Concerted aminolysis of diaryl carbonates: Kinetic sensitivity on the basicity of the nucleophile, nonleaving group, and nucleofuge

Abstract

The kinetics of the reactions of 4-methylphenyl, phenyl, and 4-chlorophenyl 2,4,6-trinitrophenyl carbonates (1, 2, and 3, respectively) with a series of anilines and secondary alicyclic (SA) amines has been carried out spectrophotometrically in 44 wt% ethanol-water, at 25.0 • C, ionic strength 0.2 M. The Brønsted plots (statistically corrected) for the reactions of carbonates 1-3 with anilines and SA amines were linear with slopes (β N ) in the range of 0.69-0.78 and 0.45-0.48, respectively, attributed to a concerted mechanism. The negative values found for the sensitivity of log k N to the basicity of the nonleaving (β nlg ) and leaving (β lg ) groups are discussed. Anilines are more reactive than isobasic SA amines, probably because of the greater steric hindrance offered by the latter. C 2012 Wiley Periodicals, Inc. Int J Chem Kinet

Kinetics and mechanism of the aminolysis of bis(4‐nitrophenyl) carbonate and O‐(4‐nitropheny) S‐(4‐nitrophenyl) thio and dithiocarbonate

“…Some of these reactions have been described as stepwise, through a zwitterionic tetrahedral intermediate (T ± ), whereas others have been found to be concerted, i.e. with no T ± intermediate in a single step . A similar behavior has been found in the aminolysis reactions on O ‐aryl S ‐aryl thiolcarbonates and O ‐aryl S ‐aryl dithiocarbonates …”

“…A). This β value is in the limit of those found for concerted mechanisms (β = 0.4–0.7) and those for stepwise mechanism where breakdown to products of a zwitterionic tetrahedral intermediate is the rate‐determining step (β = 0.8–1.1) . We propose that these reactions are concerted for the following reasons: (i) the anilinolysis of 1 in the same experimental conditions has been described as concerted .…”

“…C). This β value is in the limit of those found for concerted (β = 0.4–0.7) and those for stepwise mechanism where the formation of a zwitterionic tetrahedral intermediate is the rate‐determining step (β = 0.1–0.3) . Nevertheless, we are more inclined to propose a concerted mechanism for the following arguments: (i) In those reactions where pyridinolysis and SA aminolysis proceed by stepwise mechanism, the center of the Brønsted curvature (p K a 0 ) is similar or little greater for the latter.…”

“…The kinetics and mechanisms of the aminolysis of diaryl carbonates are well documented . Some of these reactions have been described as stepwise, through a zwitterionic tetrahedral intermediate (T ± ), whereas others have been found to be concerted, i.e.…”

Theoretical Studies on the Aminolysis Mechanism of Methomyl: Effect of the Catalysis to the Reaction of Carbamate with Ammonia

“…Many authors have expressed their keen interest in the aminolysis mechanism of carbamate experimentally and theoretically as it is crucial for the organic synthesis and biological process . For the aminolysis reaction, the ammonia attack the carbonyl group has been regarded as a typical reaction for the generation of peptide bonds in chemistry and biochemistry .…”