ANOMALOUS RATES OF PROTON-TRANSFER TO AND FROM NITROGEN AND CARBON IN THE REACTIONS OF AMINES WITH 1,1-DINITRO-2,2-DIPHENYLETHYLENE

Two kinetic processes are observed in the reactions of 1, 1-dinitro-2, 2-diphenylethylene with piperidine, morpholine, n-butylamine, and aniline in 50% aqueous dimethyl sulfoxide. The first, relatively fast and reversible, refers to nucleophilic addition of the amine to the 2 position of 1, 1 -dinitro-2, 2-diphenylethylene to form a zwitterionic addition complex (T±), which is subsequently deprotonated to the anionic addition complex (T-). In the piperidine and n-butylamine reactions proton transfer is fast and nucleophilic attack is rate determining; in the morpholine and aniline reactions proton transfer is partially rate limiting. The second kinetic process, which is relatively slow, refers to protonation of T- on carbon to form T°, followed by rapid and irreversible cleavage of T° into Ph2C=O and -CH(NO2)2. The rate constants for the various elementary steps were evaluated. They show a dramatic steric effect not only on the nucleophilic attack step but also on the proton transfer rates. For example, deprotonation by /V-methylmorpholine of T± derived from morpholine has a rate constant of 2 × 103 M-1 s-1 instead of the 108-109 M-1 s-1 expected for a diffusion-controlled reaction. Rates of protonation of T- on carbon by water and several general acids are as expected for similar dinitro compounds, but protonation by H+ is 103-104 times faster than expected. This high rate is tentatively attributed to an intramolecular proton switch mechanism, T±⟶ T°. © 1979, American Chemical Society. All rights reserved.