1,3,5-Trinitrobenzene, reactions

Unlike aliphatic hydrocarbons, aromatic hydrocarbons can be sul-phonated and nitrated they also form characteristic molecular compounds with picric acid, styphnic acid and 1 3 5-trinitrobenzene. Many of the reactions of aromatic hydrocarbons will be evident from the following discussion of crystalline derivatives suitable for their characterisation. 

A crystalline addition product of indole with picryl chloride (i.e. l-chloro-2,4,6-trinitrobenzene), together with an unidentified amorphous substance, were obtained by the action of picryl chloride on indole magnesium iodide, and analogous products were obtained in the reaction between the indole Grignard reagent and 1-chloro-2,4,5-trinitrobenzene. 

Current views (100) on the mechanism of bromination by NBS invoke the formation of molecular bromine and bromine atoms in low concentration, which subsequently act as the brominating agent. The bromination reaction was studied in detail in this laboratory under a variety of conditions using 93 (R = Ms) as a model. The product 94 (R = Ms) was indeed formed (42%) when NBS was substituted by 1.1 equivalents of bromine which was added at a slow rate to the reaction mixture. The yield was 68% when benzoyl peroxide was used as a catalyst. Using NBS alone or in the presence of reagents such as barium carbonate, pyridine, or s-trinitrobenzene, the yield was 60-70%. 

NONA was prepd in a mixed Ullman reaction using picryl chloride, 13 dichloro-2,4,6-trinitrobenzene and electrolytic Cu dust ... 

Such cyclohexadienes are easily oxidizable to benzenes (often by atmospheric oxygen), so this reaction becomes a method of alkylating and arylating suitably substituted (usually hindered) aryl ketones. A similar reaction has been reported for aromatic nitro compounds where 1,3,5-trinitrobenzene reacts with excess methyl-magnesium halide to give 2,4,6-trinitro-l,3,5-trimethylcyclohexane. Both... 

Spectroscopic and kinetic investigations of the reactions between 4,6-dinitrobenzofuroxan, 4-nitrobenzofuroxan, and tertiary and secondary amines (i.e., l,4-diazabicyclo[2.2.2]octane, quinuclidine, l,8-diazabicyclo[5.4.0]undec-7-ene, and piperidine) indicate the formation of zwitterionic or anionic complexes (Equation 2). The equilibrium between zwitterionic and anionic complexes is discussed (for reaction with piperidine) on the basis of H NMR spectral data, which indicate the presence of anionic complexes arising from the zwitterionic complex by a fast proton departure. The stability and the rate of formation of title complexes are discussed and compared to similar reactions of 1,3,5-trinitrobenzene <2001J(P2)1408>. 

In the case of the reactions between 1,3,5-trinitrobenzene (TNB) and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU)245, in toluene, shown in Scheme 16, regarding the formation of a zwitterionic cr-complex, A 0bs values are increased on increasing the [DBU]o values there is a catalytic effect of the base in a system without leaving group and proton. The increase in A 0bs values is related to the presence of the molecular complex between TNB and DBU indicated by Scheme 16. 

The reaction of l-fluoro-2,4,6-trinitrobenzene and 2,4-dimethoxyaniline, in cyclohexane, shows a negative activation enthalpy274 (—SOkJmoU1), in agreement with a desolvative association mechanism in which the nucleophile competes with the solvent in associating with the substrate in an equilibrium preceding the substitution process. 

It should also be mentioned that NO2 is the electron-attracting substituent which is most commonly used to stabilize Meisenheimer-type complexes. See, for example, recent studies of the reaction of 1,3,5-trinitrobenzene and phenoxide ions215, and the reactions of 4,6-dinitrobenzofuroxan with 5-substituted indoles216. See also the appropriate chapter in each year of the Series Organic Reaction Mechanisms1 1. 

These treatments have been also applied to S/yAr. For example, for a neutral nucleophile, all the classical pathways identified at present are represented by the general reaction mechanism shown by Scheme 2. A concerted mechanism, indicated by the diagonal path in Scheme 2, had not been discussed until lately, but was observed, among other systems, in the hydrolysis of l-chloro-2,4,6-trinitrobenzene and 1-picrylimidazole. The study was then extended to other related substrates and structure-reactivity relationships could be obtained78. 

Forlani and coworkers123 studied the reactions of l-halogeno-2,4,6-trinitrobenzene with 2-hydroxypiridine in aprotic solvents the reaction provides two isomeric products as... 

That the formation of molecular complexes (especially EDA complexes) can catalyse the decomposition of the cr-adduct has been discussed in Section n.E. Another possibility is that the substrate and catalyst (nucleophile or added base) form a complex which is then attacked by a new molecule of the nucleophile in this context catalysis need no longer be associated with proton removal. Thus, Ryzhakov and collaborators183 have recently shown that the N-oxides of 4-chloropyridine and 4-chloroquinoline act as jt-donors toward tetracyanoethylene and that the reactions of these substrates with pyridine and quinoline are strongly catalysed by the jr-acceptor. Similarly, the formation of a Meisenheimer complex between 1,3,5-trinitrobenzene and l,8-diazabicyclo[5,4,0]undec-7-ene in toluene has been assumed to take place via an association complex to explain the observed second-order in tertiary amine184. 

The reaction of 1,3,5-trinitrobenzene (TNB) and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene184 was also proposed to proceed by the mechanism shown in Scheme 16. The visible spectrum, recorded immediately after mixing appropriate solutions of TNB and DBU in toluene, shows a feeble absorbance maximum at 505 nm, which changes to a stable maximum at 468 nm, after variable reaction times. The first maximum was attributed to a molecular complex between TNB and DBU, and the second maximum at the Meisenheimer complex, 39, although NMR structural determinations were not possible, because of the low solubility of the complex in toluene. 

In some of Forlani s works, such as the reactions of l-halogeno-2,4,6-trinitrobenzene with 2-hydroxypyridine123,125, a substrate-catalyst molecular complex was assumed, but the kinetic law showed the regular second order in amine. Rather interestingly in this scheme, the authors assume that the molecular complex can lead to the formation of products following a second order in nucleophile kinetics, while in the reactions with amines it was presumed that the complex was not on the reaction coordinate, and that an additional molecule of amine was required (the authors needed to include this additional molecule to account for the third order in amine rate law). 

Sulfite is an extremely good nucleophile for activated aromatic systems and reaction with l-substituted-2,4,6-trinitrobenzenes (1) may result in cr-adduct formation or in displacement of the 1-substiment as shown in Scheme 1. When X = OEt or SEt, adducts (2) and (3) formed by reaction at unsubstituted positions are long-lived. 

A kinetic smdy of the formation of zwitterionic adducts (28) from 1,3,5-trinitrobenzene and diazabicyclo derivatives indicates that reactions are surprisingly slow, with rate constants many orders of magnitude lower than those for related reactions with primary or secondary amines. The use of rapid-scan spectrophotometry was necessary to study the kinetics of reaction of 4-substimted-2,6-dinitro-A -n-butylanilines (29) with n-butylamine in DMSO the two processes observed were identified as rapid deprotonation to give the conjugate base and competitive a-adduct formation at the 3-position. The reactions of MAf-di-n-propyl-2,6-dinitro-4-trifluoromethylaniline (30), the herbicide trifluralin, and its A -ethyl-A -n-butyl analogue with deuteroxide ions and with sulfite ions in [ H6]DMS0-D20 have been investigated by H NMR spectroscopy. With deuteroxide a-adduct formation at the 3-position is followed by... 

It has been known for a long time that polynitroaromatic compounds produce colored products in contact with aUcafis [1]. These color reactions have been extensively used for the identification of nitroaromatic explosives. In the Janowski reaction [7], a solution of the polynitroaromatic compound (di- or trinitroaromatic) in acetone is treated with concentrated aqueous KOH solution. 1,3,5-Trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT), treated with 30% aqueous KOH, produced violet-red and red colors, respectively. Many variations of the Janowski reaction were reported, using KOH or NaOH in aqueous or ethanoHc solutions as reagents, and dissolving the explosives in acetone, ethanol or acetone-ethanol mixture [3,8]. The reaction was used both for spot tests and for spraying TLC plates [9]. 

The synthesis of 1,3,5-trinitrobenzene (TNB) from the direct nitration of m-dinitrobenzene is very difficult. Desvergnes reported a 71 % yield of TNB (2) on treatment of m-dinitrobenzene (32) with a large excess of mixed acid composed of anhydrous nitric acid and 60 % oleum at a reaction temperature of 110 °C for several days. Similar results are also reported from other... 

Nitronium salts in sulfuric, triflic or fluorosulfuric acids are extremely reactive and well suited for the polynitration of deactivated substrates. Olah and Lin" studied the nitration of m-dinitrobenzene to 1,3,5-trinitrobenzene with a solution of nitronium tetrafluoroborate in fluorosulfuric acid at 150 °C. An optimum yield of 66 % was obtained after a reaction time of 3 hours. However, the crude reaction mixture was found to contain 17 % unreacted m-dinitrobenzene. After a reaction time of 3.8 hours the yield of 1,3,5-trinitrobenzene dropped to 50 % but the product was free from m-dinitrobenzene and was essentially pure. 

Borsche synthesized both 1,2,4- and 1,2,3-trinitrobenzenes by treating Af-hydroxy-2,4-dinitroaniline and Al-hydroxy-2,6-dinitroaniline, respectively, with fuming nitric acid. The method is very convenient for the synthesis of such substrates because the starting materials are readily obtainable from the reaction of hydroxylamine with the appropriate dini-trochlorobenzene isomer. Borsche also synthesized 1,2,3,5-tetranitrobenzene (60%)... 

Picryl chloride has been used successfully in a number of copper-mediated Ullmann coupling reactions. 2,2, 4,4, 6,6 -Hexanitrobiphenyl has been synthesized by heating picryl chloride with copper powder. The same reaction in the presence of a hydride source (hot aqueous alcohol) yields 1,3,5-trinitrobenzene (TNB). The Ullmann reactions between picryl chloride and isomeric iodonitrobenzenes with copper bronze in DMF has been used to synthesize 2,2, 4,6-, 2,3, 4,6-, and 2,4,4, 6-tetranitrobiphenyls. ... 

The thermally insensitive explosive (112) is synthesized by a similar route from the reaction of l,3-dichloro-2,4,6-trinitrobenzene (106) (styphnyl chloride) with two equivalents of 3-chloroaniline, followed by nitration and subsequent displacement of the chloro groups with... 

The reactions of hexanitrobenzene (55) and 2,3,4,5,6-pentanitroaniline (31) with ammonia have been used to synthesize the thermally stable explosive l,3,5-triamino-2,4,6-trinitrobenzene (TATB). Holmes and Fliirschiem have studied the reactions of 2,3,4,5,6-pentanitroaniline with nucleophiles. 

In a similar manner, of the isomeric trinitrobenzenes, only the symmetrical 1,3,5-isomer shows sufficient chemical stability for use as an explosive. Even so, the aromatic ring of 1,3,5-trinitrobenzene is highly electron deficient and reaction with alkali metal carbonates or bicarbonates in aqueous boiling methanol yields 3,5-dinitroanisole. Unsymmetrical isomers of trinitrobenzene are much more reactive than the 1,3,5-isomer, with only relatively mild conditions needed to effect the displacement of their nitro groups. ... 

All reported syntheses of TATB to date involve the nitration of substrates containing leaving groups which are subsequently replaced by amino groups. The current industrial synthesis of TATB (14) involves the nitration of 1,3,5-trichlorobenzene (33) to 1,3,5-trichloro-2,4,6-trinitrobenzene (34) followed by reaction with ammonia in toluene under pressure. Both nitration and amination steps require forced conditions with elevated temperatures. 

Similar routes have been used for the synthesis of other polynitrophenylenes. 1,3,5-Tris(2,4,6-trinitrophenyl)-2,4,6-trinitrobenzene (160) is synthesized from the reaction of 1,3,5-trichloro-2,4,6-trinitrobenzene with three equivalents of picryl chloride in the presence of activated copper powder in refluxing mesitylene. " 2,2",4,4, 4",6,6, 6"-Octanitro-m-terphenyl (161) has been synthesized from picryl chloride and l,3-dichloro-4,6-dinitrobenzene. ... 

---