Kinetics of the separately observable formation and decomposition of the intermediate complex in aromatic nucleophilic substitution. Reactions of 2,4-dinitro-1-naphthyl ethyl ether with n-butyl- and tert-butylamine in dimethyl sulfoxide solution

Abstract

The reactions named in the title, which form the respective 2,4-dinitro-l-naphthylbutylamines (8), occur in two distinct stages. The spectrum of an intermediate develops at a rate which is measurable in a stopped-flow apparatus, and then decays at a slower and easily measurable rate. The kinetics of both stage I and stage II have been studied, and equilibrium constants have been determined for the stage I equilibrium and the acid-base equilibrium between product 8 and its conjugate base 9. The evidence indicates that the observable intermediate is the conjugate base (7) of the initial complex (6). Formation of the intermediate is not base catalyzed. Its transformation to product 8 is first order in butylammonium ion but independent of amine concentration. The mechanism of base catalysis of the overall reaction is thereby indicated to be general acid catalysis of leaving group expulsion from the conjugate base of the -complex intermediate.

The reaction of 2‐phenoxy‐3,5‐dinitropyridine with substituted anilines in the presence of 1,4‐diazabicyclo[2.2.2]octane in dimethyl sulfoxide: Kinetic and equilibrium studies

“…In agreement with the classic work of Orvik and Bunnett [14], the results for ethyl 2,4,6-trinitrophenyl ether (3) indicated that substitution involves the specific base-general acid catalysis mechanism, SB-GA, in which leaving group expulsion is the overall ratelimiting step. However, the phenoxy group is a considerably better leaving group than the ethoxy group, and the observation of base catalysis in reactions of the phenyl aryl ethers was best explained in terms of rate-limiting proton transfer from a zwitterionic intermediate to base [15,16].…”

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

“…In order to explain the above observation about reaction rates, one must take into account that (i) the benzofurazan ring has a stronger inductive effect and a lower resonance effect than a nitro group [50]; (ii) the combined result for the nitrobenzofurazan is a strong electron-withdrawing effect facilitating the S N Ar substitution; (iii) methoxy and aryloxy substituents appear to be better leaving groups than chloro; and (iv) there is a transition state leading to the immediate formation of a red-colored Meisenheimer complex 4 [51][52][53][54][55] and then, more slowly, to the substitution product 3 that is detectably fluorescent. One may assume that the basic AAs, which are more nucleophilic than all other AAs, prevail whenever the aryloxy group is not activated (2a) or deactivated by an electronwithdrawing formyl group (2d), even when there are methoxy groups (2e).…”

Effects of ortho‐ and para‐Ring Activation on the Kinetics of SNAr Reactions of 1‐Chloro‐2‐nitro‐ and 1‐Phenoxy‐2‐nitrobenzenes with Aliphatic Amines in Acetonitrile

“…The latter mechanism has been shown to apply to substrates such as alkyl ethers carrying poor leaving groups. [7][8][9][10] However, there is good evidence that for substrates containing good leaving groups, such as phenyl ethers, the RLPT mechanism applies. [11][12][13][14][15] The absence of base catalysis implies [1] that the initial nucleophilic attack, k 1 step, is rate limiting.…”