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• 1817-76-1 2,2',4,4'-tetranitrodiphenylmethane 

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Relevant academic research and scientific papers

Similar catalytic behavior of oximate and phenoxide bases in the ionization of bis(2,4-dinitrophenyl)methane in 50percent water-50percent Me2SO. Revising the role of solvational imbalances in determining the nucleophilic reactivity of α-effect oximate bases

Rates of proton abstraction from bis(2,4-dinitrophenyl)methane 1 by a series of oximate bases and of reprotonation of the related diphenylmethyl carbanion C-1 by the conjugate oxime acids have been measured in a 50:50 (v/v) H2O-Me2SO mixture at 25 deg C.The results reveal an essentially identical behaviour of oximate (Ox-) and phenoxide (ArO-) bases in these proton transfer reactions.The Broensted lines for the two types of catalysts are nearly the same, showing no tendency to level off at high pKa and providing very similar values for the intrinsic reactivity of 1: logkOx0=0.9+/-0.1; logKArO0=0.5+/-0.1.A comparison with previous results obtained with carboxylate ions as well as primary and secondary amines indicates that solvational imbalances due to the catalysts are important in determining the intrinsic reactivity of 1.This conclusion implies that ArO- and Ox- bases undergo comparable solvation changes along the coordinate of the ionization reactions of 1, a result which is indirectly supported by the finding that a transfer from water to H2O-MeSO mixtures rich in Me2SO induces similar variations in the acidity of oximes and phenols of similar pKH2Oa.The identical behaviour of ArO- and Ox- bases in the ionization of 1 is in marked contrast with the situation observed in nucleophilic addition or substitution reactions.In agreement with their α-effect character, oximates are much more reactive than phenoxides in these processes but a typical features is that the nucleophilic reactivity of Ox- species is subjected to a very rapid levelling off at pKa ca. 8.5.Based on the information obtained in this work, this peculiar behaviour is re-examined and suggested to be a reflection of especially large solvational imbalances in the transition states for nucleophilic reactions.

Transient nitronic acid formation in the protonation of the carbanion of 2,2',4,4'-tetranitrodiphenylmethane in acidic methanol

Rates of deprotonation of 2.2',4,4'-tetranitrodiphenylmethane (1) by a variety of bases B- and of protonation of the resulting carbanion (2) by the conjugated acids BH in methanol have been measured at 20 deg C.The Broensted αBH coefficients for protonation of 2 by phenol and carboxylic acid buffers are equal to 0.58 and 0.43 respectively, as compared with αBH values of 0.59 and 0.52 respectively, for the same reactions in 50percent H2O-50percent DMSO.On the other hand, a comparison of the intrinsic rate constants kBH0 (in the Marcus sense) in the two solvents reveals that the effect of going from 50percent H2O - 50percent DMSO to methanol is is to lower kArOH0 for the phenol reactions by a factor 2 but to increase kRCOOH0 for carboxylic acid reactions by a factor of 5.It is shown that the solvent effects on αBH and kBH0 can all be understood in the context of the Principle of Imperfect Synchronisation (PIS) recently proposed by Bernasconi.In addition, a fast equilibrium protonation of the carbanion 2 is found to precede its conversion to 1 at low pH, i.e., pHa value associated with the ionization of 2,H is ca 4.25

Transition State Imbalance in the Ionization of Nitroaromatic Hydrocarbons : 2,2',4,4'-Tetranitrodiphenylmethane and 2,4,4'-Trinitrodiphenylmethane in Aqueous Dimethyl Sulphoxide Solutions

Rates of reversible proton abstraction from 2,2',4,4'-tetranitrodiphenylmethane and 2,4,4'-trinitrodiphenylmethane by a variety of bases in 50percent water-50percent dimethyl sulphoxide have been measured at 25 deg C.Broensted αCH and βB values have been determined and show a charge imbalance in the transition states for these reactions, in accord with findings for similar carbon acids involving extensive charge delocalization on ionization.Intrinsic rate constants (in the Marcus sense), Ko, have been obtained for these systems, and are shown to vary considerably with choice of catalyst type.As expected, high intrinsic energy barriers for these ionizations are predicted, arising from the extensive molecular and solvent reorganization required to produce planar, delocalized carbanions.Data for the former compound have also been obtained in water, which allow a direct estimation of its pKaH2O value to be made; pKaH2O = 13.16.

Solvent Dependence of the Ionization of Nitrophenylmethanes

The solvent dependence of proton abstraction from various nitrophenylmethanes has been examined for aqueous dimethyl sulphoxide and methanolic dimethyl sulphoxide solutions.Even though the compounds studied vary considerably in thermodynamic acidity (pKa), their proton-abstraction rates all show the same solvent dependence.It is suggested that the transition states for these reactions all occur at similar positions on the reaction pathway, and that transition state imbalances exist for these proton transfers.