Download this PDF book: Organic Chemistry of Explosives 1st Edition by Jai Prakash Agrawal, Robert Hodgson
Organic Chemistry of Explosives is the first text to bring together the essential methods and routes used for the synthesis of organic explosives in a single volume.
Assuming no prior knowledge, the book discusses everything from the simplest mixed acid nitration of toluene, to the complex synthesis of highly energetic caged nitro compounds.
Reviews laboratory and industrial methods, which can be used to introduce aliphatic C-nitro, aromatic C-nitro, N-nitro, and nitrate ester functionality into organic compounds
Discusses the advantages and disadvantages of each synthetic method or route, with scope, limitations, substrate compatibility and other important considerations
Features numerous examples in the form of text, reaction diagrams, and tables.
Explosives have attracted some unwanted publicity over the years for their misuse in the taking of life and the destruction of property. Although such concerns and views are not unfounded, there is a bigger picture. More explosives have been used in times of peace than in all of the wars and conflicts put together. How many of the great engineering achievements would have been possible if not for the intervention of explosives? Explosives are in fact no more than tools and remain as some of the most fascinating products of chemistry.
Organic Chemistry of Explosives is the first text which brings together in one volume the essential methods and routes used for the synthesis of organic explosives. Topics are organised based on the fact that explosive properties are imparted into a compound by the presence of certain functional groups, and include:
the methods which can be used to introduce C-nitro, O-nitro, and N-nitro functionality into organic compounds
the synthesis of energetic compounds in the form of polynitropolycycloalkanes, caged and strained nitramines, and N-heterocycles
the synthesis of explosives containing functionality less widely encountered, including: organic azides, peroxides, diazophenols, and energetic compounds derived from guanidine and its derivatives
nitration with dinitrogen pentoxide and its likely significance for the future synthesis of energetic materials.
This book also highlights important properties such as melting points, impact sensitivities and velocities of detonation etc. which are considered valuable from the end–use point of view.
Organic Chemistry of Explosives is an essential reference source for chemists working in the field of energetic materials and all those with an interest in the chemistry of nitramines, nitro compounds, nitrate esters, and nitration in general.
About the Author
Jai Prakash Agrawal is the former Director of Materials of the Indian Defence Research and Development Organization. He obtained his PhD in Chemistry from the Gorakhpur University, India, and did postdoctoral work at the University of Saint-Etienne, France, and at the Cavendish Laboratory of the University of Cambridge, UK.
In recognition of his achievements Dr. Agrawal was appointed a Fellow of the Royal Society of Chemistry, London.
The focus of his scientific and professional career is on research and development in the field of propellants, explosives and inhibitory materials.
He has written a monograph on "Composite Materials" and is recipient of several honours including the prestigious DRDO Technology Award. Together with Robert Hodgson he has authored the book "Organic Chemistry of Explosives", John Wiley & Sons.
Chapter One Synthetic Routes to Aliphatic ITLITL-Nitro Functionality 1.1 INTRODUCTION The nitro group, 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.
The chemistry of the nitro group has been extensively reviewed in several excellent works including in a functional group series. A comprehensive discussion of the synthetic methods used to introduce the nitro group into aliphatic compounds, and its diverse chemistry, would require more space than available in this book.
While every effort has been made to achieve this, some of these methods are given only brief discussion because they have not as yet found use for the synthesis of energetic materials, or their use is limited in this respect. The nature of energetic materials means that methods used to introduce polynitro functionality are of prime importance and so these are discussed in detail. Therefore, this work complements the last major review on this subject.
The chemical properties of the nitro group have important implications for the synthesis of more complex and useful polynitroaliphatic compounds and so these issues are discussed in relation to energetic materials synthesis. Aliphatic nitroalkanes can be categorized into six basic groups: primary, secondary and tertiary nitroalkanes, terminal and internal gem-dinitroalkanes, and trinitromethyl compounds.
Primary and secondary nitroalkanes, and terminal gem-dinitroalkanes, have acidic protons and find particular use in condensation reactions for the synthesis of more complex and functionalized compounds, of which some find application as energetic plasticizers and polymer precursors.
Tertiary nitroalkanes and compounds containing internal gem-dinitroaliphatic functionality exhibit high thermal and chemical stability and are frequently present in the energetic polynitropolycycloalkanes discussed in
Chapter 2. The chemical stability of these various groups is discussed in Section 1.13. 1.2 ALIPHATIC ITLITL-NITRO COMPOUNDS AS EXPLOSIVES Nitromethaneisnotusuallyregardedasanexplosive,butitsoxygenbalancesuggestsotherwise, and under certain conditions and with a strong initiator this compound can propagate its own detonation. Nitromethane has been used in combination with ammonium nitrate for blasting.
Although this explosive is more powerful than conventional ammonium nitrate-fuel oil(ANFO) it is considerably more expensive. Other simple aliphatic nitroalkanes have less favorable oxygen balances and will not propagate their own detonation. Polynitroaliphatic compounds have not found widespread use as either commercial or military explosives.
This is perhaps surprising considering the high chemical and thermal stability of compounds containing internal gem-dinitroaliphatic functionality. In fact, many polynitroaliphatic compounds are powerful explosives, for example, the explosive power of 2,2-dinitropropane exceeds that of aromatic ITLITL-nitro explosives like TNT. Tetranitromethane, although not explosive on its own, contains a large amount of available oxygen and forms powerful explosive mixtures with aromatic hydrocarbons like toluene.
The problem appears to be one of cost and availability of raw materials. Most commercial and military explosives in widespread use today contain nitrate ester, nitramine or aromatic ITLITL-nitro functionality because these groups are readily introduced into compounds with cheap and readily available reagents like mixed acid (sulfuric and nitric acids mixture).
However, sometimes other factors can outweigh the cost of synthesis if a compound finds specialized use. Over the past few decades there has been a demand for more powerful explosives of high thermal and chemical stability. Such criteria are met in the form of polynitrocycloalkanes, which are a class of energetic materials discussed in Chapter 2.
These compounds have attracted increased interest in the aliphatic ITLITL-nitro functionality which may result in the improvement of or discovery of new methods for its incorporation into compounds.
Improved methods for the synthesis of building blocks like 2-fluoro-2,2-dinitroethanol and 2,2-dinitropropanol have resulted in some polynitroaliphatic compounds finding specialized application. Bis(2-fluoro-2,2-dinitroethyl)formal (FEFO) and a 1:1 eutectic mixture of bis(2,2-dinitropropyl) formal (BDNPF) and bis(2,2-dinitropropyl)acetal (BDNPA) have both found use as plasticizers in energetic explosive and propellant formulations.
1.3 DIRECT NITRATION OF ALKANES Nitroalkanes can be formed from the direct nitration of aliphatic and alicyclic hydrocarbons with either nitric acid or nitrogen dioxide in the vapour phase at elevated temperature.
These reactions have achieved industrial importance but are of no value for the synthesis of nitroalkanes on a laboratory scale, although experiments have been conducted on a small scale in sealed tubes.
The vapour phase nitration of hydrocarbons proceeds via a radical mechanism and so it is found that tertiary carbon centres are nitrated most readily, followed by secondary and primary centres which are only nitrated with difficulty. With increased temperature these reactions become less selective; at temperatures of 410-430C hydrocarbons often yield a complex mixture of products. At these temperatures alkyl chain fission occurs and nitroalkanes of shorter chain length are obtained along with oxidation products.
An example is given by Levy and Rose who nitrated propane with nitrogen dioxide at 360C under 10 atmospheres of pressure and obtained a 75-80% yield of a mixture containing: 20-25% nitromethane, 5-10% nitroethane, 45-55% 2-nitropropane, 20% 1-nitropropane and 1% 2,2-dinitropropane.
The nitration of moderate to high molecular weight alkane substrates results in very complex product mixtures. Consequently, these reactions are only of industrial importance if the mixture of nitroalkane products is separable by distillation. Polynitroalkanes can be observed from the nitration of moderate to high molecular weight alkane substrates with nitrogen dioxide.
The nitration of aliphatic hydrocarbons has been the subject of several reviews. Both nitric acid and nitrogen dioxide, in the liquid and vapour phase, have been used for the nitration of the alkyl side chains of various alkyl-substituted aromatics without affecting the aromatic nucleus.
Thus, treatment of ethylbenzene with nitric acid of 12.5% concentration in a sealed tube at 105-108C is reported to generate a 44% yield of phenylnitroethane. The nitration of toluene with nitrogen dioxide at a temperature between 20-95C yields a mixture of phenylnitromethane and phenyldinitromethane with the proportion of the latter increasing with reaction temperature.
The nitration of aliphatic hydrocarbons with dinitrogen pentoxide and nitronium salts has been described. Topchiev gives an extensive discussion of works related to hydrocarbon nitration conducted prior to 1956. 1.4 ADDITION OF NITRIC ACID, NITROGEN OXIDES AND RELATED COMPOUNDS TO UNSATURATED BONDS 1.4.1 Nitric acid and its mixtures Alkenes can react with nitric acid, either neat or in a chlorinated solvent, to give a mixture of compounds, including: vic-dinitroalkane, -nitro-nitrate ester, vic-dinitrate ester, -nitroalcohol, and nitroalkene products. Cyclohexene reacts with 70% nitric acid to yield a mixture of 1,2-dinitrocyclohexane and 2-nitrocyclohexanol nitrate.
Frankel and Klager investigated the reactions of several alkenes with 70% nitric acid, but only in the case of 2-nitro-2-butene (1) was a product identified, namely, 2,2,3-trinitrobutane (2). The reaction of fuming nitric acid with 2-methyl-2-butene(3)isreportedtoyield 2-methyl-3-nitro-2-butene(4).
The reaction of alkenes with fuming nitric acid, either neat or in chlorinated solvents, is an important route to unsaturated nitrosteroids, which assumedly arise from the dehydration of -nitroalcohols or the elimination of nitric acid from -nitro-nitrate esters.
Temperature control in these reactions is important if an excess of oxidation by-products is to be avoided. Mixed acid has been reported to react with some alkenes to give -nitro-nitrate esters amongst other products. Solutions of acetyl nitrate, prepared from fuming nitric acid and acetic anhydride, can react with alkenes to yield a mixture of nitro and nitrate ester products, but the -nitroacetate is usually the major product.
Treatment of cyclohexene with this reagent is reported to yield a mixture of 2-nitrocyclohexanol nitrate, 2-nitrocyclohexanol acetate, 2-nitrocyclohexene and 3-nitrocyclohexene. -Nitroacetates readily undergo elimination to the [alpha]-nitroalkenes on heating with potassium bicarbonate. -Nitroacetates are also reduced to the nitroalkane on treatment with sodium borohydride in DMSO.
Solutions of acetyl nitrate have also been used for the synthesis of [alpha]-nitroketones from enol esters and ethers. The reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful.
An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene.
Nitroform is produced industrially via this method in a continuous process in 74% yield. The reaction of ethylene with 95-100% nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane.
Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. 1.4.2 Nitrogen dioxide The addition of nitrogen oxides and other sources of N[O.sub.2] across the double bonds of alkenes is an important route to nitro compounds.
Alkenes react with dinitrogen tetroxide in the presence of oxygen to form a mixture of vic-dinitro (5a), -nitro-nitrate ester (5b) and -nitro-nitrite ester (5c) compounds; the nitrite ester being oxidized to the nitrate ester in the presence of excess dinitrogen tetroxide. A stream of oxygen gas is normally bubbled through the reaction mixture to expel nitrous oxide formed during the reaction and so prevent more complex mixtures being formed.
These reactions can be synthetically useful for the synthesis of vic-dinitroalkanes because nitrate and nitrous ester by-products are chemically unstable and are readily hydrolyzed to the corresponding -nitroalcohol on treatment with methanol. 1,2-Dinitroethane and 1,2-dinitrocyclohexane can be formed in this way from the corresponding alkenes in 42% and 37% yield respectively.
The addition of dinitrogen tetroxide across the double bonds of electron deficient fluorinated alkenes is a particularly useful route to vic-dinitro compounds where yields are frequently high; tetrafluoroethylene gives a 53% yield of 1,2-dinitro-1,1,2,2-tetrafluoroethane.
The reaction of [alpha]-nitroalkenes with nitrogen dioxide or its dimer, dinitrogen tetroxide, has been used to synthesize polynitroalkanes. Thus, the reaction of dinitrogen tetroxide with 2,3-dinitro-2-butene (6) and 3,4-dinitro-3-hexene is reported to yield 2,2,3,3-tetranitrobutane (7, 25%) and 3,3,4,4-tetranitrohexane (32%) respectively. Additions of dinitrogen tetroxide across C-C double bonds are selective.
The -nitro-nitrates formed from terminal alkenes have the nitro group situated on the carbon bearing the most hydrogen and this is irrespective of neighbouring group polarity. Altering reaction conditions and stoichiometry enables the preferential formation of -nitro-nitrates over vic-dinitroalkanes, which, although inherently unstable, provide a synthetically useful route to [alpha]-nitroalkenes via base-catalyzed elimination. [beta]-Nitro-nitrates are reduced to the nitroalkane on treatment with sodium borohydride in ethanol. [beta]-Nitro-nitrates also undergo facile hydrolysis to the [beta]-nitroalcohol, and conversion of the latter to the methanesulfonate or acetate, followed by reaction with triethylamine or potassium bicarbonate respectively, yields the [alpha]-nitroalkene.
The reaction of alkenes with dinitrogen tetroxide in the presence of iodine yields [beta]-nitroalkyl iodides, which on treatment with sodium acetate also yield [alpha]-nitroalkenes. 1,4-dinitro-2-butene has been prepared in this way from butadiene.
The synthesis of [alpha]-nitroalkene has been recently reviewed by Ono. The reaction of alkenes with nitrogen oxides and other nitrating agents have been extensively discussed by Olah, Topchiev, and in numerous reviews. The reaction of alkynes with dinitrogen tetroxide is less synthetically useful as a route to nitro compounds.
The reaction of 3-hexyne with dinitrogen tetroxide yields a mixture of cis- and trans-3,4-dinitro-3-hexene (4.5% and 13% respectively), 4,4-dinitro-3-hexanone (8%), 3,4-hexanedione (16%) and propanoic acid (6%). 2-Butyne forms a mixture containing both cis- and trans-2,3-dinitro-2-butene (7% and 34% respectively). 1.4.3 Dinitrogen pentoxide Alkenes react with dinitrogen pentoxide in chlorinated solvents to give a mixture of [beta]-nitro-nitrate, vic-dinitro, vic-dinitrate ester and nitroalkene compounds.
At temperatures between -30C and -10C the -nitro-nitrate is often the main product. The -nitro-nitrates are inherently unstable and readily form the corresponding nitroalkenes. Propylene reacts with dinitrogen pentoxide in methylene chloride between -10C and 0C to form a mixture of 1-nitro-2-propanol nitrate (27%) and isomeric nitropropenes (12%).
The same reaction with cyclohexene is more complicated. At temperatures between 0C and 25C the vic-dinitrate ester is often observed in the product mixture and can be the major product in some cases.
The synthesis of vic-dinitrate esters via this route is discussed in Section 3.6.2. Fischer has given a comprehensive review of work relating to the mechanism of dinitrogen pentoxide addition to alkenes. Hydroxy-terminated polybutadiene (8) (HTPB) has been treated with dinitrogen pentoxide inmethylenechloride.
Theproduct(9)isanenergeticoligomerbutisunlikelytofindapplication because of the inherent instability of -nitronitrates. Initial peroxyacid epoxidation of some of the double bonds of HTPB followed by reaction with dinitrogen pentoxide yields a product containing vic-dinitrate ester groups and this product (NHTPB) is of much more interest as an energetic binder (see Section 3.10). 1.4.4 Nitrous oxide and dinitrogen trioxide The addition of nitrous oxide (NO) or dinitrogen trioxide ([N.sub.2][O.sub.3]) across the double bond of an alkene usually generates a mixture of dinitro (5a) and nitro-nitroso (10) alkanes.
The reaction of tetrafluoroethylene with dinitrogen trioxide is reported to give 1,2-dinitrotetrafluoroethane and 1-nitro-2-nitrosotetrafluoroethane in 8% and 42% yield respectively; the same reaction with nitrous oxide leading to increased yields of 15% and 68% respectively.
When an excess of nitrous oxide or dinitrogen trioxide is used in these reactions the vic-dinitroalkane is usually the main product. 1.4.5 Other nitrating agents Alkenes react with nitryl chloride to give -nitroalkyl chlorides, -chloroalkyl nitrites and vic-dichloroalkane products. Nitryl chloride reacts with enol esters to give [alpha]-nitroketones.
A process known as alkene nitrofluorination has been extensively used for the synthesis of -nitroalkyl fluorides. Reagents used generate the nitronium cation in the presence of fluoride anion, and include: HF/HN[O.sub.3], HF/HN[O.sub.3]/FS[O.sub.3]H, N[O.sub.2]F, S[O.sub.2]/N[O.sub.2]B[F.sub.4] and HF/pyridine/N[O.sub.2]B[F.sub.4]. A mixture of silver nitrite and iodine reacts with alkenes to give -nitroalkyl iodides, and therefore, provides a convenient route to [alpha]-nitroalkenes.
Treatment of alkenes with ammonium nitrate and trifluoroacetic anhydride in the presence of ammonium bromide, followed by treatment of the resulting -nitroalkyl bromide with triethylamine, is also a general route to [alpha]-nitroalkenes. The reaction of alkenes with nitronium salts proceeds through a nitrocarbocation. The product(s) obtained depends on both the nature of the starting alkene and the conditions used. (Continues...)
About the book:
Publisher : Wiley; 1st edition (January 5, 2007)
Language : English
Pages : 416
FIle : PDF, 12MB
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