosive formulations. Some

nitro-substituted furazans have excellent oxygen balance and exhibit

detonation velocities close to very powerful military explosives.

- 21 -

3.2. High energetic furazan derivatives

3,4-Diaminofurazan (DAF) is a starting material for the synthesis of

many nitrosubstituted furazans. DAF is readily prepared from the

cyclization of 1,2-diaminoglyoxime in the presence of aqueous base

under pressure at 180℃.36 The oxime was prepared in the reaction of

glyoxal,37 glyoxime,38 cyanogen39 or dithiooxamide40 with

hydroxylamine (Figure 14).

Figure 14. Synthesis of DAF

The oxidation of DAF with hydrogen peroxide can yield 3-amino-4-

nitrofurazan (ANF), 4,4'-diamino-3,3'-azofurazan (DAAzF), or 4,4'-

diamino-3,3'-azoxyfurazan (DAAF) depending on the reaction condition

employed (Figure 15).41 The most convenient route to ANF involves

treating DAF with a mixture of 30% aqueous hydrogen peroxide,

sodium tungstate and ammonium persulfate in concentrated sulfuric

acid (Figure 16).42,43 Both of the amino groups of DAF are oxidized to

- 22 -

give 3,4-dinitrofurazan (DNF), when 30% hydrogen peroxide is

replaced by 90% hydrogen peroxide.43 DNF is a very powerful

explosive with a positive oxygen balance but it is too sensitive to shock

to be considered as a practical explosive.

Figure 15. Several furazano compounds

Figure 16. Synthesis of ANF

DAAzF can be oxidized with a mixture of 30% aqueous hydrogen

peroxide, sodium tungstate and ammonium persulfate in concentrated

sulfuric acid to produce 4-amino-4'-nitro-3,3'-azofurazan (Figure 17).44

- 23 -

Figure 17. Synthesis of 4-amino-4'-nitro-3,3'-azofurazan

In the presence of more concentrated hydrogen peroxide solution,

the amino groups of DAAzF can be oxidized to produce either 4,4’-

dinitro-3,3’-azo-bis(furazan) (DNAzBF)43 or 4,4’-dinitro-3,3’-azoxy-

bis(furazan) (DNABF) (Figure 18).43

Figure 18. DNAzBF and DNABF

3.3. Furoxans

The dimerization of nitrile oxides provides one of the most important

methods for the synthesis of 1,2,5-oxadiazole N-oxides (furoxan).45

Nitrile oxides are generated from hydroximoyl halides, oximes, nitrolic

acids and primary nitroalkanes (Figure 19). When the reaction is

- 24 -

carried out under heterogeneous condition, aqueous alkalies are used

to promote elimination of hydrogen chloride in hydroximoyl halides. In

homogeneous media, triethylamine is used as hydrogen chloride

acceptor. Under controlled reaction conditions, products like 1,4,2,5-

dioxadiazines, 1,2,4-oxadiazole 4-oxides and nitrile oxide-derived

polymers were observed.

Figure 19. Principle sources of nitrile oxides

3.4. High energetic furoxan derivatives

The furoxan ring is a highly energetic heterocycle whose introduction

into organic compounds is a known strategy for increasing crystal

density and improving explosive performance. However simple nitro

- 25 -

derivatives of furoxan have not attracted much interest for use as

practical energetic materials because of their poor thermal stability and

the reactivity of the nitro groups to nucleophilic displacement.

3,4-Dinitrofuroxan (DNFX) has been prepared from the nitration of

glyoxime followed by cyclization of the resulting dinitroglyoxime.46

DNFX is unstable at room temperature and highly sensitive to impact

(Figure 20).

Figure 20. DNFX

3-Nitro-4-methylfuroxan is formed in low yield from the reaction of

dinitrogen tetroxide with propylene at low temperature.47 The reaction

of diazoketones with dinitrogen tetroxide has been used to synthesize

energetic 3,4-disubstituted furoxans (Figure 21).48

- 26 -

Figure 21. Synthesis of 3,4-disubstituted furoxan

Recently, 4.4’-dinitro-3,3'-diazenofuroxan (DDF) reported as a high-

energy material.49 This was synthesized from the oxidative coupling of

4-amino-3-(azidocarbonyl)furoxan, followed by Curtius rearrangement

and oxidation of the resulting amino groups to nitro groups. The

experimental detonation velocity of DDF reaches 10000 m/s at a

crystal density of 2.02 g/cm3. The high density of DDF is due to very

efficient crystal packing (Figure 22).

Figure 22. Synthesis of DDF

- 27 -

As a result, series of new energetic compounds with excellent

performance can be synthesized on the basis of the furazan and

furoxan group. Derivatives having furazano and furoxano groups have

such merits as high energy, high standard enthalpy of formation (ΔHf°),

rich nitrogen and excellent stability.50,51 As nitro groups being

substituted by furoxano groups in benzyl-rings, explosive density can

be increased by 0.06~0.08 g/cm3 and detonation velocity by 300 m/s.

Hence, furazan-ring is an effective structure unit for designing high

energetic compound. 3,4-Bis(aminofurazano)furoxan (BAFF)52 and

3,4-bis(nitrofurazano)furoxan (BNFF)53,54 are new high energetic

materials containing furazano and furoxano groups (Figure 23).

NNO

O2N

NO

N

NO2

NO

N O

NNO

H2N

NO

N

NH2

NO

N O

3,4-Bis(nitrofurazano)furoxan(BNFF)

3,4-Bis(aminofurazano)furoxan(BAFF)

Figure 23. BAFF and BNFF

- 28 -

In the explosive properties, the theoretical deotonation velocity of

BAFF (8100 m/s) is higher than that of TATB, and the mechanical

sensitivity of BAFF is similar to that of TATB.52 3,4-Bis(nitrofurazano)-

furoxan was synthesized from BAFF by oxidation, and it have the

superior explosives properties. BNFF have larger density (1.93 g/cm3),

higher detonation velocity (VOD ~ 9250 m/s) and higher detonation

pressure than HMX. And the low melting point of BNFF make it

possible to be used melt-cast mixed energetic materials.

The reason for the paucity of new energetic materials is the fact that

they must meet so many different requirements such as high energy

density, insensitivity to mechanical insults, resistance to chemical

decomposition, inexpensive synthesis from readily available reagents,

and the ability to be formulated with other materials for fabrication into

practical devices. Developing new energetic materials is a complicated

process in which many candidate molecules are considered, a few

synthesized, even fewer formulated, and only a small handful adopted

by the military or industry. In general, the laborious process involves

computer modeling, plenty of laboratory work, and thorough testing.

- 29 -

II. Results and Discussion

1. High energetic tetrazole : N2FOX-7

1.1. Retrosynthetic analysis of N2FOX-7

Retrosynthetic analysis for N2FOX-7 (1) was depicted in Scheme 1.

At first, transamination of FOX-7, developed as a high explosive

compound, might be a convenient route to make the target molecule

simply. The other potential route involves the introduction of

dinitromethylene moiety in the 5-methyl position of 5-methyltetrazole

using the same method as synthesis of FOX-7 from 2-

methylimidazole.55 Although there is a differentiation in reactivity

between tetrazole moiety and imidazole one, 5-methyltetrazole may be

converted to N2FOX-7 with a mixture of nitric acid and sulfuric acid

(mixed acid). Other route for the synthesis of target molecule is from a

key intermediate, dinitrotetrazole 4. N2FOX-7 could be introduced via

HY elimination of dinitro compound 4, a key intermediate. Dinitro

tetrazole 4 could be derived from 5-halo tetrazole 5 by nucleophilic

substitution, and in turn would be obtained from 5-aminotetrazole.56

Another approach to a key intermediate dinitro compound 4, it could be

- 30 -

derived from cyanoacetate 10 via nitration and cyclization

subsequently.57,58 Otherwise, tetrazole ring will be formed in the

reaction of cyanoacetate 10 and azide, and two nitro groups are

introduced stepwise through oxime 8.59 Here we report the synthetic

approach to target molecule, N2FOX-7, and an useful synthetic

method of 5-dinitrometyltetrazole.

Scheme 1. Retrosynthetic analysis of N2FOX-7

- 31 -

1.2. Nitration of 5-methyltetrazole

Among the tactics for synthesizing target molecule, initial attention

focused upon the nitration of 5-methyltetrazole. Previously, various

starting materials such as 2-methylimidazole, 2-methoxy-2-methyl-

imidazolidine-4,5-dione, and 2-methylpyrimidine-4,6-dione(4,5-

dihydroxy-2-methylpyrimidine) were nitrated and then hydrolyzed to

give FOX-7 by somewhat different process.55,60 Since the methyl group

was converted to dinitromethylidene moiety in all methods, nitration of

5-methyltetrazole was attempted to afford 5-dinitromethylidene-1,4-

dihydrotetrazole. But this reaction failed to proceed, and most of the

starting material was recovered(Scheme 2).

NH

NCH3

NH

HNO

O NO2

NO2

H2N

H2N

NO2

NO2nitration

FOX-7 (3)

NNN N

H

CH3nitration NN

N N NO2

NO2//

2 1

Scheme 2. Nitration of 5-methyltetrazole (2).

- 32 -

Several compounds consisted of dinitromethylene moiety were

synthesized in a reaction of FOX-7 with amino compounds via

transamination61 or 1,1-dihalo-2,2-dinitroethylene with amino

compounds via substitution.62 Since a suitable amine may be 2-

tetrazene, which is metastable at room temperature, 5-

dinitromethyltetrazole might be hardly prepared from FOX-7.63

Although treatment of 3,3-diazido-2-cyanoacrylates with substituted

amines afforded dihydrotetrazolidene moieties,64 diazodinitro

compounds might not be useful for the large scale synthesis of 5-

dinitromethyltetrazole.

1.3. Nucleophilic substitution of tetrazole

Nucleophilic substitution of 5-halo tetrazole derivatives had been

reported,65,66 but the 5-chlorotetrazole(12) derived from 5-

tetrazolyldiazonium salt (11) was not mentioned (Scheme 3). Moreover

diazonium salt 11 was an extremely explosive compound, and it’s

crystalline would be detonated at the touch of a spatula.67

- 33 -

Scheme 3. Nucleophilic substitution of 5-chloro tetrazole 13

Instead of diazonium salt 11, triazenes derivative, more stable

compound, was selected as a precursor of 5-halo tetrazole. In previous

work, we described the aromatic fluorination of triazene 15 in ionic

liquid, which involving the acid-catalyzed decomposition of a triazene

in an ionic liquid such as 1-n-butyl-3-methylimidazolium

tetrafluoroborate ([bmin][BF4]).68 The diazotization of 5-aminotetrazole

(6) with sodium nitrite in an aqeous HCl provided diazonium salt 11,

followed by addition of piperidine afforded the triazene 17 efficiently.

We next tried the fluorination of triazene 17 under the same

condition,69 but the wanted 5-fluorotetrazole (18) was not provided.

- 34 -

Several attempts of nucleophilic substitution did not afford the product

18 either under various conditions (Scheme 4).

Scheme 4. Nucleophilic substitution of triazene 17

1.4. Synthesis of ETDNA

Next, we tried to synthesize ethyl 5-tetazolyldinitroacetate (ETDNA,

19) from ethyl cyanoacetate (ECA, 10) via nitrosation, oxidation, and

cyclization sequentially (Scheme 5).57 Ethyl cyanoacetate oxime

(ECAO, 11) was synthesized from ECA by known nitrosation methods

in the nitration of ECAO with mixed acids afforded ethyl

cyanodinitroacetate (ECDNA, 7). As a result, nitrile 7 was readily

available, and used in many reactions.58 Although a tetrazole was

generally given in the reaction of a nitrile with an azide, nitrile 7 has not

- 35 -

been employed in the preparation of the corresponding tetrazole

(19).59,65,70

We attemped to carry out the reaction of ethyl cyanodinitroacetate (7)

with sodium azide, and could not earn any good result. Moreover,

preparation and purification of nitrile 7 were not suitable for a large

scale synthesis.57

Scheme 5. Synthesis of ETDNA from ECA (I)

The synthesis of ethyl 5-tetrazolylnitroacetate from ethyl 5-

tetrazolylacetate (9) was reported.59 Ethyl 5-tetrazolylnitroacetate could

be converted to dinitro 19 by the oxidative nitration, which was

employed in the synthesis of 1,3,3-trinitroazetidine.61

- 36 -

According to a general method, construction of tetrazole moiety from

ECA proceeded readily (Scheme 6).59

Treatment of a mixture of sodium azide and ammonium chloride in

dimethyl formamide with ECA furnished ethyl tetrazolylacetate (ETA, 9)

in high yield. This compound is also commercially available. Ethyl

tetrazolylacetate oxime (ETAO, 8) was afforeded in the treatment of

ETA with sodium nitrite in H2O at 50~60 ℃ for 4 h, followed by

acidification with ortho phosphoric acid. When ETA remained in the

mixture, re-nitrosation provided the relatively pure ETAO. The resulting

ETAO, purified by recrystallization from distilled water, was subjected

to mixed acids to give ethyl 5-tetazolyldinitroacetate (ETDNA, 19).

Scheme 6. Synthesis of ETDNA from ECA (II)

- 37 -

Our attempts to introduce mononitro group from the intermediate,

oxime 8 were failed under mild conditions.72,73 Instead, we found the

more convenient method to get ETDNA. Because of acidity on the

methylene position of ETA, which possesses both carbonyl group and

tetrazole moiety, we considered it's possible to introduce nitro group

directly. Thus we carried out the reaction of ethyl 5-tetrazolylacetate (9)

with mixed acids and obtained ETDNA in high yield, resulting that two

nitro groups were successfully introduced in one pot reaction (Scheme

7).74

Scheme 7. Synthesis of ETDNA from ETA

1.5. Synthesis of TDNM and it’s salts

With the key intermediates 19 in hand, we sought to construct the

N2FOX-7 via decarboxylation and elimination. Thus, various conditions

were tried as shown in Scheme 8. When ethyl 5-tetrazolyldinitro-

acetate was treated with water, 5-dinitromethyltetrazole (20) was

- 38 -

readily given. Hydrolysis followed by decarboxylation took place

completely within 2 h at 50 ℃. In the treatment of 5-

dinitromethyltetrazole with KOH, dipotassium salt 21 and mono

potassium 22 were obtained even in lower temperature, depending

upon the equivalent of KOH. Mono- and di-potassium salt were

confirmed by Inductively coupled plasma (ICP) mass analysis.

Meanwhile, only mono ammonium salt 23 was given in the reaction

with ammonia regardless of equivalents.65 5-Dinitromethyltetrazole (20)

was also afforded by an acid treatment of the salts.59 As a result,

hydrolysis and decarboxylation of ETDNA was achieved not only under

acidic or basic condition but under aqueous one at room temperature.

This process would be much more efficient and safer to obtain TDMN

and its salts than the previous methods. Preliminary experiments

showed that these compounds have some explosive properties.

- 39 -

Scheme 8. The synthesis of TDNM and it's salts

1.6. Tautomerism of Tetrazole

Tetrazole-tetrazoline tautomerism was generally observed. X-ray

analysis revealed that 1-phenyltetrazolidene cyanoacetate exists in the

form of tetrazoline.64 But dinitromethyltetrazole was depicted as in

tetrazole form without proper experimental data in the previous

papers.57,59 In IR spectra, a NO2 group generally shows higher

asymmetric mode and lower symmetric one. When an electron

withdrawing group is attached to the same carbon, the asymmetric

frequency is raised, and the symmetric one is lowered. Conjugation to

NO2 causes lowering of both modes. Nitroethane absorbs at 1558 and

- 40 -

1368 cm−1, dinitroethane at 1587 and 1337 cm−1, and nitroethylene at

1527 and 1363 cm−1.75 Since ethyl tetrazolylacetate (9) absorbs at

1394 and 1332 cm−1, which is close to the symmetric mode, we

focused on the asymmetric mode to investigate the distribution of

tautomers. Ethyl tetrazolyldinitroacetate (19) absorbed at 1594 cm−1,

which was higher than that of dinitroethane as expected. Strong

absorptions occurred at 1587 cm−1 for 2-methyl-5-dinitromethyl-

tetrazole59 and 1560, 1500 cm−1 for 2-dinitromethylenebenzimidazole.62

Since the frequency of 5-dinitromethyltetrazole (11) was 1585 and

1521 cm−1,59 similar to 2-dinitromethylenebenzimidazole, we might

consider that major portion of the compound in solid state exists in the

tetrazoline form.

To investigate the tautomer in solution, we analyzed UV spectra.

Several absorptions were observed for conjugated dinitro compounds.

1,1-Bisdimethylamino-2,2-dinitroethylene absorbed at 264, 302, 340

nm, and 2-dinitromethylenebenzimidazole at 240, 320, 335 nm (Figure

24).62

- 41 -

Figure 24. UV spectra of conjugated dinitro compounds

The absorptions of tetrazole 9 and dinitrotetrazole 19 appeared

around 225 nm, but that of 5-dinitromethyltetrazole (20) in methanol

was 227, 304, 360 nm (Figure 25). Therefore, some parts of 5-

dinitromethyl tetrazole (20) existed in the tetrazoline form. Interestingly,

dipotassium salt 21 absorbed at 230, 361 nm.

In proton NMR of TDNM (20), the chemical shift appeared at 12.9

ppm in DMSO-d6, at 8.2 and 11.4 ppm in CH3CN-d3, and at 8.8 and 8.9

ppm in acetone-d6 respectively. The polarity of the solvent also has

some effect on the stability and decreasing in the polarity shifts the

equilibrium to the tetrazole form. In addition to UV data, it could be

concluded from the proton NMR that equilibrium between tetrazole and

tetrazoline exists and the the predominant form in solution depends on

solvent properties.

- 42 -

100 200 300 400 500 600 700 800 900 1000-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0in

tens

ity

wavelength (nm)

ETA ETDNA DPS TDNM

Figure 25. UV spectra of the intermediates

On the basis of the molecular orbital calculations using RHF/6-

31G(d) and B3LYP/6-31G(d),76 the energy of tetrazoline form is lower

by 0.75 or 3.90 kcal/mol than that of tetrazole one (Figure 26). In the

case of tetrazoline form, two hydrogen bonds stabilize the structure,

resulting in the ring and two nitro groups lie in the same plane.

- 43 -

N

NN

N

H

N

N

O

O

O

O

H

-+

N

NN

N

H

H

N

O O

NO

O

(a) RHF/6-31G(d) Calculation, ΔE = 0.75 kcal/mol

(b) B3LYP/6-31G(d) Calculation, ΔE = 3.90 kcal/mol.

Figure 26. Tautomerism of tetrazole

- 44 -

Meanwhile, the tetrazole ring preserves aromaticity, and H attached

ring nitrogen lies between two nitro groups, and forms weak hydrogen

bonds. Therefore, the energy difference is so small that the molecule

may exist in the mixture of two forms.

N2FOX-7 may be illustrated as Figure 27. In the view of N2FOX-7

structure, we found that its tetrazole ring and nitro groups can not lie in

the same plane, and its form is the most unstable on the result of

molecular orbital calculations. Therefore N2FOX-7 was considered

difficult to synthesize and TDNM salt could be the alternative high

energetic compounds.

N

NN

N N

N

HO

HO

O

O

Figure 27. Structure of N2FOX-7

- 45 -

TDNM itself decomposed slowly at elevated temperature and its

potassium salt was very sensitive to friction, but its ammonium salt

was not so sensitive. Therefore, the ammonium salt may be utilized as

a high energetic compound.

- 46 -

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF)

The synthesis of 3,4-bis(nitrofurazano)furoxan (BNFF, 27) could be

depicted as in Scheme 9, based on previous reports.77-79 3-Amino-4-

aminoximido-furazan (AAOF) was obtained from malononitrile,

followed by deaminochlorination of AAOF afforded 3-amino-4-

chloroximidofurazan (ACOF, 25). Dimerization of chloro oxime 25 gave

3,4-bis(amino-furazano)furoxan (BAFF, 26), and subsequent oxidation

of BAFF produced BNFF.

Scheme 9. Synthesis of BNFF

- 47 -

2.1. Synthesis of AAOF

The preparation of 3-amino-4-aminoximidofurazan was started with

the commercially available malononitrile (Scheme 10).80,81

Malononitrile was treated with sodium nitrite in acetic acid afforded

oxime 28 at room temperature. The resulting oxime 28 was treated

with hydroxyamine hydrochloride in basic condition to afford tri-oxime

29, and the dehydration of tri-oxime 29 provided the furazano ring

compound 24 under refluxing condition. The More convenient method

to make AAOF through one pot reaction was reported.81 After the

reaction of malononitrile with sodium nitrite in aqueous acid was stirred

for overnight, hydroxyamine hydrochloride was added to the reaction

mixture, which was adjusted the pH 9~10 by using 10N NaOH. The

reaction mixture was stirred for another 2 h at 40℃, followed by

refluxing, AAOF was produced over 80% yield. The additional product

could be obtained by extraction of mother liquid with ethyl actate, but

some impurities were included.

- 48 -

N NN N

NOH

NaNO2

AcOH

NH2OHHO

N NOH

N

NH2 NH2

OH

NNO

H2NH2N

NOH

28 29

24

1. NaNO2, 2N HCl2. NH2OH, 40oC,

pH = 9~103. refulx, 2 h

Scheme 10. Synthesis of AAOF (24)

2.2. Synthesis of ACOF

The deamino-chlorination of the resulting α-amino oxime 24 with

NaNO2 in 6M HCl provided an known mixture.82 With conc. HCl in

methanol, 3-amino-4-chloroximidofurazan (ACOF, 25) was obtained

only in low yield (30%). We tried to improve the reaction yield by

changing the concentration of HCl or the equivalent reagents, but there

was a little change under various reaction conditions. The best result

was accomplished with CuCl, which was mainly used to provide a

chloro compound from diazonium salt in the Sandmeyer reaction. As a

- 49 -

result, α-chloro oxime 25 was obtained over 60% yield in pure

(Scheme 11).

Scheme 11. Synthesis of ACOF (25)

2.3. Dimerization of ACOF

With the key intermediates α-chloro oxime 25 in hand, We tried to

isolate nitrile oxide 30 which could be used a precursor of BNFF.

When chloroxime 25 was treated with base, compound 30 was not

isolated, but dimerization occurred as in previous reports (Scheme

12).82,83 The dimerization of 25 via nitrile oxide 30 usually produced a

mixture of BAFF(26) and 1,4,2,5-dioxadiazine 31. There was not much

information on the procedure. We varied reaction conditions such as

- 50 -

base and solvents to give mainly BAFF (Table 1). The best condition to

obtain BAFF was achieved by using 1.0 equiv of 3% aq. Na2CO3 and

the same volume of Et2O at lower temperature. Treatment of 25 with

Na2CO3 or K2CO3 as a base in Et2O gave BAFF over 70% yield.

According to the previous report,83 1,4,2,5-dioxadiazine derivatives

was mainly obtained from α-chloro oxime 25 with triethylamine in

acetonitrile (homogeneous media). When the reaction was carried out

under slightly heterogeneous condition such as 3% K2CO3 (aq.) in THF,

interestingly the major product was 1,4,2,5-dioxadiazine derivatives 31

(Table 1). After the reaction, a solid was filtered and the mother liquid

was extracted with ethyl acetate and the organic layer was evaporated

in vacuo to give a crude solid. To obtain a pure BAFF from a crude

solid including unwanted 1,4,2,5-dioxadiazine 31, the solid was

dissolved in alcohol and filtered off insoluble 1,4,2,5-dioxadiazine 31.

- 51 -

Scheme 12. Synthesis of BAFF (26) and 31 via nitrile oxide

Table 1. Dimerization of 3-amino-4-chloroximidofurazan (25)

base solvent temp. product yield(%)

3% Na2CO3( aq.) Et2O ~5℃ 26 > 73

3% K2CO3 (aq.) Et2O ~5℃ 26 > 70

3% K2CO3 (aq.) THF ~5℃ 31 ~ 70

2.4. Synthesis of BNFF by oxidation of BAFF

The detailed oxidation condition of BAFF did not disclosed in the

previous references, wherein BNFF can be obtained in 99% yield.

They used H2O2 and H2SO4/(NH4)2S2O8 as oxidants. Similarly the

synthesis of nitrofurazans from aminofurazans had been developed

based on H2O2 containing oxidizing mixture.84 To evaluate the relative

activity of oxidative mixtures and to develop methods for increasing

- 52 -

activity, they examined mixtures of H2O2 with H2SO4, (NH4)2S2O8, and

Na2WO4. To introduce the nitro group into the furazan ring, the

oxidation was performed under various conditions. The reaction with

60% H2O2 and H2SO4 at lower temperature did not proceed either.

However, as temperature went up to rt, the reaction mixture was

suddenly bumping with heat, and the resulting solution turned yellow.

After purification by flash chromatography, the target molecule was

afforded in about 50% yield. The amino group was successfully

converted to the nitro group by using lower concentrate H2O2, but the

yield was moderate. Peroxytrifluoroacetic acid was employed in the

oxidation of anilines to nitrobenzene.85 In the same manner, BAFF was

subjected to the mixture of TFAA, 60% H2O2 in dimethyene chloride at

low temperature, and the mixture was stirred for 1 h at room

temperature, and heated at refluxing temperature for additional 1 h. As

a result, BNFF was obtained in moderate yield (Scheme 13).

- 53 -

Scheme 13. Synthesis of BNFF by oxidation reaction

The spectroscopic data of BNFF were in full agreement with those

reported previously. Based on thermal data such as DSC and TGA,

BNFF may be used as melt castable explosives like TNT. More

efficient and convenient synthetic method of BNFF should be further

studied.

- 54 -

III. Conclusions

1. High energetic tetrazole

A novel synthetic approach to 5-dinitrometylenetetrazole, which was

selected as a new insensitive energetic material, was developed. Ethyl

5-dinitrotetrazolylacetate, a new intermediate compound, was

prepared from ethyl 5-tetrazolyl acetate by nitration. 5-dinitromethyl-

tetrazole and it’s salts were then synthesized and characterized.

Based on the results of molecular orbital calculations, the target

molecule (N2FOX-7) was considered to have an unstable structure,

because the tetrazole ring and the nitro groups of N2FOX-7 can not lie

on the same plane. Due to this reason, N2FOX-7 was considered

difficult to synthesize. Additionally, we proved that TDNM exists as a

tautomeric mixture of tetrazole and tetrazoline forms with the ratio

varies in solution or in solid. According to the thermal analysis, TDNM

itself decomposed slowly at elevated temperature. And potassium salt

of TDNM was also unstable due to its sensitivity to friction, but its

ammonium salt exhibits better properties as a high energetic

compound. Therefore, the ammonium salt of TDNM was chosen as a

- 55 -

target compound in this study and possibly utilized as a high energetic

compound.

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF)

We completed the synthesis and characterization of 3,4-bis(3-

nitrofurazano)furoxan (BNFF), recently developed as an insensitive

high explosive. The spectroscopic data of BNFF were in full agreement

with those reported previously. In the synthetic development, all the

intermediates and BNFF were obtained in yields higher than reported.

In particular, the synthesis of ACOF was achieved by the modified

Sandmeyer reaction, and the result was considerably good. BAFF was

synthesized predominantly by the dimerization of the corresponding

nitrile oxide, which was produced in situ. 1,4,2,5-Dioxadiazine

derivative, an isomer of BAFF, was selectively obtained in a modified

condition. BAFF was converted to BNFF in a moderate yield. Based on

thermal data such as DSC and TGA, BNFF may be used as melt

castable explosives like TNT.

- 56 -

IV. Experimental Section

General. All chemicals were reagent grade (Aldrich Chemical Co.)

and were used as purchased without further purification. 1H/13C NMR

spectra were recorded on Varian Oxford 200 or Unityinova 400

instruments. Fourier Transform Infrared (FT-IR) spectra were recorded

on a Nicolet 5700 FT-IR spectrophotometer, υ max in cm−1. Samples

were recorded as a KBr disc. Ultraviolet spectra were recorded on a

Lambda 40 UV-Visible Spectroscopy instrument. High resolution mass

spectra were recorded on JMS-AX505 WA mass spectrometer (JEOL).

Melting points were performed on recrystallized solids and recorded on

a SRS OptiMelt or electrothermal 9100 melting point apparatus and

were uncorrected. Column chromatographic purification was

performed using 70~230 mesh silica gel.

1. High energetic tetrazole

1-Tetrazolyl-3,3-(pentaediyl)triazene (17) To the solution of 5-amino-

tetrazole (8.51 g, 0.1 mol) in 1N-HCl (300 mL, 0.3 mol), a solution of

- 57 -

NaNO2 (6.9 g, 0.1 mol) in 40 mL of water was added dropwise for 0.5 h

at 0 ℃. The reaction mixture was stirred additional 1 h below 5 ℃,

and then added piperidine (10.9 mL, 0.11 mol). The resulting solution

was stirred overnight, and cooled to 0~5℃, which gave the pale yellow

solid. The resulting solid was filtered and dried in vacuum desiccators,

furnished the triazene product 17 as pale yellow solid (6.13g 34%).

Additional product was obtained from filtrate solution by extraction with

ethyl acetate. The crude was purified by silica gel chromatography. mp:

124~124.4℃ 1H NMR (200 MHz, CDCl3) δ 3.9 (bs, 2H), 3.8 (bs, 2H),

1.7 (bs, 3H).

Ethyl cyanoacetate oxime (ECAO, 11) To the solution of NaNO2 (19.4

g, 0.42 mol) in distilled water (250 mL), ethyl cyanoacetate oxime (33.9

g, 0.3 mol) was added portionwise at 35~40℃, and 85%

orthophosphoric acid (21.0g) was added over 30 min. The reaction

mixture was stirred for an additional 1 h at 30℃, added conc. HCl

(25.2 mL), cooled to 0~5℃, which gave the white solid. The resulting

solid was filtered, and dried in vacuum desiccator, furnished the

- 58 -

product 11 as a white solid (31.86 g, 75%). mp: 145~146℃ (decomp.)

1H NMR (200 MHz, DMSO-d6) δ 4.29 (q, 2H), 1.26 (t, 3H). 13C NMR

(200 MHz, DMSO-d6) δ 158.1, 125.9, 108.9, 62.6, 13.9

Ethyl cyanodinitroacetate (ECDNA, 7) A solution of conc. H2SO4 (9.6g,

0.1 mol) and conc. HNO3 (3.05g, 0.03 mol) was added the ethyl

cyanoacetate oxime (2.8g, 0.02 mol) at below 10℃. The reaction

mixture became cloudy and violently reacted with heat. After 2 h

stirring maintain the low temperature, the resulting mixture was poured

to ice, extracted with ethyl acetate, and the organic layer was washed

with water and brine, dried over MgSO4, and concentrated in vacuo, to

give a product as a pale yellow oil (2.35 g, 59%)

Ethyl 5-tetrazolyacetate oxime (ETAO, 8) To the solution of NaNO2

(3.46 g, 0.05 mol) in distilled water (30 mL), ETA (3.12 g, 0.02 mol)

was added portionwise at 50~60℃. After the reaction mixture was

stirred at 50℃ for 2 h, and adjusted pH = 2 using 85%

- 59 -

orthophosphoric acid maintaining the same temperature. The resulting

mixture was cooled to 0~5℃, which gave the white solid and

recrystallization with distilled water furnish the product 8 as a white

solid (2.42 g, 65%). mp: 176~177℃ (decomp.) 1H NMR (200 MHz,

DMSO-d6) δ 4.13 (q, 2H), 1.26 (t, 3H). 13C NMR (200 MHz, DMSO-d6)

δ 161.2, 145.3, 137.1, 62.1, 14.0.

Ethyl tetrazolyacetate (ETA, 9) To the solution of Sodium azide (138 g,

2.12 mol) and ammonium chloride (123 g, 2.30 mol) in DMF, ethyl

cyanoacetate (200 g, 1.77 mol) was added dropwise. The reaction

mixture stirred at 85~90℃ for 16 h. The resulting mixture was

concentrated under reduced pressure, dissolved in distilled water (1 L),

and adjusted pH = 2. After the mixture was cooled to 0~5℃, resulting

solid was filtered and recrystallized with iso-propyl alcohol to provide

the product as a pale brown solid (195g, 71%): mp 126 ℃; 1H NMR

(200 MHz, DMSO-d6) δ 4.15 (q, 2H), 4.14 (s, 2H), 1.20 (t, 3H); 13C

NMR (200 MHz, DMSO-d6) δ 167.7, 150.5, 61.3, 29.5, 13.3.

- 60 -

Ethyl 5-tetazolydinitroacetate (ETDNA, 19)

Method A. ETAO (7, 1 g, 5.4 mmol) was dissolved into sulfuric acid

(98%, 9.0 mL). The solution was cooled to 15 ℃, and nitric acid (95%,

2 mL) was added dropwise over 10 min. After stirring for 1.5 h at rt, the

reaction mixture was poured into ice. The crude was extracted with

ethyl acetate, and the organic layer was washed with water and brine,

dried over MgSO4, and concentrated in vacuo, to give a product as a

pale yellow oil (0.48 g, 36%)

Method B. Ethyl 5-tetrazolylacetate (9, 10.0 g, 0.064 mol) was

dissolved into sulfuric acid (98%, 50.0 mL, d = 1.84, 0.92 mol). The

solution was cooled to 15 ℃, and nitric acid (95%, 16.2 g, 0.244 mol)

was added dropwise over 30 min. After stirring for 2 h at rt, the

reaction mixture was poured into ice water (200 g). The precipitate was

filtered to give a crude product as a pale yellow solid (10.3 g, 65%).

The mother liquid was extracted with ethyl acetate, and the organic

layer was washed with water and brine, dried over MgSO4, and

concentrated in vacuo, to give an additional crude product as a pale

- 61 -

yellow solid (4.81 g, 31%): mp 78-80 ℃ (EtOH, dec); IR (KBr) 1773,

1594, 1314, 1244, 1047, 838 cm−1; UV (MeOH) λmax 225 nm; 1H NMR

(DMSO-d6, 200 Hz) δ 1.30 (t, 3H), 4.57 (q, 2H), 12.3 (br, 1H); 13C

NMR (DMSO-d6) 13.7, 67.1, 112.9, 152.3, 156.2; HRMS (FAB) m/z

calcd. for C5H7N6O6 (M+H+) 247.0428, found 247.0429.

5-Dinitromethyltetrazole (20). Ethyl 5-tetrazolyldinitroacetate (19, 10.0

g, 0.041 mol) was dissolved into water (100 mL), and the mixture was

stirred for 2 h at 50 ℃. The aqueous mixture was concentrated in

vacuo until a solid appeared. The precipitate was filtered to give a

crude product as a pale yellow solid (5.80 g, 82%): mp 122-123 ℃

(MeOH-CHCl3, dec); IR (KBr) 3226, 1585, 1521, 1384, 1218, 1050,

1018, 835, 754 cm−1; UV (MeOH) λmax 227, 304, 360 nm; 1H NMR

(DMSO-d6, 200 Hz) δ 12.9 (br); 13C NMR (DMSO-d6) δ 121.6, 149.1.

General Procedure for 5-Tetrazoyldinitromethylide salts.33,39 To a

solution of ethyl 5-tetrazolyldinitroacetate in CH3OH, KOH or NH4OH

was added. After stirring for 3 h at rt, the mixture was evaporated and

- 62 -

the residue was washed with ether to give almost pure salt in high

yield.

Dipotassium salt of 5-Dinitromethyltetrazole (21): mp 284-290 ℃

(H2O-MeOH, dec); IR (KBr) 1525, 1443, 1368, 1234, 1197, 1124, 1018,

826, 750 cm−1; UV (MeOH) λmax 230, 361 nm; 13C NMR (DMSO-d6) δ

128.5, 155.2.

Potassium salt of 5-Dinitromethyltetrazole (22): mp 167-171 ℃ (H2O,

dec); IR (KBr) 3215, 1525, 1479, 1420, 1362, 1317, 1245, 1194, 1114,

1052, 837, 752 cm−1; UV (MeOH) λmax 229, 357 nm; 13C NMR (DMSO-

d6) δ 121.8, 149.7.

Ammonium salt of 5-Dinitromethyltetrazole (23): mp 217 ℃ (H2O,

dec); IR (KBr) 3215, 1526, 1479, 1402, 1361, 1245, 1183, 1142, 1113,

1052, 998, 837, 752 cm−1; UV (MeOH) λmax 230, 361 nm; 13C NMR

(D2O) δ 126.7, 154.2.

- 63 -

2. 3,4-Bis(3-nitrofurazano)furoxan (BNFF)

3-Amino-4-aminoximidofurazan (AAOF, 24) To the solution of

Malononitrile (20 g, 0.3 mol) in 2N HCl (300 mL) was added dropwise

a solution of NaNO2 (42 g, 0.6 mol) in distilled water (80 mL). The

reaction mixture was stirred for 12 h at room temperature, which was

added a solution of NH2OH․HCl (46 g, 0.68 mol) in distilled water (80

mL) at 0 ℃ for 20 min. The resulting mixture was adjusted pH = 10,

heated at 35℃ for 2h and at reflux for additional 2 h. The mixture was

cooled to 0 ℃, adding the small amount of ethyl acetate, furnish the

product as white solid (35.5 g, 82%); mp 192~193℃ (ethyl acetate) 1H

NMR (DMSO-d6, 400 MHz) δ 10.49 (s, 1H), 6.26 (s, 2H), 6.16 (s, 2H);

13C NMR (DMSO-d6, 100 MHz) δ 154.5, 144.0, 140.1

3-Amino-4-chloroximidofurazan (ACOF, 25) To the suspension of

3-amino-4-aminoximidofurazan (20 g 0.14 mol) in MeOH (200 mL) was

added subsequently conc. HCl (134 mL), cuprous chloride (14.3g, 0.14

mol), and a solution of NaNO2(22.2 g, 0.32 mol) in distilled water (60

- 64 -

mL) at 0℃. The reaction mixture was standing for 3 h at 0~5℃, and

filtered. The resulting solid was washed with cold water 2 times, and

dried in the desiccator in vacuo. The crude solid dissolved in the co-

solvent (THF/Et2O), filtered, and concentrated in vacuo, to give a

product 3 as a bright ivory solid (13.3 g, 59%). (The additional product

was given when the mother liquid of the reaction mixture was

concentrated by a half in vacuo, and the resulting crude solid was

purified properly.); mp 203~206 ℃ (ether-pet. ether, dec.) 1H NMR

(DMSO-d6, 400 MHz) δ 6.23 (bs); 13C NMR (DMSO-d6, 100 MHz) δ

154.0, 141.9, 126.5

3,4-Bis (aminofurazano)furoxan (BAFF, 26) To a solution of 3-

amino-4-chloroximidofurazan (4.8g, 0.03 mol) in Et2O (60 mL) was

added dropwise a solution of 3% Na2CO3 (60 mL) for 30 min. The

reaction mixture was standing for 2 h below 10 ℃. The reaction

mixture was filtered, and the resulting mother liquid was extracted with

ethyl acetate three times. And then the organic layer was dried over

MgSO4, and concentrated in vacuo, to give a crude product as a pale

- 65 -

yellow solid. The crude solid was dissolved in MeOH, and the mixture

was filtered and concentrated in vacuo. The residue was recrystallized

to furnish a product as a white solid (2.98g, 80%); mp 209~212 ℃

(ethyl acetate/hexane, dec.) 1H NMR (DMSO-d6, 400 MHz) δ 6.63 (s,

2H), 6.58 (s, 2H); 13C NMR (DMSO-d6, 100 MHz) δ 156.0, 155.1,

146.5, 136.2, 133.3, 104.2.

3,6-Bis(4-amino-1,2,5-oxadiazol-3-yl)-1,4,2,5,-dioxadiazine (31)

To a solution of 3-amino-4-chloroximidofurazan (0.3256g, 2 mmol) in

THF (10 mL) was added dropwise a solution of 3% K2CO3 (9.56 mL)

for 30 min. The reaction mixture was standing for 2 h below 10 ℃. The

reaction mixture was filtered and furnished the product as the with

solid (55 mg, 22%). In addition, the mother liquid was concentrated in

vacuo, furnished the solid, which was filtered to obtain the product as a

solid (130 mg, 52%); mp 229~230 ℃ (dec.) 1H NMR (DMSO-d6, 400

MHz) δ 6.54 (bs); 13C NMR (DMSO-d6, 100 MHz) δ 155.0, 153.5,

136.0.

- 66 -

3,4-Bis(nitrofurazano)furoxan (BNFF, 27)

Method A. 3,4-Bis(amino-furazano)furoxan (0.25g, 1 mmol) was

dissolved conc. H2SO4 (0.85 mL, 15 mmol). To the reaction mixture, 60%

H2O2 (1.51 mL, 15 mmol) and ammonium persulfate (0.228 mg, 1

mmol) was added subsequently at 0~5 ℃. As the resulting solution

was stirred at ambient temperature, the deep blue color of reaction

solution turned a clear yellow. The reaction mixture was washed with

H2O two times and followed by 10% NaHCO3 solution two times. The

organic layer was dried over MgSO4 , filtered and concentrated under

reduced pressure. The residue was purified using flash silica gel

chromatography to give a product as a white solid (0.14g, 45%).

Method B. To the solution of 60% H2O2 (3.32 mL, 0.07 mol) in

methylene chloride (26 mL) was added slowly trifluoroacetic anhydride

(7.4 mL, 0.05 mol) maintaining below 5 ℃, and 3,4-bis(amino-

furazano)furoxan (1g, 4 mmol) was added with a small portion. The

resulting reaction mixture was stirred at room temperature for 1 h,

followed at reflux over 3 h. The reaction mixture was washed with H2O

- 67 -

two times and followed by 10% NaHCO3 solution two times. The

organic layer was dried over MgSO4 , filtered and concentrated under

reduced pressure. The residue was purified using flash silica gel

chromatography to give a product as a white solid (0.54g, 44%); mp

108~111 ℃ (dec.); 13C NMR (DMSO-d6, 100 MHz) δ 160.2, 160.0,

143.0, 139.5, 137.0, 103.5.

- 68 -

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V. Appendices

1. Definitions of abbreviations

AAOF = 3-amino-4-aminoximidofurazan

ACOF = 3-amino-4-chloroximidofurazan

ADN = ammonium dinitramide

ANF = 3-amino-4-nitrofurazan

ATTz = 6-ammino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine

BAFF = 3,4-bis(amino-furazano)furoxan

BNFF = 3,4-bis(3-nitrofurazano)furoxan

CL-20 = 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane

DAAF = 4,4'-diamino-3,3'-azoxyfurazan

DAAzF = 4,4'-diamino-3,3'-azofurazan

DAF = 3,4-diaminofurazan

DATB = 1,3-diamino-2,4,6-trinitro- benzene

DDF = 4.4-dinitro-3,3'-diazenofuroxan

DDNP = diazodinitrophenol

DINGU = 1,4-dinitroglycouril

DNABF = 4,4’-dinitro-3,3’-azoxy-bis(furazan)

DNAzBF = 4,4’-dinitro-3,3’-azo-bis(furazan)

DNF = 3,4-dinitrofurazan

DNFX = 3,4-dinitrofuroxan

ECA = ethyl cyanoacetate

ECAO = ethyl cyanoacetate oxime

ECDNA = ethyl cyanodinitroacetate

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EGDN = ethylene glycol dinitrate

ETA = ethyl tetrazolylacetate

ETAO = ethyl tetrazolylacetate oxime

ETDNA = ethyl 5-tetazolyldinitroacetate

FOX-7 = 1,1-diamino-2,2-dinitro- ethylene

GTN = glyceryl trinitrate

Hexyl = 2,2',4,4',6,6'-hexanitrodiphenylamine

HMX = 1,3,5,7- tetranitro-1,3,5,7-tetra-azacyclooctane

HNS = 2,2',4,4',6,6'-hexanitrostilbene

IHE = insensitive high explosive

N2FOX-7 = 5-dinitromethylene-5H-tetrazole

NC = nitrocellulose

NENO = N,N'-dinitro-N,N'-bis(2-hydroxyethyl)oxamide dinitrate

NG = nitroglycerine

PAT = 5-picrylamino-1,2,3,4-tetrazole

PETN = pentaerythritol tetranitrate

RDX = 1,3,5-trinitro-1,3,5-triazacyclohexane

SAT = 5,5'- styphnylamino-1,2,3,4-tetrazole

TDNM = 5-tetrazolyldinitromethane

TEX(TOIW) = 4,10-dinitro-4,10-diaza-2,6,8,12-tetraoxaisowurtzitane

TFAA = trifluoroacetic anhydride

TNAZ = 1,3,3-trinitroazetidine

TNB = 1,3,5-trinitrobenzene

TNT = 2,4,6-trinitrotoluene

VOD = velocity of detonation

DSC = differential scanning calorimeter

TGA = thermogravimetric analysis

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2. Spectral data

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- 103 -

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100 200 300 400 500 600 700 800 900 1000

0.0

0.5

1.0

1.5

2.0

2.5in

tens

ity

wavelength (nm)

ETA

100 200 300 400 500 600 700 800 900 1000-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

inte

nsity

wavelength (nm)

ETDNA

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100 200 300 400 500 600 700 800 900 1000

0.0

0.5

1.0

1.5

2.0

inte

nsity

wavelength (nm)

E206 solid 1/2 dilution

100 200 300 400 500 600 700 800 900 1000

0.0

0.5

1.0

1.5

2.0

2.5

inte

nsity

wavelength (nm)

E157 (DPS recrystall)

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200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

Inte

nsity

Wavelength (nm)

MPS of TDNM (in H2O)

200 300 400 500 600 700 800-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Inte

nsity

Wavelength (nm)

ADT (MeOH washing)

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