1.3.5- Trinitrobenzene nucleophilic reactions

Oxidation of nitro compounds to nitrophenols is another example of a nucleophilic reaction. Thus, m- dinitrobenzene and sym- trinitrobenzene were oxidized in an alkaline medium when boiled with potassium ferricyanide solution (Hepp[45]) ... 

One of the characteristic features of aromatic nitro compounds, particularly those with two or more nitro groups is their ability to react with bases and in many instances the reaction is accompanied by an intense colour. The colour had caught the attention of chemists by the late nineteenth century and initiated a considerable amount of research on the nature of the formed substances. Thus considerable literature appeared on reactions known as Janovsky or Jackson-Meisenheimer or Meisenheimer reactions which are discussed later. They are nucleophilic reactions and are not only of theoretical but also of practical importance. Thus the Janovsky reaction became an important analytical method, and reactions of di- and trinitrobenzene and their homologues with bases, are of great importance in the problem of the safety of manufacture and of the stability of these nitro compounds. 

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. 

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. 

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. 

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. 

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. 

Rate and equilibrium constants have been reported for the reactions of butylamine, pyrrolidine, and piperidine with trinitrobenzene, ethyl 2,4,6-trinitrophenyl ether, and phenyl 2,4,6-trinitrophenyl ether in acetonitrile, hi these reactions, leading to cr-adduct formation and/or nucleophilic substitution, proton transfer may be rate limiting. Comparisons with data obtained in DMSO show that, while equilibrium constants for adduct formation are lower in acetonitrile, rate constants for proton transfer are higher. This probably reflects the stronger hydrogen bonding between DMSO and NH+ protons in ammonium ions and in zwitterions.113 Reaction of 1,3,5-trinitrobenzene with indole-3-carboxylate ions in methanol has been shown to yield the re-complex (26), which is the likely precursor of nitrogen- and carbon-bonded cr-adducts expected from the reaction.114 There is evidence for the intermediacy of adducts similar to (27) from the reaction of methyl 3,5-dinitrobenzoate with l,8-diazabicyclo[5.4.0]undec-8-ene (DBU) cyclization eventually yields 2-aminoindole derivatives.115... 

Conditions were found under which 2,4,6-trinitrostyrene adds nucleophiles (thio-phenol, aniline, and aliphatic amines) at the vinyl moiety to form the corresponding / -X-ethyl-2,4,6-trinitrobenzenes (X = PhS, PhNH, or R2N). In the reactions with primary aromatic amines, the initially formed adducts undergo an intramolecular replacement of the nitro group followed by aromatization of the indolines, giving rise to the corresponding A-substi Luted 4,6-dinitroindoles.219... 

There is current interest in the quantitative comparison of electrophilicities and nucleophilicities, particularly in carbon-carbon bond-forming reactions. The rates of a-adduct formation in acetonitrile of 10 electron-deficient aromatics and heteroaromatics with a series of reference carbon nucleophiles have been used to compare their electrophilicities, E. Values of E ranging from —13.2 for 1,3,5-trinitrobenzene, the least reactive studied, to -4.7 for 4,6-dinitrotetrazolo 1,5-a Ipyridinc, the most reactive, were determined.52 A reasonable correlation was found between electrophilicities and pA a values for water addition (eq. 1). These pA a values have also been found to... 

The reaction of l,3,S-trinitroben2ene with diazomethane was carried out as early as 1898-1900 [88, 89), but only recently de Boer rationalized it as a nucleophilic addition leading to seven member ring condensed with two cyclopropane rings when the molar ratio of trinitrobenzene to diazomethane was 1 3. The first step of the reaction was a type of Jackson-Meisenheimer complex (Ai) and the final product was trismethylene-trinitrobenzene (A ) [90—92a] (19). The reaction is temperature dependent at —80 C compound (A ) was formed. 

Evidence for the formation of Meisenheimer, or a a-complex, involving aniline as a nucleophile has been presented with 1,3,5-trinitrobenzene (TNB) by Buncel and coworkers107. Reactions of the TNB-methoxide ion adduct with a series of substituted anilines in DMSO solution yield new TNB-aromatic amine o-complexes (Scheme 12). 

This study reports on the reactions of ambident nucleophiles with electron-deficient nitroaromatic and heteroaromatic substrates anionic complex formation or nucleophilic substitution result. Ambident behavior is observed in the case of phenoxide ion (O versus C attack) and aniline (N versus C attack). O or N attack is generally kinetically preferred, but C attack gives rise to stable thermodynamic control. Normal electrophiles such as 1,3,5-trinitrobenzene or picryl chloride are contrasted with superelectrophiles such as 4,6-dinitrobenzofuroxan or 4,6-dinitro-2-(2,4,6-trinitrophenyl)benzotriazole 1-oxide (PiDNBT), which give rise to exceptionally stable a complexes. Further interesting information was derived from the presence in PiDNBT of two electrophilic centers (C-7 and C-l ) susceptible to attack by the ambident nucleophilic reagent. The superelectrophiles are found to exhibit lesser selectivity toward different nucleophilic centers of ambident nucleophiles compared with normal electrophiles. 

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