Meisenheimer complex formation

Give an expression for the pseudo-first-order rate constant for Meisenheimer complex formation. 

Rieger P-G, V Sinnwell, A Preup, W Francke, H-J Knackmuss (1999) Hydride-Meisenheimer complex formation and protonation as key reactions of 2,4,6-trinitrophenol biodegradation by Rhodococcus erythropolis. J Bacterial 181 1189-1195. 

Crampton24 has also demonstrated that for Meisenheimer complex formation, increased crowding at the reaction site caused by change from primary amines to piperidine results in rate reduction of proton transfer from the complex to the amine catalyst, and Hirst199... 

The concept of pseudobase formation by heteroaromatic cations is intimately related to the covalent hydration of heteroaromatic molecules16-19 and to Meisenheimer complex formation,20-25 although this relationship has not generally been emphasized in the literature until recently26,27. All such reactions involve the formation of -complexes by nucleophilic addition to electron-deficient aromatic species, and yet, extensive reviews of covalent hydration16-19 and of Meisenheimer complex formation20-25 have neither explicitly recognized their mutual relationship nor considered pseudobase formation. 

Pseudobase formation by nucleophilic addition to heteroaromatic cations is closely related to the long-known Meisenheimer complex formation by nucleophilic addition to an electron-deficient neutral aromatic molecule.20-25 In both cases nucleophilic attack on an electron-deficient aromatic ring produces a c-complex—an anionic Meisenheimer complex or a neutral pseudobase molecule. Despite the intense interest over the past few years in Meisenheimer complexes as models for er-complex intermediates in nucleophilic aromatic substitution reactions, there has been little overt recognition of the relationship between Meisenheimer complexes and pseudobases derived from heteroaromatic cations. In this regard, it is interesting that the pseudobase 165, which can be regarded as the complex intermediate that would be expected for an SNAr reaction between the l-methyl-4-iodoquinolinium cation and hydroxide ion, has been spectroscopically characterized.89... 

Meisenheimer complex formation as separate reactions. Meisenheimer complexes can be considered as the anionic pseudobases derived from neutral aromatic molecules, and in this light it is clear that heterocyclic Meisenheimer complexes are appropriately considered in the current Review. By so doing, it is hoped that attention can be drawn to potentially mutual benefits that may be derived from comparative studies of neutral and anionic pseudobases. Certainly, the spectroscopic techniques applicable to the study of pseudobase and Meisenheimer complex formation are identical. Quantitative studies of substituent effects and structural effects on rates and equilibria for nucleophilic addition should be relevant both to neutral and to anionic e-complex formation. The general rules enunciated by Strauss23,318 and Fendler319 for the prediction of the relative stabilities of Meisenheimer complexes should be directly applicable to analogous pseudobases. Terrier et al.2n have made an important contribution in this area with a detailed comparison of kinetic and thermodynamic parameters for formation of a benzofuroxan Meisenheimer complex and an isoquinoline pseudobase. 

Meisenheimer complex formation from the 2-dimethylamino and 2-(2-hydroxyethyl) derivatives was also obtained. In the latter case, the intramolecular tr-complex 167 is suggested.320 Dickeson et a/.321 and Illuminati et a/.322,323 reported the isolation of the sodium salt of the C-4 methoxide adduct (168) of 3,5-dinitro-4-methoxypyridine, and rate and equilibrium... 

Considerable work has been done on Meisenheimer complex formation from nitrobenzofuroxans (e.g., 189) and nitrobenzofurazans 27,341-345 however, since these reactions involve nucleophilic attack in the homocyclic ring, they will not be considered further in the present work. 

The relevant kinetic studies of spiro Meisenheimer complex formation from 2,4,6-trinitrophenyl ether of 3,6-dimethylcatechol (157, R = H or Me) was reported [72] (Scheme 50). It was found that the presence of methyl groups, accelerates the rearrangement, although the increase in the rate was not so dramatic as in the case of suhbne 153 (Scheme 49). It was suggested that the steric effect of the methyl groups increases the population of the conformation leading to rearrangement. The authors discussed two mechanisms for Meisenheimer complex formation—diffusion and pre-association controlled. 

The kinetics and mechanism of Meisenheimer complex formation involving O - O exchange has been studied [74,168-171]. 

Most of the above references simply provide data on absorption maxima. The spectra are depicted in detail for simple furoxans,83 benzofuroxan88,89 and its methoxy88 and nitro89 derivatives, and nitrobenzodifuroxan and benzotrifuroxan.89 Meisenheimer complex formation in nitrobenzofuroxans is accompanied by ultraviolet spectral changes, whereby the kinetics and equilibria of the reactions can be measured. This work is mentioned in Section VIII. 

The reaction of l,2-dichloro-4,5-dinitrobenzene with dilute aqueous sodium hydroxide results in substitution of a nitro-group by hydroxide. However, in hydroxide concentrations greater than 2 mol-dm", only the formation of monohydroxy- and dihydroxy-adducts (42) is observed, and acidification yields the original reactant. The cyanide adduct (43) of 1,3,5-trinitrobenzene has been observed by electrospray ionization mass spectrometry, using acetonitrile as the cyanide source. X-ray structures of the stable crystalline adducts formed from 4,6-dinitrobenzofiiroxan and dodecyl- and hexadecyl-amine have been reported. There has also been a report, related to the destruction of energetic materials, of Meisenheimer complex formation during the alkaline hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole. ... 

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