Chemistry of high-energy materials

Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 High Energy Materials Explosives Non-explosive materials High Explosives Low Explosives 1° Explosives 2° Explosives Propellants Pyrotechnics - Fireworks - Color/flash/sound [detonate by ignition] - Lead azide - Tetrazene [need detonator] - TNT - RDX - Black powder - liquid/solid Organic Chemistry of Explosives by J.P. Agrawal and R.D. Hodgson Prof. Thomas Klapotke - Ludwig-Maximilians-Universität München - Germany Chair of inorganic chemistry Dr. Michael A. Hiskey - Los Alamos National Laboratory History of Explosives What makes an explosion? Exothermic chemical reaction comprised of an oxidant and fuel, which releases energy (gas and heat) in a given time interval. Whats the difference between explosive, propellants and pyrotechnics? Rate at which it burns (Flamming gummy bear vs. rocket booster vs. TNT) Speed of reaction will determine subsonic vs. supersonic blast pressure waves 7th century A.D.- "Greek Fire" petroleum distillate used by Byzantines of Constantinopole 13th century - black powder (aka gunpowder) Chinese alchemists 18th century - black powder composition became standardized: KNO3/charcoal/sulfur (75/15/10 w/w) 19th century - NH4NO3 replacement for KNO3 in black powder 1846 - Italian Chemist Ascanio Sobrero invented nitroglycerin (NG) 1863 - German chemist Julius Wilbrand invented 2,4,6-trinitrotoluene (TNT) originally used as a yellow dye. Potential as an explosive not appreciated due to difficulty to detonate (insensative). 1866 - Mixing of NG with silica (PBX) to make malleable paste (dynamite) late 19th century - nitration chemistry on common materials (resins,cotton, etc.) 1910 - military use of TNT for artillery shells and armour-piercing shells 1939-1945 - World War II - Research on explosives intesified (nitration chemistry) Developlment of cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX). [detonate] [deflagrate-burn rapidly] Introduction to high energy materials terminology Brisance: Shattering capabiliy of explosive. Measure of rate an explosive develops its maximum pressure. Relative effectiveness factor (R.E. factor): Measurement of an explosive's power for military purposese. It is used to compare an explosive's effectiveness relative to TNT by weight (TNT equivalent/kg or TNTe/kg). Detonation velocity (VoD): The velocity at which the shock wave front travels through a detonated explosive. Difficult to measure in practice so use gas theory to make prediction. Specific impulse (Isp): The force with respect to the amount of propellant used per unit time. Used to calculate propulsion performance. Oxygen balance (OB%): Expression used to indicate degree to which explosive can be oxidized. If explosive contains just enough oxygen to form carbon dioxide from carbon, water from hydrogen molecules and all metal oxides from metals with no excess, the explosive is said to have zero oxygen balance. Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 N N NN O2N O2N NO2 NO2 Aliphatic C-nitro compounds R NO2 R1 NO2 R2 R1 NO2 R3R2 R NO2 NO2 R1 NO2 NO2R2 1° nitroalkane 2° nitroalkane 3° nitroalkane Terminal gem-dinitroalkane Internal gem-dinitroalkane acidic protons (condensation chemistry) high explosive with high thermal and chemical stability R1 R2 NO2 NO2 NO2 Trinitromethyl ONO2 Me O2N NO2 NO2 N N N NO2 O2N NO2 ONO2 O2NO TNT Nitroglycerin (VOD=7750 m/s) RDX (VOD=8440 m/s) Chemical types/class of organic explosives NO2 NO2 O2N NO2 O2NN NNO2 O2NN NNO2 O2NN NNO2 O2N NO2 NF2F2N N N N N NN NO2 NO2 O2N O2N O2N NO2 ONO2 ONO2 O2NO O2NO NO2 NO2 ONO2 Si ONO2 O2NO O2NO ONO2 ONO2 O2NO O2NO Pentaerythritol tetranitrate (PETN) (VOD=8310 m/s) Aromatic C-nitro compounds Aliphatic O-nitro compounds HMX (VOD=9110 m/s) O2N NO2 NO2 O2N NO2 NO2 HO (NO2)x x ≥ 4 poor chemical stability Aliphatic N-nitro compounds N H O N H NO2 H2N N NH2 NO2 N,N'-dinitrourea (DNU) nitroguanadine 1,3,5-trinitrobenzene (TNB) 2,4,6-trinitrophenol (picric acid) O2NN H Nitro derivatives of pyrroles, thiopenes, and furans are not practical explosives: 1. heat of formation offers no benefits over standard arylene hydrocarbons 2. during nitration, these heterocycles are much more prone to oxidation and acid cat. ring opening compared to arenes S O heterocycles N N H NO2H2N O2N 4-amino-3,5-dinitropyrazole (LLM-116) NHN O2N NO2 2,4-dinitroimidazole (2,4-DNI) N N O furazans/benzofurazans furoxans/benzofuroxans O Hexanitrohexa- azaisowurtzitane (HNIW or CL-20) (VOD=9380 m/s)Si-PETN novel energetic nitrate eseter 3,3-bis(difluoroamino) octahydro-1,5,7,7- tetranitro-1,5-diazocine (TNFX) N N N H H2N NO2 N H N NH O2N ON N N Ar N N O ArAr 1,3,4-oxadiazoles 3-nitro-1,2,4-triazol-5-one (NTO) O2N NO2 benzotriazoles N N N N H H2N N O2N H2N NO2 NH2 NH2 N NO2N H2N NO2 NH2 O O O N N N N NH2 NH2 O O tetrazoles 1,2,4 triazolespyridine N-oxide tetrazine N-oxidepyrazine N-oxide H-bonding reduction in sensativity Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 Routes to C-Nitro functionality Nitration chemistry Borgardt et al. Chem Rev 1964. 64, 19 (polynitro functionality) The nitro gorup whether attached to aromatic or aliphatic carbon, is probably the most widely studied of the functional groups and this is in part attributed to its use as an 'explosophore' in many energetic materials. Direct nitration of aliphatic and alicyclic hydrocarbons possible in the vapor phase using HNO3 or NO2 (toxic redish-brown gas) at elevated temperatures. Me NO2H Me HNO3 25% Me NO2 Me Nitration with HNO3 is difficult Me MeMe Me N2O4 N N O OO O + O2N NO2H Me NO2 Me O2N MeMe Me ONO Me O2N MeMe Me ONO2 Me O2N MeMe nitro-nitratenitro-nitritedinitro + - colorless liquid Radical methods Ph 1 atm NO DCE/ rt Ph NO2 Ph NO2 OH 76% 23% + Mukaiyama et al. Chem Lett 1995. 505 Al2O3 Ph NO2 92% R HH R R NO2H R H R NO2H R H R NO2H R 80 - 90% NaNO3 xs, CAN 2eq AcOH/CHCl3 Hwu et al. J Chem Soc Chem Commun 1994. 1425 Taniguchi et al. JOC 2010. 75, 8126 R R R NO2 ClRFe(NO3)3 9H2O FeCl3 MeCN, reflx N Cl N CO2R KNO3 H2SO4 TBAN Ph MeCN NO2BF4 Ph NHAc NO2 84% 80 - 90% S Br 1. nBuLi 2. N2O4 -78 °C S NO2 TMS AcONO2 NO2 NO2 O2N O2N NO2 1. NaHMDS 2. N2O4 NO2 O2N O2N NO2 NO2 O2N O2N NO2 NO2 O2N O2N NO2 NO2 N Cl N CO2R N Cl N CO2R NO2 O2N traditional [NO2+] F3C O O CF3 O TFAA F3C O O NO2 TBAN * No rxn in presence of TEMPO TMS O N O [2+2] _ OAc NO2+ NO2 O N O _ OAc NO2 O N O OAc Nef O ONO2 AcONO2 ONO2 NO2 NO2 alkaline nitration NItration selectivity on arene/heteroarene 76% 44% 77% Kakiuchi, et al. Synlett 1999. 901 74% Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 Victor Meyer rxn - alkyl chlorides too slow - only good for 1° (2° alkyl halide gives nitrate ester) - nitrate ester arises from desproportionation of silver nitrate acc. by heat/light modified VM (alkali metal nitrites e.g. NaNO2) time and solubility is VIMP Kornblum et al. JACS 1956. 78, 1497 NO2 R R O R R + NaNO2 NO2 R R OH R RNO OH HO OH phloroglucinol N O nitrite ester 1° and 2° nitro compounds oxidation of isocyanates O NOH O NO2H 1.KOtBu amyl nitrate 2. H+ 1. NBS 2. [O] 3. [H] NO2 CF3CO3H N O OH NO2 O2N NO2 S2O8 2- H+ NO2O2NNO2 + C+H3N C+H3N NH3+C NH3+Cl- NCO OCN NO2 O2N O2N O2N NO2 NO2 F NO2 NO2 NO2 O2N NO2 NO2 NO2 (or) NO2 F NO2 NO2 CO2H R R HNO3 20 - 30% R R NO2 NO2 MeO2C CO2H HNO3 60 % MeO2C NO2 NO2 oxidation of amines Synthesis of an energetic nitrate ester ONO2 ONO2 O2NO O2NO NO2 NO2 Chavez, D.E. et al. Angew. 2008, 47, 8307 Original Target/Route via modified Kaplan Shechter Rxn NH O O NO2 Me Me N N N NH N O O Me Me O O O O Me Me NO2 OH R1 R2 NO2 N R1 R2 OO NaOH 1. NaNO2 2. AgNO3 R1 R2 NO2O2N N R1 R2 OO N O O Na R1 R2 NN O O O O Ag+ R1 R2 NN O O O O Ag R1 R2 NN O O O O-Ag0 Ag0 Ag+ nitronate -CH2O retro aldol N O O NH O O N Me Me N N N NH OO NH O O N Me Me N N N NH OO Fe activation [O] NH R R N N N N NH OO DMDO Acetone/H2O 85% DMDO Acetone 91% gem-dinitros from acids Fluorotrinitromethane R X N O OAg + ether R NO2 R O NO+ AgX O O O N O OR slowX R R fast NaNO2 DMSO NO2 R R H+ Eaton et al. JOC 1988. 5353 NO2O2N NO2+ (low yields) Kaplan Shechter Rxn via amine thus H2O essential only useful oxidant Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 + Routes to O-Nitro functionalityInitial Results: homocoupled product HO HO NO2 OH H2N N N N H N 1.cat. K3[Fe(CN)6] Na2S2O8 1. 2-methoxypropene cat. H+ X O O NO2 Me Me O O NO2 Me Me O O NO2 Me Me 12% NH N N N NH 2. NaOH N O O Me Me O O N O O Me Me OO N O O Me Me OO O O N Me Me OO N O O Fe O O N Me Me O O O O N Me Me OO O O Me Me activation O O SO3Na NaO3S FeNC CN CN OSO3Na NC NC -NaSO4- +CN-FeNC CN CN CN NC NC - CN- O O NO2 Me Me O O NO2 Me Me 65% optimized 1.HCl, MeOH 2. Ac2O/HNO3 O2NO O2NO NO2 ONO2 ONO2 NO2 72% (2 steps) - Use of mixed acids (esterification) and nitrogen oxides described for C-Nitraion Key points: 1. fuming (anhydrous) HNO3 prep: dry air bubbled through anhydrous HNO3 to remove any oxides of nitrogen present, followed by addition of trace urea to remove any nitrous acid present. AKA "white nitric acid" 2. Urea destruction of nitrous acid important to avoid violent fume-off 3. O-nitrations with mixed acids of "white nitric acid" above ambient temperatures is dangerous and has increase risk of explosion 4. anhydrous HNO3/Ac2O- Acetyl nitrate is generally a weak nitrating agent but in the presence of a strong acid like HNO3, ionization to nitronium ion occurs NO2 HO HO NO2 OH OHanh HNO3 Ac2O 90% HNO3 Ac2O NO2 HO O2NO NO2 OH ONO2 NO2 O2NO O2NO NO2 ONO2 ONO2 70%90% shock sensative Transfer nitration (neutral conditions - good for acid sensative alcohols) OH OH N Me Me Me NO2 ONO2 ONO2 N Me Me Me H BF4- BF4- 2 eq Olah G.A. et al JOC, 1965. 30, 3373 works for 1°, 2°, 3° alcohols in situ halide displacement with AgNO3 R OH PPh3, I2 R I AgNO3 R ONO2 Low yields for 2° HgNO3 can be used for 2° and 3° alkyl halide displacements decomposition of nitrocarbonates (very mild, rt or reflux MeCN) RO O Cl RO O ONO2 AgNO3 Py R ONO2 -AgCl -CO2 O O (or) ring opening of strained oxygen heterocycles N2O4 CH2Cl2 ONO ONO2 [O] H2O HO ONO2 O2NO ONO2 20,164 MPH!! ONO2 ONO2 O2NO O2NO comparable stability to PETN N N NN O2N O2N NO2 NO2 N2O5 CHEETAH calculates as powerful as HMX m.p. 86 °C Det.Temp 140 °C MeCN quant yield 80% Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 Routes to N-Nitro functionality nitrodesilylation deamination R NH2 R ONO2 NO2F MeCN RO SiR3 RO ONO2 N2O5 CH2Cl2 + O2NO SiR3 - Compounds resulting from nitration of nitrogen are of far less use for mainstream organic synthesis. However the N-NO2 group is an important 'explosophore' and is present in many enrgetic materials selective O-nitrations HO OH OH 1 eq SOCl(NO3) 2 eq SOCl(NO3) 3 eq SOCl(NO3) O2NO ONO2 ONO2 O2NO OH ONO2 HO OH ONO2 65% 70% 100% HN N O O H+ R OH + N2O - Direct nitration of a 1° amine to a nitramine using HNO3/mixed acids is not possible due to instability of the tautomeric isonitramine in strongly acidic conditions. 2° amines are more stable and can undergo electrophilic nitration using HNO3/Ac2O R 2° w/ HNO3/Ac2O N CNNC N Me N Me NO2NO2 NO2 93% 22% 6% analines - must contain one or more nitro groups on the aromatic ring How to get around this problem?? - synthesis via condensation chemistry (Mannich, 1,4 addition, etc) What about if need more direct method?? -non-acidic nitrating reagents (nucleophilic nitration) -chloride ion catalysis - Nitrolysis of fully substituted nitrogen R NH2 nBuLi -78 °C R NHLi Et ONO2 R N N OLi H+ R NH NO2 Ar NH2 1. Na 2. EtONO2 Ar NH2 Ar N N ONa H+ Ar NH NO2 EtONO2 Na+ - anhydrous ZnCl2, hydrochloride salt of amine, or dissolved HCl(g) can serve as a source of electropositive chloride under the oxidizing conditions of nitration 2 HCl + 2HNO3 + 3Ac2O 2AcOCl + N2O3 + 4AcOH AcOCl + R2NH R2NCl + AcOH R2NCl + HNO3 + Ac2O R2NNO2 + AcOCl + AcOH Wright et al. Can. J. Res. 1948. 26B, 294 HNO3/Ac2O (w/o chloride) N CNNC NO2 93% N NC CN X HNO3/Ac2O R = H N NC CN HNO3/Ac2O R = Cl- (N+) R NO2 70% Ease of alkyl nitrolysis depends on stability of the resulting cation: benzyl, tertiary (t-Bu), etc... R NH2 2 HOCl R NCl2 HNO3/Ac2O R N NO2 Cl R NHNO2 NaHSO3 (aq) rupture of C−N bond leading to formation on N−NO2 R1 N O R2 R2 A B Path A Path B R1 CO2H N R2 R2 O2N + R1 N O NO2 R2 R2 OH+ Nitramine formation via nitrolysis possible from: R1 N R1 Ph R2N NR2 R1 N O R2 R2 - carbamate - urea - formamide - acetamide - sulfonamide R1 N R1 Ph NO2 NO2+ R2N SiR3 R2N NO O O N N OH OR Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 Synthesis of Hexanitrohexaazaisowurtzitane (HNIW) - Many nitramines are more powerful than aromatic C-nitro compounds and have high brisance and high chemical stability and low sensativity to impact and friction compared to nitrate ester explosives. This is why they are of interest to military applications. Syntheses of some nitramine explosives OH OH O O NNs NNs O O NNs NNs NOH O O NNs NNs O N N NsNs NO2O2N F2N NF2 NO2O2N N N NO2O2N F2N NF2 NO2O2N TNFX (3,3 bis(difluoroamino)octahydro 1,5,7,7 tetranitro 1,5 diazocine) NH2 HO OH OH NH3+Br- Br Br Br N Br N NO CH2BrO2N N NO2 CH2BrO2N N NO2 NO2O2N HBr-AcOH 160 °C 72% NaOH, 80 °C 60 mmHg 1. NaNO2 (aq) 2. HCl (aq) 10% HNO3/TFAA 81% 1. NaHCO3, NaI DMSO, 100 °C 2. NaNO2, NaOH K3Fe(CN)6, K2S2O8 29% (2 steps)TNAZ NsCl, K2CO3 (aq) 95% 1. CrO3, AcOH 2. HOCH2CH2OH TsOH 82% (2 steps) NH2 NH2 NNs NNs NNs NNs Br Br K2CO3 76% 1. O3, CH2Cl2 2. DMS 3. NH2OH/NaOAc 86% (3 steps) 1. HNO3/NH4NO3 urea, 33% 2. H2SO4 92% F2NSO3H, HNF2, H2SO4, CFCl3 90% HNO3/SbF6 CF3SO3H NH2 Ph H O O H+ 2 eq. MeCN/H2O cat. H+ N N N NN N Bn Bn Bn BnBnBn N N N N NN Bn Bn Bn Bn Bn Bn NO2+ messy. Nitration of aromatic rings X N Ph [O] N Ph O Ac2O N Me O N Ph CrO3 N Ph O H2, [Pd] decomp. X N N N N NN Bn Bn Bn Bn Bn Bn H2, Pd(OAc)2 Ac2O, PhBr cat. N N N N NN Ac Ac Ac Ac Bn Bn65% N N N N NN NO2 NO2 O2N O2N O2N NO2 1. N2O4 2. HNO3/H2SO4 via nitroso 93% H2, [Pd] N N N N NHHN Ac Ac Ac Ac DANGER! 1. HCO2H 2. Ph, Δ -H2O N N N N NCHOOHCN Ac Ac Ac Ac 99% HNO3 N N N N NN NO2 NO2 O2N O2N O2N NO2 HNIW aka CL-20 - explosive/propellant (low smoke-emission) - most powerful to date (better oxidizer-to-fuel than RDX/HMX) - first prep by Nielsen 1987 Naval Air Warefare - pilot plant in 1990 for 200 kg in China Lake facility - unmatched performance in specific impulse, burn rate, detonation velocity (9.38 km/s = 21,000 MPH!!) - highest density than any other explosive (d = 2.044 g/cm3) - thermally stable (250 -260 °C) but sensative to mechanical stress still greater stability than nitrocellulose, PETN and others. - 4 different polymprphs with different densities/properties Chemistry of High Energy Materials R.A. Rodriguez Baran GM2012-08-18 N2O5 N2O5 O NN O O O O [NO2+][NO3-] - adopts two structures depending on condition polarsublime slightly above rt non-acidic nitrating reagents (neutral) 1° amines/nitramines leads to deamination and formation of nitrate ester by-product but analines are successful. - 1st prepared over 150 years ago but due to difficult prep and low thermal stability (require -60 °C long term storage) received little attention. - Environmental restrictions and push for green chemistry sparked interest Advantage: Rxns are very clean - faster and less exothermic (due to absence of oxidation byproducts) - high yields - simple isolation - non-acidic conditions possible with this reagent (compared to mixed acids) condition: anhyd. HNO3 - powerful but acidic and non-selective condition: chlorinated solvents - clean and selective - non-oxidizing &n non-acidic N2O5 2 N2O4 + O2 rt Stable for 2 weeks at -20 °C Stable for up to 1 yr at -60 °C nitronium nitrate salt No single nitrating agent is as diverse and versatile It is considered as the future for energetic materials synthesis Preparation of N2O5 [Deville 1849] AgNO3 + Cl2 (g) O N Cl O + AgNO3 N2O5 Dehydration of nitric acid HNO3 + P2O5 N2O5 + H3PO4 - isolation by sublimation and collection trap at -78 °C - stream of ozone needed to avoid collection on N2O4 - if don't care about acidity, can use HNO3/P2O5 mixture directly (no ozone stream) O3N2O4 Δ N2O5 Process chemist at Defense and Evaluation Research Agency (DERA) in the UK Development of a flow process: Using commercial ozonizer to generate 5 - 10% mix of ozone in oxygen and mixed in flow with N2O4. N2O5 is trapped in solid condenser tubes (cooled by dry ice/acetone). Me NO2 NO2 N2O5/HNO3 32 °C, quant yield Me NO2 NO2 O2N No explosion hazard N H H N H N N H OO N H NN N H OO O2N NO2 N NN N OO O2N NO2 NO2 O2N HNO3 P2O5 HNO3 H2SO4 N-nitrations of ureas HO OH OH OH OH OH N2O5, CCl4 0 °C quant yield O2NO ONO2 ONO2 ONO2 ONO2 ONO2 synthesis of TNT under mild conditions O-nitrations of polyols Klapotke T.M. JACS 2007. 129, 6908 O2NO ONO2 O2NO ONO2PETN - Det. Velocity 8,400 m/s - d= 1.7 g/cm3 - Used in WW I - One of most high energy explosives known - more shock sensative than TNT. used as booster mix - Europe marketed as lentonitrat (vasodilator) like NG SiO2NO ONO2 O2NO ONO2 Silicon analogue of PETN Si(CH2OAc)4 Si(CH2Cl)4 "The crystalline compound exploded on every occasion upon contact with Teflon spatula... Solutions in diethyl ether exploded upon the slighest evaporation of the solvent." Explosives in JACS: Sila explosives Why does Si-PETN have drastically increased sensativity? Theoretical: electrostatic potential: 1. Surface electrostatic potential, in general, is related to the sensitivity of the bulk 2. The more evenly distributed the electrostatic potential is over the surface of a molecule, the more stable it is to impact. Si O N O O2NO O2NO O2NO O VERY low e- dens VERY high e- dens