High Energy Materials

O2N NO2 N N N N N3 N N N

NO2

NO O2N 2 NO O2N 2 NO O2N 2 O2N NO2

Vlad Bacauanu MacMillan Research Group Group Meeting July 25th, 2019 What Are High Energy Materials?

compound that stores chemical energy high energy material and which upon stimulation undergoes (HEM) rapid decomposition with release of energy and gas

explosives propellants pyrotechnics Applications of High Energy Materials

The obvious – military applications

Civil and scientific applications

mining civil engineering oil industry space exploration High Energy Materials – Outline

Generals aspects of high energy materials Very brief history

Fundamental properties

Decomposition via deflagration or detonation

Primary vs secondary explosives

Oxygen balance

Synthesis of high energy materials

Safety precautions in HEM labs

Explosophore functional groups

Examples of synthetic approaches

Recent avenues within the field

Nitrogen-rich molecules

Strained energetic materials: HNIW and ONC

Exploring stereochemistry of materials Book References for High Energy Materials

High Energy Materials Chemistry of High-Energy Materials Organic Chemistry of Explosives Jai P. Agrawal Thomas M. Klapötke Jai P. Agrawal & Robert D. Hodgson 1st ed. (2010) 4th ed. (2017) 1st ed. (2007) History of Development of High Energy Materials

1943 CH3 O2N NO2 gunpowder N N O2N NO2 (KNO3 + C + S) N N 1863 1880 TNT O NO 1894 O2N NO2 2 HMX ONO2 NO2 O2NO ONO2 O2NO ONO2 PETN nitroglycerin ONO2

800 1000 1850 1900 1950 present

OH O N NO 2 N N 2 1855 O2N NO2 O N 2 N N NO2 ONO 2 picric O2NO 1885 1930’s N N O acid O N NO O NO 2 CL-20 2 2 O2N NO2 N N ONO 1987 2 n RDX nitrocellulose 1867 N dynamite NO2

in Radical Chemistry, 1st ed.;, C., Wiley-VCH: Weinheim, Germany, 2004. Fundamental Properties of High Energy Materials

ΔHf heat of formation (ΔHf) C + H2 + N2 + O2 explosive

Q heat of explosion (Q) explosive explosion products (CO2, CO, H2O, N2, etc.)

density of material (ρ) volume of gases released (V)

velocity of detonation (VOD) detonation pressure (DP) speed with which detonation wave propagates peak pressure in detonation wave

explosive power = Q x V brisance ~ ρ x VOD2 “ability of explosive to do useful work” shattering power of an explosive

specific impulse (Isp) sensitivity total impulse delivered by a unit of propellant to heat, shock, friction, electrical discharge, etc. Deflagration vs. Detonation in High Energy Materials

deflagration to detonation

transition

Deflagration – propellants (always for explosives; Detonation – explosives

very rapid burning avoid for propellants) extremely rapid decomposition subsonic propagation wave supersonic propagation wave controlled, regular process uncontrollable past initiation Deflagration vs. Detonation in High Energy Materials

Detonation – explosives

extremely rapid decomposition supersonic propagation wave uncontrollable past initiation

how does a detonation wave propagate? hot gases high pressure material is material material decomposes released shock front compressed heats up with release of gas Classification of High Energy Materials

OH Primary Secondary (high) Hg(CNO)2 Pb(N3)2 explosives explosives O2N NO2

NO K+ 2 very sensitive to stimuli relatively insensitive N NO2 N N N N rapid detonation high performance O2N NO2 N N N N N N inititate decomposition of main load of N + 2º explosive or propellant explosive ensemble N N O2N K O2N NO2 Classification of High Energy Materials

OH Primary Secondary (high) Hg(CNO)2 Pb(N3)2 explosives explosives O2N NO2

NO K+ 2 very sensitive to stimuli relatively insensitive N NO2 N N N N rapid detonation high performance O2N NO2 N N N N N N inititate decomposition of main load of N + 2º explosive or propellant explosive ensemble N N O2N K O2N NO2 Traditional Approach To Explosives Design

Me H O CO O2N NO2 C H + O + N 2 2 N2 combustable fuel oxidant (neither) exothermic NO2 products

an explosive is a mixture of fuel and oxidant – balancing the two is ideal

Ω oxygen balance

for generic CaHbNcOd

(d – 2a – b/2) x 1600 Ω = ΩCO2 = M

(d – a – b/2) x 1600 ΩCO = M Importance of Having Good Oxygen Balance for Secondary Explosives

How is oxygen balance important?

Me

O2N NO2 explosion 1 CO2 1 H2O + + 1.5 N2 3 CO 3 C 1.5 H2 Ω = –74% NO2

enthalpy of formation incomplete oxidation of C,H backbone ΔHf,CO2 << ΔHf,CO < ΔHf,C = 0 wasted potential energy of the fuel ΔHf,H2O < ΔHf,H2 = 0

Ideal explosion for TNT How do I fix my bad OB?

Me Me O2NO O2N NO2 5.25 O 2 O2N NO2 + + O2NO ONO2 oxidizer deficit ONO NO2 2 NO2

bad Ω good Ω

issues overcome by formulation

7 CO2 + 2.5 H2O + 1.5 N2 with others HEMs Most Commonly Used Explosives in Military

Me O N NO O2N NO2 2 2 O2N NO2 N N N N

N N N NO 2 O2N NO2 NO2 TNT RDX HMX trinitrotoluene (1880) research department explosive (1930’s) high melting explosive (1943) stable, cheap, melt-castable stable, more expensive, very powerful

next generation high-performance explosive?

organic synthesis! Safety Precautions for High Energy Materials

Safety precautions in HEM labs

first synthesis on 250 mg scale or less keep distance from experiments (tongs, clamps)

protective equipment must be used

z

protective gloves Kevlar wrist protectors full-visor face shield ear protectors

protective leather or Kevlar jacket Student in the Klapötke group

Safety is not a joke – refusing to follow the safety guidelines gets you fired!

Kemsley, J. Chem. Eng. News 2008, 86, 22 Explosophores – Common Functional Groups in HEM

V. Plets’ theory of explosophores (1953) –– several common functional groups in explosives

nitro, nitrate, and nitroso azo and azide

O O N N N N N N N N O O O O

N-haloamino chlorate and perchlorate

F Cl O O N N Cl Cl O O O O F Cl O

fulminates peroxide and ozonide metal acetylides

O O O C C M C N O O O M

Kemsley, J. Chem. Eng. News 2008, 86, 22 Synthesis of Nitrate Esters and Nitramines

Direct nitration of alcohols

HO O O2N NO + source HO OH 2 O O O2N NO2

OH O O N alcohol substrate 2

conc. HNO N2O5 100% HNO 3 NO BF 3 2 4 N – w/ conc. H2SO4 + – BF4 [NO2] [NO3] NO2

Direct nitration of amines

F3C CF3 F3C CF3 Me HNO3 Me

H H 100% HNO3 O2N NO2 ZnCl N N N N 2 NH N NO2 N TFAA N Ac2O HO O2NO NO2 NO2

acidic conditions work best for non-basic amines proceeds via N-chloro intermediate (from AcOCl) Synthesis of Nitrate Esters and Nitramines

Tertiary amides undergo nitrolysis readily to form nitramines

Ac Ac O N NO O 2 2 nitrolysis N N N N O N2O5 NO2 N R N HO R N N N N HNO3 Ac Ac O2N NO2

N-alkyl bonds can also undergo nitrolysis to form nitramine products

O N NO O N NO N 2 2 2 2 HNO3, NH4NO3 N N N N

N N N N Ac2O N N NO 2 O2N NO2

Nitrosation followed by oxidation or exchange nitration is also a viable strategy

O N NO + ON NO + 2 2 HN NH NO N N NO2 N N

N N N H or [O] NO NO2 Synthesis of Aromatic and Aliphatic C–NO2 Compounds

Aromatic C–NO2 products

Cl Cl NH2 O N NO O N NO H2SO4, HNO3 2 2 NH3 2 2

Cl Cl 150 ºC Cl Cl toluene, 150 ºC H2N NH2

NO2 NO2

electrophilic aromatic substitution is a staple subsequent SNAr is facile and enabling

Aliphatic C–NO2 products

+ – NH3 Cl NO2 DMDO oxidation of amines

– + + – with various reagents Cl H3N NH3 Cl acetone O2N NO2 – + Cl H3N O2N

O2N NO2 O O H NO2 O2N NO2 additions of nitro nucleophiles aq. MeOH O2N NO2 O2N NO2 Synthesis of Nitrogen-Rich Compounds for HEM Development

Cl Cl NH2 cyanogen azide for tetrazole synthesis N N N N N N

Cl N Cl Cl Cl NH2 Cl H2N

N N 1) SNAr, DMF, 90 ºC N3 CN N SNAr is H2N 2) H2SO4, HNO3 N widely employed Na+ H2N 3) NH3, acetone N N N N N N N SNAr NH 2 N NH O2N NO2 2

N N H2N NH NH2 HNO3 N H N O2N O2N NO2 2 N N N

N N HN N N NH2 N H O2N NH N N O N NO NO 2 2 2 N N N N N N N NH2 N H2N NH2 HN NO N 2 N N NO2 Design of Novel Energetic Materials

Higher performance materials

increased heat of explosion maximize energy of material higher detonation pressure (per unit volume) higher detonation velocity

Oxidation of C,H backbone Inherent strain Nitrogen-rich molecules

N N Me N O N NO N 2 N 2 N N N N O2N NO2 O N NO N 2 N N 2 N N H2N NH N N 2 H2N NH2 NO2 O2N NO2 N N H H

energy from “combustion” strain release – extra energy energy from formation of N2 traditional approach newer approach newer approach Nitrogen-Rich Molecules as High Energy Materials

Nitrogen-rich molecules BDEs normalized by bond order

N N N N N N N N N=N N N N N N N

good performance (Q, VOD, P)

candidates for “green” HEM

N-rich propellants lead to less erosion very endothermic compounds (ΔHf >> 0)

N N N N N N N N N R N N N R R R

stable relatively stable too unstable

not endothermic enough high energy high energy

Klapötke, T. M.; Stierstorfer, J. J. Am. Chem. Soc. 2009, 131, 1122 Synthesis of Family of Azidotetrazolate Salts

Na+ H M+ BrCN MeOH N HCl N base N N N N N3 N3 N3 N N N 2 NaN3 H2O N N H2O N

several counterions were installed Cs+ N N CsCN7 NH + N3 2 N + + N H2N NH3 NH4 H2N NH2

Li+ Na+ K+ “The aqueous solution was left for crystallization H2N NH+ on a watch glass, and “fortunately” three single Cs+ Ca2+ crystals could be isolated […] A few hours later H N NH 2 2 the whole preparation exploded spontaneously.”

“Synthesis of rubidinium 5-azidotetrazole has been tried a few Rb+ N N times. However, we never could observe any solid material, and N3 N the reaction mixture (left undisturbed in an explosive case and in N the dark) detonated spontaneously for each preparation”

Klapotke, T. M.; Stierstorfer, J. J. Am. Chem. Soc. 2009, 131, 1122 Properties of Azidoterazolates

Na+ “In the measurement of 7 a violent explosion destroyed the setup.”

H2N NH+ Differential H2N NH2 M+ N scanning N + NH N3 2 calorimetry N (DSC) N H2N NH2

+ NH4

“The compounds decompose/explode + H2N NH3 violently, most of them without melting.”

some experimental measurements hindered by sensitivity thermodynamic parameters derived computationally instead

Klapotke, T. M.; Stierstorfer, J. J. Am. Chem. Soc. 2009, 131, 1122 Properties of Azidoterazolates

“probably too sensitive for practical applications”

Klapotke, T. M.; Stierstorfer, J. J. Am. Chem. Soc. 2009, 131, 1122 Other Publications on Highly Nitrogenous Compounds

N 3 N NO N N 2 N N N N N O N O N N N N3 N O2N N N N3

Klapötke Angew. Chem. Int. Ed. 2011, 50, 4227 Shreeve J. Am. Chem. Soc. 2011, 132, 15081

O N isolated as N N N N N N (N5)6(H3O)3(NH4)4Cl N N N N N N O

Hu & Lu Science 2017, 355, 374 Klapötke J. Mater. Chem. 2012, 22, 20418 Development of Strain and Caged Molecules for High Energy Materials

O2N NO2 O2N NO2 NO2 Strained and caged structures O2N NO2 N NO2 NO2 NO2 NO2 high crystal density NO2 O2N O N NO O O 2 2 additional energy as strain NO O O 2 very high energy density! O2N O2N N N NO2 NO2 NO2

2,4,6,8,10,12-hexanitro- O N NO 2 N N 2 density 2.04 g/mL 2,4,6,8,10,12-hexaazaisowurtzitane O N NO 2 N N 2 enthalpy of formation 100 kcal/mol synthesized in 1987 N N detonation velocity 9400 m/s at Naval Air Warfare Center O2N NO2

already produced on 100 kg scale HNIW (CL–20) decomp T 228 ºC

Nielsen, A. T. et al. Tetrahedron 1998, 54, 11793 Syntheses of HNIW

Bn Bn Ac Ac + N N N N O O H Bn Bn H2, Pd/C Ac Ac NH2 N N N N

H H MeCN N N Ac2O, PhBr N N Bn Bn Bn Bn 6 equiv. 3 equiv. 75% yield 60% yield

Ac Ac Ac Ac O N NO2 N N NOBF (3 eq.) N N NO BF (12 eq.) 2 N N Ac Ac 4 Ac Ac 2 4 O N NO N N N N 2 N N 2 sulfolane sulfolane N N N N N N

Bn Bn ON NO O2N NO2 90% yield

Ac Ac Ac Ac O N NO2 N N N O (excess) N N 99% HNO 2 N N Ac Ac 2 4 Ac Ac 3 O N NO N N N N 2 N N 2 96% H SO N N N N 2 4 N N

Bn Bn ON NO O2N NO2 92% yield 93% yield

Nielsen, A. T. et al. Tetrahedron 1998, 54, 11793 Co-Crystallization of HNIW with TNT

Disadvantage of HNIW: sensitivity

Me O N NO2 2 N N O2N NO2 O N NO O2N NO2 N N 2 N N 2 N N N NO2 O2N NO2 NO2

impact sensitivity: 4 J 15 J 7.5 J

friction sensitivity: 48 N > 353 N 120 N

Me O N NO 2 N N 2 O N NO O2N NO2 2 N N 2 + N N

O2N NO2 NO2

HNIW:TNT 1:1 cocrystal density drops by 5–10%

sensitivity improved two fold!

Bolton, O.; Matzger, A. J. Angew. Chem. Int. Ed. 2011, 50, 8960 Octanitrocubane – Idealistic Dream or Tangible Reality?

Octanitrocubane Caveat in synthesis

NO O2N 2 NO2 NH NH O2N 2 [O] 2 NH2 NO O2N 2 O O O2N NO2 NH2 N N O O predicted properties

high energy push-pull intermediates must avoid high density will lead to 1,2-diamino opening of the cube precursors kinetically stable

Synthesis of a 1,3,5,7-substituted precursor

COCl COCl COCl ClOC COCl (COCl) 2 ClOC COCl COCl

UV light, 3 h ClOC ClOC COCl ClOC ClOC

70% selectivity 8% selectivity 22% selectivity Kharasch-Brown 31% yield reaction undesired regioisomers (recrystalization)

Lukin, K. A.; Li, J.; Eaton, P. E.; Kanomata, N.; Hain, J.; Punzalan, E.; Gilardi, R. J. Am. Chem. Soc. 1997, 119, 9591 Synthesis of Tetranitrocubane

COCl CON3 NCO TMSN heat ClOC 3 N3OC OCN

ClOC N3OC OCN COCl CON3 NCO

O O

NCO NO2 Me Me OCN O2N

OCN wet acetone O2N NCO NO2

45% yield (overall from acyl chloride)

O O NHCO2H NH2 H2O HO CHN H N 2 2 Me Me

HO2CHN H2N – CO2 NHCO2H NH2

Lukin, K. A.; Li, J.; Eaton, P. E.; Kanomata, N.; Hain, J.; Punzalan, E.; Gilardi, R. J. Am. Chem. Soc. 1997, 119, 9591 Synthesis of More Highly Substituted Nitrocubanes

NO2 NO2 NO2 NaHMDS N2O4 H NO2 O2N O2N O2N Na+

O2N O2N O2N pKa ~ 21 (THF) –196 ºC NO2 NO2 NO2

density = 1.81 g/mL 40% yield stable up to 300 ºC “Despite the predictions of naysayers, (chromatography) pentanitrocubane is stable […], showing no obvious shock sensitivity or special thermal sensitivity.”

Lukin, K. A.; Li, J.; Eaton, P. E.; Kanomata, N.; Hain, J.; Punzalan, E.; Gilardi, R. J. Am. Chem. Soc. 1997, 119, 9591

Synthesis of octanitrocubane is achieved in 2000

i) NaHMDS (4 eq.), –78 ºC i) LiHMDS, –78 ºC NO NO NO 2 O2N 2 O2N 2 ii) N2O4, –125 ºC H ii) NOCl, –78 ºC NO O2N O2N O2N 2

+ NO2 NO2 O2N iii) H , –30 ºC O2N iii) O3, –78 ºC O2N NO2 O2N NO2 O2N NO2 74% yield ~50% yield

Zhang, M.-X.; Eaton, P. E.; Gilardi, R. Angew. Chem. Int. Ed. 2000, 39, 401 Properties of Heptanitrocubane and Octanitrocubane

NO2 NO O2N O2N 2 H “Beautiful, colorless, solvent- stable up to 200 ºC NO O2N O2N 2 free crystals formed when its O N NO2 perfect oxygen balance NO2 2 solution in fuming nitric acid O2N O2N NO2 O2N NO2 was diluted with sulfuric acid.” “smokefree” detonation heptanitrocubane octanitrocubane

Me O N NO O2N NO2 2 2 NO2 O N NO N N O2N 2 2 N N NO predicted or O2N 2 measured N NO N N O2N 2 properties NO O N NO 2 O2N NO2 2 2 NO2 TNT RDX HMX octanitrocubane

density 1.6 g/mL 1.8 g/mL 1.9 g/mL 2.0 g/mL

oxygen balance –74% –22% –22% 0%

detonation velocity 7000 m/s 8800 m/s 9100 m/s 10100 m/s detonation pressure 190 kbar 338 kbar 390 kbar 500 kbar

Zhang, M.-X.; Eaton, P. E.; Gilardi, R. Angew. Chem. Int. Ed. 2000, 39, 401 New Avenues in HEM Development – Stereo- and Regiochemistry?

ONO2

ONO2 computation desirable properties predicted synthesize (ΔH , density, detonation pressure O2NO f candidate detonation velocity, etc.) ONO2 generic candidate

Stereochemistry – traditionally ignored aspect within HEM design

ONO2 ONO2 ONO2 ONO2

ONO2 ONO2 ONO2 ONO2

O2NO O2NO O2NO O2NO

ONO2 ONO2 ONO2 ONO2

Baran, P. S. et al. ChemRxiv 2019 DOI 10.26434/chemrxiv.8521955 New Avenues in HEM Development – Stereo- and Regiochemistry?

O2NO ONO2 O2NO ONO2 O2NO ONO2

O2NO ONO2 O2NO ONO2 O2NO ONO2 similar detonation velocities: 7500 m/s similar detonation pressures: 23 GPa

O2NO ONO2 O2NO ONO2 O2NO ONO2 O2NO ONO2

O2NO ONO2 ONO2 ONO2

similar specific impulse: 240 s similar enthalpy of formation: –500 kJ/mol

Baran, P. S. et al. ChemRxiv 2019 DOI 10.26434/chemrxiv.8521955 New Avenues in HEM Development – Stereo- and Regiochemistry?

O2NO ONO2 O2NO ONO2 O2NO ONO2

O2NO ONO2 O2NO ONO2 O2NO ONO2 melting T 106 48 < –40 (ºC) decomp T 199 200 187 (ºC)

O2NO ONO2 O2NO ONO2 O2NO ONO2 O2NO ONO2

O2NO ONO2 ONO2 ONO2 melting T 101 86 147 (ºC) decomp T 194 193 196 (ºC)

Range of melting points across family of stereo- and regioisomers

Baran, P. S. et al. ChemRxiv 2019 DOI 10.26434/chemrxiv.8521955 New Avenues in HEM Development – Stereo- and Regiochemistry?

Me

predicted or O2N NO2 O2NO ONO2 O2NO ONO2 O NO ONO measured 2 2 Me ONO2 properties O2NO ONO2 O2NO ONO2

NO2 melt-castable propellant candidate candidate explosive plasticizer

melting T (ºC) 80 106 < –40 –3

decomp T (ºC) 295 199 187 182

density (g/mL) 1.65 1.64 1.54 1.27

detonation velocity (m/s) 6950 7438 7577 7050 detonation pressure (GPa) 19.3 24.5 24.5 23.7

specific impulse (s) –– 241 240 247

Baran, P. S. et al. ChemRxiv 2019 DOI 10.26434/chemrxiv.8521955 High Energy Materials – Outline

Generals aspects of high energy materials Very brief history

Fundamental properties

Decomposition via deflagration or detonation

Primary vs secondary explosives

Oxygen balance

Synthesis of high energy materials

Safety precautions in HEM labs

Explosophore functional groups

Examples of synthetic approaches

Recent avenues within the field

Nitrogen-rich molecules

Strained energetic materials: HNIW and ONC

Exploring stereochemistry of materials